Issue published February 1, 2012

R etinoblastoma is a pediatric retinal tumor initiated by biallelic inactivation of the retinoblastoma gene (RB1). RB1 was the first identified tumor suppressor gene and has defined roles in the regulation of cell cycle progression, DNA replication, and terminal differentiation. However, despite the abundance of work demonstrating the molecular function and identifying binding partners of pRb, the challenge facing molecular biologists and clinical oncologists is how to integrate this vast body of molecular knowledge into the development of targeted therapies for treatment of retinoblastoma. We propose that a more thorough genetic understanding of retinoblastoma would inform targeted treatment decisions and could improve outcomes and quality of life in children affected by this disease.

D ermatologic disease, although seldom life threatening, can be extremely disfiguring and interfere with the quality of life. In addition, as opposed to other organs, just the aging of skin and its adnexal structure the hair follicle can result in cosmetic concerns that affect most of us. The articles in this dermatology Review Series demonstrate recent progress in understanding the cell biology and molecular pathophysiology of the epidermis and hair follicles, which harbor keratinocyte and melanocyte stem cells. They reveal a dynamic relationship between research and clinical care: knowledge of dermatologic disease has facilitated the understanding of the biology of the epidermis and, in turn, progress in basic science has informed our understanding of disease. This type of synergy is a profound strength of clinical research of the type that the JCI is dedicated to publishing.

C lassic atopic dermatitis is complicated by asthma, allergic rhinitis, and food allergies, cumulatively referred to as atopic diseases. Recent discoveries of mutations in the filaggrin gene as predisposing factors for atopic diseases have refocused investigators’ attention on epidermal barrier dysfunction as a causative mechanism. The skin’s barrier function has three elements: the stratum corneum (air-liquid barrier), tight junctions (liquid-liquid barrier), and the Langerhans cell network (immunological barrier). Clarification of the molecular events underpinning epidermal barrier function and dysfunction should lead to a better understanding of the pathophysiological mechanisms of atopic diseases.

T he adult hair follicle houses stem cells that govern the cyclical growth and differentiation of multiple cell types that collectively produce a pigmented hair. Recent studies have revealed that hair follicle stem cells are heterogeneous and dynamic throughout the hair cycle. Moreover, interactions between heterologous stem cells, including both epithelial and melanocyte stem cells, within the hair follicle are just now being explored. This review will describe how recent findings have expanded our understanding of the development, organization, and regeneration of hair follicle stem cells. At a basic level, this review is intended to help construct a reference point to integrate the surge of studies on the molecular mechanisms that regulate these cells.

B asal cell carcinoma (BCC) of the skin, the most common malignancy in individuals of mixed European descent, is increasing in incidence due to an aging population and sun exposure habits. The realization that aberrant activation of Hedgehog signaling is a pathognomonic feature of BCC development has opened the way for exciting progress toward understanding BCC biology and translation of this knowledge to the clinic. Genetic mouse models closely mimicking human BCCs have provided answers about the tumor cell of origin, and inhibition of Hedgehog signaling is emerging as a potentially useful targeted therapy for patients with advanced or multiple BCCs that have hitherto lacked effective treatment.

C utaneous squamous cell carcinoma (cSCC) is the second most common human cancer with over 250,000 new cases annually in the US and is second in incidence only to basal cell carcinoma. cSCC typically manifests as a spectrum of progressively advanced malignancies, ranging from a precursor actinic keratosis (AK) to squamous cell carcinoma (SCC) in situ (SCCIS), invasive cSCC, and finally metastatic SCC. In this Review we discuss clinical and molecular parameters used to define this range of cutaneous neoplasia and integrate these with the multiple experimental approaches used to study this disease. Insights gained from modeling cSCCs have suggested innovative therapeutic targets for treating these lesions.

I recently had the opportunity to visit a very relaxing and beautiful day spa during the middle-of-the-day break from the sessions at a Keystone meeting. I was having a very tranquil and restorative day, when I went in for my final treatment — a facial. The very chipper and cheerful esthetician began examining my skin and applying various creams, when I then heard her say something that nearly ruined my experience: she claimed that the topical treatment she was about to apply would, in her words, “cleanse my liver.”

T hrombotic complications represent a highly significant component of morbidity and mortality associated with hypercholesterolemia and atherosclerosis. In this issue of the JCI, Owens et al. report possible mechanisms underlying the prothrombotic, proinflammatory state accompanying hypercholesterolemia. Using rodent, monkey, and human subjects, they show that circulating oxidized LDL and circulating monocyte-derived tissue factor are important instigating factors driving the thrombotic, inflammatory phenotype and, surprisingly, that statin therapy ameliorated the phenotype even in the absence of lowering cholesterol levels. The studies raise the intriguing possibility that therapies directed at pathways generating oxidant stress or pathways involved in transmitting oxidized LDL–mediated signals in circulating platelets and monocytes could have antiatherothrombotic potential, probably with minimal anticoagulant and hemorrhagic potential.

