Cell biology
Abstract
Lysosomal enzymes are synthesized in the endoplasmic reticulum (ER) and transferred to the Golgi complex by interaction with the Batten disease protein CLN8 (ceroid lipofuscinosis, neuronal, 8). Here we investigated the relationship of this pathway with CLN6, an ER-associated protein of unknown function that is defective in a different Batten disease subtype. Experiments focused on protein interaction and trafficking identified CLN6 as an obligate component of a CLN6-CLN8 complex (herein referred to as EGRESS: ER-to-Golgi relaying of enzymes of the lysosomal system), which recruits lysosomal enzymes at the ER to promote their Golgi transfer. Mutagenesis experiments showed that the second luminal loop of CLN6 is required for the interaction of CLN6 with the enzymes but dispensable for interaction with CLN8. In vitro and in vivo studies showed that CLN6 deficiency results in inefficient ER export of lysosomal enzymes and diminished levels of the enzymes at the lysosome. Mice lacking both CLN6 and CLN8 did not display aggravated pathology compared with the single deficiencies, indicating that the EGRESS complex works as a functional unit. These results identify CLN6 and the EGRESS complex as key players in lysosome biogenesis and shed light on the molecular etiology of Batten disease caused by defects in CLN6.
Authors
Lakshya Bajaj, Jaiprakash Sharma, Alberto di Ronza, Pengcheng Zhang, Aiden Eblimit, Rituraj Pal, Dany Roman, John R. Collette, Clarissa Booth, Kevin T. Chang, Richard N. Sifers, Sung Y. Jung, Jill M. Weimer, Rui Chen, Randy W. Schekman, Marco Sardiello
Abstract
Ligand-dependent activation of Hedgehog (Hh) signaling in cancer occurs without mutations in canonical pathway genes. Consequently, the genetic basis of Hh pathway activation in adult solid tumors, such as small-cell lung cancer (SCLC), is unknown. Here we show that combined inactivation of Trp53 and Rb1, a defining genetic feature of SCLC, leads to hypersensitivity to Hh ligand in vitro, and during neural tube development in vivo. This response is associated with the aberrant formation of primary cilia, an organelle essential for canonical Hh signaling through smoothened, a transmembrane protein targeted by small-molecule Hh inhibitors. We further show that loss of both Trp53 and Rb1 disables transcription of genes in the autophagic machinery necessary for the degradation of primary cilia. In turn, we also demonstrate a requirement for Kif3a, a gene essential for the formation of primary cilia, in a mouse model of SCLC induced by conditional deletion of both Trp53 and Rb1 in the adult airway. Our results provide a mechanistic framework for therapeutic targeting of ligand-dependent Hh signaling in human cancers with somatic mutations in both TP53 and RB1.
Authors
Catherine R. Cochrane, Vijesh Vaghjiani, Anette Szczepny, W. Samantha N. Jayasekara, Alvaro Gonzalez-Rajal, Kazu Kikuchi, Geoffrey W. McCaughan, Andrew Burgess, Daniel J. Gough, D. Neil Watkins, Jason E. Cain
Abstract
Connexin 43 (Cx43) gap junctions provide intercellular coupling which ensures rapid action potential propagation and synchronized heart contraction. Altered Cx43 localization and reduced gap junction coupling occur in failing hearts, contributing to ventricular arrhythmias and sudden cardiac death. Recent reports have found that an internally translated Cx43 isoform, GJA1-20k, is an auxiliary subunit for the trafficking of Cx43 in heterologous expression systems. Here, we have created a mouse model by using CRISPR technology to mutate a single internal translation initiation site in Cx43 (M213L mutation), which generates full length Cx43 but not GJA1-20k. We find that GJA1M213L/M213L mice have severely abnormal electrocardiograms despite preserved contractile function, reduced total Cx43, reduced gap junctions, and die suddenly at two to four weeks of age. Heterozygous GJA1M213L/WT mice survive to adulthood with increased ventricular ectopy. Biochemical experiments indicate that cytoplasmic Cx43 has a half life that is 50% shorter than membrane associated Cx43. Without GJA1-20k, poorly trafficked Cx43 is degraded. The data support that GJA1-20k, an endogenous entity translated independently of Cx43, is critical for Cx43 gap junction trafficking, maintenance of Cx43 protein, and normal electrical function of the mammalian heart.
