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 al pha was developed using the synthetic peptide [Cys-Aca(o)]-human proth ymosin ct (90-109)-OH coupled to KLH as antigen and the analogue [Tyr- Aca(o)]-human prothymosin alpha (90-109)-OH labelled with I-125 as tra cer. The radioimmunoassay measured intact prothymosin alpha, in the ra nge of 2-100 pmol and does not cross-react with the partly homologous polypeptide parathymosin alpha. A major epitope was located in the seg ment 95-107. A radioimmunoassay specific for the N-terminus of human p arathymosin alpha, also measuring intact parathymosin a in the range o f 1-20 pmol and not cross-reacting with prothymosin alpha, was develop ed using the synthetic peptide [Cys-Aca(o)]-human parathymosin alpha ( 1-30)-OH as antigen coupled to KLH and the analogue [Tyr-Aca(o)]-human parathymosin alpha (1-10)-OH labelled with I-125 as tracer. A major e pitope was located in the segment 1-10. These radioimmunoassays, toget her with a previously established radioimmunoassay for the N-terminus of prothymosin alpha, permitted the identification of the molecular fo rms of the cross-reactive materials in both normal and neoplastic brea st tissue extracts as intact prothymosin alpha and parathymosin alpha. It was also possible to reveal significantly higher levels of both al pha-thymosins in breast cancer tissue compared to the nearby healthy t issue - the mean of 14 samples was over 14-fold higher - suggesting a role of both prothymosin alpha and parathymosin alpha in cell prolifer ation. The reported radioimmunoassays are expected to facilitate the s earch for prognostic and/or diagnostic applications of these polypepti des in human cancer.