Oncogenes: clues to carcinogenesis.

Recent applications of recombinant DNA techniques in cancer research led to the detection of cellular genes with potential transforming activity, called oncogenes (c-onc). Regularly they seem to be involved in normal cell differentiation and proliferation: a number of oncogene-encoded proteins specifically phosphorylates tyrosine, a key reaction in growth control. Certain human tumors exhibit activated forms of these genes and DNA fragments isolated from these neoplasms transform nonneoplastic cells (transfection assay). Oncogenes were first discovered and defined in a number of retroviruses; these viral oncogenes (v-onc) are thought to have been derived from the cellular oncogenes (c-onc). By integration of the v-onc genes into the host genome acute neoplastic transformation of the cell may occur. Several modes of oncogene activation are discussed that lead either to an increased dosage of gene product or to the formation of an altered gene product. The localization of oncogenes in the human genome near the breakpoints of specific chromosome aberrations involved in various neoplasms like Burkitt lymphoma and several leukemias emphasizes the importance of these genes in carcinogenesis.