Authors
Shaohua Xiao, Daisuke Shimura, Rachel Baum, Diana M. Hernandez, Sosse Agvanian, Yoshiko Nagaoka, Makoto Katsumata, Paul D. Lampe, Andre G. Kleber, TingTing Hong, Robin M. Shaw
Abstract
The tight junction protein claudin-2 is upregulated in disease. Although many studies have linked intestinal barrier loss to local and systemic disease, these have relied on macromolecular probes. In vitro analyses show however that these probes cannot be accommodated by size- and charge-selective claudin-2 channels. We sought to define the impact of claudin-2 channels on disease. Transgenic claudin-2 overexpression or IL-13-induced claudin-2 upregulation increased intestinal small cation permeability in vivo. IL-13 did not however affect permeability in claudin-2-knockout mice. Claudin-2 is therefore necessary and sufficient to effect size- and charge-selective permeability increases in vivo. In chronic disease, T-cell transfer colitis severity was augmented or diminished in claudin-2 transgenic or knockout mice, respectively. We translated in vitro data suggesting that casein kinase-2 (CK2) inhibition blocks claudin-2 channel function and found that CK2 inhibition prevented IL-13-induced, claudin-2-mediated permeability increases in vivo. In chronic immune-mediated colitis, CK2 inhibition attenuated progression in claudin-2-sufficient, but not claudin-2-knockout, mice, i.e., the effect was claudin-2-dependent. Paracellular flux mediated by claudin-2 channels can therefore promote immune-mediated colitis progression. Although the mechanisms by which claudin-2 channels intensify disease remain to be defined, these data suggest that claudin-2 may be an accessible target in immune-mediated disorders, including inflammatory bowel disease.
Authors
Preeti Raju, Nitesh Shashikanth, Pei-Yun Tsai, Pawin Pongkorpsakol, Sandra Chanez-Parades, Peter R. Steinhagen, Wei-Ting Kuo, Gurminder Singh, Sachiko Tsukita, Jerrold R. Turner
Abstract
Emerging immune therapy, such as with the anti–programmed cell death–1 (anti–PD-1) monoclonal antibody nivolumab, has shown efficacy in tumor suppression. Patients with terminal cancer suffer from cancer pain as a result of bone metastasis and bone destruction, but how PD-1 blockade affects bone cancer pain remains unknown. Here, we report that mice lacking Pdcd1 (Pd1−/−) demonstrated remarkable protection against bone destruction induced by femoral inoculation of Lewis lung cancer cells. Compared with WT mice, Pd1−/− mice exhibited increased baseline pain sensitivity, but the development of bone cancer pain was compromised in Pd1−/− mice. Consistently, these beneficial effects in Pd1−/− mice were recapitulated by repeated i.v. applications of nivolumab in WT mice, even though nivolumab initially increased mechanical and thermal pain. Notably, PD-1 deficiency or nivolumab treatment inhibited osteoclastogenesis without altering tumor burden. PD-L1 and CCL2 are upregulated within the local tumor microenvironment, and PD-L1 promoted RANKL-induced osteoclastogenesis through JNK activation and CCL2 secretion. Bone cancer upregulated CCR2 in primary sensory neurons, and CCR2 antagonism effectively reduced bone cancer pain. Our findings suggest that, despite a transient increase in pain sensitivity following each treatment, anti–PD-1 immunotherapy could produce long-term benefits in preventing bone destruction and alleviating bone cancer pain by suppressing osteoclastogenesis.
