Notch-induced endoplasmic reticulum-associated degradation governs mouse thymocyte β-selection

Requirements for nuclear GRP78 transcriptional regulatory activities and interaction with nuclear GRP94

GRP78, a molecular chaperone primarily located in the endoplasmic reticulum (ER), has recently been discovered to translocate into the nucleus of stressed and cancer cells where it assumes a new function reprogramming the transcriptome. This study explores the requirements of GRP78 nuclear translocation and its transcriptional activity and investigates the role of ER-associated degradation in the process. We show that the ER-processed, mature form of GRP78 is the major form of nuclear GRP78 and is the form with transcriptional regulatory activity. In contrast, exogenously expressed GRP78 designed to lack its ER signal peptide, thus preventing it from entering the ER or undergoing any ER-related processing/modification, while able to enter the nucleus, lacks transcriptional regulatory activity toward E-Box containing target genes. Additionally, the ATP-binding and substrate-binding activities of GRP78 are critical for this transcriptional regulatory function. We further discover that GRP94, an ER chaperone that acts in concert with GRP78 on protein folding, can translocate to the nucleus and colocalize with nuclear GRP78 upon ER stress. These findings suggest that some form of ER processing of GRP78, in addition to cleavage of the ER signal peptide, is critical for its nuclear activity and that in stressed cells, ER chaperones may assume new functions in the nucleus yet to be explored.

The impact of SEC23A on 5-FU chemotherapy sensitivity and its involvement in endoplasmic reticulum stress-induced apoptosis in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) represents a significant global health burden, with chemotherapy resistance representing a significant challenge to effective treatment. SEC23A, a core component of the COPII vesicle trafficking system, is of critical importance with regard to protein transport and cellular homeostasis. Nevertheless, its function in CRC progression and chemoresistance remains uncertain. The present study investigates the correlation between SEC23A expression and sensitivity to 5-fluorouracil (5-FU), a widely used chemotherapeutic agent, with particular emphasis on ER stress-induced apoptosis.

METHODS

A bioinformatic analysis was conducted to evaluate SEC23A expression in CRC and its association with patient prognosis. Chemotherapy sensitivity was predicted using GDSC data and validated experimentally using CRC cell lines with manipulated SEC23A expression. In order to explore the role of SEC23A in acquired drug resistance, patient-derived xenograft (PDX) models and 5-FU-resistant cell lines were employed. Apoptosis assays, cell cycle analysis, and ER stress modulation experiments were performed to elucidate the underlying mechanisms.

RESULTS

SEC23A expression was significantly reduced in CRC samples compared to normal tissues. This reduction was linked to a poorer prognosis, including both overall and disease-specific survival. A correlation was observed between low SEC23A expression and increased resistance to 5-FU, as evidenced by both bioinformatic predictions and in vitro experiments. In PDX models, metastatic lesions exhibited decreased SEC23A expression following 5-FU treatment in comparison to primary tumors. Overexpression of SEC23A in 5-FU-resistant cell lines restored sensitivity to the drug and increased apoptosis. Bioinformatic and experimental analyses revealed a robust correlation between SEC23A and ER stress-related apoptotic pathways. Elevated expression of SEC23A was observed to facilitate the accumulation of misfolded proteins in response to 5-FU treatment, which in turn resulted in increased ER stress and apoptosis.

CONCLUSIONS

SEC23A plays a crucial role in modulating the sensitivity of CRC cells to 5-FU by regulating ER stress-induced apoptosis. Its downregulation contributes to chemoresistance, indicating that SEC23A may serve as a prognostic marker and therapeutic target in CRC. Strategies aimed at upregulating SEC23A or enhancing ER stress may provide new avenues for overcoming chemoresistance and improving treatment outcomes for CRC patients.

