The Wnt/β-catenin pathway regulates key cellular processes such as differentiation, proliferation, apoptosis; and its activation promotes development of several cancer types. Expression of CD43 (leukosialin), the predominant leukocyte transmembrane sialoglycoprotein, has been detected in many tumors of non-hematopoietic origin. CD43 participates in cell adhesion and regulates intracellular signal transduction pathways involved in cell proliferation and survival. The cytoplasmic domain of CD43 has been reported to translocate to the nucleus, interact with β-catenin and affect its target gene expression, but the impact of this action on cell fate is still unknown. We demonstrate, here, by colony formation assay and siRNA-mediated gene silencing that CD43 and β-catenin co-operate in promoting cell growth. Moreover, in cells with down-regulated β-catenin expression the activation of p53 in response to CD43 overexpression is significantly impaired. In addition, the presence of both CD43 and β-catenin is required for the TCF/LEF-mediated transcription. Presumably, the fulllength CD43 participates in this transcriptional regulation. We show that the mature CD43 localizes to the nucleus, where it binds chromatin, co-localizes and co-immunoprecipitates with β-catenin, and enhances the reporter gene expression regulated by β-catenin. These observations provide clear evidence linking CD43 to the Wnt/APC/β-catenin signaling pathway and supporting our hypothesis according to which CD43 plays a role in tumor development.

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