BIK ubiquitination by the E3 ligase Cul5-ASB11 determines cell fate during cellular stress

Epigallocatechin gallate attenuated high glucose-induced pancreatic beta cell dysfunction by modulating DRP1-mediated mitochondrial apoptosis pathways

Long-term exposure to hyperglycemic conditions leads to β-cell dysfunction, particularly mitochondrial dysfunction, and inflammatory and oxidative stress responses, which are considered the primary causes of β-cell death and the hallmarks of diabetes. Plant-active ingredients may play a key role in glycemic control. Epigallocatechin gallate (EGCG) is a characteristic catechin derived from tea that possesses anti-diabetic properties. Nonetheless, its underlying mechanisms remain elusive. Herein, the protective role of EGCG on high glucose (33 mM)-induced pancreatic beta cell dysfunction and its possible molecular mechanisms were investigated. Briefly, MIN6 cells were treated with glucose and EGCG (10 µM, 20 µM, and 40 µM) for 48 h. Our results revealed that EGCG dose-dependently restored mitochondrial membrane potential and concomitantly alleviated cell apoptosis. Mechanistically, the expression level of apoptotic protein BAX and Dynamic related protein 1 (DRP1) was significantly downregulated following EGCG treatment, whereas that of the anti-apoptotic protein BCL-2 was significantly upregulated. Taken together, EGCG alleviated high glucose-induced pancreatic beta cell dysfunction by targeting the DRP1-related mitochondrial apoptosis pathway and thus can serve as a nutritional intervention for the preservation of beta cell dysfunction in patients with type 2 diabetes mellitus.

The UBE2F-CRL5ASB11-DIRAS2 axis is an oncogene and tumor suppressor cascade in pancreatic cancer cells

UBE2F, a neddylation E2, neddylates CUL5 to activate cullin-RING ligase-5, upon coupling with neddylation E3 RBX2/SAG. Whether and how UBE2F controls pancreatic tumorigenesis is previously unknown. Here, we showed that UBE2F is essential for the growth of human pancreatic cancer cells with KRAS mutation. In the mouse KrasG12D pancreatic ductal adenocarcinoma (PDAC) model, Ube2f deletion suppresses cerulein-induced pancreatitis, and progression of acinar-to-ductal metaplasia (ADM) and pancreatic intraepithelial neoplasia. Mechanistically, Ube2f deletion inactivates the Mapk-c-Myc signals via blocking ubiquitylation of Diras2, a substrate of CRL5Asb11 E3 ligase. Biologically, DIRAS2 suppresses growth and survival of human pancreatic cancer cells harboring mutant KRAS, and Diras2 deletion largely rescues the phenotypes induced by Ube2f deletion. Collectively, Ube2f or Diras2 plays a tumor-promoting or tumor-suppressive role in the mouse KrasG12D PDAC model, respectively. The UBE2F-CRL5ASB11 axis could serve as a valid target for pancreatic cancer, whereas the levels of UBE2F or DIRAS2 may serve as prognostic biomarkers for PDAC patients.

ASB3 promotes hepatocellular carcinoma progression by mediating DR5 ubiquitination in TRAIL resistance

Ankyrin-repeat proteins with a suppressor of cytokine signaling box (ASB) proteins belong to the E3 ubiquitin ligase family. 18 ASB members have been identified whose biological functions are mostly unexplored. Here, we discovered that ASB3 was essential for hepatocellular carcinoma (HCC) development and high ASB3 expression predicted poor clinical outcomes. ASB3 silencing induced HCC cell growth arrest and apoptosis in vitro and in vivo. Liver-specific deletion of Asb3 gene suppressed diethylnitrosamine (DEN)-induced liver cancer development. Mechanistically, ASB3 interacted with death receptor 5 (DR5), which promoted ubiquitination and degradation of DR5. We further showed that ASB3 knockdown stabilized DR5 and increased the sensitivity of liver cancer cells to the treatment of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in a DR5-dependent manner in cellular and in animal models. In summary, we demonstrated that ASB3 promoted ubiquitination and degradation of DR5 in HCC, suggesting the potential of targeting ASB3 to HCC treatment and overcome TRAIL resistance.

