Testosterone activates mitogen-activated protein kinase and the cAMP response element binding protein transcription factor in Sertoli cells

Abstract

The androgen testosterone is essential for the Sertoli cell to support the maturation of male germ cells and the production of spermatozoa (spermatogenesis). In the classical view of androgen action, binding of androgen to the intracellular androgen receptor (AR) produces a conformational change in AR such that the receptor-steroid complex has high affinity for specific DNA regulatory elements and is able to stimulate gene transcription. Here, we demonstrate that testosterone can act by means of an alternative, rapid, and sustainable mechanism in Sertoli cells that is independent of AR-DNA interactions. Specifically, the addition of physiological levels of testosterone to Sertoli cells stimulates the mitogen-activated protein kinase signaling pathway and causes phosphorylation of the cAMP response element binding protein transcription factor on serine 133, a modification known to be required for Sertoli cells to support spermatogenesis. Androgenmediated activation of mitogen-activated protein kinase and cAMP response element binding protein occurs within 1 min, extends for at least 12 h and requires AR. Furthermore, androgen induces endogenous cAMP response element binding protein-mediated transcription in Sertoli cells. These newly identified mechanisms of androgen action in Sertoli cells suggest new targets for developing male contraceptive agents.testis ͉ spermatogenesis ͉ nongenomic ͉ signal transduction A ndrogen actions are critical in the testis for the maturation of male germ cells into spermatozoa (spermatogenesis). In the absence of relatively high levels of testosterone (Ͼ70 nM) in the testis, spermatogenesis is halted before the completion of meiosis so that few if any spermatozoa are produced (1, 2). The molecular mechanisms by which testosterone regulates spermatogenesis are not well understood, but like other steroid hormones, androgens exert many of their actions by diffusing into target cells and binding specific intracellular receptor proteins that are located in the cytoplasm and the nucleus (3). The importance of the androgen receptor (AR) for maintaining spermatogenesis is confirmed by mutations that eliminate AR activity. These mutations result in the testicular feminization phenotype (tfm) and the absence of mature male germ cells (4). In the classical view of androgen action, binding of androgen to its receptor produces a conformational change in AR such that the receptor-steroid complex has high affinity for specific DNA regulatory elements and is able to stimulate gene transcription (5). The entire process required to initiate gene expression by means of this classical mechanism takes at least 30-45 min (6, 7), and the length of time required to produce significant levels of nascent proteins is in the order of hours.

Testosterone induction of prostaglandin-endoperoxide synthase 2 expression and prostaglandin F2α production in hamster Leydig cells

“…DHT did not activate MAPK3/1 or PI3K/AKT signalling pathways in hamster Leydig cells (results not shown). Although testosterone failed to activate PI3K/AKT (results not shown), this androgen induced a rapid phosphorylation of MAPK3/1 within short-term incubations (1-3 min), which was also detected after 2-3 h. These results are similar to those observed in studies performed in breast cancer, skeletal muscle cells, prostate stroma cells and Sertoli cells in which androgen activates MAPK3/1 too quickly to be explained by the classical androgen receptor pathway (Peterziel et al 1999, Zhu et al 1999, Estrada et al 2003, Fix et al 2004, Rahman & Christian 2007. We also found that Bi prevented the effects of testosterone on phospho-MAPK3/1 indicating that androgen receptors are required for testosterone-mediated MAPK activation.…”

“…Moreover, testosterone and/or DHT effects could take place through non-classical mechanisms. It has been recently reported the activation of the MAP kinase pathway and the phosphoinositide-3 (PI3) kinase/serine threonine kinase AKT signalling cascade by androgens in Sertoli, prostate and osteoblast cells (Fix et al 2004, Kang et al 2004, Chen et al 2007, Cinar et al 2007, Pinthus et al 2007, Rahman & Christian 2007, Agoulnik et al 2008. As a consequence, we have investigated the participation of those signalling pathways in the regulation of PTGS2 expression by testosterone and DHT in hamster Leydig cells.…”

Anchoring Junctions As Drug Targets: Role in Contraceptive Development

“…This compromises Sertoli-germ cell adhesion without affecting blood-testis barrier dynamics. Moreover, the importance of ERK in the testis is supported by another study, which demonstrated that testosterone can mediate its effects on Sertoli-germ cell adhesion via the Src-ERK signaling cascade instead of the classic androgen receptor-mediated pathway (Fix et al, 2004). Indeed, testosterone is known to play a critical function in the regulation of the blood-testis barrier and anchoring junctions in the testis (O'Donnell et al, 2000;Meng et al, 2005).…”

Androgen cell signaling pathways involved in neuroprotective actions

“…In neurons, CREB activation is known to regulate a variety of neurotrophic and neuroprotective effects (Crino et al, 1998;Finkbeiner, 2000;Kelly et al, 2000). It is not known whether androgens activate CREB in neurons, although androgens have been shown to activate CREB signaling in nonneural cells (Fix et al, 2004;Unni et al, 2004;Walker, 2003). In fact, androgen-induced, ARdependent MAPK/ERK-CREB signaling in prostate cancer cells attenuates apoptosis (Kousteni et al, 2003).…”