Developmental regulation of p70 S6 kinase by a G protein-coupled receptor dynamically modelized in primary cells

Abstract

The mechanisms whereby G protein-coupled receptors (GPCR) activate signalling pathways involved in mRNA translation are ill-defined, in contrast to tyrosine kinase receptors (TKR). We compared a GPCR and a TKR, both endogenously expressed, for their ability to mediate phosphorylation of 70-kDa ribosomal S6 kinase p70S6K in primary rat Sertoli cells at two developmental stages. In proliferating cells stimulated with follicle-stimulating hormone (FSH), active p70S6K was phosphorylated on T389 and T421/S424, through cAMP-dependent kinase (PKA) and phosphatidyl-inositide-3 kinase (PI3K) antagonizing actions. In FSH-stimulated differentiating cells, active p70S6K was phosphorylated solely on T389, PKA and PI3K independently enhancing its activity. At both developmental stages, insulin-induced p70S6K regulation was consistent with reported data. Therefore, TKR and GPCR trigger distinct p70S6K active conformations. p70S6K developmental regulation was formalized in a dynamic mathematical model fitting the data, which led to experimentally inaccessible predictions on p70S6K phosphorylation rate.

FSH-stimulated PTEN activity accounts for the lack of FSH mitogenic effect in prepubertal rat Sertoli cells

“…Neither was phosphorylation of Akt Thr308 visible in FSH-stimulated cells (data not shown). Accordingly, phosphorylation of the PtdIns-dependent transcription factor Foxo1 was not enhanced upon FSH stimulation of these cells (Musnier et al, 2009). …”

G protein‐dependent signaling triggers a β‐arrestin‐scaffolded p70S6K/ rpS6 module that controls 5'TOP mRNA translation

“…That is, in primary Sertoli cells, insulin enhances the phosphorylation of T421/S424 residues located in the auto-inhibitory loop of p70S6K, as expected (10). In contrast, in cells primed with FSH, this regulatory site is dephosphorylated in a cAMP/PKA-dependent manner, and p70S6K activity correlates with this dephosphorylation event (6,7). This unusual activation mode has also been observed in the case of agonist stimulation of the LH receptor, another Gs-coupled receptor that binds a closely related gonadotropin hormone (11).…”

“…The agonist-bound FSHR also stimulates p70S6K in a Gs-dependent manner (6,7). Furthermore, other researchers have reported that a b-arrestin-biased ligand at the angiotensin II type 1 receptor (AT1R) affects protein neosynthesis (26) and p70S6K phosphorylation (27).…”

“…We have previously reported that follicle-stimulating hormone (FSH) stimulates mRNA-selective, cap-dependent, and cap-independent translation in primary Sertoli cells (4) and in HEK293 cells stably expressing the FSHR (5). Accordingly, some signaling pathways controlling translation are stimulated in response to FSH, including mTOR/p70 S6 kinase (6,7). This latter kinase phosphorylates components of the translation preinitiation complex such as eIF4B (8) and ribosomal proteins like rpS6 (9), hence its name.…”

Activation of a GPCR leads to eIF4G phosphorylation at the 5′ cap and to IRES-dependent translation

“…In Sertoli cells of the male gonad, we have reported that a subtle interplay between cAMP-and PtdIns-dependent signaling was required for FSH to stimulate p70S6K. A stimulatory effect of FSH on several proteins of the mTOR pathway, such as p70S6K, has been reported a while ago, in granulosa cells (Alam et al 2004, Kayampilly & Menon 2007, as well as in Sertoli cells (Lécureuil et al 2005, Musnier et al 2009). However, the involvement of FSH in translation has been conclusively demonstrated only recently, in Sertoli cells, where our group has reported that FSH enhances the eIF4F assembly leading to the recruitment of selective mRNA to the polysomes (Musnier et al 2012).…”