Authors
Kaiyuan Wang, Yun Gu, Yihan Liao, Sangsu Bang, Christopher R. Donnelly, Ouyang Chen, Xueshu Tao, Anthony J. Mirando, Matthew J. Hilton, Ru-Rong Ji
Abstract
Dominant mutations in the HSP70 co-chaperone DNAJB6 cause a late onset muscle disease termed limb girdle muscular dystrophy type D1 (LGMDD1), which is characterized by protein aggregation and vacuolar myopathology. Disease mutations reside within the G/F domain of DNAJB6, but the molecular mechanisms underlying dysfunction are not well understood. Using yeast, cell culture, and mouse models of LGMDD1, we found that the toxicity associated with disease-associated DNAJB6 required its interaction with HSP70, and that abrogating this interaction genetically or with small molecules was protective. In skeletal muscle, DNAJB6 localizes to the Z-disc with HSP70. Whereas HSP70 normally diffused rapidly between the Z-disc and sarcoplasm, the rate of HSP70’s diffusion in LGMDD1 mouse muscle was diminished likely because it has an unusual affinity for the Z-disc and mutant DNAJB6. Treating LGMDD1 mice with a small molecule inhibitor of the DNAJ-HSP70 complex re-mobilized HSP70, improved strength and corrected myopathology. These data support a model in which LGMDD1 mutations in DNAJB6 are a gain-of-function disease that is, counter-intuitively, mediated via HSP70 binding. Thus, therapeutic approaches targeting HSP70:DNAJB6 may be effective in treating this inherited muscular dystrophy.
Authors
Rocio Bengoechea, Andrew R. Findlay, Ankan K. Bhadra, Hao Shao, Kevin C. Stein, Sara K. Pittman, Jill Daw, Jason E. Gestwicki, Heather L. True, Conrad C. Weihl
Abstract
While Canakinumab Anti-Inflammatory Thrombosis Outcomes Study (CANTOS) established the role of treating inflammation in atherosclerosis, our understanding of endothelial activation at atherosclerosis-prone sites remains limited. Disturbed flow at atheroprone regions primes plaque inflammation by enhancing endothelial NF-κB signaling. Herein, we demonstrate a role for the Nck adaptor proteins in disturbed flow-induced endothelial activation. Although highly similar, only Nck1 deletion, but not Nck2 deletion, limited flow-induced NF-κB activation and proinflammatory gene expression. Nck1 knockout mice showed reduced endothelial activation and inflammation in both models of disturbed flow and high fat diet-induced atherosclerosis, whereas Nck2 deletion did not. Bone marrow chimeras confirmed that vascular Nck1, but not hematopoietic Nck1, mediated this effect. Domain swap experiments and point mutations identified the Nck1 SH2 domain and the first SH3 domain as critical for flow-induced endothelial activation. We further characterized Nck1’s proinflammatory role by identifying interleukin-1 type I receptor kinase-1 (IRAK-1) as a Nck1-selective binding partner, demonstrating IRAK-1 activation by disturbed flow required Nck1 in vitro and in vivo, showing endothelial Nck1 and IRAK-1 staining in early human atherosclerosis, and demonstrating that disturbed flow-induced endothelial activation required IRAK-1. Taken together, our data reveal a hitherto unknown link between Nck1 and IRAK-1 in atherogenic inflammation.
Authors
Mabruka Alfaidi, Christina H. Acosta, Dongdong Wang, James G. Traylor, A. Wayne Orr
Abstract
Haploinsufficiency of factors governing genome stability underlies hereditary breast and ovarian cancer. Homologous recombination (HR) repair is a major pathway disabled in these cancers. With the aim of identifying new candidate genes, we examined early onset breast cancer patients negative for BRCA1 and BRCA2 pathogenic variants. Here, we focused on CtIP (RBBP8 gene) that mediates HR repair through the end-resection of DNA double-strand breaks (DSB). Notably, the patients exhibited a number of rare germline RBBP8 variants, and functional analysis revealed that these variants did not affect DNA DSB end-resection efficiency. However, expression of a subset of variants led to deleterious nucleolytic degradation of stalled DNA replication forks in a manner similar to cells lacking BRCA1 or BRCA2. In contrast to BRCA1 and BRCA2, CtIP deficiency promoted the helicase-driven destabilization of RAD51 nucleofilaments at damaged DNA replication forks. Taken together, our work identifies CtIP as a critical regulator of DNA replication fork integrity, which when compromised, may predispose to the development of early onset breast cancer.
