Expression and targeting of the apoptosis inhibitor, survivin, in human melanoma

Abstract

The newly described apoptosis inhibitor survivin is expressed in many human cancers and appears to play a critical part in both apoptosis regulation and cell cycle progression. Its potential role in malignant melanoma is unknown. In a panel of 30 malignant melanomas, survivin was strongly expressed in all cases (15 of 15) of metastatic malignant melanomas and 13 of 15 cases of invasive malignant melanomas by immunohistochemistry. In invasive malignant melanomas, survivin was also expressed in the in-situ component of the lesion. Survivin expression was found in all cases (11 of 11) of nevi, but not in melanocytes in sections of normal skin. The apoptosis inhibitor bcl-2 was expressed in 26 of 30 cases, but generally at lower levels than that of infiltrating lymphocytes. The mitotic index, as assessed by MIB-1 staining, was consistently higher in metastatic than invasive malignant melanomas. Assessment of apoptotic index by in situ end-labeling revealed extremely low rates of apoptosis in most malignant melanomas. Survivin expression by western blotting was detected in four human metastatic malignant melanoma cell lines but not in cultured normal human melanocytes. Transfection of both YUSAC-2 and LOX malignant melanoma cells with green fluorescence protein-conjugated survivin anti-sense or green fluorescence protein-conjugated survivin dominant negative mutant (Cys84Ala) [corrected] resulted in increased apoptosis in the absence of other genotoxic stimuli. Two-color flow cytometry confirmed that YUSAC-2 cells transfected with survivin anti-sense expressed less endogenous survivin and exhibited an increased fraction of cells with sub-G1 DNA content. These data demonstrate that apoptosis inhibition by survivin may participate in the onset and progression of malignant melanomas, and suggest that therapeutic targeting of survivin may be beneficial in patients with recurrent or metastatic disease.