A radioimmunoassay for parathymosin alpha using antibodies to synthetic N-terminal peptide 1-30

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.

Expression of alpha-thymosins in human tissues in normal and abnormal growth

Radioimmunoassays specific for the N and C termini of human prothymosin alpha and the N terminus of human parathymosin alpha were employed for the measurement of the levels of alpha-thymosins in human thymus, spleen, and liver during normal growth and intestine and breast in malignant growth. A differential expression of the two alpha-thymosins was observed in thymus (prothymosin alpha-rich) and liver (parathymosin alpha-rich). A decline in the levels of both alpha-thymosins was found with age, with prothymosin alpha in thymus showing the sharpest change (15- to 30-fold). The levels of both alpha-thymosins were higher in malignant tissues as compared with healthy ones. In breast cancer, in particular, the mean increase for prothymosin alpha and parathymosin alpha was 17.9- and 11.5-fold, respectively. The major crossreactive material was characterized in all cases as intact prothymosin alpha and parathymosin alpha. These results suggest an in vivo relationship of the expression of alpha-thymosins with the human tissue cell proliferation activity.

Evidence for the extranuclear localization of thymosins in thymus

A new radioimmunoassay has been developed for thymosin beta 4 by generating rabbit polyclonal antibodies against the synthetic N-terminal peptide fragment 1-15 coupled to KLH. The synthetic analogue [Tyr12]-thymosin beta 4 (1-15) was used as tracer. This radioimmunoassay, with a useful range of 10-1000 pmoles, showed cross-reactivity with the second homologous beta-thymosin of man and rat (thymosin beta 10) but not of calf (thymosin beta 9). This radioimmunoassay, together with an improved radioimmunoassay for the N-terminus of parathymosin alpha, was employed for the measurement of the levels of thymosin beta 4 and parathymosin alpha in nuclear and extranuclear extracts of calf thymus. The bulk of these polypeptides was found in the extranuclear material whereas only traces were observed in the nuclear environment, which indicates the extranuclear localisation of alpha- and beta-thymosins.

A sensitive and specific competition microELISA for the immunoactive polypeptide parathymosin and detection of this peptide in porcine tissues

A sensitive and specific microELISA assay is described for the immunoactive polypeptide parathymosin. Antibodies against a synthetic peptide corresponding to the rat parathymosin sequence 5-30 were raised in rabbits immunised with this peptide conjugated to keyhole limpet hemocyanin (KLH). The useful range of the assay was 0.25-30 pmol (3-330 ng) of parathymosin and the assay was specific. The related immunoactive polypeptides prothymosin alpha or thymosin alpha 1 showed no cross-reactivity. In spiking experiments the recovery of the assay was found to be greater than 92% at all concentrations tested. The intra-assay variation was 17%, whereas the inter-assay variation was 26%. Using this assay the highest concentration of parathymosin was found in porcine liver, followed by kidney, lung, thymus and spleen. This assay compares favorably with one microELISA and two RIA methods already published, in that it is more sensitive by at least an order of magnitude, and it is simpler and quicker.

The primary sequence of the PFK-1 inactivating zinc-binding protein as deduced from cDNA sequencing. Identity of the zinc-binding protein with rat parathymosin

We have recently described the sequence of the Zn2+-binding domain (43 amino acid residues) of a newly detected Zn2+-binding protein which reversibly inactivates phosphofructokinase-1 in a Zn2+-dependent manner [(1986) J. Biol. Chem. 269, 5895-5900; (1988) Eur. J. Biochem. 177, 561-568]. Here, we describe the primary sequence of this protein based on a full-length cDNA. A sequence comparison reveals the identity of the Zn2+-binding protein with a protein called parathymosin-alpha.

Prothymosin alpha is not a nuclear polypeptide

Using a radioimmunoassay for the NH2-terminus of prothymosin alpha, the crossreactive material was measured in subcellular fractions of calf thymus and liver. No significant amount of crossreactive material was found in the nucleus. This provides experimental evidence against a recent hypothesis, based on structural evidence, that prothymosin alpha is a nuclear polypeptide.

Evidence for the monomeric nature of thymosins

According to gel-filtration experiments, alpha- and beta-thymosins appear to form oligomers, which are 4-5-fold larger than the corresponding polypeptides. However, on analysis by sedimentation equilibrium ultracentrifugation, prothymosin alpha and thymosin beta 4 showed relative molecular masses of 12,800 and 4600, which are close to the values calculated from their amino acid sequences, confirming their existence in solution as discrete monomeric entities.