Prothymosin α Receptors on Lymphocytes

Abstract

Recent results indicate that prothymosin α (ProTα) may be useful in designing future therapeutic interventions in cancer patients and in potentiating the immune system. We described recently the presence and characteristics of two binding sites for ProTα on human peripheral blood mononuclear cells (PBMC). In search of a receptor upregulation, we decided to corroborate this finding on two lymphocytic populations, (PHA-activated) lymphoblasts and YT cells. The kinetics of [¹²⁵I]ProTα binding to lymphoblasts were fast at room temperature but with YT cells were slower. Analysis of steady-state binding data identified two binding sites in lymphoblasts with an apparent equilibrium K_d of 44–75 pM and 4228–9143 sites per cell for the high-affinity receptor and 1.7–2.9 nM and 20,534–35,044 sites per cell for the low-affinity receptor. However, it identified only one site with a K_d of 265–435 pM and 8318–27,237 sites per cell in YT cells. We conclude that exists a ProTα receptor in the CD3⁺ T cell population, and this presence is regulated. After binding to cell surface, [¹²⁵I]ProTα is internalized in a short period of time and then degraded; therefore, we conclude that the dynamics of ProTα receptor turnover in part determines the concentration of ProTα available to induce its enhancing effects.