Characterization and hormonal modulation of immunoreactive thiamin carrier protein secreted by adult rat Leydig cells in vitro

Abstract

Leydig cells isolated from adult rats and maintained under defined conditions in culture secrete a protein of molecular weight (M_r) 70 000 which is immunologically similar to chicken thiamin carrier protein (TCP). Synthesis of immunoreactive TCP by these cells is demonstrated by immunoprecipitation of [³⁵S]methionine incorporated, newly synthesized proteins with monoclonal and polyclonal antibodies to chicken TCP. The amount of immunoreactive TCP secreted into the culture supernatant is quantitated by using a specific radioimmunoassay. Under the influence of LH, secretion of immunoreactive TCP is enhanced 3-fold and can be inhibited by up to 70% with aromatase inhibitor (1,4,6-androstatrien-3,17-dione). Cyclic AMP acts as a second messenger in the sequence of events involved in LH-induced elevation of immunoreactive TCP in Leydig cells. The effects of exogenous estradiol-17beta and diethylstilbestrol are comparable in terms of stimulation of secretion of immunoreactive TCP by these cells. Tamoxifen brought about a 70% decrease in the elevated levels of immunoreactive TCP. These results suggest that estrogen mediates immunoreactive TCP induction in hormonally stimulated adult rat Leydig cells.