EXPRESSION AND REGULATION OF INTERFERON-GAMMA-INDUCIBLE PROTEIN-10 GENE IN RAT LEYDIG-CELLS

In the present study, we report the cloning of a gene that is differen tially expressed in normal adult rat Leydig cells and whose expression is inhibited by hCG but is induced by interferon-gamma (IFN gamma). D NA sequence analysis identified this gene as rat IFN gamma-inducible p rotein 10 (TP 10), a member of the -C-X-C- chemokine superfamily of pr oinflammatory cytokines. High levels of IP-10 messenger RNA (mRNA) wer e constitutively expressed in freshly isolated and primary cultured Le ydig cells. hCG inhibited this expression in a dose-dependent manner. The addition of 1 ng/ml hCG inhibited IP-10 mRNA levels more than 80%. Conversely, IP-10 mRNA levels were markedly increased in response to murine interleukin-1 alpha, murine tumor necrosis factor-alpha, and mu rine IFN gamma by 3.3-, 10-, and 26-fold, respectively. Concomitant ad dition of murine interleukin-la, murine tumor necrosis factor-alpha, a nd murine IFN gamma synergistically increased IP-10 mRNA levels by 58- fold. Furthermore, in addition to one previously described rat IP-10 m RNA transcript (1.5 kb), another larger transcript (2.7 kb) was identi fied by Northern blot in rat Leydig cells. After screening a rat testi s complementary DNA library, we obtained a partial structural gene and an intron sequence, which possibly originated from the larger transcr ipt of rat IP-10 mRNA. Histochemical and immunocytochemical staining r evealed that purified cells were positive for 3 beta-hydroxysteroid de hydrogenase and IP-10, confirming that IP-10 is indeed present in Leyd ig cells. IP-10 antisense oligonucleotides enhanced basal and hCG-indu ced testosterone formation. This suggests that endogenous IP-10 has an inhibitory effect on Leydig cell steroidogenesis. In conclusion, IP-1 0 is expressed in rat Leydig cells and may have paracrine and autocrin e effects on testicular function.