The tumor suppressor HINT1 regulates MITF and β-catenin transcriptional activity in melanoma cells

Histidine triad nucleotide-binding protein 1 (HINT1) is a haploinsufficient tumor suppressor gene that inhibits the Wnt/β-catenin pathway in colon cancer cells and Microphthalmia-associated transcription factor (MITF) activity in human mast cells. MITF and β-catenin play a central role in melanocyte and melanoma cell survival, and this study aimed to investigate the effects of HINT1 on the MITF and β-catenin pathways in malignant melanoma cells. We found that HINT1 inhibits MITF and β-catenin transcriptional activity, and both proteins can be co-immunoprecipitated with an anti-HINT1-specific antibody in melanoma cell lines. Stable, constitutive overexpression of the HINT1 protein in human melanoma cells significantly impaired cell proliferation in vitro and tumorigenesis in vivo. These effects were associated with a decreased expression of cyclin D1 and BCL2, well known MITF and β-catenin transcription targets, respectively. We also demonstrated that BCL2 and cyclin D1 can partially rescue the HINT1-driven phenotype. Moreover, we found in ChIP assays that HINT1 binds the chromatin at MITF and β-catenin sites in BCL2 and cyclin D1 promoters, respectively, and that mSIN3a and HDAC1, well known transcriptional repressors, can be co-immunoprecipitated with an anti-HINT1-specific antibody. These findings support the tumor suppressor activity of HINT1 gene in melanoma cells by promoting the formation of non-functional complexes with oncogenic transcription factors like MITF and β-catenin.