KDEL Receptors: Pathophysiological Functions, Therapeutic Options, and Biotechnological Opportunities

The interplay between gut microbiota and the unfolded protein response: Implications for intestinal homeostasis preservation and dysbiosis-related diseases

The unfolded protein response (UPR) is a complex intracellular signal transduction system that orchestrates the cellular response during Endoplasmic Reticulum (ER) stress conditions to reestablish cellular proteostasis. If, on one side, prolonged ER stress conditions can lead to programmed cell death and autophagy as a cytoprotective mechanism, on the other, unresolved ER stress and improper UPR activation represent a perilous condition able to trigger or exacerbate inflammatory responses. Notably, intestinal and immune cells experience ER stress physiologically due to their high protein secretory rate. Indeed, there is evidence of UPR's involvement in both physiological and pathological intestinal conditions, while less is known about its bidirectional interaction with gut microbiota. However, gut microbes and their metabolites can influence ER stress and UPR pathways, and, in turn, ER stress conditions can shape gut microbiota composition, with important implications for overall intestinal health. Thus, targeting UPR components is an intriguing strategy for treating ER stress-linked dysbiosis and diseases, particularly intestinal inflammation.

Unfolded protein responses in T cell immunity

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are integral to T cell biology, influencing immune responses and associated diseases. This review explores the interplay between the UPR and T cell immunity, highlighting the role of these cellular processes in T cell activation, differentiation, and function. The UPR, mediated by IRE1, PERK, and ATF6, is crucial for maintaining ER homeostasis and supporting T cell survival under stress. However, the precise mechanisms by which ER stress and the UPR regulate T cell-mediated immunity remain incompletely understood. Emerging evidence suggests that the UPR may be a potential therapeutic target for diseases characterized by T cell dysfunction, such as autoimmune disorders and cancer. Further research is needed to elucidate the complex interactions between ER stress, the UPR, and T cell immunity to develop novel therapeutic strategies for T cell-associated diseases.

Disease-Associated Factors at the Endoplasmic Reticulum-Golgi Interface

The endoplasmic reticulum (ER)-Golgi interface is essential for directing the transport of proteins synthesized in the ER to the Golgi apparatus via the ER-Golgi intermediate compartment, as well as for recycling proteins back to the ER. This transport is facilitated by various components, including COPI and COPII coat protein complexes and the transport protein particle complex. Recently, the ER-Golgi transport pathway has gained attention due to emerging evidence of nonvesicular transport mechanisms and the regulation of trafficking through liquid-liquid phase separation. Numerous diseases have been linked to mutations in proteins localized at the ER-Golgi interface, highlighting the need for comprehensive analysis of these conditions. This review examines the disease phenotypes associated with dysfunctional ER-Golgi transport factors and explores their cellular effects, providing insights into potential therapeutic strategies.

Ubiquitin-Specific Protease 22 Plays a Key Role in Increasing Extracellular Vesicle Secretion and Regulating Cell Motility of Lung Adenocarcinoma

Tumor-derived extracellular vesicles (EVs) are potential biomarkers for tumors, but their reliable molecular targets have not been identified. The previous study confirms that ubiquitin-specific protease 22 (USP22) promotes lung adenocarcinoma (LUAD) metastasis in vivo and in vitro. Moreover, USP22 regulates endocytosis of tumor cells and localizes to late endosomes. However, the role of USP22 in the secretion of tumor cell-derived EVs remains unknown. In this study, it demonstrates that USP22 increases the secretion of tumor cell-derived EVs and accelerates their migration and invasion, invadopodia formation, and angiogenesis via EV transfer. USP22 enhances EV secretion by upregulating myosin IB (MYO1B). This study further discovers that USP22 activated the SRC signaling pathway by upregulating the molecule KDEL endoplasmic reticulum protein retention receptor 1 (KDELR1), thereby contributing to LUAD cell progression. The study provides novel insights into the role of USP22 in EV secretion and cell motility regulation in LUAD.

Exploring the potential biological significance of KDELR family genes in lung adenocarcinoma

The Lys-Asp-Glu-Leu receptor (KDELR) family genes play critical roles in a variety of biological processes in different tumors. Our study aimed to provide a comprehensive analysis of the potential roles of KDELRs in lung adenocarcinoma (LUAD). Utilizing data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database, as well as clinical samples, we conducted a series of analyses and validations using R software tools and various online resources. The results showed that KDELR family genes and proteins were highly expressed and associated with a poor prognosis of LUAD. Promoter hypomethylation and the competing endogenous RNA (ceRNA) network of PCAT6/hsa-miR-326/KDELR1 might be potential causes of aberrant KDELR1 overexpression in LUAD. Three key Transcription factors (TFs) (SPI1, EP300, and MAZ) and a TFs-miRNAs-KDELRs network (involving 11 TFs) might be involved in modulating KDELRs expression abnormalities. Gene Set Enrichment Analysis (GSEA) indicated enrichment of genes highly expressing KDELR1, KDELR2, and KDELR3 in MTORC1_SIGNALING, P53_PATHWAY, and ANGIOGENESIS. Negative correlations between KDELRs expression and CD8 + T cell infiltration, as well as CTLA-4 expression. Our multiple analyses suggested that the KDELRs are important signaling molecules in LUAD. These results provided novel insights for developing prognostic markers and novel therapies of LUAD.

