Effects of host cell sterol composition upon internalization of Yersinia pseudotuberculosis and clustered β1 integrin

Responses of digestive metabolism to marine heatwaves in pearl oysters

Marine heatwaves (MHWs) have increased in intensity and frequency in global oceans, causing deleterious effects on many marine organisms and ecosystems they support. Bivalves are among the most vulnerable taxonomic groups to intensifying MHWs, yet little is known about the underlying mechanisms. Here, we investigated the impact of MHWs on the digestive metabolism of pearl oysters (Pinctada maxima). Two moderate and severe scenarios of MHWs were performed by increasing seawater temperature respectively from 24 °C to 28 °C and 32 °C for 3 days. When subjected to MHWs and with increasing intensity, pearl oysters significantly enhanced their digestive enzymatic activities, such as lipase and amylase. LC-MS-based metabolomics revealed negative responses in the lipid metabolism (e.g., steroid biosynthesis, glycerophospholipid metabolism, and sphingolipid metabolism), the amino acid metabolism (e.g., glutamate, histidine, arginine, and proline), and the B-vitamins metabolism. These findings indicate that the digestive metabolism of marine bivalves can likely succumb to intensifying MHWs events.

Integrin β1 in Pancreatic Cancer: Expressions, Functions, and Clinical Implications

Simple Summary

Pancreatic cancer (PC) is a highly aggressive malignant tumor with an extremely poor prognosis. Early diagnosis and treatment are key to improving the survival rate of PC patients. Emerging studies show that integrins might contribute to the pathogenesis of PC. This review presents the various signaling pathways that are mediated by integrins in PC and emphasizes the multiple functions of integrin β1 in malignant behaviors of PC. It also discusses the clinical significance of integrin β1 as well as integrin β1-based therapy in PC patients.

Abstract

Pancreatic cancer (PC) is characterized by rapid progression and a high mortality rate. The current treatment is still based on surgical treatment, supplemented by radiotherapy and chemotherapy, and new methods of combining immune and molecular biological treatments are being explored. Despite this, the survival rate of PC patients is still very disappointing. Therefore, clarifying the molecular mechanism of PC pathogenesis and developing precisely targeted drugs are key to improving PC prognosis. As the most common β subunit of the integrin family, integrin β1 has been proved to be closely related to the vascular invasion, distant metastasis, and survival of PC patients, and treatment targeting integrin β1 in PC has gained initial success in animal models. In this review, we summarize the various signaling pathways by which integrins are involved in PC, focusing on the roles of integrin β1 in the malignant behaviors of PC. Additionally, recent studies regarding the feasibility of integrin β1 as a diagnostic and prognostic biomarker in PC are also discussed. Finally, we present the progress of several integrin β1-based clinical trials to highlight the potential of integrin β1 as a target for personalized therapy in PC.

Using cyclodextrin-induced lipid substitution to study membrane lipid and ordered membrane domain (raft) function in cells

Methods for efficient cyclodextrin-induced lipid exchange have been developed in our lab. These make it possible to almost completely replace the lipids in the outer leaflet of artificial membranes or the plasma membranes of living cells with exogenous lipids. Lipid replacement/substitution allows detailed studies of how lipid composition and asymmetry influence the structure and function of membrane domains and membrane proteins. In this review, we both summarize progress on cyclodextrin exchange in cells, mainly by the use of methyl-alpha cyclodextrin to exchange phospholipids and sphingolipids, and discuss the issues to consider when carrying out lipid exchange experiments upon cells. Issues that impact interpretation of lipid exchange are also discussed. This includes how overly naïve interpretation of how lipid exchange-induced changes in domain formation can impact protein function.