I miquimod is a TLR agonist that is used as an antitumor agent, mainly against skin tumors. Its clinical benefits are well described in several studies; however, the mechanisms behind its antitumor effects are not completely understood. In this issue of the JCI, Drobits and colleagues demonstrate that topical application of imiquimod suppresses cutaneous melanoma by TLR7-dependent recruitment and transformation of plasmacytoid dendritic cells into killer cells; this occurs independently of conventional adaptive immune mechanisms.

T he evolutionary struggles from which mutants arise have been documented in almost every living system. In this issue of the JCI, Varela and colleagues extend this list of systems to include neural derivatives of human embryonic stem cells, which they show exhibit a repeated gain of material from chromosome 1q. Although this raises safety issues for therapeutic use of such cells, the frequent observation of a particular change may direct screening strategies for detection and removal of these unwanted cellular variants.

T hat adult humans possess brown fat is now accepted — but is the brown fat metabolically active? Does human brown fat actually combust fat to release heat? In this issue of the JCI, Ouellet et al. demonstrate that metabolism in brown fat really is increased when adult humans are exposed to cold. This boosts the possibility that calorie combustion in brown fat may be of significance for our metabolism and, correspondingly, that the absence of brown fat may increase our proneness to obesity — provided that brown fat becomes activated not only by cold but also through food-related stimuli.

A ortic aneurysms are a common clinical condition that can cause death due to aortic dissection or rupture. The association between aortic aneurysm pathogenesis and altered TGF-β signaling has been the subject of numerous investigations. Recently, a TGF-β–responsive microRNA (miR), miR-29, has been identified to play a role in cellular phenotypic modulation during aortic development and aging. In this issue of JCI, Maegdefessel and colleagues demonstrate that decreasing the levels of miR-29b in the aortic wall can attenuate aortic aneurysm progression in two different mouse models of abdominal aortic aneurysms. This study highlights the relevance of miR-29b in aortic disease but also raises questions about its specific role.

S everal adenosine receptor subtypes on endothelial, epithelial, mesangial, and inflammatory cells have been implicated in ischemic acute kidney injury, a life-threatening condition that frequently complicates the care of hospitalized patients. In this issue of the JCI, Grenz and coworkers provide novel insight into how preservation of postischemic renal perfusion by endothelial cell adenosine A2B receptors is antagonized by adenosine reuptake into proximal tubule cells by equilibrative nucleotide transporter 1, which can be inhibited by dipyridamole. The work suggests that adenosine A2B receptor agonists and inhibition of equilibrative nucleoside transporters by dipyridamole may have therapeutic potential in ischemic acute kidney injury, a condition for which there are currently no specific therapeutic interventions.

M icroRNAs (miRs) regulate gene expression at the posttranscriptional level and play crucial roles in vascular integrity. As such, they may have a role in modifying abdominal aortic aneurysm (AAA) expansion, the pathophysiological mechanisms of which remain incompletely explored. Here, we investigate the role of miRs in 2 murine models of experimental AAA: the porcine pancreatic elastase (PPE) infusion model in C57BL/6 mice and the AngII infusion model in Apoe^–/– mice. AAA development was accompanied by decreased aortic expression of miR-29b, along with increased expression of known miR-29b targets, Col1a1, Col3a1, Col5a1, and Eln, in both models. In vivo administration of locked nucleic acid anti–miR-29b greatly increased collagen expression, leading to an early fibrotic response in the abdominal aortic wall and resulting in a significant reduction in AAA progression over time in both models. In contrast, overexpression of miR-29b using a lentiviral vector led to augmented AAA expansion and significant increase of aortic rupture rate. Cell culture studies identified aortic fibroblasts as the likely vascular cell type mediating the profibrotic effects of miR-29b modulation. A similar pattern of reduced miR-29b expression and increased target gene expression was observed in human AAA tissue samples compared with that in organ donor controls. These data suggest that therapeutic manipulation of miR-29b and its target genes holds promise for limiting AAA disease progression and protecting from rupture.

P aroxysmal nonkinesigenic dyskinesia (PNKD) is an autosomal dominant episodic movement disorder. Patients have episodes that last 1 to 4 hours and are precipitated by alcohol, coffee, and stress. Previous research has shown that mutations in an uncharacterized gene on chromosome 2q33–q35 (which is termed PNKD) are responsible for PNKD. Here, we report the generation of antibodies specific for the PNKD protein and show that it is widely expressed in the mouse brain, exclusively in neurons. One PNKD isoform is a membrane-associated protein. Transgenic mice carrying mutations in the mouse Pnkd locus equivalent to those found in patients with PNKD recapitulated the human PNKD phenotype. Staining for c-fos demonstrated that administration of alcohol or caffeine induced neuronal activity in the basal ganglia in these mice. They also showed nigrostriatal neurotransmission deficits that were manifested by reduced extracellular dopamine levels in the striatum and a proportional increase of dopamine release in response to caffeine and ethanol treatment. These findings support the hypothesis that the PNKD protein functions to modulate striatal neuro­transmitter release in response to stress and other precipitating factors.

