Depletion of MUC5B mucin in gastrointestinal cancer cells alters their tumorigenic properties: implication of the Wnt/β-catenin pathway

Abstract

Secreted mucins are large O-glycosylated proteins which participate in the protection/defence of underlying mucosae in normal adults. Alteration of their expression is a hallmark of numerous epithelial cancers and has often been correlated to bad prognosis of the tumor. The secreted mucin MUC5B is over-expressed in certain sub-types of gastric and intestinal cancers but the consequences of this altered expression on the cancer cell behavior is not known. To investigate the role of MUC5B in carcinogenesis, its expression was knocked-down in the human gastric cancer cell line KATO-III and in the colonic cancer cell line LS174T by using transient and stable approaches. Consequences of MUC5B knocking-down on cancer cells were studied with respect to in vitro proliferation, migration and invasion, and in vivo on tumour growth using a mice subcutaneous xenograft model. Western-blotting, luciferase assay and qRT-PCR were used to identify proteins and signalling pathways involved. In vitro MUC5B downregulation leads to a decrease of proliferation, migration and invasion properties in both cell lines. Molecular mechanisms involved alteration of beta-catenin expression, localization and activity and decreased expression of several of its target genes. In vivo xenografts of MUC5B-deficient cells induced a decrease of tumour growth when compared with MUC5B-expressing Mock cells. Altogether, this study shows that downregulation of MUC5B profoundly alters proliferation, migration and invasion of human gastrointestinal cancer cells and that these alterations may be in part mediated by the Wnt/beta-catenin pathway emphasizing the potential of MUC5B as an actor of gastrointestinal carcinogenesis.