Prolactin and Testicular Leydig Cell Function: Characterization of Prolactin Receptors in the Murine MA-10 Testicular Leydig Cell Line

Abstract

Abstract

The direct role of prolactin (PRL) in testicular function is still unclear, mostly because of lack of a suitable in vitro model. To establish the suitability of the MA-10 murine tumor Leydig cell line for the study of PRL receptors (PRLR) and effects on steroidogenesis, we initially characterized PRLR on cultured MA-10 cells. The specific binding (B_s) of [¹²⁵l]human growth hormone (hGH) depends on time, temperature, and Mg²⁺ ion and protein concentrations, with absolute specificity for the lactogenic hormones hGH and ovine PRL. B_s is saturable and is to a single class of high-affinity (K_a = 3.6 × 10⁹ M ^-1) low-capacity (B _max = 19.5 fmol/mg protein) binding sites. The molecular weight of PRLR, determined by cross-linking to [¹²⁵l]hGH, SDS-PAGE and autoradiography, is 35 kDa for the free receptor, suggesting that the short-form PRLR protein, previously described in liver and mammary glands, is that primarily found in MA-10 cells. Thus, the demonstration of specific PRL binding sites on MA-10 Leydig cells, with characteristics similar to primary Leydig cell PRLR, suggests that this cell line can serve as a good model for both the study of PRLR mechanism of action and the role of PRL in Leydig cell function.