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[beta] Cell apoptosis and dedifferentiation are 2 hotly debated mechanisms underlying [beta] cell loss in type 2 diabetes; however, the molecular drivers underlying such events remain largely unclear. Here, we performed a side-by-side comparison of mice carrying [beta] cell-specific deletion of ER-associated degradation (ERAD) and autophagy. We reported that, while autophagy was necessary for [beta] cell survival, the highly conserved Sel1L-Hrd1 ERAD protein complex was required for the maintenance of [beta] cell maturation and identity. Using single-cell RNA-Seq, we demonstrated that Sel1L deficiency was not associated with [beta] cell loss, but rather loss of [beta] cell identity. Sel1L-Hrd1 ERAD controlled [beta] cell identity via TGF-[beta] signaling, in part by mediating the degradation of TGF-[beta] receptor 1. Inhibition of TGF-[beta] signaling in Sel1L-deficient [beta] cells augmented the expression of [beta] cell maturation markers and increased the total insulin content. Our data revealed distinct pathogenic effects of 2 major proteolytic pathways in [beta] cells, providing a framework for therapies targeting distinct mechanisms of protein quality control., Introduction Type 2 diabetes (T2D) is a heterogeneous multicomponent disease, in which disease initiation and progression are triggered and propelled by pancreatic [beta] cell dysfunction and death. Recent studies have [...]

Myc activation is a primary oncogenic event in many human cancers; however, these transcription factors are difficult to inhibit pharmacologically, suggesting that Myc-dependent downstream effectors may be more tractable therapeutic targets. Here, we show that Myc overexpression induces endoplasmic reticulum (ER) stress and engages the inositol-requiring enzyme 1[alpha] (IRE1[alpha])/X-box binding protein 1 (XBP1) pathway through multiple molecular mechanisms in a variety of c- Myc- and N-Myc-dependent cancers. In particular, Myc-overexpressing cells require IRE1[alpha]/XBP1 signaling for sustained growth and survival in vitro and in vivo, dependent on elevated stearoyl-CoA-desaturase 1 (SCD1) activity. Pharmacological and genetic XBP1 inhibition induces Myc-dependent apoptosis, which is alleviated by exogenous unsaturated fatty acids. Of note, SCD1 inhibition phenocopies IRE1[alpha] RNase activity suppression in vivo. Furthermore, IRE1[alpha] inhibition enhances the cytotoxic effects of standard chemotherapy drugs used to treat c-Myc-overexpressing Burkitt's lymphoma, suggesting that inhibiting the IRE1[alpha]/XBP1 pathway is a useful general strategy for treatment of Myc- driven cancers., Introduction The Myc family of proto-oncogenes (MYC, MYCN, MYCL) encodes bHLHZ (basic helix-loop-helix leucine zipper) transcription factors, which regulate thousands of genes coordinating numerous cellular processes, including proliferation, differentiation, self-renewal, [...]

Myeloid-derived suppressor cells (MDSCs) are major negative regulators of immune responses in cancer and chronic infections. It remains unclear if regulation of MDSC activity in different conditions is controlled by similar mechanisms. We compared MDSCs in mice with cancer and lymphocytic choriomeningitis virus (LCMV) infection. Chronic LCMV infection caused the development of monocytic MDSCs (M-MDSCs) but did not induce polymorphonuclear MDSCs (PMN-MDSCs). In contrast, both MDSC populations were present in cancer models. An acquisition of immune-suppressive activity by PMN-MDSCs in cancer was controlled by IRE1[alpha] and ATF6 pathways of the endoplasmic reticulum (ER) stress response. Abrogation of PMN-MDSC activity by blockade of the ER stress response resulted in an increase in tumor-specific immune response and reduced tumor progression. In contrast, the ER stress response was dispensable for suppressive activity of M-MDSCs in cancer and LCMV infection. Acquisition of immune-suppressive activity by M-MDSCs in spleens was mediated by IFN-[gamma] signaling. However, it was dispensable for suppressive activity of M-MDSCs in tumor tissues. Suppressive activity of M-MDSCs in tumors was retained due to the effect of IL-6 present at high concentrations in the tumor site. These results demonstrate disease- and population-specific mechanisms of MDSC accumulation and the need for targeting different pathways to achieve inactivation of these cells., Introduction Myeloid-derived suppressor cells (MDSCs) with potent immune-suppressive activity are widely implicated in negative regulation of immune responses in many pathological conditions including cancer, chronic inflammation, infections, autoimmune diseases, and [...]

