Prothymosin alpha in human blood.

Abstract

The major cross-reacting peptide in human plasma detected with a radioimmunoassay (RIA) for thymosin a, was identified as prothymosin a, based on its elution properties in gel-filtration chromatography and its amino acid composition after purification by HPLC. A small quantity (<10%) of the total cross-reacting material was recovered in fractions corresponding to lower molecular weight thymosin al-like peptides. The total quantity of cross-reacting material detected in human blood, expressed as thymosin a, equivalents, was 11-14 pmol/ml (-90% was recovered in the leukocyte fraction, =10% was in the plasma fraction, and 1-2% was in the erythrocyte fraction). The peptide present in leukocytes was also identified as prothymosin a. After correction for the 5-times lower molar reactivity of prothymosin a in the thymosin a, RIA employed in these experiments, we estimate that the content of prothymosin a in human blood is 55-70 pmol/ml (0.6-0.8 pg/ml). The relatively small quantities recovered in the erythrocyte and plasma fractions may be attributed to contamination of the former by leukocytes or to leakage from leukocytes into the plasma.Thymosin a1, an acidic peptide containing 28 amino acid residues (1), was first isolated from a calf thymus preparation called thymosin fraction 5, a biologically active mixture of peptides ranging in molecular weight from 1000 to 15,000 (2). Thymosin a1 has been reported not only to be active in several assay systems for enhancement of immune function, both in vitro and in vivo, but also to be much more potent than the thymosin fraction 5 preparations from which it was isolated (for reviews, see refs. 3-5).Radioimmunoassays (RIAs) for thymosin a1 have been developed in several laboratories (6)(7)(8)25) and employed for the analysis of cross-reacting material in serum or plasma (6, 9-12). Highest levels of immunoreactive peptides were found in cord plasma (6), but detectable quantities (0.6-3.7 ng of thymosin a1 equivalents per ml) were also present in the serum of adolescents (6) or normal adults (12). Of particular interest were reports that the levels of immunoreactive thymosin a,-like material were elevated in serum from patients with acquired immunodeficiency syndrome and also in a group of homosexual men (13,14). Another report, however, suggests that the high levels in serum from patients with acquired immunodeficiency syndrome may be due to the presence of a product of the gag gene of human immunodeficiency virus, which contains an amino acid sequence homologous to the sequence in thymosin a1 that was recognized by the antibody employed (15). This antiserum was also reported to block the replication of human immunodeficiency virus in permissive H9 cells (15).The identity and possible origin of the cross-reacting material in normal blood have not yet been established. A cross-reacting peptide purified from a preparation of Cohn fraction IV-1 by immunoaffinity chromatography was reported to resemble thymosin a1 in size and chromatographic properties (16). However, the i...

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

“…This is in agreement with previous reports for tissues of various mammals, including human thymus (19,20) and blood plasma (21). The lower quantities The expression of the two a-thymosins was found to be both tissue and age specific.…”

Novel Function of Prothymosin Alpha as a Potent Inhibitor of Human Immunodeficiency Virus Type 1 Gene Expression in Primary Macrophages

“…ProT␣ has a well-defined nuclear localization signal sequence, and it has been identified in the nucleus of a number of cells (11,50,51). While this protein has no secretory signal sequence, it has, nonetheless, been detected in human serum and the supernatants of cultured lymphocytes (10,37), and in this report we have demonstrated its presence in supernatants of the HVS-transformed CD8 ϩ cell line K#1 50K. Furthermore, a number of cell surface binding proteins have been identified as candidate receptors for extracellular ProT␣.…”

Prothymosin alpha antisense oligomers inhibit myeloma cell division.

“…Evidence from this and other laboratories suggests that the protein is neither a precursor of thymosin a,, a putative thymic hormone, nor a secreted thymic hormone itself (1)(2)(3). Instead, several observations support a role in cell proliferation: (i) Prothymosin a mRNA and protein are present in virtually all mammalian tissues, and a homologous protein has been detected in yeast (1,(4)(5)(6)(7)(8); these findings are consistent with an activity essential to most cells. (ii) The amounts of prothymosin a and its mRNA are roughly proportional to the proliferative activity of the tissue from which they are isolated (1,4,7).…”