Endoplasmic reticulum (ER) protein degradation by ER-associated degradation and ER-phagy

Protein misfolding and aggregation in the endoplasmic reticulum (ER) have been causally linked to a variety of human diseases. Two key pathways for eliminating misfolded proteins and aggregates in the ER are ER-associated degradation (ERAD) and ER-phagy, respectively. While both pathways have been well characterized biochemically, our understanding of their physiological relevance and significance remains limited. In recent years, significant advances have been made, including the generation and characterization of various knockout and knockin mouse models, the identification of human disease-associated or -causing variants, and insights into the coordination between ERAD and autophagy in physiological contexts. In this review, we summarize these advancements, highlighting the key roles of a highly conserved suppressor of lin-12-like-hydroxymethyl glutaryl-coenzyme A reductase degradation 1 (SEL1L-HRD1) protein complex of ERAD and ER-phagy in health and disease.

E3 ubiquitin ligase SYVN1 as a promising therapeutic target for diverse human diseases

Numerous studies conducted in recent years indicate that mammalian E3 ubiquitin ligases serve as key regulators in the maintenance of cellular homeostasis by targeting the ubiquitination of substrate proteins and activating downstream signaling pathways. SYVN1, an E3 ubiquitin ligase, is characterized by its significant functions in regulating various biological processes, including molecular mechanisms related to gene expression, signaling pathways, and cell death, among others. Consequently, SYVN1 plays a crucial role in both normal human physiology and the pathogenesis of various diseases, such as oncogenesis, cardiovascular disorders, immune regulation, skeletal anomalies, and neurological diseases. This review synthesizes recent findings regarding the physiological and pathophysiological roles of SYVN1, offering new insights into potential strategies for the prevention and treatment of human diseases, as well as suggesting avenues for future drug development. In this Review, we summarize the latest findings regarding the physiological and pathophysiological roles of SYVN1, elucidating the mechanisms by which SYVN1 can regulate the progression of various diseases in humans. These important findings provide new avenues for further investigation of SYVN1 protein, new insights into potential strategies to prevent and treat human diseases, and new directions for future drug development.

Food for thought: Nutrient metabolism controlling early T cell development

T cells develop in the thymus by expressing a diverse repertoire of either αβ- or γδ-T cell receptors (TCR). While many studies have elucidated how TCR signaling and gene expression control T cell ontogeny, the role of nutrient metabolism is just emerging. Here, we discuss how metabolic reprogramming and nutrient availability impact the fate of developing thymic T cells. We focus on how the PI3K/mTOR signaling mediates various extracellular inputs and how this signaling pathway controls metabolic rewiring during highly proliferative and anabolic developmental stages. We highlight the role of the hexosamine biosynthetic pathway that generates metabolites that are utilized for N- and O-linked glycosylation of proteins and how it impacts TCR expression during T cell ontogeny. We consider the dichotomy in metabolic needs during αβ- versus γδ-T cell lineage commitment as well as how metabolism is also coupled to molecular signaling that controls cell fate.

Purkinje cell-specific deficiency in SEL1L-hrd1 endoplasmic reticulum-associated degradation causes progressive cerebellar ataxia in mice

Recent studies have identified multiple genetic variants of SEL1L-HRD1 endoplasmic reticulum-associated degradation (ERAD) in humans with neurodevelopmental disorders and locomotor dysfunctions, including ataxia. However, the relevance and importance of SEL1L-HRD1 ERAD in the pathogenesis of ataxia remain unexplored. Here, we showed that SEL1L deficiency in Purkinje cells leads to early-onset progressive cerebellar ataxia with progressive loss of Purkinje cells with age. Mice with Purkinje cell-specific deletion of SEL1L (Sel1LPcp2Cre) exhibited motor dysfunction beginning around 9 weeks of age. Transmission electron microscopy analysis revealed dilated ER and fragmented nuclei in Purkinje cells of adult Sel1LPcp2Cre mice, indicative of altered ER homeostasis and cell death. Finally, loss of Purkinje cells was associated with a secondary neurodegeneration of granular cells, as well as robust activation of astrocytes and proliferation of microglia, in the cerebellums of Sel1LPcp2Cre mice. These data demonstrate the pathophysiological importance of SEL1L-HRD1 ERAD in Purkinje cells in the pathogenesis of cerebellar ataxia.