Bik promotes proteasomal degradation to control low-grade inflammation

Although chronic low-grade inflammation does not cause immediate clinical symptoms, over the longer term, it can enhance other insults or age-dependent damage to organ systems and thereby contribute to age-related disorders, such as respiratory disorders, heart disease, metabolic disorders, autoimmunity, and cancer. However, the molecular mechanisms governing low-level inflammation are largely unknown. We discovered that Bcl-2-interacting killer (Bik) deficiency causes low-level inflammation even at baseline and the development of spontaneous emphysema in female but not male mice. Similarly, a single nucleotide polymorphism that reduced Bik levels was associated with increased inflammation and enhanced decline in lung function in humans. Transgenic expression of Bik in the airways of Bik-deficient mice inhibited allergen- or LPS-induced lung inflammation and reversed emphysema in female mice. Bik deficiency increased nuclear but not cytosolic p65 levels because Bik, by modifying the BH4 domain of Bcl-2, interacted with regulatory particle non-ATPase 1 (RPN1) and RPN2 and enhanced proteasomal degradation of nuclear proteins. Bik deficiency increased inflammation primarily in females because Bcl-2 and Bik levels were reduced in lung tissues and airway cells of female compared with male mice. Therefore, controlling low-grade inflammation by modifying the unappreciated role of Bik and Bcl-2 in facilitating proteasomal degradation of nuclear proteins may be crucial in treating chronic age-related diseases.

PAICS ubiquitination recruits UBAP2 to trigger phase separation for purinosome assembly

Purinosomes serve as metabolons to enhance de novo purine synthesis (DNPS) efficiency through compartmentalizing DNPS enzymes during stressed conditions. However, the mechanism underpinning purinosome assembly and its pathophysiological functions remains elusive. Here, we show that K6-polyubiquitination of the DNPS enzyme phosphoribosylaminoimidazole carboxylase and phosphoribosylaminoimidazolesuccinocarboxamide synthetase (PAICS) by cullin-5/ankyrin repeat and SOCS box containing 11 (Cul5/ASB11)-based ubiquitin ligase plays a driving role in purinosome assembly. Upon several purinosome-inducing cues, ASB11 is upregulated by relieving the H3K9me3/HP1α-mediated transcriptional silencing, thus stimulating PAICS polyubiquitination. The polyubiquitinated PAICS recruits ubiquitin-associated protein 2 (UBAP2), a ubiquitin-binding protein with multiple stretches of intrinsically disordered regions, thereby inducing phase separation to trigger purinosome assembly for enhancing DNPS pathway flux. In human melanoma, ASB11 is highly expressed to facilitate a constitutive purinosome formation to which melanoma cells are addicted for supporting their proliferation, viability, and tumorigenesis in a xenograft model. Our study identifies a driving mechanism for purinosome assembly in response to cellular stresses and uncovers the impact of purinosome formation on human malignancies.

Broadening horizons: the contribution of mitochondria-associated endoplasmic reticulum membrane (MAM) dysfunction in diabetic kidney disease

Diabetic kidney disease (DKD) is a global health issue that presents a complex pathogenesis and limited treatment options. To provide guidance for precise therapies, it is crucial to accurately identify the pathogenesis of DKD. Several studies have recognized that mitochondrial and endoplasmic reticulum (ER) dysfunction are key drivers of the pathogenesis of DKD. The mitochondria-associated ER membrane (MAM) is a dynamic membrane contact site (MSC) that connects the ER and mitochondria and is essential in maintaining the normal function of the two organelles. MAM is involved in various cellular processes, including lipid synthesis and transport, calcium homeostasis, mitochondrial fusion and fission, and ER stress. Meanwhile, recent studies confirm that MAM plays a significant role in the pathogenesis of DKD by regulating glucose metabolism, lipid metabolism, inflammation, ER stress, mitochondrial fission and fusion, and autophagy. Herein, this review aims to provide a comprehensive summary of the physiological function of MAMs and their impact on the progression of DKD. Subsequently, we discuss the trend of pharmaceutical studies that target MAM resident proteins for treating DKD. Furthermore, we also explore the future development prospects of MAM in DKD research, thereby providing a new perspective for basic studies and clinical treatment of DKD.

