Epigenetic Alteration of PRKCDBP in Colorectal Cancers and Its Implication in Tumor Cell Resistance to TNF alpha-Induced Apoptosis

Abstract

Purpose: PRKCDBP is a putative tumor suppressor in which alteration has been observed in several human cancers. We investigated expression and function of PRKCDBP in colorectal cells and tissues to explore its candidacy as a suppressor in colorectal tumorigenesis. Experimental Design: Expression and methylation status of PRKCDBP and its effect on tumor growth were evaluated. Transcriptional regulation by NF-kappa B signaling was defined by luciferase reporter and chromatin immunoprecipitation assays. Results: PRKCDBP expression was hardly detectable in 29 of 80 (36%) primary tumors and 11 of 19 (58%) cell lines, and its alteration correlated with tumor stage and grade. Promoter hypermethylation was commonly found in cancers. PRKCDBP expression induced the G(1) cell-cycle arrest and increased cellular sensitivity to various apoptotic stresses. PRKCDBP was induced by TNF alpha, and its level correlated with tumor cell sensitivity to TNF alpha-induced apoptosis. PRKCDBP induction by TNF alpha was disrupted by blocking NF-kappa B signaling while it was enhanced by RelA transfection. The PRKCDBP promoter activity was increased in response to TNF alpha, and this response was abolished by disruption of a kappa B site in the promoter. PRKCDBP delayed the formation and growth of xenograft tumors and improved tumor response to TNF alpha-induced apoptosis. Conclusions: PRKCDBP is a proapoptotic tumor suppressor which is commonly altered in colorectal cancer by promoter hypermethylation, and its gene transcription is directly activated by NF-kappa B in response to TNF alpha. This suggests that PRKCDBP inactivation may contribute to tumor progression by reducing cellular sensitivity to TNF alpha and other stresses, particularly under chronic inflammatory microenvironment. Clin Cancer Res; 17(24); 7551-62. (C)2011 AACR.