Short-chain chlorinated paraffins may induce thymic aging in mice by activating PERK-CHOP

Humans indirectly consume approximately 0.02 mg/kg/day of short-chained chlorinated paraffins (SCCPs) through the environment; however, the thymic senescence/damage induced by SCCPs has not been assessed. In this study, 16 female mice (4-week-old) per group were orally administered 0, 0.01, 0.1, and 1 mg/kg/day of SCCPs for 21 days, and the phenotypes and levels of superoxide dismutase (SOD), malondialdehyde (MDA), Tβ4, αβ TCR, SA-β-Gal, GRP78, PERK/CHOP, P53/P21, and CASPASE-1 of the thymus were assessed as indicators. Another group comprising 16 mice was killed at 4-week-old and these indicators were assessed. Thereafter, the thymuses cultured in vitro were exposed to 0, 14, 140, and 1400 μg/L SCCPs, respectively, and the above indicators were measured after 7-day. Based on the results, the oral administration of ≥0.01 mg/kg/day SCCPs to mice and ≥14 μg/L of SCCPs in medium caused thymic aging features, such as a decrease in the ratio of cortex to medulla, gradual blurring of the boundary between the cortex and medulla, dose-dependent oxidative stress (decreased SOD and increased MDA), and decreased levels of Tβ4 and αβ TCRs in the thymus. The oral administration of ≥1 mg/kg/day of SCCPs also impeded the growth and development of female mice and their thymuses. Exposure to the low levels of SCCPs activated PERK-CHOP in the mouse thymus, which modulated increases in SA-β-Gal, IL-1β, P53, and CASPASE-1 in vivo and in vitro. Overall, environmental levels and human blood concentrations (14.8-1400 μg/L) of SCCPs may induce mouse thymus senescence by activating PERK-CHOP in vivo and in vitro, respectively.

Transcriptomic profiling of thymic dysregulation and viral tropism after neonatal roseolovirus infection

Introduction

Herpesviruses, including the roseoloviruses, have been linked to autoimmune disease. The ubiquitous and chronic nature of these infections have made it difficult to establish a causal relationship between acute infection and subsequent development of autoimmunity. We have shown that murine roseolovirus (MRV), which is highly related to human roseoloviruses, induces thymic atrophy and disruption of central tolerance after neonatal infection. Moreover, neonatal MRV infection results in development of autoimmunity in adult mice, long after resolution of acute infection. This suggests that MRV induces durable immune dysregulation.

Methods

In the current studies, we utilized single-cell RNA sequencing (scRNAseq) to study the tropism of MRV in the thymus and determine cellular processes in the thymus that were disrupted by neonatal MRV infection. We then utilized tropism data to establish a cell culture system.

Results

Herein, we describe how MRV alters the thymic transcriptome during acute neonatal infection. We found that MRV infection resulted in major shifts in inflammatory, differentiation and cell cycle pathways in the infected thymus. We also observed shifts in the relative number of specific cell populations. Moreover, utilizing expression of late viral transcripts as a proxy of viral replication, we identified the cellular tropism of MRV in the thymus. This approach demonstrated that double negative, double positive, and CD4 single positive thymocytes, as well as medullary thymic epithelial cells were infected by MRV in vivo. Finally, by applying pseudotime analysis to viral transcripts, which we refer to as "pseudokinetics," we identified viral gene transcription patterns associated with specific cell types and infection status. We utilized this information to establish the first cell culture systems susceptible to MRV infection in vitro.

Conclusion

Our research provides the first complete picture of roseolovirus tropism in the thymus after neonatal infection. Additionally, we identified major transcriptomic alterations in cell populations in the thymus during acute neonatal MRV infection. These studies offer important insight into the early events that occur after neonatal MRV infection that disrupt central tolerance and promote autoimmune disease.