Authors
Reihaneh Zarrizi, Martin R. Higgs, Karolin Voßgröne, Maria Rossing, Birgitte Bertelsen, Muthiah Bose, Arne N. Kousholt, Heike I. Rösner, Bent Ejlertsen, Grant S. Stewart, Finn Cilius Nielsen, Claus Sørensen
Abstract
Although autophagy is generally protective, uncontrolled or excessive activation of autophagy can be detrimental. However, it is often difficult to distinguish death by autophagy from death with autophagy, and whether autophagy contributes to death in cardiomyocytes (CMs) is still controversial. Excessive activation of autophagy induces a morphologically and biochemically defined form of cell death termed autosis. Whether autosis is involved in tissue injury induced under pathologically relevant conditions is poorly understood. In the present study, myocardial ischemia/reperfusion (I/R) induced autosis in CMs, as evidenced by cell death with numerous vacuoles and perinuclear spaces, and depleted intracellular membranes. Autosis was observed frequently after 6 hours of reperfusion, accompanied by upregulation of Rubicon, attenuation of autophagic flux, and marked accumulation of autophagosomes. Genetic downregulation of Rubicon inhibited autosis and reduced I/R injury, whereas stimulation of autosis during the late phase of I/R with Tat–Beclin 1 exacerbated injury. Suppression of autosis by ouabain, a cardiac glycoside, in humanized Na+,K+-ATPase–knockin mice reduced I/R injury. Taken together, these results demonstrate that autosis is significantly involved in I/R injury in the heart and triggered by dysregulated accumulation of autophagosomes due to upregulation of Rubicon.
Authors
Jihoon Nah, Peiyong Zhai, Chun-Yang Huang, Álvaro F. Fernández, Satvik Mareedu, Beth Levine, Junichi Sadoshima
Abstract
Cancer cells can develop a strong addiction to discrete molecular regulators, which control the aberrant gene expression programs that drive and maintain the cancer phenotype. Here, we report the identification of the RNA-binding protein HuR/ELAVL1 as a central oncogenic driver for malignant peripheral nerve sheath tumours (MPNSTs), which are highly aggressive sarcomas that originate from cells of the Schwann cell lineage. HuR was found to be highly elevated and bound to a multitude of cancer-associated transcripts in human MPNST samples. Accordingly, genetic and pharmacological inhibition of HuR had potent cytostatic and cytotoxic effects on tumour growth, and strongly supressed metastatic capacity in vivo. Importantly, we linked the profound tumorigenic function of HuR to its ability to simultaneously regulate multiple essential oncogenic pathways in MPNST cells, including the Wnt/beta-Catenin, YAP/TAZ, Rb-E2F and BET proteins, which converge on key transcriptional networks. Given the exceptional dependency of MPNST cells on HuR for survival, proliferation, and dissemination, we propose that HuR represents a promising therapeutic target for MPNST treatment.
Authors
Marta Palomo-Irigoyen, Encarnación Pérez-Andrés, Marta Iruarrizaga-Lejarreta, Adrián Barreira Manrique, Miguel Tamayo-Caro, Laura Vila-Vecilla, Leire Moreno-Cugnon, Nagore Beitia Telletxea, Daniela Medrano, David Fernández-Ramos, Juan-Jose Lozano, Satoshi Okawa, José Luis Lavín, Natalia Martin-Martin, James D. Sutherland, Virginia Gutiérrez-de Juan, Monika Gonzalez-Lopez, Nuria Macias-Camara, David Mosén-Ansorena, Liyam Laraba, C. Oliver Hanemann, Emanuela Ercolano, David B. Parkinson, Christopher W. Schultz, Marcos J. Araúzo-Bravo, Alex M. Ascensión, Daniela Gerovska, Haizea Iribar, Ander Izeta, Peter Pytel, Philipp Krastel, Alessandro Provenzani, Pierfausto Seneci, Ruben D. Carrasco, Antonio del Sol, Maria L. Martinez Chantar, Rosa Barrio, Eduard Serra, Conxi Lázaro, Adrienne M. Flanagan, Myriam Gorospe, Nancy Ratner, Arkaitz Carracedo, Ana María Aransay, Marta Varela-Rey, Ashwin Woodhoo
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Copyright © 2020 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)