Homeodomain-interacting protein kinase-2 restrains cytosolic phospholipase A2-dependent prostaglandin E2 generation in human colorectal cancer cells

Purpose: Homeodomain-interacting protein kinase-2 (HIPK2), a corepressor for homeodomain transcription factors, is a multifunctional kinase whose role in tumor cell survival is not completely clarified. We addressed whether HIPK2 restrains colon tumorigenesis by turning off cytosolic phospholipase A(2) (cPLA(2)) -dependent prostaglandin E-2 (PGE(2)) generation in the light of overwhelming evidence suggesting the contribution of this prostanoid in a variety of cancers. Experimental Design: In the human colorectal cancer cell line, RKO, we studied the effect of RNA interference for HIPK2 (HIPK2i) on prostanoid biosynthesis, both in the absence and in the presence of the cPLA(2) inhibitor arachidonyl trifluoromethyl ketone. We evaluated the role of HIPK2 in the cPLA(2) gene regulation by reverse transcriptase-PCR, transcriptional activity, and chromatin immunoprecipitation analyses. The involvement of HIPK2 in tumorigenicity in vivo was studied by tumor growth of HIPK2i cells in nude mice. We compared the gene expression of HIPK2 and c PLA(2) in human colorectal cancer specimens by reverse transcriptase-PCR. Results: HIPK2 silencing was associated with rousing PGE(2) biosynthesis that was profoundly suppressed by the cPLA(2) inhibitor. HIPK2 overexpression, along with histone deacetylase-1, inhibited the cPLA(2)-luc promoter that is strongly acetylated in HIPK2i cells. The tumors derived from HIPK2i cells injected in nude mice showed noticeably increased growth compared with parental cells. HIPK2 mRNA levels were significantly higher in colorectal cancers of patients with familial adenomatous polyposis, which showed undetectable cPLA(2) levels compared with sporadic colorectal cancer expressing cPLA(2) Conclusions: Our findings reveal the novel mechanism of HIPK2 to restrain progression of human colon tumorigenesis, at least in part, by turning off cPLA(2)-dependent PGE(2) generation.