The Proteostasis of Thymic Stromal Cells in Health and Diseases

The thymus is the key immune organ for the development of T cells. Different populations of thymic stromal cells interact with T cells, thereby controlling the dynamic development of T cells through their differentiation and function. Proteostasis represents a balance between protein expression, folding, and modification and protein clearance, and its fluctuation usually depends at least partially on related protein regulatory systems for further survival and effects. However, in terms of the substantial requirement for self-antigens and their processing burden, increasing evidence highlights that protein regulation contributes to the physiological effects of thymic stromal cells. Impaired proteostasis may expedite the progression of thymic involution and dysfunction, accompanied by the development of autoimmune diseases or thymoma. Hence, in this review, we summarize the regulation of proteostasis within different types of thymic stromal cells under physiological and pathological conditions to identify potential targets for thymic regeneration and immunotherapy.

ER-associated degradation adapter Sel1L is required for CD8+ T cell function and memory formation following acute viral infection

The maintenance of antigen-specific CD8+ T cells underlies the efficacy of vaccines and immunotherapies. Pathways contributing to CD8+ T cell loss are not completely understood. Uncovering the pathways underlying the limited persistence of CD8+ T cells would be of significant benefit for developing novel strategies of promoting T cell persistence. Here, we demonstrate that murine CD8+ T cells experience endoplasmic reticulum (ER) stress following activation and that the ER-associated degradation (ERAD) adapter Sel1L is induced in activated CD8+ T cells. Sel1L loss limits CD8+ T cell function and memory formation following acute viral infection. Mechanistically, Sel1L is required for optimal bioenergetics and c-Myc expression. Finally, we demonstrate that human CD8+ T cells experience ER stress upon activation and that ER stress is negatively associated with improved T cell functionality in T cell-redirecting therapies. Together, these results demonstrate that ER stress and ERAD are important regulators of T cell function and persistence.

SEL1L-HRD1 interaction is required to form a functional HRD1 ERAD complex

The SEL1L-HRD1 protein complex represents the most conserved branch of endoplasmic reticulum (ER)-associated degradation (ERAD). Despite recent advances in both mouse models and humans, in vivo evidence for the importance of SEL1L in the ERAD complex formation and its (patho-)physiological relevance in mammals remains limited. Here we report that SEL1L variant p.Ser658Pro (SEL1LS658P) is a pathogenic hypomorphic mutation, causing partial embryonic lethality, developmental delay, and early-onset cerebellar ataxia in homozygous mice carrying the bi-allelic variant. Biochemical analyses reveal that SEL1LS658P variant not only reduces the protein stability of SEL1L, but attenuates the SEL1L-HRD1 interaction, likely via electrostatic repulsion between SEL1L F668 and HRD1 Y30 residues. Proteomic screens of SEL1L and HRD1 interactomes reveal that SEL1L-HRD1 interaction is a prerequisite for the formation of a functional HRD1 ERAD complex, as SEL1L is required for the recruitment of E2 enzyme UBE2J1 as well as DERLIN to HRD1. These data not only establish the disease relevance of SEL1L-HRD1 ERAD, but also provide additional insight into the formation of a functional HRD1 ERAD complex.

Proteomic screens of SEL1L-HRD1 ER-associated degradation substrates reveal its role in glycosylphosphatidylinositol-anchored protein biogenesis

Endoplasmic reticulum-associated degradation (ERAD) plays indispensable roles in many physiological processes; however, the nature of endogenous substrates remains largely elusive. Here we report a proteomics strategy based on the intrinsic property of the SEL1L-HRD1 ERAD complex to identify endogenous ERAD substrates both in vitro and in vivo. Following stringent filtering using a machine learning algorithm, over 100 high-confidence potential substrates are identified in human HEK293T and mouse brown adipose tissue, among which ~88% are cell type-specific. One of the top shared hits is the catalytic subunit of the glycosylphosphatidylinositol (GPI)-transamidase complex, PIGK. Indeed, SEL1L-HRD1 ERAD attenuates the biogenesis of GPI-anchored proteins by specifically targeting PIGK for proteasomal degradation. Lastly, several PIGK disease variants in inherited GPI deficiency disorders are also SEL1L-HRD1 ERAD substrates. This study provides a platform and resources for future effort to identify proteome-wide endogenous substrates in vivo, and implicates SEL1L-HRD1 ERAD in many cellular processes including the biogenesis of GPI-anchored proteins.

