Importance of ASC expression levels in the development of chemoresistance in human melanoma cell lines

Abstract

ASC (Apoptosis-associated speck like protein containing a CARD) is an adapter protein containing PYRIN and CARD interaction domains. ASC is implicated in apoptosis and innate immune signaling and is required for IL-1 and IL-18 processing via the activation of caspase 1. ASC protein expression is suppressed via methylation of its promoter regions in a high percentage of melanoma and other cancer types, including colorectal, prostate, lung, breast cancers and glioblastomas. ASC protein is absent or downregulated in 62.5 per cent of the melanoma tissue samples and in 58.3 per cent of the investigated melanoma cell lines. Most melanoma cells are highly resistant to widely used chemotherapeutic drugs, thus novel pathways and targets need to be investigated for the development of effective therapies. We aimed to clarify the role of ASC in increasing the chemo-sensitivity of melanoma cell lines, which lack its expression. ASC was reintroduced into two of these cell lines, MeWo and Skmel 19, using a lentiviral infection system, which establishes the stable expression of ASC. Control GFP vector- and ASC vector- infected cells were treated with DNA damaging drugs - doxorubicin, etoposide and dacarbazine and the death receptor ligand TRAIL. In short term viability assays we have found that ASC expression confers slight chemosensitization to doxorubicin (Skmel 19) and etoposide (Skmel 19). A more pronounced effect was observed with TRAIL in Mewo cells. More importantly, we found in long term assays that re-expression of ASC in Mewo and Skmel 19 dramatically decreased their colony forming capacity.