The immunologically active site of prothymosin α is located at the carboxy-terminus of the polypeptide. Evaluation of its in vitro effects in cancer patients
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Prothymosin α (proTα) is a 109 amino acid long polypeptide presenting distinct immunoenhancing activity in vitro and in vivo. Recent reports suggest that in apoptotic cells, proTα is cleaved by caspases at its carboxy(C)-terminus generating potentially bioactive fragments. In this study, we identified the peptide segment of proTα presenting maximum immunomodulatory activity. Calf thymus proTα was trypsinised, and the five fragments produced (spanning residues 1–14, 21–30, 31–87, 89–102 and 103–109) were tested for their ability to stimulate healthy donor- and cancer patient-derived peripheral blood mononuclear cell (PBMC) proliferation in autologous mixed lymphocyte reaction (AMLR), natural killer and lymphokine-activated killer cell activity, intracellular production of perforin, upregulation of adhesion molecules and CD25 expression. ProTα(89–102) and proTα(103–109) significantly fortified healthy donor-lymphocytes’ immune responses to levels comparable to those induced by intact proTα. These effects were more pronounced in cancer patients, where peptides proTα(89–102) and proTα(103–109) partly, however significantly, restored the depressed AMLR and cytolytic ability of PBMC, by simulating the biological activity exerted by intact proTα. ProTα(1–14), proTα(21–30) and proTα(31–87) marginally upregulated lymphocyte activation. This is the first report showing that proTα’s immunomodulating activity can be substituted by its C-terminal peptide(s). Whether generation and externalization of such immunoactive proTα fragments occurs in vivo, needs further investigation. However, if these peptides can trigger immune responses, they may eventually be used therapeutically to improve some PBMC functions of cancer patients.
KeywordsProthymosin α fragmentation Immune responses Cell proliferation Cytotoxicity Anticancer activity
Autologous mixed lymphocyte reaction
Biologic response modifiers
- LAK cells
Lymphokine-activated killer cells
- NK cells
Natural killer cells
Nuclear localization signal
Peripheral blood mononuclear cells
Supported in part by Grants 7285/02 from the GSRT, Greece (to OET and MN) and IKYDA 61/2003 from the Hellenic State Scholarships Foundation and the Deutscher Akademischer Austausch Dienst (to OET and WV). We thank Dr. N. Cacoullos for critically reviewing the manuscript and Dr. C. N. Baxevanis for help with FACS analysis. OET and WV wish to dedicate this report to the memory of Athanassios (Nassos) A. Haritos on his eleventh death anniversary.
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