Dual treatment with COX-2 inhibitor and sodium arsenite leads to induction of surface Fas Ligand expression and Fas-Ligand-mediated apoptosis in human melanoma cells

Abstract

Most human melanomas express Fas receptor on the cell surface, and treatment with exogenous Fas Ligand (FasL) efficiently induces apoptosis of these cells. In contrast, endogenous surface expression of FasL is suppressed in Fas-positive melanomas. We report here the use of a combination of sodium arsenite, an inhibitor of NF-κB activation, and NS398, a cyclooxygenase-2 (COX-2) inhibitor, for restoration of the surface FasL expression. We observed a large increase of Fas-mediated apoptosis in Fas-positive melanomas. This was due to induction of FasL surface expression and increased susceptibility to Fas death signaling after arsenite and NS398 treatment. Furthermore, silencing COX-2 expression by specific RNAi also effectively increased surface FasL expression following arsenite treatment. Upregulation of the surface FasL levels was based on an increase in the efficiency of translocation to the cell surface and stabilization of FasL protein on the cell surface, rather than on acceleration of the FasL gene transcription. Data obtained demonstrate that the combination of arsenite with inhibitors of COX-2 may affect the target cancer cells via induction of FasL-mediated death signaling.

Sodium arsenite accelerates TRAIL-mediated apoptosis in melanoma cells through upregulation of TRAIL-R1/R2 surface levels and downregulation of cFLIP expression

“…7A and B), indicating a possible role of COX-2 in the regulation of TRAIL protein translocation to the cell surface. Unexpectedly, the effect of COX-2 suppression combined with arsenite on TRAIL surface expression was the reverse to the previously observed upregulation of FasL surface expression in these conditions [48]. However, arsenite-induced apoptosis of melanoma cells with suppressed COX-2 was dramatically increased.…”

“…However, the COX-2--prostaglandin E2 pathway possess multiple targets in the cell, in addition to regulation of cFLIP expression. COX-2 suppression dramatically increased sensitivity to sodium arsenite treatment in human melanomas, due to both cFLIP downregulation and upregulation of surface expression FasL [48], increasing levels of FasLmediated apoptosis.…”

“…4A, D and E). However, at least two critical parameters are different in LU1205 and WM9 cells: higher basal levels of active AKT, due to PTEN dysfunction, and higher levels of basal NF-κB activity in LU1205, compared to WM9 cells [47,48]. These differences are well correlated with substantially higher levels of the cFLIP promoter activity and cFLIP protein expression in LU1205 cells (Fig.…”

“…However, since FLIP protein levels are known to be NF-κB-dependent based on several studies [42,49], it probably indicated an indirect relationship, which could be mediated by the product of another NF-κB-regulated gene. In this regard, the COX-2 gene that is permanently active in melanomas [48] and is under direct control of NF-κB [50], is a possible candidate. A detailed characterization of human FLIP promoter and regulation of cFLIP gene expression are still in progress.…”

Sensitivity to sodium arsenite in human melanoma cells depends upon susceptibility to arsenite-induced mitotic arrest

“…Studies have demonstrated that arsenite has in vitro activity against melanoma as a single agent (Ivanov et al, 2004) or in combination with inhibitors of Epidermal Growth Factor Receptor (EGFR) (Ivanov et al, 2005) or cyclooxygenase 2 (COX-2) (Ivanov et al, 2006). The current study not only confirms that arsenite alone or in combination with inhibitors of arsenite detoxification is effective at killing melanoma cells, but also indicates that the broad variance in sensitivity to pharmacological concentrations of arsenic across different cell types may not be a consequence of reduced intracellular drug accumulation but rather due to mitotic spindle checkpoint dysfunction.…”