B ilirubin, a breakdown product of heme, is normally glucuronidated and excreted by the liver into bile. Failure of this system can lead to a buildup of conjugated bilirubin in the blood, resulting in jaundice. The mechanistic basis of bilirubin excretion and hyperbilirubinemia syndromes is largely understood, but that of Rotor syndrome, an autosomal recessive disorder characterized by conjugated hyperbilirubinemia, coproporphyrinuria, and near-absent hepatic uptake of anionic diagnostics, has remained enigmatic. Here, we analyzed 8 Rotor-syndrome families and found that Rotor syndrome was linked to mutations predicted to cause complete and simultaneous deficiencies of the organic anion transporting polypeptides OATP1B1 and OATP1B3. These important detoxification-limiting proteins mediate uptake and clearance of countless drugs and drug conjugates across the sinusoidal hepatocyte membrane. OATP1B1 polymorphisms have previously been linked to drug hypersensitivities. Using mice deficient in Oatp1a/1b and in the multispecific sinusoidal export pump Abcc3, we found that Abcc3 secretes bilirubin conjugates into the blood, while Oatp1a/1b transporters mediate their hepatic reuptake. Transgenic expression of human OATP1B1 or OATP1B3 restored the function of this detoxification-enhancing liver-blood shuttle in Oatp1a/1b-deficient mice. Within liver lobules, this shuttle may allow flexible transfer of bilirubin conjugates (and probably also drug conjugates) formed in upstream hepatocytes to downstream hepatocytes, thereby preventing local saturation of further detoxification processes and hepatocyte toxic injury. Thus, disruption of hepatic reuptake of bilirubin glucuronide due to coexisting OATP1B1 and OATP1B3 deficiencies explains Rotor-type hyperbilirubinemia. Moreover, OATP1B1 and OATP1B3 null mutations may confer substantial drug toxicity risks.

H BV infection remains a leading cause of death worldwide. IFN-α inhibits viral replication in vitro and in vivo, and pegylated IFN-α is a commonly administered treatment for individuals infected with HBV. The HBV genome contains a typical IFN-stimulated response element (ISRE), but the molecular mechanisms by which IFN-α suppresses HBV replication have not been established in relevant experimental systems. Here, we show that IFN-α inhibits HBV replication by decreasing the transcription of pregenomic RNA (pgRNA) and subgenomic RNA from the HBV covalently closed circular DNA (cccDNA) minichromosome, both in cultured cells in which HBV is replicating and in mice whose livers have been repopulated with human hepatocytes and infected with HBV. Administration of IFN-α resulted in cccDNA-bound histone hypoacetylation as well as active recruitment to the cccDNA of transcriptional corepressors. IFN-α treatment also reduced binding of the STAT1 and STAT2 transcription factors to active cccDNA. The inhibitory activity of IFN-α was linked to the IRSE, as IRSE-mutant HBV transcribed less pgRNA and could not be repressed by IFN-α treatment. Our results identify a molecular mechanism whereby IFN-α mediates epigenetic repression of HBV cccDNA transcriptional activity, which may assist in the development of novel effective therapeutics.

H ereditary spastic paraplegias (HSPs) are a group of genetically heterogeneous neurodegenerative conditions. They are characterized by progressive spastic paralysis of the legs as a result of selective, length-dependent degeneration of the axons of the corticospinal tract. Mutations in 3 genes encoding proteins that work together to shape the ER into sheets and tubules — receptor accessory protein 1 (REEP1), atlastin-1 (ATL1), and spastin (SPAST) — have been found to underlie many cases of HSP in Northern Europe and North America. Applying Sanger and exome sequencing, we have now identified 3 mutations in reticulon 2 (RTN2), which encodes a member of the reticulon family of prototypic ER-shaping proteins, in families with spastic paraplegia 12 (SPG12). These autosomal dominant mutations included a complete deletion of RTN2 and a frameshift mutation predicted to produce a highly truncated protein. Wild-type reticulon 2, but not the truncated protein potentially encoded by the frameshift allele, localized to the ER. RTN2 interacted with spastin, and this interaction required a hydrophobic region in spastin that is involved in ER localization and that is predicted to form a curvature-inducing/sensing hairpin loop domain. Our results directly implicate a reticulon protein in axonopathy, show that this protein participates in a network of interactions among HSP proteins involved in ER shaping, and further support the hypothesis that abnormal ER morphogenesis is a pathogenic mechanism in HSP.