γδ T cell IFNγ production is directly subverted by Yersinia pseudotuberculosis outer protein YopJ in mice and humans

Yersinia pseudotuberculosis is a foodborne pathogen that subverts immune function by translocation of Yersinia outer protein (Yop) effectors into host cells. As adaptive γδ T cells protect the intestinal mucosa from pathogen invasion, we assessed whether Y. pseudotuberculosis subverts these cells in mice and humans. Tracking Yop translocation revealed that the preferential delivery of Yop effectors directly into murine Vγ4 and human Vδ2⁺ T cells inhibited anti-microbial IFNγ production. Subversion was mediated by the adhesin YadA, injectisome component YopB, and translocated YopJ effector. A broad anti-pathogen gene signature and STAT4 phosphorylation levels were inhibited by translocated YopJ. Thus, Y. pseudotuberculosis attachment and translocation of YopJ directly into adaptive γδ T cells is a major mechanism of immune subversion in mice and humans. This study uncovered a conserved Y. pseudotuberculosis pathway that subverts adaptive γδ T cell function to promote pathogenicity.

Unconventional γδ T cells are a dynamic immune population important for mucosal protection of the intestine against invading pathogens. We determined that the foodborne pathogen Y. pseudotuberculosis preferentially targets an adaptive subset of these cells to subvert immune function. We found that direct injection of Yersinia outer proteins (Yop) into adaptive γδ T cells inhibited their anti-pathogen functions. We screened all Yop effectors and identified YopJ as the sole effector to inhibit adaptive γδ T cell production of IFNγ. We determined that adaptive γδ T cell subversion occurred by limiting activation of the transcription factor STAT4. When we infected mice with Y. pseudotuberculosis expressing an inactive YopJ, this enhanced the adaptive γδ T cell response and led to greater cytokine production from this subset of cells to aid mouse recovery. This mechanism of immune evasion appears conserved in humans as direct injection of Y. pseudotuberculosis YopJ into human γδ T cells inhibited cytokine production. This suggested to us that Y. pseudotuberculosis actively inhibits the adaptive γδ T cell response through YopJ as a mechanism to evade immune surveillance at the site of pathogen invasion.

Statin-Induced Chronic Cholesterol Depletion Switches GPCR Endocytosis and Trafficking: Insights from the Serotonin1A Receptor

Endocytosis is a key regulatory mechanism adopted by G protein-coupled receptors (GPCRs) to modulate downstream signaling responses within a stringent spatiotemporal regime. Although the role of membrane lipids has been extensively studied in the context of the function, organization, and dynamics of GPCRs, their role in receptor endocytosis remains largely unexplored. Cholesterol, the predominant sterol in higher eukaryotes, plays a crucial role in maintaining the structure and organization of cell membranes and is involved in essential cellular processes in health and disease. The serotonin_1A receptor is a representative GPCR involved in neuronal development and in neuropsychiatric disorders such as anxiety and depression. We recently combined quantitative flow cytometric and confocal microscopic approaches to demonstrate that the serotonin_1A receptor undergoes clathrin-mediated endocytosis upon agonist stimulation and subsequently traffics along the endosomal recycling pathway. In this work, we show that statin-induced chronic cholesterol depletion switches the endocytic pathway of the serotonin_1A receptor from clathrin- to caveolin-mediated endocytosis. Interestingly, under these conditions, a significant proportion of endocytosed receptors is rerouted toward lysosomal degradation. To the best of our knowledge, these results constitute one of the first comprehensive reports on the role of membrane cholesterol in GPCR endocytosis and trafficking. These results are significant in our overall understanding of the modulatory effects of membrane lipids on GPCR endocytosis and trafficking and could provide novel insight in developing therapeutic interventions against neuropsychiatric disorders such as depression.

