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Sox9 inhibits Wnt signaling by promoting beta-catenin phosphorylation in the nucleus.

ABSTRACT: Chondrocyte fate determination and maintenance requires Sox9, an intrinsic transcription factor, but is inhibited by Wnt/beta-catenin signaling activated by extrinsic Wnt ligands. Here we explored the underlying molecular mechanism by which Sox9 antagonizes the Wnt/beta-catenin signaling in chondrocyte differentiation. We found that Sox9 employed two distinct mechanisms to inhibit Wnt/beta-catenin signaling: the Sox9 N terminus is necessary and sufficient to promote beta-catenin degradation, whereas the C terminus is required to inhibit beta-catenin transcriptional activity without affecting its stability. Sox9 binds to beta-catenin and components of the beta-catenin "destruction complex," glycogen synthase kinase 3 and beta-transducin repeat containing protein, to promote their nuclear localization. Independent of its DNA binding ability, nuclear localization of Sox9 is both necessary and sufficient to enhance beta-catenin phosphorylation and its subsequent degradation. Thus, one mechanism whereby Sox9 regulates chondrogenesis is to promote efficient beta-catenin phosphorylation in the nucleus. This mechanism may be broadly employed by other intrinsic cell fate determining transcription factors to promptly turn off extrinsic inhibitory Wnt signaling mediated by beta-catenin.

SUBMITTER: Topol L

PROVIDER: S-EPMC2631972 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundChemotherapeutic agents that modulate cell cycle checkpoints and/or tumor-specific pathways have shown immense promise in preclinical and clinical studies aimed at anti-cancer therapy. MASTL (Greatwall in Xenopus and Drosophila), a serine/threonine kinase controls the final G2/M checkpoint and prevents premature entry of cells into mitosis. Recent studies suggest that MASTL expression is highly upregulated in cancer and confers resistance against chemotherapy. However, the role and mechanism/s of MASTL mediated regulation of tumorigenesis remains poorly understood.MethodsWe utilized a large patient cohort and mouse models of colon cancer as well as colon cancer cells to determine the role of Mastl and associated mechanism in colon cancer.ResultsHere, we show that MASTL expression increases in colon cancer across all cancer stages compared with normal colon tissue (P < 0.001). Also, increased levels of MASTL associated with high-risk of the disease and poor prognosis. Further, the shRNA silencing of MASTL expression in colon cancer cells induced cell cycle arrest and apoptosis in vitro and inhibited xenograft-tumor growth in vivo. Mechanistic analysis revealed that MASTL expression facilitates colon cancer progression by promoting the β-catenin/Wnt signaling, the key signaling pathway implicated in colon carcinogenesis, and up-regulating anti-apoptotic proteins, Bcl-xL and Survivin. Further studies where colorectal cancer (CRC) cells were subjected to 5-fluorouracil (5FU) treatment revealed a sharp increase in MASTL expression upon chemotherapy, along with increases in Bcl-xL and Survivin expression. Most notably, inhibition of MASTL in these cells induced chemosensitivity to 5FU with downregulation of Survivin and Bcl-xL expression.ConclusionOverall, our data shed light on the heretofore-undescribed mechanistic role of MASTL in key oncogenic signaling pathway/s to regulate colon cancer progression and chemo-resistance that would tremendously help to overcome drug resistance in colon cancer treatment.

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Sox9 inhibits Wnt signaling by promoting beta-catenin phosphorylation in the nucleus.

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