Article

IRS1 regulation by Wnt/beta-catenin signaling and varied contribution of IRS1 to the neoplastic phenotype.

Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 10/2009; 285(3):1928-38. DOI: 10.1074/jbc.M109.060319
Source: PubMed

ABSTRACT Dysregulation of beta-catenin levels and localization and constitutive activation of beta-catenin/TCF (T cell factor)-regulated gene expression occur in many cancers, including the majority of colorectal carcinomas and a subset of ovarian endometrioid adenocarcinomas. Based on the results of microarray-based gene expression profiling we found the insulin receptor substrate 1 (IRS1) gene as one of the most highly up-regulated genes upon ectopic expression of a mutant, constitutively active form of beta-catenin in the rat kidney epithelial cell line RK3E. We demonstrate expression of IRS1 can be directly activated by beta-catenin, likely in part via beta-catenin/TCF binding to TCF consensus binding elements located in the first intron and downstream of the IRS1 transcriptional start site. Consistent with the proposal that beta-catenin is an important regulator of IRS1 expression in vivo, we observed that IRS1 is highly expressed in many cancers with constitutive stabilization of beta-catenin, such as colorectal carcinomas and ovarian endometrioid adenocarcinomas. Using a short hairpin RNA approach to abrogate IRS1 expression and function, we found that IRS1 function is required for efficient de novo neoplastic transformation by beta-catenin in RK3E cells. Our findings add to the growing body of data implicating IRS1 as a critical signaling component in cancer development and progression.

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