Issue published June 15, 2002

W e recently showed that human skin fibroblasts internalize fluorescent analogues of the glycosphingolipids lactosylceramide and globoside almost exclusively by a clathrin-independent mechanism involving caveolae. In contrast, a sphingomyelin analogue is internalized approximately equally via clathrin-dependent and caveolar routes. Here, we further characterized the caveolar pathway for glycosphingolipids, showing that Golgi targeting of sphingolipids internalized via caveolae required microtubules and phosphoinositol 3-kinases and was inhibited in cells expressing dominant-negative Rab7 and Rab9 constructs. In addition, overexpression of wild-type Rab7 or Rab9 (but not Rab11) in Niemann-Pick type C (NP-C) lipid storage disease fibroblasts resulted in correction of lipid trafficking defects, including restoration of Golgi targeting of fluorescent lactosylceramide and endogenous GM₁ ganglioside, and a dramatic reduction in intracellular cholesterol stores. Our results demonstrate a role for Rab7 and Rab9 in the Golgi targeting of glycosphingolipids and suggest a new therapeutic approach for restoring normal lipid trafficking in NP-C cells.

T GF-βs are potent inhibitors of epithelial cell proliferation. However, in established carcinomas, autocrine/paracrine TGF-β interactions can enhance tumor cell viability and progression. Thus, we studied the effect of a soluble Fc:TGF-β type II receptor fusion protein (Fc:TβRII) on transgenic and transplantable models of breast cancer metastases. Systemic administration of Fc:TβRII did not alter primary mammary tumor latency in MMTV-Polyomavirus middle T antigen transgenic mice. However, Fc:TβRII increased apoptosis in primary tumors, while reducing tumor cell motility, intravasation, and lung metastases. These effects correlated with inhibition of Akt activity and FKHRL1 phosphorylation. Fc:TβRII also inhibited metastases from transplanted 4T1 and EMT-6 mammary tumors in syngeneic BALB/c mice. Tumor microvessel density in a mouse dorsal skin window chamber was unaffected by Fc:TβRII. Therefore, blockade of TGF-β signaling may reduce tumor cell viability and migratory potential and represents a testable therapeutic approach against metastatic carcinomas.

G roup B coxsackieviral (CVB) infection commonly causes viral myocarditis. Mice are protected from CVB3 myocarditis by gene-targeted knockout of p56^Lck(Lck), the Src family kinase (Src) essential for T cell activation. Extracellular signal-regulated kinase 1 and 2 (ERK-1/2) can influence cell function downstream of Lck. Using T cell lines and neonatal cardiac myocytes we investigated the role of ERK-1/2 in CVB3 infection. In Jurkat T cells ERK-1/2 is rapidly activated by CVB3; but, this response is absent in Lck-negative JCaM T cells. Inhibition of ERK-1/2 with UO126 reduced CVB3 titers in Jurkat cells, but not in JCaM cells. In cardiac myocytes CVB3 activation of ERK-1/2 is blocked by the Src inhibitor PP2. In addition, viral production in myocytes is decreased by Src or ERK-1/2 inhibition. In vitro, in both immune and myocardial cells, ERK-1/2 is activated by CVB3 downstream of Lck and other Src’s and is necessary for efficient CVB3 replication. In vivo, following CVB3 infection, ERK-1/2 activation is evident in the myocardium. ERK-1/2 activation is intense in the hearts of myocarditis-susceptible A/J mice. In contrast, significantly less ERK-1/2 activation is found in the hearts of myocarditis-resistant C57BL/6 mice. Therefore, the ERK-1/2 response to CVB3 infection may contribute to differential host susceptibility to viral myocarditis.

T issue-type plasminogen activator (tPA) is a highly specific serine proteinase expressed in the CNS during events that require neuronal plasticity. In this study we demonstrate that endogenous tPA mediates the progression of kainic acid–induced (KA-induced) seizures by promoting the synchronization of neuronal activity required for seizure spreading, and that, unlike KA-induced cell death, this activity is plasminogen-independent. Specifically, seizure induction by KA injection into the amygdala induces tPA activity and cell death in both hippocampi, and unilateral treatment of rats with neuroserpin, a natural inhibitor of tPA in the brain, enhances neuronal survival in both hippocampi. Inhibition of tPA within the hippocampus by neuroserpin treatment does not prevent seizure onset but instead markedly delays the progression of seizure activity in both rats and wild-type mice. In tPA-deficient mice, seizure progression is significantly delayed, and neuroserpin treatment does not further delay seizure spreading. In contrast, plasminogen-deficient mice show a pattern of seizure spreading and a response to neuroserpin that is similar to that of wild-type animals. These findings indicate that tPA acts on a substrate other than plasminogen and that the effects of neuroserpin on seizure progression and neuronal cell survival are mediated through the inhibition of tPA.