Podocytes are key to the glomerular filtration barrier by forming a slit diaphragm between interdigitating foot processes; however, the molecular details and functional importance of protein folding and degradation in the ER remain unknown. Here, we show that the SEL1L-HRD1 protein complex of ER-associated degradation (ERAD) is required for slit diaphragm formation and glomerular filtration function. SEL1L-HRD1 ERAD is highly expressed in podocytes of both mouse and human kidneys. Mice with podocyte-specific Sel1L deficiency develop podocytopathy and severe congenital nephrotic syndrome with an impaired slit diaphragm shortly after weaning and die prematurely, with a median lifespan of approximately 3 months. We show mechanistically that nephrin, a type 1 membrane protein causally linked to congenital nephrotic syndrome, is an endogenous ERAD substrate. ERAD deficiency attenuated the maturation of nascent nephrin, leading to its retention in the ER. We also show that various autosomal-recessive nephrin disease mutants were highly unstable and broken down by SEL1L-HRD1 ERAD, which attenuated the pathogenicity of the mutants toward the WT allele. This study uncovers a critical role of SEL1L-HRD1 ERAD in glomerular filtration barrier function and provides insights into the pathogenesis associated with autosomal-recessive disease mutants., Introduction The key function of the kidneys is the ultrafiltration of blood in the glomerulus, where podocytes, specialized differentiated epithelial cells, wrap around capillaries of the glomerulus via a unique [...]

Activation of the ER stress response is associated with malignant progression of B cell chronic lymphocytic leukemia (CLL). We developed a murine CLL model that lacks the ER stress-associated transcription factor XBP-1 in B cells and found that XBP-1 deficiency decelerates malignant progression of CLL-associated disease. XBP-1 deficiency resulted in acquisition of phenotypes that are disadvantageous for leukemic cell survival, including compromised BCR signaling capability and increased surface expression of sphingosine-1phosphate receptor 1 (S1P1). Because XBP-1 expression requires the RNase activity of the ER transmembrane receptor IRE-1, we developed a potent IRE-1 RNase inhibitor through chemical synthesis and modified the structure to facilitate entry into cells to target the IRE-1/XBP-1 pathway. Treatment of CLL cells with this inhibitor (B-I09) mimicked XBP-1 deficiency, including upregulation of IRE-1 expression and compromised BCR signaling. Moreover, B-I09 treatment did not affect the transport of secretory and integral membrane-bound proteins. Administration of B-I09 to CLL tumor-bearing mice suppressed leukemic progression by inducing apoptosis and did not cause systemic toxicity. Additionally, B-I09 and ibrutinib, an FDA-approved BTK inhibitor, synergized to induce apoptosis in B cell leukemia, lymphoma, and multiple myeloma. These data indicate that targeting XBP-1 has potential as a treatment strategy, not only for multiple myeloma, but also for mature B cell leukemia and lymphoma., Introduction The functional role of the ER stress response in mature B cell leukemia or lymphoma has been largely overlooked because leukemia and lymphoma cells do not expand their ER [...]

Abstract: Rana catesbeiana ribonuclease (RC-RNase) possesses tumor-specific cytotoxicity, which can be synergized by IFN-γ. However, it is unclear how RC-RNase and RC-RNase/IFN-γ induce cell death. In this study, we use substrate cleavage assays to systematically investigate RC-RNase- and RC-RNase/IFN-γ-induced caspase activation in HL-60, MCF-7, and SK-Hep-1 cells. We find that RC-RNase and RC-RNase/IFN-γ induce mitochondria-mediated caspase activation in HL-60 and MCF-7 cells but not in SK-Hep-1 cells, although death of SK-Hep-1 cells is closely related to mitochondrial disruptions. Our findings provide evidence that RC-RNase and RC-RNase/IFN-γ can kill different cancer cells by distinct mechanisms. Compared with onconase, RC-RNase seems to harbor a more specific anti-cancer activity. [Copyright &y& Elsevier]

Rana catesbeiana ribonuclease (RC-RNase) exerted strong anti-tumor activity and its cytotoxicity was shown to correlate with differentiation stages of three different hepatoma cell lines. In this study, we demonstrate different RC-RNase cytotoxicity in undifferentiated HL-60 cells and in those that had been induced to differentiate by retinoic acid or dimethylsulfoxide. RC-RNase showed cytotoxicity in undifferentiated HL-60 cells, but not in HL-60 cells undergoing terminal differentiation. Furthermore, the caspase-9/caspase-3 pathway was activated when RC-RNase induced death in undifferentiated HL-60 cells and induction of differentiation led to a reversal of the caspase activation pathway. [Copyright &y& Elsevier]

Myc activation is a primary oncogenic event in many human cancers; however, these transcription factors are difficult to inhibit pharmacologically, suggesting that Myc-dependent downstream effectors may be more tractable therapeutic targets. Here, we show that Myc overexpression induces endoplasmic reticulum (ER) stress and engages the inositol-requiring enzyme 1α (IRE1α)/X-box binding protein 1 (XBP1) pathway through multiple molecular mechanisms in a variety of c-Myc- and N-Myc-dependent cancers. In particular, Myc-overexpressing cells require IRE1α/XBP1 signaling for sustained growth and survival in vitro and in vivo, dependent on elevated stearoyl-CoA-desaturase 1 (SCD1) activity. Pharmacological and genetic XBP1 inhibition induces Myc-dependent apoptosis, which is alleviated by exogenous unsaturated fatty acids. Of note, SCD1 inhibition phenocopies IRE1α RNase activity suppression in vivo. Furthermore, IRE1α inhibition enhances the cytotoxic effects of standard chemotherapy drugs used to treat c-Myc-overexpressing Burkitt's lymphoma, suggesting that inhibiting the IRE1α/XBP1 pathway is a useful general strategy for treatment of Myc-driven cancers. [ABSTRACT FROM AUTHOR]