Inactivation of the apoptosis effector Apaf-1 in malignant melanoma

Abstract

Metastatic melanoma is a deadly cancer that fails to respond to conventional chemotherapy and is poorly understood at the molecular level. p53 mutations often occur in aggressive and chemoresistant cancers but are rarely observed in melanoma. Here we show that metastatic melanomas often lose Apaf-1, a cell-death effector that acts with cytochrome c and caspase-9 to mediate p53-dependent apoptosis. Loss of Apaf-1 expression is accompanied by allelic loss in metastatic melanomas, but can be recovered in melanoma cell lines by treatment with the methylation inhibitor 5-aza-2'-deoxycytidine (5aza2dC). Apaf-1-negative melanomas are invariably chemoresistant and are unable to execute a typical apoptotic programme in response to p53 activation. Restoring physiological levels of Apaf-1 through gene transfer or 5aza2dC treatment markedly enhances chemosensitivity and rescues the apoptotic defects associated with Apaf-1 loss. We conclude that Apaf-1 is inactivated in metastatic melanomas, which leads to defects in the execution of apoptotic cell death. Apaf-1 loss may contribute to the low frequency of p53 mutations observed in this highly chemoresistant tumour type.

Effects of demethylating agent 5-aza-2′-deoxycytidine and histone deacetylase inhibitor FR901228 on maspin gene expression in oral cancer cell lines

“…Kondo et al [20] have reported that 5Aza-dC dramatically decreases histone H3 Lys-9 methylation, slightly increases Lys-9 acetylation, and moderately increases histone H3 Lys-4 methylation and reactivated gene expression. These findings could explain the previously reported 5Aza-dC induced activation of the un-methylated gene [21,22] and could also explain the maspin activation in our results.…”

A proteomic analysis reveals the loss of expression of the cell death regulatory gene GRIM-19 in human renal cell carcinomas

“…Mutations in the genes coding for transcription factors p53 (Vogelstein et al, 2000), the retinoblastoma protein (Sherr and McCormick, 2002), BRCA1, BRCA2 (Venkitaraman, 2002) and the Interferon (IFN)-gene regulatory factor-1 (Willman et al, 1993;Tanaka et al, 1996) yield functionally-inactive proteins, which fail to inhibit cell growth and thus have been linked to the development of tumors. In addition to these transcription factors, mutations or loss of expression of cellular genes coding for the apoptotic machinery also promotes tumor cell growth (Lowe et al, 1994;Knudson et al, 1995;Soengas et al, 2001;Pingoud-Meier et al, 2003;Stupack et al, 2006).…”

Dual role of TMS1/ASC in death receptor signaling

“…Once established, this state is mitotically heritable and contributes to the stable silencing of tumor suppressor and other genes. Several proapoptotic genes succumb to epigenetic silencing in human tumors, including CASP8, the TNFrelated apoptosis-inducing ligand (TRAIL) receptors TNFRSF10A and TNFRSF10B, the caspase-9 adaptor APAF1 and the death-associated protein kinase, DAPK (Kissel et al, 1997;Teitz et al, 2000;Soengas et al, 2001;van Noesel et al, 2002;Furukawa et al, 2005;Horak et al, 2005), suggesting that acquired epigenetic alterations also contribute to apoptotic resistance during tumor progression.…”