TRANSCRIPTIONAL REGULATION OF CATHEPSIN-B EXPRESSION IN B16 MELANOMASOF VARYING METASTATIC POTENTIAL

The highly metastatic B16a melanoma has been shown to express higher l evels of cathepsin B (CB) mRNA when compared to the less metastatic va riants, B16-F1 and B16-F10, and with normal mouse tissues. This increa sed expression is now shown to be due to increased gene transcription by nuclear run-off assays and measurements of mRNA stability. Transien t expression assays, using promoter fragments from the mouse and human CB genes, demonstrated that both promoters were more active in B16a t han in the less metastatic melanomas, B16-F1 and B16-F10. The differen tial gene expression did not depend on the presence of multiple Spl si tes in both promoters. A Gel shift assay revealed a specific CB promot er binding protein whose levels are correlated with CB expression and the metastatic potential of the three B16 melanoma variants. These res ults indicate that the increased expression of CB in the B16a melanoma is due to a specific increase in the amount or activity of a transcri ptional activator of the CB gene. The ability of the human CB promoter to activate gene expression in B16a melanoma cells suggests similarit ies in the regulation of CB expression in tumors from humans and mice. (C) 1994 Academic Press, Inc.