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Glycosyltransferase POMGnT1 deficiency affects N-cadherin-mediated cell-cell adhesion

ABSTRACT: Deficiencies in the protein O-mannose β1,2-N-acetylglucosaminyltransferase 1 (POMGNT1), a glycosyltransferase involved in the elongation of classic O-mannosyl glycans, are mainly associated with muscle-eye-brain disease (MEB), a genetically heterogeneous congenital muscular dystrophy with brain and eye anomalies. Although occasional aberrant cell-cell adhesion has been observed in response to changes in POMGNT1 levels, direct molecular mechanisms are largely unknown. POMGNT1 knock-out HEK293T cells and fibroblasts derived from MEB patients were used to get deeper insight in POMGNT1 deficiency by the combination of biochemical, cell and molecular biological techniques with proteomics and glycan-profile.

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ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Early Embryonic Cell, Kidney

SUBMITTER: Patrick Winterhalter

LAB HEAD: Sabine Strahl

PROVIDER: PXD021321 | Pride | 2021-02-18

REPOSITORIES: Pride

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Project description:Progression and relapse-free survival of ovarian carcinoma are associated with the abundance of immunosuppressed CD163highCD206high tumor-associated macrophages (TAMs) and high levels of polyunsaturated fatty acids (PUFAs), in particular arachidonic acid (AA), in the tumor microenvironment. In the present study, we have investigated whether both associations are functionally linked. Methods: The effect of PUFAs on cytokine-mediated pro-inflammatory signal transduction was studied in primary monocyte-derived macrophages (MDMs) by transcriptomics, bioinformatics, phosphoprotein analysis of signal transduction proteins and MS-based proteomics of lipid rafts. Results: Pathway analysis of transcriptional profiles revealed that high CD163 and CD206/MRC1 expression in TAMs is strongly associated with an inhibition of cytokine-triggered signal transduction. This is mirrored by an impairment of the transcriptional response to interferon-beta (IFNbeta), IFNgamma and IL-6 in monocyte-derived macrophages (MDMs) by AA. This AA-mediated inhibition of pro-inflammatory signaling is caused by dysfunctions of the cognate receptors, as indicated by the inhibition by PUFAs of JAK1, JAK2, STAT1 and STAT3 phosphorylation, with the strongest inhibitory effects exerted by AA and its non-metabolizable analog ETYA. AA/ETYA treatment of MDMs results in altered composition of lipid rafts, including reduced amounts of the interferon receptor IFNAR1, STAT1 and other immune-regulatory proteins. The AA-mediated inhibition of IFN-triggered STAT1 phosphorylation was reversed by water-soluble cholesterol, known to prevent the perturbation of lipid raft structure by PUFAs. Conclusion: Our data suggest that AA, and to a lesser degree other PUFAs, impair pro-inflammatory signaling in macrophages, at least in part by altering the structure of lipid rafts, and thereby contribute to the reeducation of tumor-associated macrophages. Our findings also suggest that the pharmacologic restoration of lipid raft functions in TAM may be a promising strategy for the development of new therapeutic approaches.

Project description:Diaphanous-related formin-3 (DIAPH3), a cytoskeletal regulator of the formin family, is lost at high frequency in metastatic breast and prostate cancers and has characteristics of a non-canonical metastasis suppressor. We previously demonstrated that DIAPH3 silencing evokes transition to an “amoeboid” phenotype, characterized by rapid motility, RhoA/ROCK and MEK/ERK pathway activation, dynamic membrane blebbing, and increased shedding of microvesicles. Here we report that low DIAPH3 mRNA expression correlates with reduced survival in multiple cancer patient cohorts. In line with induction of amoeboid behavior, traction force microscopy (TFM) revealed that polarized force generation, contractility, and response to substrate stiffness are reduced by DIAPH3 loss. Proteomic analyses revealed that DIAPH3 precipitates with tubulins, and reciprocal co-immunoprecipitation analyses revealed greater binding of DIAPH3 to MT polymers than soluble tubulin. DIAPH3 also bound to acetylated-tubulin (Ac-tubulin), suggesting association with a stable MT population. DIAPH3 silencing reduced Ac-tubulin and increased the cellular content of dynamic MT, as indicated by TFM and live cell imaging. DIAPH3 silencing also increased responsiveness to MT-disrupting agents. Treatment with the taxanes paclitaxel and docetaxel, and the non-taxane epothilone B, induced a greater change in Ac-tubulin when cells lacked DIAPH3. Intracellular accumulation of Oregon Green 488-paclitaxel was also increased by DIAPH3 loss, and accordingly, DIAPH3 silencing enhanced cytotoxicity by paclitaxel, docetaxel, or epothilone B. Gene expression profiles of breast cancer patients treated with chemotherapeutic regimens containing taxanes revealed an association of low DIAPH3 expression with improved relapse-free survival. Collectively, these results suggest that regulation of MT stability/dynamics by DIAPH3 enhances amoeboid tumor cell susceptibility to microtubule poisons. These findings have potential therapeutic implications.

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Glycosyltransferase POMGnT1 deficiency affects N-cadherin-mediated cell-cell adhesion

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