Polystyrene nanoplastics promote CHIP-mediated degradation of tight junction proteins by activating IRE1α/XBP1s pathway in mouse Sertoli cells

Microplastics (MPs) and nanoplastics (NPs) widely exist in human living environment and enter the body through water, food chain and breathing. Several studies have shown that MPs or NPs disrupt the blood-testis barrier in rodents. However, the molecular mechanism by which MPs and NPs damage the blood-testis barrier remains unclear. In the present study, our aim was to investigate the molecular mechanism of the destruction of blood-testis barrier induced by polystyrene (PS)-NPs. Mice were treated with 50 μg/kg·day PS-NPs by tail vein injection once daily for two consecutive days. The results showed that PS-NPs exposure significantly decreased the levels of tight junction (TJ) proteins ZO-2, occludin and claudin-11 in testis of mice. In vitro, we used TM4 Sertoli cells to explore the underlying mechanism of the decrease in TJ proteins induced by PS-NPs. We found that PS-NPs activated IRE1α and induced its downstream XBP1 splicing, which in turn elevated the expression of the E3 ubiquitin ligase CHIP, then CHIP triggers proteasomal degradation of ZO-2, occludin, and claudin-11 proteins. Our findings suggest that IRE1α/XBP1s/CHIP pathway is a pivotal mechanism of TJ proteins degradation induced by PS-NPs in mouse Sertoli cells. In conclusion, our results reveal that the degradation of TJ proteins is one of the mechanisms of blood-testis barrier destruction caused by acute exposure to PS-NPs.

UBXD8 mediates mitochondria-associated degradation to restrain apoptosis and mitophagy

The hexameric AAA-ATPase valosin-containing protein (VCP) is essential for mitochondrial protein quality control. How VCP is recruited to mammalian mitochondria remains obscure. Here we report that UBXD8, an ER- and lipid droplet-localized VCP adaptor, also localizes to mitochondria and locally recruits VCP. UBXD8 associates with mitochondrial and ER ubiquitin E3 ligases and targets their substrates for degradation. Remarkably, both mitochondria- and ER-localized UBXD8 can degrade mitochondrial and ER substrates in cis and in trans. UBXD8 also associates with the TOM complex but is dispensable for translocation-associated degradation. UBXD8 knockout impairs the degradation of the pro-survival protein Mcl1 but surprisingly sensitizes cells to apoptosis and mitochondrial stresses. UBXD8 knockout also hyperactivates mitophagy. We identify pro-apoptotic BH3-only proteins Noxa, Bik, and Bnip3 as novel UBXD8 substrates and determine that UBXD8 inhibits apoptosis via degrading Noxa and restrains mitophagy via degrading Bnip3. Collectively, our characterizations reveal UBXD8 as the major mitochondrial adaptor of VCP and unveil its role in apoptosis and mitophagy regulation.

ASB17 Facilitates the Burst of LPS-Induced Inflammation Through Maintaining TRAF6 Stability

ASB17, a member of the ankyrin repeat and SOCS box-containing protein (ASB) family, has been supposed to act as an E3 ubiquitin ligase. Actually, little is known about its biological function. In this study, we found that ASB17 knocking-out impaired the expression of the pro-inflammatory cytokines CCL2 and IL-6 in bone marrow-derived dendritic cells (BMDCs) stimulated by lipopolysaccharide (LPS), indicating an inflammation-promoting role of this gene. We reveal that ASB17 promotes LPS-induced nuclear factor kappa B (NF-κB) signal activation through interacting with TNF receptor-associated factor 6 (TRAF6) which is a crucial adaptor protein downstream of toll-like receptors (TLR). ASB17 via its aa177-250 segment interacts with the Zn finger domain of TRAF6. The interaction of ASB17 stabilizes TRAF6 protein through inhibiting K48-linked TRAF6 polyubiquitination. Therefore, we suggest that ASB17 facilitates LPS-induced NF-κB activation by maintaining TRAF6 protein stability. The inflammation enhancer role of ASB17 is recognized here, which provides new understanding of the activation process of inflammation and immune response.

Shared Gene Expression and Immune Pathway Changes Associated with Progression from Nevi to Melanoma

Simple Summary

Melanoma is a deadly skin cancer, and the incidence of melanoma is rising. Chemoprevention, using small molecule drugs to prevent the development of cancer, is a key strategy that could reduce the burden of melanoma on society. The long-term goal of our study is to develop a gene signature biomarker of progression from nevi to melanoma. We found that a small number of genes can distinguish nevi from melanoma and identified shared genes and immune-related pathways that are associated with progression from nevi to melanoma across independent datasets. This study demonstrates (1) a novel approach to aid melanoma chemoprevention trials by using a gene signature as a surrogate endpoint and (2) the feasibility of determining a gene signature biomarker of melanoma progression.

