Cross-talk between G Protein-coupled and Epidermal Growth Factor Receptors Regulates Gonadotropin-mediated Steroidogenesis in Leydig Cells

Abstract

Gonadal steroid production is stimulated by gonadotropin binding to G protein-coupled receptors (GPCRs). Although GPCR-mediated increases in intracellular cAMP are known regulators of steroidogenesis, the roles of other signaling pathways in mediating steroid production are not well characterized. Recent studies suggest that luteinizing hormone (LH) receptor activation leads to trans-activation of epidermal growth factor (EGF) receptors in the testes and ovary. This pathway is critical for LH-induced steroid production in ovarian follicles, probably through matrix metalloproteinase (MMP)-mediated release of EGF receptor (EGFR) binding ectodomains. Here we examined LH and EGF receptor crosstalk in testicular steroidogenesis using mouse MLTC-1 Leydig cells. We demonstrated that, similar to the ovary, trans-activation of the EGF receptor was critical for gonadotropin-induced steroid production in Leydig cells. LH-induced increases in cAMP and cAMP-dependent protein kinase (PKA) activity mediated trans-activation of the EGF receptor and subsequent mitogen-activated protein kinase (MAPK) activation, ultimately leading to StAR phosphorylation and mitochondrial translocation. Steroidogenesis in Leydig cells was unaffected by MMP inhibitors, suggesting that cAMP and PKA trans-activated EGF receptors in an intracellular fashion. Interestingly, although cAMP was always needed for steroidogenesis, the EGFR/MAPK pathway was activated and necessary only for early (30 -60 min), but not late (120 min or more), LH-induced steroidogenesis in vitro. In contrast, 36-h EGF receptor inhibition in vivo significantly reduced serum testosterone levels in male mice, demonstrating the physiologic importance of this cross-talk. These results suggest that GPCR-EGF receptor cross-talk is a conserved regulator of gonadotropin-induced steroidogenesis in the gonads, although the mechanisms of EGF receptor trans-activation may vary.

Gonadotropin-releasing hormone positively regulates steroidogenesis via extracellular signal-regulated kinase in rat Leydig cells

“…EEK1/2 activation by GnRHa followed a much shorter time course (in minutes) compared with the GnRHa-induced effects on 3b-HSD protein expression and testosterone production (in hours), which is consistent with the results from a previous study examining MLTC-1 mouse Leydig cells. 30 Furthermore, the GnRHa-induced activation of ERK1/2 in this study also occurred more rapidly than the previous reports of ERK1/2 activation by other stimuli. For example, ERK1/2 MAPK activation by interleukin-1a takes 15 minutes in the same cells.…”

Expression of LH receptor in nonpregnant mouse endometrium: LH induction of 3β-HSD and de novo synthesis of progesterone

“…It is therefore possible that the major signaling pathway regulating endometrial steroidogenesis in this study including adenylate cyclase and MAPK-dependent pathways converge at a point distal to activation of PKA and ERK1/2. The possible target for coordinated regulation of this signaling pathway may be the STAR protein and/or transcription factors regulating its synthesis because there is evidence that in steroidogenic cells, cAMP, PKA, and MAPK can modulate the activity of this protein or associated transcription factors (Cherradi et al 1997, Manna et al 1999, Tajima et al 2003, Evaul & Hammes 2008. In our present study, we also observed a stimulatory role of Lh on Star gene expression in mouse endometrium for P 4 production.…”

“…The mechanism by which gonadotropin binding to its GPCRs triggers activation of the MEK/ERK pathway is still controversial. As suggested previously (Pierce et al 2001, Kim et al 2002, Drube et al 2006, Evaul & Hammes 2008, it may be possible that gonadotropin binding to GPCRs in mouse endometrium activates the MEK/ERK pathway through transactivation of EGFRs and further studies would need to explore the actual mechanism of such transactivation.…”

Androgen actions in the ovary: balance is key

“…2). Recently (Sen et al , 2012(Sen et al , 2014, it has been found that androgens can promote Erk signaling via matrixmetaloproteinases (MMPs)-mediated trans-activation of the epidermal growth factor receptor (EGFR), a mechanism that is conserved from Xenopus (Rasar et al 2006) to mice (Carbajal et al 2011) and humans (Evaul & Hammes 2008). These observations have given rise to the interesting concept that, outside the nucleus, androgen actions are very similar to those of growth factors.…”