Structure and promoter analysis of the gene encoding the human melanoma-inhibiting protein MIA

Abstract

We have recently described the isolation of a novel protein, MIA, which is secreted from malignant melanoma cells and elicits growth inhibition on melanoma cells in vitro (Blesch, A., Bosserhoff, A. K., Apfel, R., Behl, C., Hessdörfer, B., Schmitt, A., Jachimczak, P., Lottspeich, F., Schlingensiepen, H., Buettner, R., and Bogdahn, U. (1994) Cancer Res. 54, 5695-5701). Here, we report the structure of the human MIA gene locus, describe its expression pattern in melanocytic tumors in vivo, and provide an initial characterization of the MIA promoter. The MIA gene is encoded by four exons, and the mRNA initiation site was identified 70 base pairs upstream from the translation start codon. MIA mRNA expression in vivo correlated with progressive malignancy of melanocytic lesions and was inducible in other cells by phorbol esters. To investigate mechanisms mediating this melanoma-associated expression pattern, we analyzed the promoter activity of the 1.3-kilobase genomic sequences located 5'-upstream of the MIA gene. The MIA promoter conferred high levels of gene activation specifically in human and murine melanoma cells, and its activity was further enhanced by treatment with phorbol esters. Site-directed mutation of an NF-kB site within the MIA promoter did reduce the basal promoter activity in melanoma cells but did not change significantly enhancement by phorbol esters.