Effects of Retinoic Acid on Beta-Catenin Transcriptional Activity in Melanoma Cells

Melanoma is the most dangerous form of skin cancer and its incidence has been increasing in the United States. Most melanomas are resistant to current chemotherapies; therefore, understanding the mechanism of melanomagenesis is beneficial to treatment of the diseases. Accumulation of β-catenin has been shown in colon and other cancers, including melanomas, but the transcriptional role of β-catenin in melanomas is still unclear. All-trans retinoic acid (ATRA) is an anti-tumor agent that has an inhibitory effect on β-catenin, but this effect has not been studied in melanomas. It has been shown that Microphthalmia-associated transcription factor (MITF), a melanocyte specific protein, can redirect the function of β-catenin from cell proliferation to melanocytespecific gene expression. In addition, ATRA induced Mitf mRNA expression was observed in mouse melanocyte. My objective is to understand the effects of ATRA on the β-catenin signal pathway in ATRA-sensitive melanoma cells. I hypothesize that ATRA will decrease β-catenin transcriptional activity. Western blotting was used to determine the effects of ATRA on β-catenin target genes. Gel Shift assays were used to investigate DNA/ protein interactions. Reporter gene assays were used to examine the effects of ATRA on the transcriptional activity of β-catenin. Results showed a 20% and 40% reduction in c-Myc protein expression after 2 days and 4 days ATRA treatment, respectively. Cyclin D-1 protein expression was reduced by 40% after 4 days treatment compared to the control. ATRA increased the protein levels of MITF after 2 days treatment. Reporter gene assay showed that ATRA reduced transcriptional activity of exogenous active β-catenin in human melanoma cells. Together, ATRA inhibits 5 Fung Chan 5/2/2007