ASC/TMS1, a caspase‐1 activating adaptor, is downregulated by aberrant metylation in human melanoma

Abstract

ASC/TMS1 is an adaptor protein activating caspase-1 that stimulates processing of proIL-1␤ and proIL-18. ASC was reported to be aberrantly methylated and silenced in human breast cancers. In our present study, ASC expression was examined in 12 melanoma cell lines by Western blot analysis and in 18 benign melanocytic nevi and 32 melanoma tissues by immunohistochemical staining. ASC expression was absent or reduced in 7 of 12 (58.3%) cell lines and in 20 of 32 (62.5%) melanoma tissues, whereas all 18 benign melanocytic nevi showed intensive ASC expression. To investigate whether ASC silencing in melanoma is involved in aberrant methylation, methylation specific PCR was carried out. Five of ten (50%) melanoma tissues exhibited methylation in CpG island of ASC companied with reduced ASC expression. Six of twelve (50%) melanoma cell lines showed aberrant methylation in the ASC gene, and 4 of the 6 (66.7%) methylation positive cell lines exhibited reduced ASC expression. We characterized methylation patterns in melanoma cell lines by using bisulfite genomic sequencing, and found that the degree of aberrant methylation correlated with the level of reductive ASC expression. Treatment with demethylating agent 5-aza-2-deoxycytidine resulted in both demethylation of the ASC gene and the upregulation of ASC expression in the methylation positive melanoma cell lines. Our study shows that ASC is downregulated in melanoma, and that its suppression is partially mediated by aberrant methylation.

Dual role of TMS1/ASC in death receptor signaling

“…TMS1 was also independently identified by Masumoto et al (1999) as a protein that forms cytoplasmic 'specks' during retinoic acid induced differentiation or drug-induced apoptosis in HL60 cells, and called ASC. Subsequent studies by our lab and others have implicated the epigenetic silencing of TMS1 in a number of other tumor types, including melanomas, glioblastomas, non-small cell lung cancers, gastric and colorectal cancers (Moriai et al, 2002;Guan et al, 2003;Virmani et al, 2003;Yokoyama et al, 2003;Stone et al, 2004). Ectopic expression of TMS1 suppresses the growth of breast cancer cells, consistent with a role in tumor suppression (Conway et al, 2000).…”

“…TMS1 is a novel tumor suppressor gene that is subject to frequent epigenetic silencing in several different tumor types, including breast, gliomas, melanomas and nonsmall cell lung cancers, however the mechanism by which TMS1 silencing promotes carcinogenesis is not well understood (Conway et al, 2000;Moriai et al, 2002;Guan et al, 2003;Virmani et al, 2003;Yokoyama et al, 2003;Stone et al, 2004). Here, we examined the role of TMS1 in the cellular response of breast epithelial cells and human fibroblasts to death receptor activation and DNA damaging agents.…”

Genomic profiling of C/EBPβ2 transformed mammary epithelial cells: A role for nuclear interleukin-1β

“…PYCARD promoter methylation has been observed in many other cancer types. [32][33][34][35][36] When combined with the known expression of IL1b in many of these same cancer types, it is possible proIL1b may be present in these cancers as well. These results establish proIL1b as an intracellular nuclear factor relevant for further study.…”

Methylation-induced silencing of ASC and the effect of expressed ASC on p53-mediated chemosensitivity in colorectal cancer

“…ASC interacts with Bax through the Pyrin domain to regulate Bax translocation to the mitochondria, thus resulting in mitochondrial permiabilization, cytochrome c release, and activation of caspase-9 and -3 (Ohtsuka et al, 2004). ASC is also known as TMS1 (target gene of methylation-induced silencing-1), and inactivated in 40% of breast cancer and 50% of melanoma (Conway et al, 2000;Guan et al, 2003). Although the significance of methylation-induced ASC silencing remains obscure, the methylation of ASC might cause resistance to anticancer drugs in colorectal cancer, the same as in other p53 target genes.…”