TESTICULAR LEUKEMIA INHIBITORY FACTOR (LIF) AND LIF RECEPTOR MEDIATE PHOSPHORYLATION OF SIGNAL TRANSDUCERS AND ACTIVATORS OF TRANSCRIPTION (STAT)-3 AND STAT-1 AND INDUCE C-FOS TRANSCRIPTION AND ACTIVATOR PROTEIN-1 ACTIVATION IN RAT SERTOLI BUT NOT GERM-CELLS

Increasing amounts of evidence suggest noninflammatory roles for growt h factor and cytokines in development and differentiation. Leukemia in hibitory factor (LIF) belongs to a gp130 pleiotropic family of growth factors that has recently been shown to enhance the survival of rat te sticular gonocytes and Sertoli cells. In this study, we show the expre ssion of gp130 and LIF messenger RNAs (mRNAs) in the somatic (the Sert oli and Leydig cells) and specific germ cells (spermatogonia, pachyten e, round, and elongated spermatids) of rodent testis, suggestive of ce ll-specific LIF-mediated functions. LIF receptor mRNA was demonstrated in rat somatic cells, rat elongating spermatids, and all of the mouse germ cells. In addition, we characterized the effects of LIF on the s ignal transducers and activators of transcription (STAT)-3 and STAT-1, c-fos gene expression, and activator protein-1 regulation in primary rat Sertoli cells. Electrophoretic mobility shift assay and Western bl ot analysis demonstrated that LIF translocates STAT-3 (and to a lesser extent STAT-1) transcription factor(s) to the nucleus within 2 min of exposure in a tyrosine but not serine/threonine phosphorylation-depen dent pathway. Quantitative solution hybridization analysis revealed a transient increase in c-fos mRNA levels by 20-fold following 30-45 min of LIF treatment, an effect that was inhibited by the tyrosine, as we ll as serine/threonine kinase inhibitors, genistein, and H7. Subsequen tly, LIF treatment of the Sertoli cells increased nuclear activator pr otein-1 binding proteins at 2 h after its addition, an effect that was also sensitive to genistein and H7 pretreatments. In contrast, LIF tr eatment of primary rat germ cells did not alter c-fos mRNA levels. Spe cies specificity in the expression of LIF receptor as well as ligand b inding may play a role in LIF signaling in these germ cells. Thus, usi ng a primary Sertoli cell model, we demonstrated that the testicular L IF signaling pathway is contingent on the phosphorylation of latent tr anscription factors. Our data are consistent with LIF-mediated signali ng events involving both somatic and germ cells during spermatogenesis .