Methylation-Mediated Repression of GADD45 in Prostate Cancer and Its Role as a Potential Therapeutic Target

¹Sylvester Comprehensive Cancer Center, University of Miami, Miami, Florida and ²Department of Urology, Heinrich Heine University, Düsseldorf, Germany

^* To whom correspondence should be addressed. E-mail: rsingal{at}med.miami.edu.

	Abstract

Defects in apoptotic pathway contribute to uncontrolled proliferation of cancer cells and confer resistance to chemotherapy. Growth arrest and DNA damage inducible, alpha (GADD45) is up-regulated on docetaxel treatment and may contribute to docetaxel-mediated cytotoxicity. We examined the mechanism of regulation of GADD45 in prostate cancer cells and the effect of its up-regulation on sensitivity to docetaxel chemotherapy. Expression of GADD45 in PC3 cells was higher than that in Du145 and LNCaP cells (17- and 12-fold, respectively; P < 0.05). Although the proximal promoter region was unmethylated in all three cell lines, methylation of a 4 CpG region upstream of the proximal promoter correlated inversely with gene expression levels. Methylation was reversed by treatment of Du145 and LNCaP cells with DNA methyltransferase inhibitors, leading to reactivation of GADD45 expression in these cells. The 5' 4 CpG region was also frequently methylated in prostate cancer tissues. Methylation of this region correlated inversely with gene expression in prostate cancer and benign prostate tissues. The methyl binding protein MeCP2 was associated with the methylated 4 CpGs in Du145 cells, and knockdown of MeCP2 in these cells (Du145 MeCP2^-) led to a significantly increased expression of GADD45 (3-fold; P = 0.035) without affecting the methylation status of the gene. Enhanced sensitivity to docetaxel was observed by up-regulation of GADD45 in Du145 cells by recombinant expression of GADD45 or pretreatment with 5-azacytidine. Our results show that GADD45 is epigenetically repressed and is a potential target for treatment of prostate cancer. [Cancer Res 2009;69(4):1527–35]

Key Words: DNA methylation, gene expression, methyl binding proteins, apoptosis, chemotherapy, docetaxel

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