In previous studies we have characterized a cDNA clone corresponding to a mRNA that is found in carcinomas produced by a two-stage carcinogenesis protocol in mouse skin, but that is not expressed in papillomas produced by the same protocol or in normal mouse epidermis. We have also demonstrated that the protein product of the RNA, referred to as transin, is a secreted protein associated with proteolytic activity. These observations have suggested the hypothesis that inappropriate expression of transin plays a causal role in tumor progession. The transin protein will be purified to determine if extracellular matrix proteins are possible substrates for transin proteolysis. The hypothesis will be tested directly by introducing transin DNA into papilloma-derived cell lines to examine in vivo progression of benign tumors. Transin-producing cell lines will also be tested in an in vitro invasion assay utilizing human amnionic tissue for an increased ability to traverse basement membrane. Studies will be initiated to further characterize the transin protein; the mechanism of activation of latent proteolytic activity will be examined and the carboxy-terminus of the molecule will be tested for a possible function in substrate specificity or cell binding characteristics. In addition, regulation of transin expression will be examined at the molecular level. The promoter region of the transin gene will be examined for regulatory elements controlling inducibility of this gene by oncogenes and by the polypeptide growth factor, epidermal growth factor. These studies should further characterize the transin molecule and its regulatory mechanisms and determine if inappropriate transin expression plays a causal role in tumor progression.
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