B rown adipose tissue (BAT) is vital for proper thermogenesis during cold exposure in rodents, but until recently its presence in adult humans and its contribution to human metabolism were thought to be minimal or insignificant. Recent studies using PET with ¹⁸F-fluorodeoxyglucose (¹⁸FDG) have shown the presence of BAT in adult humans. However, whether BAT contributes to cold-induced nonshivering thermogenesis in humans has not been proven. Using PET with ¹¹C-acetate, ¹⁸FDG, and ¹⁸F-fluoro-thiaheptadecanoic acid (¹⁸FTHA), a fatty acid tracer, we have quantified BAT oxidative metabolism and glucose and nonesterified fatty acid (NEFA) turnover in 6 healthy men under controlled cold exposure conditions. All subjects displayed substantial NEFA and glucose uptake upon cold exposure. Furthermore, we demonstrated cold-induced activation of oxidative metabolism in BAT, but not in adjoining skeletal muscles and subcutaneous adipose tissue. This activation was associated with an increase in total energy expenditure. We found an inverse relationship between BAT activity and shivering. We also observed an increase in BAT radio density upon cold exposure, indicating reduced BAT triglyceride content. In sum, our study provides evidence that BAT acts as a nonshivering thermogenesis effector in humans.

M utations in the gene encoding the p110α subunit of PI3K (PIK3CA) that result in enhanced PI3K activity are frequently observed in human cancers. To better understand the role of mutant PIK3CA in the initiation or progression of tumorigenesis, we generated mice in which a PIK3CA mutation commonly detected in human cancers (the H1047R mutation) could be conditionally knocked into the endogenous Pik3ca locus. Activation of this mutation in the mouse ovary revealed that alone, Pik3ca^H1047R induced premalignant hyperplasia of the ovarian surface epithelium but no tumors. Concomitantly, we analyzed several human ovarian cancers and found PIK3CA mutations coexistent with KRAS and/or PTEN mutations, raising the possibility that a secondary defect in a co-regulator of PI3K activity may be required for mutant PIK3CA to promote transformation. Consistent with this notion, we found that Pik3ca^H1047R mutation plus Pten deletion in the mouse ovary led to the development of ovarian serous adenocarcinomas and granulosa cell tumors. Both mutational events were required for early, robust Akt activation. Pharmacological inhibition of PI3K/mTOR in these mice delayed tumor growth and prolonged survival. These results demonstrate that the Pik3ca^H1047R mutation with loss of Pten is enough to promote ovarian cell transformation and that we have developed a model system for studying possible therapies.

H ypercholesterolemia is a major risk factor for atherosclerosis. It also is associated with platelet hyperactivity, which increases morbidity and mortality from cardiovascular disease. However, the mechanisms by which hypercholesterolemia produces a procoagulant state remain undefined. Atherosclerosis is associated with accumulation of oxidized lipoproteins within atherosclerotic lesions. Small quantities of oxidized lipoproteins are also present in the circulation of patients with coronary artery disease. We therefore hypothesized that hypercholesterolemia leads to elevated levels of oxidized LDL (oxLDL) in plasma and that this induces expression of the procoagulant protein tissue factor (TF) in monocytes. In support of this hypothesis, we report here that oxLDL induced TF expression in human monocytic cells and monocytes. In addition, patients with familial hypercholesterolemia had elevated levels of plasma microparticle (MP) TF activity. Furthermore, a high-fat diet induced a time-dependent increase in plasma MP TF activity and activation of coagulation in both LDL receptor–deficient mice and African green monkeys. Genetic deficiency of TF in bone marrow cells reduced coagulation in hypercholesterolemic mice, consistent with a major role for monocyte-derived TF in the activation of coagulation. Similarly, a deficiency of either TLR4 or TLR6 reduced levels of MP TF activity. Simvastatin treatment of hypercholesterolemic mice and monkeys reduced oxLDL, monocyte TF expression, MP TF activity, activation of coagulation, and inflammation, without affecting total cholesterol levels. Our results suggest that the prothrombotic state associated with hypercholesterolemia is caused by oxLDL-mediated induction of TF expression in monocytes via engagement of a TLR4/TLR6 complex.

H uman pluripotent stem cells offer a limitless source of cells for regenerative medicine. Neural derivatives of human embryonic stem cells (hESCs) are currently being used for cell therapy in 3 clinical trials. However, hESCs are prone to genomic instability, which could limit their clinical utility. Here, we report that neural differentiation of hESCs systematically produced a neural stem cell population that could be propagated for more than 50 passages without entering senescence; this was true for all 6 hESC lines tested. The apparent spontaneous loss of evolution toward normal senescence of somatic cells was associated with a jumping translocation of chromosome 1q. This chromosomal defect has previously been associated with hematologic malignancies and pediatric brain tumors with poor clinical outcome. Neural stem cells carrying the 1q defect implanted into the brains of rats failed to integrate and expand, whereas normal cells engrafted. Our results call for additional quality controls to be implemented to ensure genomic integrity not only of undifferentiated pluripotent stem cells, but also of hESC derivatives that form cell therapy end products, particularly neural lines.