W hole-body irradiation at the minimal lethal dose causes bone marrow failure and death within 12–18 days. To identify the principal components of the hematopoietic system that are radioprotective, we transplanted lethally irradiated mice with purified progenitors: common myeloid progenitors (CMPs), megakaryocyte/erythrocyte-restricted progenitors (MEPs), or granulocyte/monocyte-restricted progenitors (GMPs). Transplanted CMPs gave rise to cells both of the granulocyte/monocyte (GM) series and the megakaryocyte/erythrocyte series, whereas GMPs or MEPs showed reconstitution of only GM or ME cells, respectively. CMPs and MEPs but not GMPs protected mice in a dose-dependent manner, suggesting that erythrocytes, platelets, or both are the critical effectors of radioprotection. Accordingly, CMPs and MEPs formed robust colonies in recipient bone marrow and spleen, whereas GMPs formed small colonies that rapidly disappeared. Direct comparisons of spleen CFU (CFU-S) potentials among each progenitor subset showed that MEPs contain the vast majority of day 8 CFU-S activity, suggesting that day 8 CFU-S are the precursors of radioprotective cell subsets. All animals radioprotected for 30 days subsequently survived for at least 6 months post-transplant, and showed only host-derived hematopoiesis after 30 days. These findings suggest that rare hematopoietic stem cells survive myeloablation that can eventually repopulate irradiated hosts if myeloerythroid-restricted progenitors transiently rescue ablated animals through the critical window of bone marrow failure.

T he TNF-like ligands APRIL and BLyS are close relatives and share the capacity to bind the receptors TACI and BCMA. BLyS has been shown to play an important role in B cell homeostasis and autoimmunity, but the biological role of APRIL remains less well defined. Analysis of T cells revealed an activation-dependent increase in APRIL mRNA expression. We therefore generated mice expressing APRIL as a transgene in T cells. These mice appeared normal and showed no signs of B cell hyperplasia. Transgenic T cells revealed a greatly enhanced survival in vitro as well as enhanced survival of staphylococcal enterotoxin B–reactive CD4⁺ T cells in vivo, which both directly correlate with elevated Bcl-2 levels. Analysis of humoral responses to T cell–dependent antigens in the transgenic mice indicated that APRIL affects only IgM but not IgG responses. In contrast, T cell–independent type 2 (TI-2) humoral response was enhanced in APRIL transgenic mice. As TACI was previously reported to be indispensable for TI-2 antibody formation, these results suggest a role for APRIL/TACI interactions in the generation of this response. Taken together, our data indicate that APRIL is involved in the induction and/or maintenance of T and B cell responses.

O besity is the result of an imbalance between energy intake and energy expenditure. Using high-density DNA microarrays and Northern analyses, we demonstrated that the activation of a nutrient-sensing pathway, the hexosamine biosynthesis pathway (HBP), rapidly decreased the expression of a cluster of nuclear-encoded mitochondrial genes involved in skeletal muscle oxidative phosphorylation. Conversely, the expression of uncoupling protein-1 and of the same mitochondrial genes was increased in brown adipose tissue. Most important, these transcriptional changes were accompanied by a marked decrease in whole-body energy expenditure. Short-term overfeeding replicated this transcriptional pattern, suggesting that this adaptation to nutrient abundance occurs under physiological conditions. Thus, the activation of the HBP by nutrients represents a biochemical link between nutrient availability, mitochondrial proteins, and energy expenditure, and it is likely to play an important role in the regulation of energy balance.

