Mcl-1, Bcl-XL and Stat3 expression are associated with progression of melanoma whereas Bcl-2, AP-2 and MITF levels decrease during progression of melanoma

Members of the Bcl-2 family of antiapoptotic proteins (Bcl-2, Bcl-XL and Mcl-1) are key regulators of apoptosis. The purpose of the present study was to examine and better define the role of Bcl-2, Bcl-XL and Mcl-1 in the progression of melanoma. Immunohistochemical staining for Bcl-2, Bcl-XL and Mcl-1 was performed on paraffin sections of 100 cases of benign nevi, primary melanoma and metastatic melanoma. Expression was correlated with histopathologic features, clinical progress and expression of transcription factors (AP-2, MITF and p-Stat3). Bcl-2 was expressed in 100% of benign nevi and thin melanoma (<= 1.0mm) but was less in thick melanoma (> 1.0mm) (88%), subcutaneous (62%) and lymph node metastases (35%). In contrast, Bcl-XL and Mcl-1 were expressed at lower levels in nevi and thin melanoma compared to Bcl-2 but their expression was much higher in thick melanoma and in subcutaneous and lymph node metastases (P < 0.0001). Bcl-2 expression was negatively associated with tumor thickness (P < 0.05) but Bcl-XL expression increased with increasing tumor thickness (P < 0.05) and dermal tumor mitotic rate ( P < 0.05). Similarly Mcl-1 expression increased with increasing tumor thickness (P < 0.09) and dermal tumor mitotic rate (P < 0.17). Bcl-2 expression was positively correlated with expression of the transcription factors microphthalmia transcription factor (MITF) and nuclear AP-2 whereas Bcl-XL (and Mcl-1) expression were positively correlated with p-Stat3. This study is the first to show a clear dissociation between changes in Bcl-2 expression (downregulation) and Bcl-XL, Mcl-1 expression (upregulation) during progression of melanoma. The results were also consistent with a role for AP-2 and MITF in regulation of Bcl-2 and pStat3 in regulation of Bcl-XL. These findings have important implications for the development of treatments targeting antiapoptotic proteins in patients with melanoma.