Prolactin and testicular Leydig cell function: characterization of prolactin receptors in the murine MA-10 testicular...

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 (Bs) of [125I]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. Bs is saturable and is to a single class of high-affinity (Ka = 3.6 x 10(9) M-1) low-capacity (Bmax = 19.5 fmol/mg protein) binding sites. The molecular weight of PRLR, determined by cross-linking to [125I]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.