Expression of the c-src protooncogene in human skin tumors.

Retroviral oncogenes are genetic elements, the expression of which is responsible for the transformed phenotype of cells. These genes are derived from normal cellular DNA sequences called cellular protooncogenes, which are present in all human cells and seem to have potential transforming ability in tumors of nonviral origin, since it is possible that they undergo structural alterations and/or changes in their expression. Human skin tumors were analyzed in this study with respect to the expression of the c-src protooncogene, the cellular homologue of the Rous sarcoma virus transforming gene, by measuring the enzymatic activity of its gene product, the pp60c-src kinase activity. Tyrosine-specific kinase activity was detected in all skin tumors tested. The expression pattern of the c-src gene product in the melanomas tested was differential and varying kinase levels in different metastases from the same patient were detected. The elevation of kinase activity as compared to normal skin ranged from about 4- to 20-fold.