I miquimod is a synthetic compound with antitumor properties; a 5% cream formulation is successfully used to treat skin tumors. The antitumor effect of imiquimod is multifactorial, although its ability to modulate immune responses by triggering TLR7/8 is thought to be key. Among the immune cells suggested to be involved are plasmacytoid DCs (pDCs). However, a direct contribution of pDCs to tumor killing in vivo and the mechanism of their recruitment to imiquimod-treated sites have never been demonstrated. Using a mouse model of melanoma, we have now demonstrated that pDCs can directly clear tumors without the need for the adaptive immune system. Topical imiquimod treatment led to TLR7-dependent and IFN-α/β receptor 1–dependent (IFNAR1-dependent) upregulation of expression of the chemokine CCL2 in mast cells. This was essential to induce skin inflammation and for the recruitment of pDCs to the skin. The recruited pDCs were CD8α⁺ and induced tumor regression in a TLR7/MyD88- and IFNAR1-dependent manner. Lack of TLR7 and IFNAR1 or depletion of pDCs or CD8α⁺ cells from tumor-bearing mice completely abolished the effect of imiquimod. TLR7 was essential for imiquimod-stimulated pDCs to produce IFN-α/β, which led to TRAIL and granzyme B secretion by pDCs via IFNAR1 signaling. Blocking these cytolytic molecules impaired pDC-mediated tumor killing. Our results demonstrate that imiquimod treatment leads to CCL2-dependent recruitment of pDCs and their transformation into a subset of killer DCs able to directly eliminate tumor cells.

H epatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Its pathogenesis is frequently linked to liver inflammation. Gain-of-function mutations in the gene encoding β-catenin are frequent genetic modifications found in human HCCs. Thus, we investigated whether inflammation was a component of β-catenin–induced tumorigenesis using genetically modified mouse models that recapitulated the stages of initiation and progression of this tumoral process. Oncogenic β-catenin signaling was found to induce an inflammatory program in hepatocytes that involved direct transcriptional control by β-catenin and activation of the NF-κB pathway. This led to a specific inflammatory response, the intensity of which determined the degree of tumor aggressiveness. The chemokine-like chemotactic factor leukocyte cell–derived chemotaxin 2 (LECT2) and invariant NKT (iNKT) cells were identified as key interconnected effectors of liver β-catenin–induced inflammation. In genetic deletion models lacking the gene encoding LECT2 or iNKT cells, hepatic β-catenin signaling triggered the formation of highly malignant HCCs with lung metastasis. Thus, our results identify inflammation as a key player in β-catenin–induced liver tumorigenesis. We provide strong evidence that, by activating pro- and antiinflammatory mediators, β-catenin signaling produces an inflammatory microenvironment that has an impact on tumoral development. Our data are consistent with the fact that most β-catenin–activated HCCs are of better prognosis.

I ncreased expression of the regulatory subunit of HIFs (HIF-1α or HIF-2α) is associated with metabolic adaptation, angiogenesis, and tumor progression. Understanding how HIFs are regulated is of intense interest. Intriguingly, the molecular mechanisms that link mitochondrial function with the HIF-regulated response to hypoxia remain to be unraveled. Here we describe what we believe to be novel functions of the human gene CHCHD4 in this context. We found that CHCHD4 encodes 2 alternatively spliced, differentially expressed isoforms (CHCHD4.1 and CHCHD4.2). CHCHD4.1 is identical to MIA40, the homolog of yeast Mia40, a key component of the mitochondrial disulfide relay system that regulates electron transfer to cytochrome c. Further analysis revealed that CHCHD4 proteins contain an evolutionarily conserved coiled-coil-helix-coiled-coil-helix (CHCH) domain important for mitochondrial localization. Modulation of CHCHD4 protein expression in tumor cells regulated cellular oxygen consumption rate and metabolism. Targeting CHCHD4 expression blocked HIF-1α induction and function in hypoxia and resulted in inhibition of tumor growth and angiogenesis in vivo. Overexpression of CHCHD4 proteins in tumor cells enhanced HIF-1α protein stabilization in hypoxic conditions, an effect insensitive to antioxidant treatment. In human cancers, increased CHCHD4 expression was found to correlate with the hypoxia gene expression signature, increasing tumor grade, and reduced patient survival. Thus, our study identifies a mitochondrial mechanism that is critical for regulating the hypoxic response in tumors.

