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

Abstract

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