Ion channel trafficking implications in heart failure

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.

Modulating Golgi Stress Signaling Ameliorates Cell Morphological Phenotypes Induced by CHMP2B with Frontotemporal Dementia-Associated p.Asp148Tyr

Some charged multivesicular body protein 2B (CHMP2B) mutations are associated with autosomal-dominant neurodegenerative frontotemporal dementia and/or amyotrophic lateral sclerosis type 7 (FTDALS7). The main aim of this study is to clarify the relationship between the expression of mutated CHMP2B protein displaying FTD symptoms and defective neuronal differentiation. First, we illustrate that the expression of CHMP2B with the Asp148Tyr (D148Y) mutation, which preferentially displays FTD phenotypes, blunts neurite process elongation in rat primary cortical neurons. Similar results were observed in the N1E-115 cell line, a model that undergoes neurite elongation. Second, these effects were also accompanied by changes in neuronal differentiation marker protein expression. Third, wild-type CHMP2B protein was indeed localized in the endosomal sorting complexes required to transport (ESCRT)-like structures throughout the cytoplasm. In contrast, CHMP2B with the D148Y mutation exhibited aggregation-like structures and accumulated in the Golgi body. Fourth, among currently known Golgi stress regulators, the expression levels of Hsp47, which has protective effects on the Golgi body, were decreased in cells expressing CHMP2B with the D148Y mutation. Fifth, Arf4, another Golgi stress-signaling molecule, was increased in mutant-expressing cells. Finally, when transfecting Hsp47 or knocking down Arf4 with small interfering (si)RNA, cellular phenotypes in mutant-expressing cells were recovered. These results suggest that CHMP2B with the D148Y mutation, acting through Golgi stress signaling, is negatively involved in the regulation of neuronal cell morphological differentiation, providing evidence that a molecule controlling Golgi stress may be one of the potential FTD therapeutic targets at the molecular and cellular levels.

Intracellular spatially-targeted chemical chaperones increase native state stability of mutant SOD1 barrel

Amyotrophic lateral sclerosis (ALS) is a progressive neurological disorder with currently no cure. Central to the cellular dysfunction associated with this fatal proteinopathy is the accumulation of unfolded/misfolded superoxide dismutase 1 (SOD1) in various subcellular locations. The molecular mechanism driving the formation of SOD1 aggregates is not fully understood but numerous studies suggest that aberrant aggregation escalates with folding instability of mutant apoSOD1. Recent advances on combining organelle-targeting therapies with the anti-aggregation capacity of chemical chaperones have successfully reduce the subcellular load of misfolded/aggregated SOD1 as well as their downstream anomalous cellular processes at low concentrations (micromolar range). Nevertheless, if such local aggregate reduction directly correlates with increased folding stability remains to be explored. To fill this gap, we synthesized and tested here the effect of 9 ER-, mitochondria- and lysosome-targeted chemical chaperones on the folding stability of truncated monomeric SOD1 (SOD1bar) mutants directed to those organelles. We found that compound ER-15 specifically increased the native state stability of ER-SOD1bar-A4V, while scaffold compound FDA-approved 4-phenylbutyric acid (PBA) decreased it. Furthermore, our results suggested that ER15 mechanism of action is distinct from that of PBA, opening new therapeutic perspectives of this novel chemical chaperone on ALS treatment.

The Unfolded Protein Response and Its Implications for Novel Therapeutic Strategies in Inflammatory Bowel Disease

The endoplasmic reticulum (ER) is a multifunctional organelle playing a vital role in maintaining cell homeostasis, and disruptions to its functions can have detrimental effects on cells. Dysregulated ER stress and the unfolded protein response (UPR) have been linked to various human diseases. For example, ER stress and the activation of the UPR signaling pathways in intestinal epithelial cells can either exacerbate or alleviate the severity of inflammatory bowel disease (IBD), contingent on the degree and conditions of activation. Our recent studies have shown that EPICERTIN, a recombinant variant of the cholera toxin B subunit containing an ER retention motif, can induce a protective UPR in colon epithelial cells, subsequently promoting epithelial restitution and mucosal healing in IBD models. These findings support the idea that compounds modulating UPR may be promising pharmaceutical candidates for the treatment of the disease. In this review, we summarize our current understanding of the ER stress and UPR in IBD, focusing on their roles in maintaining cell homeostasis, dysregulation, and disease pathogenesis. Additionally, we discuss therapeutic strategies that promote the cytoprotection of colon epithelial cells and reduce inflammation via pharmacological manipulation of the UPR.