Siah2 control of T-regulatory cells limits anti-tumor immunity.

Understanding the mechanisms underlying anti-tumor immunity is pivotal for improving immune-based cancer therapies. Here, we report that growth of BRAF-mutant melanoma cells is inhibited, up to complete rejection, in Siah2-/- mice. Growth-inhibited tumors exhibit increased numbers of intra-tumoral activated T cells and decreased expression of Ccl17, Ccl22, and Foxp3. Marked reduction in Treg proliferation and tumor infiltration coincide with G1 arrest in tumor infiltrated Siah2-/- Tregs in vivo or following T cell stimulation in culture, attributed to elevated expression of the cyclin-dependent kinase inhibitor p27, a Siah2 substrate. Growth of anti-PD-1 therapy resistant melanoma is effectively inhibited in Siah2-/- mice subjected to PD-1 blockade, indicating synergy between PD-1 blockade and Siah2 loss. Low SIAH2 and FOXP3 expression is identified in immune responsive human melanoma tumors. Overall, Siah2 regulation of Treg recruitment and cell cycle progression effectively controls melanoma development and Siah2 loss in the host sensitizes melanoma to anti-PD-1 therapy

Genetic Inhibition of the Ubiquitin Ligase Rnf5 Attenuates Phenotypes Associated to F508del Cystic Fibrosis Mutation

Cystic fibrosis (CF) is caused by mutations in the CFTR chloride channel. Deletion of phenylalanine 508 (F508del), the most frequent CF mutation, impairs CFTR trafficking and gating. F508del-CFTR mistrafficking may be corrected by acting directly on mutant CFTR itself or by modulating expression/activity of CFTR-interacting proteins, that may thus represent potential drug targets. To evaluate possible candidates for F508del-CFTR rescue, we screened a siRNA library targeting known CFTR interactors. Our analysis identified RNF5 as a protein whose inhibition promoted significant F508del-CFTR rescue and displayed an additive effect with the investigational drug VX-809. Significantly, RNF5 loss in F508del-CFTR transgenic animals ameliorated intestinal malabsorption and concomitantly led to an increase in CFTR activity in intestinal epithelial cells. In addition, we found that RNF5 is differentially expressed in human bronchial epithelia from CF vs. control patients. Our results identify RNF5 as a target for therapeutic modalities to antagonize mutant CFTR proteins

The Anaphase-Promoting Complex or Cyclosome Supports Cell Survival in Response to Endoplasmic Reticulum Stress

The anaphase-promoting complex or cyclosome (APC/C) is a multi-subunit ubiquitin ligase that regulates exit from mitosis and G1 phase of the cell cycle. Although the regulation and function of APC/CCdh1 in the unperturbed cell cycle is well studied, little is known of its role in non-genotoxic stress responses. Here, we demonstrate the role of APC/CCdh1 (APC/C activated by Cdh1 protein) in cellular protection from endoplasmic reticulum (ER) stress. Activation of APC/CCdh1 under ER stress conditions is evidenced by Cdh1-dependent degradation of its substrates. Importantly, the activity of APC/CCdh1 maintains the ER stress checkpoint, as depletion of Cdh1 by RNAi impairs cell cycle arrest and accelerates cell death following ER stress. Our findings identify APC/CCdh1 as a regulator of cell cycle checkpoint and cell survival in response to proteotoxic insults

The ER-Bound RING Finger Protein 5 (RNF5/RMA1) Causes Degenerative Myopathy in Transgenic Mice and Is Deregulated in Inclusion Body Myositis

Growing evidence supports the importance of ubiquitin ligases in the pathogenesis of muscular disorders, although underlying mechanisms remain largely elusive. Here we show that the expression of RNF5 (aka RMA1), an ER-anchored RING finger E3 ligase implicated in muscle organization and in recognition and processing of malfolded proteins, is elevated and mislocalized to cytoplasmic aggregates in biopsies from patients suffering from sporadic-Inclusion Body Myositis (sIBM). Consistent with these findings, an animal model for hereditary IBM (hIBM), but not their control littermates, revealed deregulated expression of RNF5. Further studies for the role of RNF5 in the pathogenesis of s-IBM and more generally in muscle physiology were performed using RNF5 transgenic and KO animals. Transgenic mice carrying inducible expression of RNF5, under control of β-actin or muscle specific promoter, exhibit an early onset of muscle wasting, muscle degeneration and extensive fiber regeneration. Prolonged expression of RNF5 in the muscle also results in the formation of fibers containing congophilic material, blue-rimmed vacuoles and inclusion bodies. These phenotypes were associated with altered expression and activity of ER chaperones, characteristic of myodegenerative diseases such as s-IBM. Conversely, muscle regeneration and induction of ER stress markers were delayed in RNF5 KO mice subjected to cardiotoxin treatment. While supporting a role for RNF5 Tg mice as model for s-IBM, our study also establishes the importance of RNF5 in muscle physiology and its deregulation in ER stress associated muscular disorders

Emerging roles of ATF2 and the dynamic AP1 network in cancer

Cooperation among transcription factors is central for their ability to execute specific transcriptional programmes. The AP1 complex exemplifies a network of transcription factors that function in unison under normal circumstances and during the course of tumour development and progression. This Perspective summarizes our current understanding of the changes in members of the AP1 complex and the role of ATF2 as part of this complex in tumorigenesis.Fil: Lopez Bergami, Pablo Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental (i); Argentina; ArgentinaFil: Lau, Eric . Burnham Institute for Medical Research; Estados UnidosFil: Ronai, Zeev . Burnham Institute for Medical Research; Estados Unido

Cdh1 depletion sensitizes cells to ER stress-induced cell death.