Hypomorphic human SEL1L and HRD1 variants uncouple multilayered ER-associated degradation machinery

The suppressor of lin-12-like-HMG-CoA reductase degradation 1 (SEL1L-HRD1) complex of the endoplasmic reticulum-associated degradation (ERAD) machinery is a key cellular proteostasis pathway. Although previous studies have shown ERAD as promoting the development and maintenance of many cell types in mice, its importance to human physiology remained undetermined. In two articles in this issue of the JCI, Qi and colleagues describe four biallelic hypomorphic SEL1L and HRD1 variants that were associated with neurodevelopment disorders, locomotor dysfunction, impaired immunity, and premature death in patients. These pathogenic SEL1L-HRD1 variants shine a light on the critical importance of ERAD in humans and pave the way for future studies dissecting ERAD mechanisms in specific cell types.

Hypomorphic variants of SEL1L-HRD1 ER-associated degradation are associated with neurodevelopmental disorders

Recent studies using cell type-specific knockout mouse models have improved our understanding of the pathophysiological relevance of suppressor of lin-12-like-HMG-CoA reductase degradation 1 (SEL1L-HRD1) endoplasmic reticulum-associated (ER-associated) degradation (ERAD); however, its importance in humans remains unclear, as no disease variant has been identified. Here, we report the identification of 3 biallelic missense variants of SEL1L and HRD1 (or SYVN1) in 6 children from 3 independent families presenting with developmental delay, intellectual disability, microcephaly, facial dysmorphisms, hypotonia, and/or ataxia. These SEL1L (p.Gly585Asp, p.Met528Arg) and HRD1 (p.Pro398Leu) variants were hypomorphic and impaired ERAD function at distinct steps of ERAD, including substrate recruitment (SEL1L p.Gly585Asp), SEL1L-HRD1 complex formation (SEL1L p.Met528Arg), and HRD1 activity (HRD1 p.Pro398Leu). Our study not only provides insights into the structure-function relationship of SEL1L-HRD1 ERAD, but also establishes the importance of SEL1L-HRD1 ERAD in humans.

Biallelic Cys141Tyr variant of SEL1L is associated with neurodevelopmental disorders, agammaglobulinemia, and premature death

Suppressor of lin-12-like-HMG-CoA reductase degradation 1 (SEL1L-HRD1) ER-associated degradation (ERAD) plays a critical role in many physiological processes in mice, including immunity, water homeostasis, and energy metabolism; however, its relevance and importance in humans remain unclear, as no disease variant has been identified. Here, we report a biallelic SEL1L variant (p. Cys141Tyr) in 5 patients from a consanguineous Slovakian family. These patients presented with not only ERAD-associated neurodevelopmental disorders with onset in infancy (ENDI) syndromes, but infantile-onset agammaglobulinemia with no mature B cells, resulting in frequent infections and early death. This variant disrupted the formation of a disulfide bond in the luminal fibronectin II domain of SEL1L, largely abolishing the function of the SEL1L-HRD1 ERAD complex in part via proteasomal-mediated self destruction by HRD1. This study reports a disease entity termed ENDI-agammaglobulinemia (ENDI-A) syndrome and establishes an inverse correlation between SEL1L-HRD1 ERAD functionality and disease severity in humans.

SEL1L preserves CD8+ T-cell survival and homeostasis by fine-tuning PERK signaling and the IL-15 receptor-mediated mTORC1 axis

