Importance of ASC expression for melanoma tumorigenesis in vivo and a role for inflammasome activation in apoptosis induction

Abstract

ASC is an adaptor protein which is capable of binding to numerous partners due to its two oligomerization domains, PYRIN and CARD. Its involvement in the inflammasome complex as an essential adaptor, in the regulation of the cleavage and secretion of IL-1β and IL-18, in apoptosis induction and its evident silencing via methylation in variety of cancer types make ASC an important protein to be examined. Preliminary data from our laboratory showed that introduction of ASC into melanoma cell lines, with silenced ASC, via lentiviral transfection decreased the number and the size of the colonies formed by these cells in an anchorage independent medium up to 50 per cent. In this study, first, we hypothesized that injection of ASC-introduced human melanoma cell lines into immunodeficient mice may show the importance of ASC silencing in human melanoma progression. We observed a slight difference in the tumorigenicity between ASC expressing and control groups. Secondly, we tested the importance of ASC expression in tumorigenesis using mice with a normal immune system. In these experiments, mouse melanoma cells with varying ASC expression levels were utilized. We also transduced the ASC non-expression mouse melanoma cell line (B16 F1) with the mouse ASC gene. Unfortunately, with the small number of animals, we could not observe a clear reduction in the tumor sizes produced by these cells in an ASC dependent manner. Finally, we aimed to analyze the combinatorial/synergistic effect of the DNA damaging agent (etoposide) and an inflammasome activating substrate (imiquimod) treatment on the chemoresistance of ASC-introduced and control melanoma cell lines. We observed a combinatorial effect of treatment with both agents in SKMEL-19 and SKMEL- 28 cell lines, although this effect was regardless of the ASC expression status.