T he CBX7 gene encodes a polycomb group protein that is known to be downregulated in many types of human cancers, although the role of this protein in carcinogenesis remains unclear. To shed light on this issue, we generated mice null for Cbx7. Mouse embryonic fibroblasts derived from these mice had a higher growth rate and reduced susceptibility to senescence compared with their WT counterparts. This was associated with upregulated expression of multiple cell cycle components, including cyclin E, which is known to play a key role in lung carcinogenesis in humans. Adult Cbx7-KO mice developed liver and lung adenomas and carcinomas. In in vivo and in vitro experiments, we demonstrated that CBX7 bound to the CCNE1 promoter in a complex that included HDAC2 and negatively regulated CCNE1 expression. Finally, we found that the lack of CBX7 protein expression in human lung carcinomas correlated with CCNE1 overexpression. These data suggest that CBX7 is a tumor suppressor and that its loss plays a key role in the pathogenesis of cancer.

C hronic myelogenous leukemia (CML) results from a chromosomal translocation in hematopoietic stem or early progenitor cells that gives rise to the oncogenic BCR/ABL fusion protein. Clinically, CML has a chronic phase that eventually evolves into an accelerated stage and blast crisis. A CML-specific immune response is thought to contribute to the control of disease. Whether the immune system can also promote disease progression is not known. In the present study, we investigated the possibility that the TNF receptor family member CD27 is present on leukemia stem cells (LSCs) and mediates effects of the immune system on CML. In a mouse model of CML, BCR/ABL⁺ LSCs and leukemia progenitor cells were found to express CD27. Binding of CD27 by its ligand, CD70, increased expression of Wnt target genes in LSCs by enhancing nuclear localization of active β-catenin and TRAF2- and NCK-interacting kinase (TNIK). This resulted in increased proliferation and differentiation of LSCs. Blocking CD27 signaling in LSCs delayed disease progression and prolonged survival. Furthermore, CD27 was expressed on CML stem/progenitor cells in the bone marrow of CML patients, and CD27 signaling promoted growth of BCR/ABL⁺ human leukemia cells by activating the Wnt pathway. Since expression of CD70 is limited to activated lymphocytes and dendritic cells, our results reveal a mechanism by which adaptive immunity contributes to leukemia progression. In addition, targeting CD27 on LSCs may represent an attractive therapeutic approach to blocking the Wnt/β-catenin pathway in CML.

P ancreatic cancer is almost invariably associated with mutations in the KRAS gene, most commonly KRAS^G12D, that result in a dominant-active form of the KRAS GTPase. However, how KRAS mutations promote pancreatic carcinogenesis is not fully understood, and whether oncogenic KRAS is required for the maintenance of pancreatic cancer has not been established. To address these questions, we generated two mouse models of pancreatic tumorigenesis: mice transgenic for inducible Kras^G12D, which allows for inducible, pancreas-specific, and reversible expression of the oncogenic Kras^G12D, with or without inactivation of one allele of the tumor suppressor gene p53. Here, we report that, early in tumorigenesis, induction of oncogenic Kras^G12D reversibly altered normal epithelial differentiation following tissue damage, leading to precancerous lesions. Inactivation of Kras^G12D in established precursor lesions and during progression to cancer led to regression of the lesions, indicating that Kras^G12D was required for tumor cell survival. Strikingly, during all stages of carcinogenesis, Kras^G12D upregulated Hedgehog signaling, inflammatory pathways, and several pathways known to mediate paracrine interactions between epithelial cells and their surrounding microenvironment, thus promoting formation and maintenance of the fibroinflammatory stroma that plays a pivotal role in pancreatic cancer. Our data establish that epithelial Kras^G12D influences multiple cell types to drive pancreatic tumorigenesis and is essential for tumor maintenance. They also strongly support the notion that inhibiting Kras^G12D, or its downstream effectors, could provide a new approach for the treatment of pancreatic cancer.

H erpes simplex virus type 1 (HSV-1) not only causes painful recurrent oral-labial infections, it can also cause permanent brain damage and blindness. There is currently no HSV-1 vaccine. An effective vaccine must stimulate coordinated T cell responses, but the large size of the genome and the low frequency of HSV-1–specific T cells have hampered the search for the most effective T cell antigens for inclusion in a candidate vaccine. We have now developed what we believe to be novel methods to efficiently generate a genome-wide map of the responsiveness of HSV-1–specific T cells, and demonstrate the applicability of these methods to a second complex microbe, vaccinia virus. We used cross-presentation and CD137 activation–based FACS to enrich for polyclonal CD8⁺ T effector T cells. The HSV-1 proteome was prepared in a flexible format for analyzing both CD8⁺ and CD4⁺ T cells from study participants. Scans with participant-specific panels of artificial APCs identified an oligospecific response in each individual. Parallel CD137-based CD4⁺ T cell research showed discrete oligospecific recognition of HSV-1 antigens. Unexpectedly, the two HSV-1 proteins not previously considered as vaccine candidates elicited both CD8⁺ and CD4⁺ T cell responses in most HSV-1–infected individuals. In this era of microbial genomics, our methods — also demonstrated in principle for vaccinia virus for both CD8⁺ and CD4⁺ T cells — should be broadly applicable to the selection of T cell antigens for inclusion in candidate vaccines for many pathogens.

