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Pyruvate kinase M2 controls lipid homeostasis via regulation of SREBPs activation and intestinal cholesterol absorption

ABSTRACT: The pyruvate kinase M2 isoform (PKM2) is preferentially expressed in cancer to regulate anabolic metabolism. However, the metabolic requirements of PKM2 in tumorigenesis have yielded contradictory results. Herein we discovered that this glycolytic enzyme regulates lipid homeostasis in cancer cell autonomous manner and at systemic levels. Transmembrane protein 33 (TMEM33) was identified as a downstream effector of PKM2, whose expression level positively correlates with plasma total cholesterol level in vivo. Loss of PKM2 leads to up-regulation of TMEM33, which recruits ring finger protein 5 (RNF5) to promote SCAP ubiquitination and degradation, thereby inhibiting Golgi translocation and activation of sterol regulatory element binding protein 1 (SREBP1). Moreover, global PKM2 knockout promoted allografted tumor growth, at least partially attributes to the elevated plasma cholesterol level caused by increased intestinal Niemann-Pick C1-Like 1 (NPC1L1) to facilitate cholesterol absorption. Collectively, PKM2-TMEM33 axis modulates cell autonomous lipid metabolism by regulating SREBP activation. PKM2 in small intestine plays critical functions in controlling systemic cholesterol level. Overall, our results underscore unappreciated functions of PKM2 in lipid homeostasis and imply that combining an allosteric activator of PKM2 with NPC1L1 inhibitor represents a therapeutic invention for cancer treatment.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Min Ma

LAB HEAD: lingjun Li

PROVIDER: PXD026434 | Pride | 2021-08-06

REPOSITORIES: Pride

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Project description:To cause disease, Salmonella enterica serovar Typhimurium requires two type-III secretion systems, encoded on Salmonella Pathogenicity Islands 1 and 2 (SPI-1 and -2). These secretion systems serve to deliver virulence proteins, termed effectors, into the host cell cytosol. While the importance of these effector proteins to promote colonization and replication within the host has been established, the specific roles of individual secreted effectors in the disease process are not well understood. In this study, we used an in vivo gallbladder epithelial cell infection model to study the function of the SPI-2-encoded effector, SseL. Deletion of the sseL gene resulted in bacterial filamentation and elongation and unusual localization of Salmonella within infected epithelial cells. Infection with the ?sseL strain also caused dramatic changes in lipid metabolism and led to massive accumulation of lipid droplets in infected cells. Some of these changes were investigated through metabolomics of gallbladder tissue. This phenotype was directly attributed to the deubiquitinase activity of SseL, as a Salmonella strain carrying a single point mutation in the catalytic cysteine resulted in the same phenotype as the deletion mutant. Excessive buildup of lipids due to the absence of a functional sseL gene was also observed in S. Typhimurium-infected livers. These results demonstrate that SseL alters host lipid metabolism in infected epithelial cells by modifying ubiquitination patterns of cellular targets. Female C57BL/6 mice were infected with the indicated strain of Salmonella enterica serovar Typhimurium by oral gavage. Four gallbladders were collected and pooled per sample group and metabolites extracted using a mixture of methanol and chloroform. Extracts were infused into a 12-T Apex-Qe hybrid quadrupole-FT-ICR mass spectrometer equipped with an Apollo II electrospray ionization source, a quadrupole mass filter and a hexapole collision cell. Raw mass spectrometry data were processed as described elsewhere (Han et al. 2008. Metabolomics. 4:128-140). To identify differences in metabolite composition between different groups of samples, we filtered the list of masses for metabolites which were present on one set of samples but not the other. Additionally, we calculated the ratios between averaged intensities of metabolites from each group of mice. To assign possible metabolite identities, monoisotopic neutral masses of interest were queried against MassTrix (http://masstrix.org). Masses were searched against the Mus musculus database within a mass error of 3 ppm.

Project description:Purpose: PKM2-mediated metabolic switch to aerobic glycolysis plays a critical role in promoting cell survival and proliferation. However, little is known about the function of intestinal epithelial PKM2 in intestinal homeostasis. Here we investigated whether and how intestinal epithelial PKM2 modulates the morphology and function of the adult intestine in experimental murine colitis. Methods: Colonoscopic biopsies from the Crohn’s disease (CD) and ulcerative colitis (UC) patients (10 each) were analyzed for PKM2 expression. We also generated intestinal epithelial-specific Pkm2 knockout mice and employed them to examine PKM2 function. Mouse intestinal inflammation was induced with dextran sulfate sodium (DSS) in drinking water. Disease phenotypes were investigated by mouse survival, body weight, colon length and analysis of immune cell infiltration in colon, intestinal epithelial cell gene profiling and signal pathway. Results: Intestinal epithelial PKM2 level in UC and CD patients was significantly decreased compared to that from non-inflamed intestinal epithelium. Similar reduction of intestinal epithelial PKM2 was observed in mice with experimental colitis. Supporting the notion that PKM2 serves as a safeguard against colitis, intestinal epithelial-specific Pkm2-deficient (Pkm2-/-) mice displayed a severer intestinal inflammation, companying with shortened colon, disruption of epithelial tight junction, higher permeability, elevation of inflammatory cytokines and immune cell infiltration, compared with wild-type mice. Gene profiling and western blot analysis indicated that cell survival signaling, particularly the Akt/β-catenin pathways, were downregulated in Pkm2-/- mice. Functional assay using mouse primary colonic epithelial cells confirmed that Pkm2 reduction decreased proliferation and migration of epithelial cells, while enhanced expression of Pkm2 was associated with increased transcriptional activity of β-catenin. Moreover, increasing mouse intestinal epithelial Pkm2 expression via delivery of Pkm2-expressing plasmid attenuated DSS-induced experimental colitis. Conclusions: Intestinal epithelial PKM2, through activating Wnt/β-catenin signaling, induces a strong proliferative and migratory response that increases cell survival and wound healing under colitic condition.

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Pyruvate kinase M2 controls lipid homeostasis via regulation of SREBPs activation and intestinal cholesterol absorption

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