<p>(A) Empty vector-transfected or Cdh1-KD cells were treated with DMSO or 0.5, 1, or 2 µg/ml of TM for 9 h or 24 h. Total cell lysates were immunoblotted for cleaved PARP and indicated endogenous proteins. (B) Empty vector-transfected or Cdh1-KD cells were treated with DMSO, 0.5 µg/ml, or 1 µg/ml of TM for 9 h or 12 h. Total cell lysates were analyzed as in (A). (C) Empty vector-transfected or Cdh1-KD cells were treated with solvent (mock) or 1–3 mM DTT for 9 h or 12 h. Total cell lysates were immunoblotted as in (A). (D) <i>Left</i>, empty vector-transfected or Cdh1-KD cells were collected at 9, 12, and 24 h after treatment with DMSO or 0.5 µg/ml of TM for DNA content analysis by flow cytometry. Graph shows percentage of sub-G1 population at each time point. <i>Right</i>, empty vector-transfected or Cdh1-KD cells were collected at 9, 12, and 24 h after treatment with solvent (mock) or 1 mM DTT for DNA content analysis by flow cytometry. Graph shows percentage of sub-G1 population at each time point.</p

Mechanisms supporting APC/C^Cdh1 activity under ER stress conditions.

<p>(A) HeLa cells were treated with DMSO, 0.5 µg/ml of TM alone, or 0.5 µg/ml of TM plus 5 µM of MG-132 for 16 h. Immunoprecipitates of endogenous Cdc27 were immunoblotted for endogenous Cdh1. Immunoprecipitation using IgG served as negative control. ** indicates Cdh1-specific top band; *indicates non-specific bottom band. (B) HeLa cells were treated with DMSO or 1 µg/ml of TM for 16 h. CDK2 or CDK1 antibodies were used to immunoprecipitate endogenous CDK2 or CDK1 complexes, respectively. Immunoprecipitates were then used in <i>in vitro</i> kinase assays using histone H1 as substrate. <i>Left</i>, autoradiography of ³²P-histone H1 phosphorylated by CDK2 complexes. Coomassie stains input of histone H1 in the reactions. Intensity of the autoradioactive bands were quantified by Image J, normalized to histone H1 input, and presented as arbitrary units (A.U.). Immunoblot shows comparable levels of endogenous CDK2 and the indicated proteins before and after TM treatment. <i>Right</i>, autoradiography of ³²P-histone H1 phosphorylated by CDK1 complexes, analyzed as indicated for CDK2. (C) <i>Left</i>, total cell lysates from HeLa cells treated with DMSO or 1 µg/ml of TM for 16 h were immunoblotted for the indicated endogenous proteins. <i>Right</i>, quantification of endogenous Emi1 mRNA levels in HeLa cells treated with DMSO or 1 µg/ml of TM for 16 h, measured by SYBR-green qRT-PCR.</p

APC/C^Cdh1 is activated under ER stress conditions.

<p>(A) <i>Left</i>, HeLa cells were treated with DMSO or 2.5 µg/ml of tunicamycin (TM) for 8 h. Total cell lysates were immunoblotted for the indicated endogenous proteins. GRP78 served as a marker of ER stress. <i>Right</i>, HeLa cells were harvested at the indicated times after addition of DMSO or 2.5 µg/ml of TM. Total cell lysates were immunoblotted for the indicated endogenous proteins. HSP90 was used as a loading control. (B) HeLa cells were treated with DMSO or 1 µg/ml of tunicamycin for the indicated times. <i>Immunoblots</i>, total cell lysates were immunoblotted for the indicated endogenous proteins. <i>Graphs</i>, transcript levels as measured by SYBR-green qRT-PCR and protein levels as quantified by LiCOR-Odyssey software on immunoblots are compared for the indicated proteins. All measurements were normalized to the DMSO-0 h sample with relative value of 1. (C) HeLa cells were transfected with pSUPER (empty vector) or pSUPER-Cdh1-shRNA (Cdh1-KD). 24 h after transfection, cells were treated with DMSO, 1 µg/ml of TM alone, or 1 µg/ml of TM plus MG-132 (2 or 5 µM) for 16 h. Total cell extracts were immunoblotted for the indicated endogenous proteins.</p