Abstract

There is a need to identify molecular biomarkers of melanoma progression to assist the development of chemoprevention strategies to lower melanoma incidence. Using datasets containing gene expression for dysplastic nevi and melanoma or melanoma arising in a nevus, we performed differential gene expression analysis and regularized regression models to identify genes and pathways that were associated with progression from nevi to melanoma. A small number of genes distinguished nevi from melanoma. Differential expression of seven genes was identified between nevi and melanoma in three independent datasets. C1QB, CXCL9, CXCL10, DFNA5 (GSDME), FCGR1B, and PRAME were increased in melanoma, and SCGB1D2 was decreased in melanoma, compared to dysplastic nevi or nevi that progressed to melanoma. Further supporting an association with melanomagenesis, these genes demonstrated a linear change in expression from benign nevi to dysplastic nevi to radial growth phase melanoma to vertical growth phase melanoma. The genes associated with melanoma progression showed significant enrichment of multiple pathways related to the immune system. This study demonstrates (1) a novel application of bioinformatic approaches to aid clinical trials of melanoma chemoprevention and (2) the feasibility of determining a gene signature biomarker of melanomagenesis.

E3 Ubiquitin Ligase ASB17 Promotes Apoptosis by Ubiquitylating and Degrading BCLW and MCL1

Simple Summary

B-cell lymphoma-2 family proteins have been widely accepted as the critical regulators in cell apoptosis, often found to be abnormally expressed in many cancers. Among them, B-cell leukemia/lymphoma w and myeloid cell leukemia-1 are two pro-survival proteins. Here, we reported that the ankyrin repeat and SOCS box protein 17 can degrade the two proteins in a ubiquitylation -dependent way. Furthermore, we generated the first ASB17 knockout C57BL/6J mice line. The results revealed that ASB17 deficiency inhibited apoptosis but did not affect testes development. Moreover, the ASB17-deficient mice were more resistant to the stimuli of etoposide, Altogether, these findings indicate that ASB17 is a novel positive mediator of cell apoptosis.

Abstract

Apoptosis is a very important process of cell death controlled by multiple genes during which cells undergo certain events before dying. Apoptosis helps to clean the unnecessary cells and has critical physiological significance. Altered apoptosis results in a disorder of cell death and is associated with many diseases such as neurodegenerative diseases and cancers. Here, we reported that the ankyrin repeat and SOCS box protein 17 (ASB17) was mainly expressed in the testis and promoted apoptosis both in vivo and in vitro. Analyzing ASB17-deficient mice generated by using the CRISPR/Cas9 system, we demonstrated that ASB17 deficiency resulted in the reduction of apoptosis in spermatogenic cells, but it did not affect the development of spermatozoa or normal fertility. Next, in an in vivo model, ASB17 deficiency prevented the apoptosis of spermatogonia induced by etoposide in male mice. We noted that ASB17 promoted apoptosis in a caspase-dependent manner in vitro. Moreover, ASB17 interacted with the members of the BCL2 family, including BCL2, BCLX, BCLW, and MCL1. Interestingly, ASB17 specifically degraded the two anti-apoptotic factors, BCLW and MCL1, in a ubiquitylation-dependent fashion. Collectively, our findings suggested that ASB17 acted as a distinct positive regulator of cell apoptosis.

DNA damage promotes ER stress resistance through elevation of unsaturated phosphatidylcholine in Caenorhabditis elegans

DNA damage triggers the cellular adaptive response to arrest proliferation and repair DNA damage; when damage is too severe to be repaired, apoptosis is initiated to prevent the spread of genomic insults. However, how cells endure DNA damage to maintain cell function remains largely unexplored. By using Caenorhabditis elegans as a model, we report that DNA damage elicits cell maintenance programs, including the unfolded protein response of the endoplasmic reticulum (UPRER). Mechanistically, sublethal DNA damage unexpectedly suppresses apoptotic genes in C. elegans, which in turn increases the activity of the inositol-requiring enzyme 1/X-box binding protein 1 (IRE-1/XBP-1) branch of the UPRER by elevating unsaturated phosphatidylcholine. In addition, UPRER activation requires silencing of the lipid regulator skinhead-1 (SKN-1). DNA damage suppresses SKN-1 activity to increase unsaturated phosphatidylcholine and activate UPRER. These findings reveal the UPRER activation as an organismal adaptive response that is important to maintain cell function during DNA damage.