T GF-βs play diverse and complex roles in many biological processes. In tumorigenesis, they can function either as tumor suppressors or as pro-oncogenic factors, depending on the stage of the disease. We have developed transgenic mice expressing a TGF-β antagonist of the soluble type II TGF-β receptor:Fc fusion protein class, under the regulation of the mammary-selective MMTV-LTR promoter/enhancer. Biologically significant levels of antagonist were detectable in the serum and most tissues of this mouse line. The mice were resistant to the development of metastases at multiple organ sites when compared with wild-type controls, both in a tail vein metastasis assay using isogenic melanoma cells and in crosses with the MMTV-neu transgenic mouse model of metastatic breast cancer. Importantly, metastasis from endogenous mammary tumors was suppressed without any enhancement of primary tumorigenesis. Furthermore, aged transgenic mice did not exhibit the severe pathology characteristic of TGF-β null mice, despite lifetime exposure to the antagonist. The data suggest that in vivo the antagonist may selectively neutralize the undesirable TGF-β associated with metastasis, while sparing the regulatory roles of TGF-βs in normal tissues. Thus this soluble TGF-β antagonist has potential for long-term clinical use in the prevention of metastasis.

W e describe a 3-year-old boy with biotin dependency not caused by biotinidase, holocarboxylase synthetase, or nutritional biotin deficiency. We sought to define the mechanism of his biotin dependency. The child became acutely encephalopathic at age 18 months. Urinary organic acids indicated deficiency of several biotin-dependent carboxylases. Symptoms improved rapidly following biotin supplementation. Serum biotinidase activity and Biotinidase gene sequence were normal. Activities of biotin-dependent carboxylases in PBMCs and cultured skin fibroblasts were normal, excluding biotin holocarboxylase synthetase deficiency. Despite extracellular biotin sufficiency, biotin withdrawal caused recurrent abnormal organic aciduria, indicating intracellular biotin deficiency. Biotin uptake rates into fresh PBMCs from the child and into his PBMCs transformed with Epstein Barr virus were about 10% of normal fresh and transformed control cells, respectively. For fresh and transformed PBMCs from his parents, biotin uptake rates were consistent with heterozygosity for an autosomal recessive genetic defect. Increased biotin breakdown was ruled out, as were artifacts of biotin supplementation and generalized defects in membrane permeability for biotin. These results provide evidence for a novel genetic defect in biotin transport. This child is the first known with this defect, which should now be included in the identified causes of biotin dependency.

E strogen is thought to contribute to the increased frequency of autoimmune disorders occurring in females, but a molecular basis for its effects on autoimmunity remains to be elucidated. We have shown previously that estrogen leads to the survival and activation of autoreactive cells in the naive repertoire. To identify the molecular pathways involved in B cell tolerance, we sought to identify genes that are differentially regulated by estrogen in mouse B cells. Several genes involved in B cell activation and survival, including cd22, shp-1, bcl-2, and vcam-1, were upregulated by estrogen in B cells. We found that overexpression of CD22 and SHP-1 in B cells decreased B cell receptor signaling. Estrogen receptors α and β are expressed on B cells and are functional, since they can directly upregulate expression of CD22, SHP-1, and Bcl-2. Estrogen treatment protected isolated primary B cells from B cell receptor–mediated apoptosis. These results suggest that estrogen induces a genetic program that alters survival and activation of B cells in a B cell–autonomous fashion and thus skews the naive immune system toward autoreactivity.

C opolymer 1 (Cop 1, Copaxone [Teva Marion Partners, Kansas City, Missouri, USA]), a random amino acid copolymer of tyrosine (Y), glutamic acid (E), alanine (A), and lysine (K), reduces the frequency of relapses by 30% in relapsing-remitting multiple sclerosis (MS) patients. In the present study, novel random four–amino acid copolymers, whose design was based on the nature of the anchor residues of the immunodominant epitope of myelin basic protein (MBP) 85-99 and of the binding pockets of MS-associated HLA-DR2 (DRB1*1501), have been synthesized by solid-phase chemistry. Poly (Y, F, A, K) (YFAK) inhibited binding of the biotinylated MBP 86-100 epitope to HLA-DR2 molecules more efficiently than did either unlabeled MBP 85-99 or any other copolymer including Cop 1. Moreover, YFAK and poly (F, A, K) (FAK) were much more effective than Cop 1 in inhibition of MBP 85-99–specific HLA-DR2–restricted T cell clones. Most importantly, these novel copolymers suppressed experimental autoimmune encephalomyelitis, induced in the susceptible SJL/J (H-2^s) strain of mice with the encephalitogenic epitope PLP 139-151, more efficiently than did Cop 1. Thus, random synthetic copolymers designed according to the binding motif of the human immunodominant epitope MBP 85-99 and the binding pockets of HLA-DR2 might be more beneficial than Cop 1 in treatment of MS.