Increased expression of the src proto-oncogene in hairy cell leukemia and a subgroup of B-cell lymphomas.

The c-src proto-oncogene encodes a M(r) 60,000 phosphoprotein, pp60c-src, with tyrosine-specific protein kinase activity. We have used an immune complex protein kinase assay for pp60c-src to analyze a spectrum of B-cell neoplasms. pp60c-src activity was elevated in all five hairy cell leukemia specimens and in a number of the large cell and immunoblastic lymphomas; neoplasms representing later stages in B-cell development. pp60c-src activity was low in neoplastic cells which correspond to early and intermediate stages in B-cell development (acute and chronic lymphatic leukemia, lymphoblastic lymphoma, small lymphocytic lymphoma). The enhanced pp60c-src activity was associated with high levels of pp60c-src protein. However, increased expression of c-src was not associated with amplification or gross structural rearrangement of the c-src gene. This preliminary study demonstrates elevated levels of pp60c-src protein and tyrosine protein kinase activity in neoplasms corresponding to the later stages of B-cell ontogeny.