When Endoplasmic Reticulum Proteostasis Meets the DNA Damage Response

Sustaining both proteome and genome integrity (GI) requires the integration of a wide range of mechanisms and signaling pathways. These comprise, in particular, the unfolded protein response (UPR) and the DNA damage response (DDR). These adaptive mechanisms take place respectively in the endoplasmic reticulum (ER) and in the nucleus. UPR and DDR alterations are associated with aging and with pathologies such as degenerative diseases, metabolic and inflammatory disorders, and cancer. We discuss the emerging signaling crosstalk between UPR stress sensors and the DDR, as well as their involvement in cancer biology.

Endoplasmic reticulum stress and protein degradation in chronic liver disease

Endoplasmic reticulum (ER) stress is easily observed in chronic liver disease, which often causes accumulation of unfolded or misfolded proteins in the ER, leading to unfolded protein response (UPR). Regulating protein degradation is an integral part of UPR to relieve ER stress. The major protein degradation system includes the ubiquitin-proteasome system (UPS) and autophagy. All three arms of UPR triggered in response to ER stress can regulate UPS and autophagy. Accumulated misfolded proteins could activate these arms, and then generate various transcription factors to regulate the expression of UPS-related and autophagy-related genes. The protein degradation process regulated by UPR has great significance in many chronic liver diseases, including non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), viral hepatitis, liver fibrosis, and hepatocellular carcinoma(HCC). In most instances, the degradation of excessive proteins protects cells with ER stress survival from apoptosis. According to the specific functions of protein degradation in chronic liver disease, choosing to promote or inhibit this process is promising as a potential method for treating chronic liver disease.

A Bunyavirus-Inducible Ubiquitin Ligase Targets RNA Polymerase IV for Degradation during Viral Pathogenesis in Rice

The ubiquitin-proteasome system (UPS) is an important post-translational regulatory mechanism that controls many cellular functions in eukaryotes. Here, we show that stable expression of P3 protein encoded by Rice grassy stunt virus (RGSV), a negative-strand RNA virus in the Bunyavirales, causes developmental abnormities similar to the disease symptoms caused by RGSV, such as dwarfing and excess tillering, in transgenic rice plants. We found that both transgenic expression of P3 and RGSV infection induce ubiquitination and UPS-dependent degradation of rice NUCLEAR RNA POLYMERASE D1a (OsNRPD1a), one of two orthologs of the largest subunit of plant-specific RNA polymerase IV (Pol IV), which is required for RNA-directed DNA methylation (RdDM). Furthermore, we identified a P3-inducible U-box type E3 ubiquitin ligase, designated as P3-inducible protein 1 (P3IP1), which interacts with OsNRPD1a and mediates its ubiquitination and UPS-dependent degradation in vitro and in vivo. Notably, both knockdown of OsNRPD1 and overexpression of P3IP1 in rice plants induced developmental phenotypes similar to RGSV disease symptomss. Taken together, our findings reveal a novel virulence mechanism whereby plant pathogens target host RNA Pol IV for UPS-dependent degradation to induce disease symptoms. Our study also identified an E3 ubiquitin ligase, which targets the RdDM compotent NRPD1 for UPS-mediated degradation in rice.

Cullin-RING Ligase 5: Functional characterization and its role in human cancers

Cullin-RING ligase 5 (CRL5) is a multi-protein complex and consists of a scaffold protien cullin 5, a RING protein RBX2 (also known as ROC2 or SAG), adaptor proteins Elongin B/C, and a substrate receptor protein SOCS. Through targeting a variety of substrates for proteasomal degradation or modulating various protein-protein interactions, CRL5 is involved in regulation of many biological processes, such as cytokine signal transduction, inflammation, viral infection, and oncogenesis. As many substrates of CRL5 are well-known oncoproteins or tumor suppressors, abnormal regulation of CRL5 is commonly found in human cancers. In this review, we first briefly introduce each of CRL5 components, and then discuss the biological processes regulated by four members of SOCS-box-containing substrate receptor family through substrate degradation. We next describe how CRL5 is hijacked by a variety of viral proteins to degrade host anti-viral proteins, which facilitates virus infection. We further discuss the regulation of CUL5 and its various roles in human cancers, acting as either a tumor suppressor or an oncoprotein in a context-dependent manner. Finally, we propose novel insights for future perspectives on the validation of cullin5 and other CRL5 components as potential targets, and possible targeting strategies to discover CRL5 inhibitors for anti-cancer and anti-virus therapies.