SEL1L-mediated endoplasmic reticulum-associated degradation (ERAD) plays critical roles in controlling protein homeostasis by degrading misfolded or terminal unfolded proteins. However, it remains unclear how SEL1L regulates peripheral T-cell survival and homeostasis. Herein, we found that SEL1L deficiency led to a greatly reduced frequency and number of mature T cells, which was further validated by adoptive transfer experiments or bone marrow chimera experiments, accompanied by the induction of multiple forms of cell death. Furthermore, SEL1L deficiency selectively disrupted naïve CD8+ T-cell homeostasis, as indicated by the severe loss of the naïve T-cell subset but an increase in the memory T-cell subset. We also found that SEL1L deficiency fueled mTORC1/c-MYC activation and induced a metabolic shift, which was largely attributable to enhanced expression of the IL-15 receptor α and β chains. Mechanistically, single-cell transcriptomic profiling and biochemical analyses further revealed that Sel1l-/- CD8+ T cells harbored excessive ER stress, particularly aberrant activation of the PERK-ATF4-CHOP-Bim pathway, which was alleviated by supplementing IL-7 or IL-15. Importantly, PERK inhibition greatly resolved the survival defects of Sel1l-/- CD8+ T cells. In addition, IRE1α deficiency decreased mTORC1 signaling in Sel1l-/- naïve CD8+ T cells by downregulating the IL-15 receptor α chain. Altogether, these observations suggest that the ERAD adaptor molecule SEL1L acts as an important checkpoint for preserving the survival and homeostasis of peripheral T cells by regulating the PERK signaling cascade and IL-15 receptor-mediated mTORC1 axis.

Modulation of the proteostasis network promotes tumor resistance to oncogenic KRAS inhibitors

Despite substantial advances in targeting mutant KRAS, tumor resistance to KRAS inhibitors (KRASi) remains a major barrier to progress. Here, we report proteostasis reprogramming as a key convergence point of multiple KRASi-resistance mechanisms. Inactivation of oncogenic KRAS down-regulated both the heat shock response and the inositol-requiring enzyme 1α (IRE1α) branch of the unfolded protein response, causing severe proteostasis disturbances. However, IRE1α was selectively reactivated in an ER stress-independent manner in acquired KRASi-resistant tumors, restoring proteostasis. Oncogenic KRAS promoted IRE1α protein stability through extracellular signal-regulated kinase (ERK)-dependent phosphorylation of IRE1α, leading to IRE1α disassociation from 3-hydroxy-3-methylglutaryl reductase degradation (HRD1) E3-ligase. In KRASi-resistant tumors, both reactivated ERK and hyperactivated AKT restored IRE1α phosphorylation and stability. Suppression of IRE1α overcame resistance to KRASi. This study reveals a druggable mechanism that leads to proteostasis reprogramming and facilitates KRASi resistance.

Endoplasmic reticulum stress in T cell-mediated diseases

T cells synthesize a large number of proteins during their development, activation, and differentiation. The build-up of misfolded and unfolded proteins in the endoplasmic reticulum, however, causes endoplasmic reticulum (ER) stress. Thus, T cells can maintain ER homeostasis via endoplasmic reticulum-associated degradation, unfolded protein response, and autophagy. In T cell-mediated diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjogren's syndrome, type 1 diabetes and vitiligo, ER stress caused by changes in the internal microenvironment can cause disease progression by affecting T cell homeostasis. This review discusses ER stress in T cell formation, activation, differentiation, and T cell-mediated illnesses, and may offer new perspectives on the involvement of T cells in autoimmune disorders and cancer.

T cells in health and disease

T cells are crucial for immune functions to maintain health and prevent disease. T cell development occurs in a stepwise process in the thymus and mainly generates CD4+ and CD8+ T cell subsets. Upon antigen stimulation, naïve T cells differentiate into CD4+ helper and CD8+ cytotoxic effector and memory cells, mediating direct killing, diverse immune regulatory function, and long-term protection. In response to acute and chronic infections and tumors, T cells adopt distinct differentiation trajectories and develop into a range of heterogeneous populations with various phenotype, differentiation potential, and functionality under precise and elaborate regulations of transcriptional and epigenetic programs. Abnormal T-cell immunity can initiate and promote the pathogenesis of autoimmune diseases. In this review, we summarize the current understanding of T cell development, CD4+ and CD8+ T cell classification, and differentiation in physiological settings. We further elaborate the heterogeneity, differentiation, functionality, and regulation network of CD4+ and CD8+ T cells in infectious disease, chronic infection and tumor, and autoimmune disease, highlighting the exhausted CD8+ T cell differentiation trajectory, CD4+ T cell helper function, T cell contributions to immunotherapy and autoimmune pathogenesis. We also discuss the development and function of γδ T cells in tissue surveillance, infection, and tumor immunity. Finally, we summarized current T-cell-based immunotherapies in both cancer and autoimmune diseases, with an emphasis on their clinical applications. A better understanding of T cell immunity provides insight into developing novel prophylactic and therapeutic strategies in human diseases.