T he morphology of healthy podocyte foot processes is necessary for maintaining the characteristics of the kidney filtration barrier. In most forms of glomerular disease, abnormal filter barrier function results when podocytes undergo foot process spreading and retraction by remodeling their cytoskeletal architecture and intercellular junctions during a process known as effacement. The cell adhesion protein nephrin is necessary for establishing the morphology of the kidney podocyte in development by transducing from the specialized podocyte intercellular junction phosphorylation-mediated signals that regulate cytoskeletal dynamics. The present studies extend our understanding of nephrin function by showing that nephrin activation in cultured podocytes induced actin dynamics necessary for lamellipodial protrusion. This process required a PI3K-, Cas-, and Crk1/2-dependent signaling mechanism distinct from the previously described nephrin-Nck1/2 pathway necessary for assembly and polymerization of actin filaments. Our present findings also support the hypothesis that mechanisms governing lamellipodial protrusion in culture are similar to those used in vivo during foot process effacement in a subset of glomerular diseases. In mice, podocyte-specific deletion of Crk1/2 prevented foot process effacement in one model of podocyte injury and attenuated foot process effacement and associated proteinuria in a delayed fashion in a second model. In humans, focal adhesion kinase and Cas phosphorylation — markers of focal adhesion complex–mediated Crk-dependent signaling — was induced in minimal change disease and membranous nephropathy, but not focal segmental glomerulosclerosis. Together, these observations suggest that activation of a Cas-Crk1/2–dependent complex is necessary for foot process effacement observed in distinct subsets of human glomerular diseases.

A complex biologic network regulates kidney perfusion under physiologic conditions. This system is profoundly perturbed following renal ischemia, a leading cause of acute kidney injury (AKI) — a life-threatening condition that frequently complicates the care of hospitalized patients. Therapeutic approaches to prevent and treat AKI are extremely limited. Better understanding of the molecular pathways promoting postischemic reflow could provide new candidate targets for AKI therapeutics. Due to its role in adapting tissues to hypoxia, we hypothesized that extracellular adenosine has a regulatory function in the postischemic control of renal perfusion. Consistent with the notion that equilibrative nucleoside transporters (ENTs) terminate adenosine signaling, we observed that pharmacologic ENT inhibition in mice elevated renal adenosine levels and dampened AKI. Deletion of the ENTs resulted in selective protection in Ent1^–/– mice. Comprehensive examination of adenosine receptor–knockout mice exposed to AKI demonstrated that renal protection by ENT inhibitors involves the A2B adenosine receptor. Indeed, crosstalk between renal Ent1 and Adora2b expressed on vascular endothelia effectively prevented a postischemic no-reflow phenomenon. These studies identify ENT1 and adenosine receptors as key to the process of reestablishing renal perfusion following ischemic AKI. If translatable from mice to humans, these data have important therapeutic implications.

B M-derived endothelial progenitor cells (EPCs) are critical and essential for neovascularization in tissue repair and tumorigenesis. EPCs migrate from BM to tissues via the bloodstream, but specific chemotactic cues have not been identified. Here we show in mice that the absence of CCR5 reduced vascular EPC accumulation and neovascularization, but not macrophage recruitment, and eventually delayed healing in wounded skin. When transferred into Ccr5^–/– mice, Ccr5^+/+ BM cells, but not Ccr5^–/– cells, accumulated in the wound site, were incorporated into the vasculature, and restored normal neovascularization. Consistent with these observations, CCL5 induced in vitro EPC migration in a CCR5-dependent manner. Moreover, expression of VEGF and TGF-β was substantially diminished at wound sites in Ccr5^–/– mice, which suggests that EPCs are important not only as the progenitors of endothelial cells, but also as the source of growth factors during tissue repair. Taken together, these data identify the CCL5/CCR5 interaction as what we believe to be a novel molecular target for modulation of neovascularization and eventual tissue repair.

Z inc deficiency can be an inherited disorder, in which case it is known as acrodermatitis enteropathica (AE), or an acquired disorder caused by low dietary intake of zinc. Even though zinc deficiency diminishes cellular and humoral immunity, patients develop immunostimulating skin inflammation. Here, we have demonstrated that despite diminished allergic contact dermatitis in mice fed a zinc-deficient (ZD) diet, irritant contact dermatitis (ICD) in these mice was more severe and prolonged than that in controls. Further, histological examination of ICD lesions in ZD mice revealed subcorneal vacuolization and epidermal pallor, histological features of AE. Consistent with the fact that ATP release from chemically injured keratinocytes serves as a causative mediator of ICD, we found that the severe ICD response in ZD mice was attenuated by local injection of soluble nucleoside triphosphate diphosphohydrolase. In addition, skin tissue from ZD mice with ICD showed increased levels of ATP, as did cultured wild-type keratinocytes treated with chemical irritants and the zinc-chelating reagent TPEN. Interestingly, numbers of epidermal Langerhans cells (LCs), which play a protective role against ATP-mediated inflammatory signals, were decreased in ZD mice as well as samples from ZD patients. These findings suggest that upon exposure to irritants, aberrant ATP release from keratinocytes and impaired LC-dependent hydrolysis of nucleotides may be important in the pathogenesis of AE.