A Study of a Potent Inhibitor Against a GDP-6-Deoxy-α-d-Manno-Heptose Biosynthesis Pathway as Antibiotic Candidates

The GDP-6-deoxy-α-d-manno-heptose is a key building block molecule in constructing lipopolysaccharide of Gram-negative bacteria. Therefore, blockage of the biosynthesis pathway of GDP-6-deoxy-α-d-manno-heptose is lethal or increases antibiotics susceptibility to pathogens. In this study, we assayed d-glycero-α-d-manno-heptose-1-phosphate guanylyltransferase (HddC) from Yersinia pseudotuberculosis (Yp) using an efficient assay method supplying its natural substrate. Using the method, 102 chemical compounds were tested to search inhibitory compounds and electrospray ionization mass spectrometry was used to detect the HddC from Y. pseudotuberculosis (YpHddC) reaction product, GDP-d-glycero-α-d-manno-heptose. Interestingly, one promising lead, ethyl 5-({[(5-benzyl-1, 3, 4-oxadiazol-2-yl) thio] acetyl} amino)-4-cyano-3-methyl-2-thiophenecarboxylate (Chembridge 7929959), was discovered. The inhibitory activity of the lead compound against YpHddC has been proven by blocking its nucleotidyltransferase activity transferring the GMP moiety to α-d-mannose-1-phosphate (αM1P). Chembridge 7929959 shows that the half maximal inhibitory concentration (IC₅₀) is 0.222 μM indicating its affinity with αM1P.

Effect of sterol structure on ordered membrane domain (raft) stability in symmetric and asymmetric vesicles

Sterol structure influences liquid ordered domains in membranes, and the dependence of biological functions on sterol structure can help identify processes dependent on ordered domains. In this study we compared the effect of sterol structure on ordered domain formation in symmetric vesicles composed of mixtures of sphingomyelin, 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol, and in asymmetric vesicles in which sphingomyelin was introduced into the outer leaflet of vesicles composed of DOPC and cholesterol. In most cases, sterol behavior was similar in symmetric and asymmetric vesicles, with ordered domains most strongly stabilized by 7-dehydrocholesterol (7DHC) and cholesterol, stabilized to a moderate degree by lanosterol, epicholesterol and desmosterol, and very little if at all by 4-cholesten-3-one. However, in asymmetric vesicles desmosterol stabilized ordered domain almost as well as cholesterol, and to a much greater degree than epicholesterol, so that the ability to support ordered domains decreased in the order 7-DHC > cholesterol > desmosterol > lanosterol > epicholesterol > 4-cholesten-3-one. This contrasts with values for intermediate stabilizing sterols in symmetric vesicles in which the ranking was cholesterol > lanosterol ~ desmosterol ~ epicholesterol or prior studies in which the ranking was cholesterol ~ epicholesterol > lanosterol ~ desmosterol. The reasons for these differences are discussed. Based on these results, we re-evaluated our prior studies in cells and conclude that endocytosis levels and bacterial uptake are even more closely correlated with the ability of sterols to form ordered domains than previously thought, and do not necessarily require that a sterol have a 3β-OH group.

Sterol structure dependence of insulin receptor and insulin-like growth factor 1 receptor activation

The plasma membrane is a dynamic environment with a complex composition of lipids, proteins, and cholesterol. Areas enriched in cholesterol and sphingolipids are believed to form lipid rafts, domains of highly ordered lipids. The unique physical properties of these domains have been proposed to influence many cellular processes. Here, we demonstrate that the activation of insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R) depends critically on the structures of membrane sterols. IR and IGF1R autophosphorylation in vivo was inhibited by cholesterol depletion, and autophosphorylation was restored by the replacement with exogenous cholesterol. We next screened a variety of sterols for effects on IR activation. The ability of sterols to support IR autophosphorylation was strongly correlated to the propensity of the sterols to form ordered domains. IR autophosphorylation was fully restored by the incorporation of ergosterol, dihydrocholesterol, 7-dehydrocholesterol, lathosterol, desmosterol, and allocholesterol, partially restored by epicholesterol, and not restored by lanosterol, coprostanol, and 4-cholesten-3-one. These data support the hypothesis that the ability to form ordered domains is sufficient for a sterol to support ligand-induced activation of IR and IGF1R in intact mammalian cells.