SEL1L-HRD1 interaction is prerequisite for the formation of a functional HRD1 ERAD complex

The SEL1L-HRD1 protein complex represents the most conserved branch of endoplasmic reticulum (ER)-associated degradation (ERAD); however, definitive evidence for the importance of SEL1L in HRD1 ERAD is lacking. Here we report that attenuation of the interaction between SEL1L and HRD1 impairs HRD1 ERAD function and has pathological consequences in mice. Our data show that SEL1L variant p.Ser658Pro ( SEL1L S 658 P ) previously identified in Finnish Hound suffering cerebellar ataxia is a recessive hypomorphic mutation, causing partial embryonic lethality, developmental delay, and early-onset cerebellar ataxia in homozygous mice carrying the bi-allelic variant. Mechanistically, SEL1L S 658 P variant attenuates the SEL1L-HRD1 interaction and causes HRD1 dysfunction by generating electrostatic repulsion between SEL1L F668 and HRD1 Y30 residues. Proteomic screens of SEL1L and HRD1 interactomes revealed that the SEL1L-HRD1 interaction is prerequisite for the formation of a functional HRD1 ERAD complex, as SEL1L recruits not only the lectins OS9 and ERLEC1, but the E2 UBE2J1 and retrotranslocon DERLIN, to HRD1. These data underscore the pathophysiological importance and disease relevance of the SEL1L-HRD1 complex, and identify a key step in organizing the HRD1 ERAD complex.

SEL1L-HRD1 endoplasmic reticulum-associated degradation controls STING-mediated innate immunity by limiting the size of the activable STING pool

Stimulator of interferon genes (STING) orchestrates the production of proinflammatory cytokines in response to cytosolic double-stranded DNA; however, the pathophysiological significance and molecular mechanism underlying the folding and maturation of nascent STING protein at the endoplasmic reticulum (ER) remain unknown. Here we report that the SEL1L-HRD1 protein complex-the most conserved branch of ER-associated degradation (ERAD)-is a negative regulator of the STING innate immunity by ubiquitinating and targeting nascent STING protein for proteasomal degradation in the basal state. SEL1L or HRD1 deficiency in macrophages specifically amplifies STING signalling and immunity against viral infection and tumour growth. Mechanistically, nascent STING protein is a bona fide substrate of SEL1L-HRD1 in the basal state, uncoupled from ER stress or its sensor inositol-requiring enzyme 1α. Hence, our study not only establishes a key role of SEL1L-HRD1 ERAD in innate immunity by limiting the size of the activable STING pool, but identifies a regulatory mechanism and therapeutic approach to targeting STING.

The role and therapeutic implication of endoplasmic reticulum stress in inflammatory cancer transformation

Endoplasmic reticulum (ER) stress occurs when proteins are affected by various factors, fail to fold properly into higher structures and accumulate in the lumen of the ER, which activates the unfolded protein response (UPR) to restore normal cellular function or induce apoptosis as a self-protective mechanism. However, a growing number of studies have shown that the three branches of ER stress and the UPR can mediate inflammation and cancer development by interacting with inflammatory transformation-related signaling pathways. Targeting the UPR, especially the use of small molecules that target the active sites of the enzymes IRE1α and PERK and BIP/GRP78 inhibitors are potential strategies for treating tumors and have shown promising results in some tumor models. Therefore, in this review, we summarize the progress of ER stress/UPR research and the signaling pathways associated with inflammatory cancer transformation, provide an in-depth description of the mechanisms of these pathways, and outline strategies in the field of UPR biology in tumor therapy to provide new ideas for the mechanisms of inflammatory cancer transformation and tumor-related treatment.