Bcl-xL and bcl-2 proteins in melanoma progression and UVB-induced apoptosis

Whether bcl-xL and bcl-2 play an essential role in melanoma progression and UVB-induced apoptosis is not completely understood. We investigated the expression of bcl-xL and bcl-2 in matched primary and metastatic melanoma tumors and melanoma cell lines from the same melanoma patients to clarify the importance of bcl-xL and bcl-2 in melanoma progression and in UVB-induced apoptosis. The expression of bcl-xL and bcl-2 proteins was examined by immunohisto(cyto)chemistry and Western blot in melanoma tumors and melanoma cells. Cellular viability and apoptosis were estimated after the melanoma cells were exposed to 30, 60 and 180 mJ/cm2 UVB. Both primary melanoma tumors and melanoma cells showed lower expression of bcl-xL and bcl-2 proteins estimated as frequency of positive cells than their matched metastatic tumors and cells in vitro. After exposure to UVB, the cell viability decreased and the number of apoptotic cells increased in both primary and metastatic melanoma cell lines. These changes were more pronounced in the primary melanoma cells than in the matched metastatic cells. After UVB exposure, the expression of bcl-xL protein decreased in primary melanoma cells in a dose- and time-dependent manner, but the expression of bcl-2 was not influenced. The expression of bcl-xL and bcl-2 proteins was increased during melanoma progression from primary to metastatic melanoma. Reduction of bcl-xL, but not bcl-2 expression was involved in UVB-induced apoptosis in primary melanoma cells.