R ASA1 (also known as p120 RasGAP) is a Ras GTPase–activating protein that functions as a regulator of blood vessel growth in adult mice and humans. In humans, RASA1 mutations cause capillary malformation–arteriovenous malformation (CM-AVM); whether it also functions as a regulator of the lymphatic vasculature is unknown. We investigated this issue using mice in which Rasa1 could be inducibly deleted by administration of tamoxifen. Systemic loss of RASA1 resulted in a lymphatic vessel disorder characterized by extensive lymphatic vessel hyperplasia and leakage and early lethality caused by chylothorax (lymphatic fluid accumulation in the pleural cavity). Lymphatic vessel hyperplasia was a consequence of increased proliferation of lymphatic endothelial cells (LECs) and was also observed in mice in which induced deletion of Rasa1 was restricted to LECs. RASA1-deficient LECs showed evidence of constitutive activation of Ras in situ. Furthermore, in isolated RASA1-deficient LECs, activation of the Ras signaling pathway was prolonged and cellular proliferation was enhanced after ligand binding to different growth factor receptors, including VEGFR-3. Blockade of VEGFR-3 was sufficient to inhibit the development of lymphatic vessel hyperplasia after loss of RASA1 in vivo. These findings reveal a role for RASA1 as a physiological negative regulator of LEC growth that maintains the lymphatic vasculature in a quiescent functional state through its ability to inhibit Ras signal transduction initiated through LEC-expressed growth factor receptors such as VEGFR-3.

A llergic asthma is the most common form of asthma, affecting more than 10 million Americans. Although it is clear that mast cells have a key role in the pathogenesis of allergic asthma, the mechanisms by which they regulate airway narrowing in vivo remain to be elucidated. Here we report that mice lacking αvβ6 integrin are protected from exaggerated airway narrowing in a model of allergic asthma. Expression microarrays of the airway epithelium revealed mast cell proteases among the most prominent differentially expressed genes, with expression of mouse mast cell protease 1 (mMCP-1) induced by allergen challenge in WT mice and expression of mMCP-4, -5, and -6 increased at baseline in β6-deficient mice. These findings were most likely explained by loss of TGF-β activation, since the epithelial integrin αvβ6 is a critical activator of latent TGF-β, and in vitro–differentiated mast cells showed TGF-β–dependent expression of mMCP-1 and suppression of mMCP-4 and -6. In vitro, mMCP-1 increased contractility of murine tracheal rings, an effect that depended on intact airway epithelium, whereas mMCP-4 inhibited IL-13–induced epithelial-independent enhancement of contractility. These results suggest that intraepithelial activation of TGF-β by the αvβ6 integrin regulates airway responsiveness by modulating mast cell protease expression and that these proteases and their proteolytic substrates could be novel targets for improved treatment of allergic asthma.

H emolytic uremic syndrome (HUS) is a potentially life-threatening condition. It often occurs after gastrointestinal infection with E. coli O157:H7, which produces Shiga toxins (Stx) that cause hemolytic anemia, thrombocytopenia, and renal injury. Stx-mediated changes in endothelial phenotype have been linked to the pathogenesis of HUS. Here we report our studies investigating Stx-induced changes in gene expression and their contribution to the pathogenesis of HUS. Stx function by inactivating host ribosomes but can also alter gene expression at concentrations that minimally affect global protein synthesis. Gene expression profiling of human microvascular endothelium treated with Stx implicated a role for activation of CXCR4 and CXCR7 by their shared cognate chemokine ligand (stromal cell–derived factor-1 [SDF-1]) in Stx-mediated pathophysiology. The changes in gene expression required a catalytically active Stx A subunit and were mediated by enhanced transcription and mRNA stability. Stx also enhanced the association of CXCR4, CXCR7, and SDF1 mRNAs with ribosomes. In a mouse model of Stx-mediated pathology, we noted changes in plasma and tissue content of CXCR4, CXCR7, and SDF-1 after Stx exposure. Furthermore, inhibition of the CXCR4/SDF-1 interaction decreased endothelial activation and organ injury and improved animal survival. Finally, in children infected with E. coli O157:H7, plasma SDF-1 levels were elevated in individuals who progressed to HUS. Collectively, these data implicate the CXCR4/CXCR7/SDF-1 pathway in Stx-mediated pathogenesis and suggest novel therapeutic strategies for prevention and/or treatment of complications associated with E. coli O157:H7 infection.