Down-regulation of COOH-terminal binding protein expression in malignant melanomas leads to induction of MIA...

Malignant transformation of melanocytes to melanoma cells closely parallels activation of MIA expression and involves a promoter region that we referred to previously as a HCR (highly conserved region). The HCR element interacts with the melanoma-associated transcription factor and confers strong activation of the promoter. Furthermore, mutation and deletion studies described in this study revealed that the permissive site for cell-specific promoter activity was located directly 5' to the HCR region. Changes in the DNA sequence 5' adjacent to the melanoma-associated transcription factor binding site led to an MIA promoter activity in benign melanocytes and nonmelanocytic cells that usually do not express MIA. Detailed analysis revealed binding of T-cell factor family transcription factors to the repressor element. Because this family is known to interact with COOH-terminal binding protein, we explored the role of COOH-terminal binding protein 1(CtBP1) in silencing MIA gene expression. By reporter gene analysis, we determined a strict negative regulation of MIA promoter activity in melanoma cells by CtBP1. Furthermore, we observed strong expression of CtBP1 in primary melanocytes but a loss of wild-type CtBP1 expression in malignant melanoma in vitro and in vivo. Therefore, we speculate that CtBP1 has an important negative role in MIA regulation, and loss of CtBP1 is implicated in melanoma progression.