Radioimmunoassays for the C-terminus of prothymosin alpha and the N-terminus of parathymosin alpha for the measurement of the levels of alpha-thymosins in human cancer.

A radioimmunoassay specific for the C-terminus of human prothymosin alpha was developed using the synthetic peptide [Cys-Aca degrees]-human prothymosin alpha (90-109)-OH coupled to KLH as antigen and the analogue [Tyr-Aca degrees]-human prothymosin alpha (90-109)-OH labelled with 125I as tracer. The radioimmunoassay measured intact prothymosin alpha, in the range of 2-100 pmol and does not cross-react with the partly homologous polypeptide parathymosin alpha. A major epitope was located in the segment 95-107. A radioimmunoassay specific for the N-terminus of human parathymosin alpha, also measuring intact parathymosin alpha in the range of 1-20 pmol and not cross-reacting with prothymosin alpha, was developed using the synthetic peptide [Cys-Aca degrees]-human parathymosin alpha (1-30)-OH as antigen coupled to KLH and the analogue [Tyr-Aca degrees]-human parathymosin alpha (1-10)-OH labelled with 125I as tracer. A major epitope was located in the segment 1-10. These radioimmunoassays, together with a previously established radioimmunoassay for the N-terminus of prothymosin alpha, permitted the identification of the molecular forms of the cross-reactive materials in both normal and neoplastic breast tissue extracts as intact prothymosin alpha and parathymosin alpha. It was also possible to reveal significantly higher levels of both alpha-thymosins in breast cancer tissue compared to the nearby healthy tissue--the mean of 14 samples was over 14-fold higher--suggesting a role of both prothymosin alpha and parathymosin alpha in cell proliferation. The reported radioimmunoassays are expected to facilitate the search for prognostic and/or diagnostic applications of these polypeptides in human cancer.