Abstract
Abstract: :
Purpose:Tumor necrosis factor–related apoptosis–inducing ligand (TRAIL) is a potent inducer of apoptosis in most cancer cell lines. However, many tumor cells are resistant to apoptosis mediated by TRAIL. This study evaluated the mechanisms of resistance and susceptibility of human uveal melanoma cells to TRAIL– induced apoptosis. Methods:Twelve human melanoma cell lines were tested by flow cytometry for their expression of TRAIL and its agonistic and antagonistic receptors. Flow cytometry was also used to test the melanoma cells for their cytoplasmic expression of the anti–apoptosis protein, survivin. Melanoma cells susceptibility to TRAIL–induced apoptosis was examined using the active capase–3 assay. Results:Only 5 of 12 melanoma cell lines were sensitive to TRAIL–induced apoptosis (the range of apoptosis was 15–35 % after treatment with TRAIL). TRAIL receptor 2 is the main TRAIL receptor that is expressed on uveal melanomas. Resistance to TRAIL–induced apoptosis did not correlate with the expression of TRAIL decoy receptors (DcR1 and DcR2). TRAIL–resistant melanoma cell lines (92–1, MEL202, MEL285, OCM1, OCM8, OMM1.5, and OMM2.3) expressed high levels of survivin (the range of the survivin expression was 20–65%). Immunohistochemical analysis of human intraocular melanoma cells (OCM8) transplanted into the eyes of nude mice revealed abundant in situ expression of survivin in the intraocular melanoma. However, survivin expression was not detected in normal ocular tissues. Pretreatment of TRAIL–resistant melanoma cells with actinomycin D resulted in a 20–50% decrease in intracellular expression of survivin (P<0.01) and a 5 to 7 fold increase in TRAIL–induced apoptosis (P<0.001). Conclusions: These results indicate that resistance to TRAIL–induced apoptosis is regulated by the apoptotic cascades that are sensitive to actinomycin D treatment and expression of at least one anti–apoptotic gene, survivin.
Keywords: melanoma • tumors • apoptosis/cell death