Insulin augments gonadotropin-releasing hormone induction of translation in LβT2 cells

Abstract

SummaryThe integrated signaling of insulin and gonadotropin-releasing hormone in the pituitary gonadotropes may have a profound bearing on reproductive function, although the cross-receptor signaling mechanisms are unclear. We demonstrate that the insulin receptor is constitutively localized to noncaveolar lipid raft microdomains in the pituitary gonadotrope cell line LβT2. The localization to rafts is consistent with similar localization of the GnRH receptor. Insulin receptor phosphorylation occurs in raft domains and activates the downstream signaling targets Insulin Receptor Substrate1 and Akt/ Protein Kinase B. Although insulin alone does not strongly activate the extracellular signal-regulated kinase second messenger cascade, co-stimulation potentiates the phosphorylation of the extracellular signal-regulated kinase by gonadotropin-releasing hormone. The co-stimulatory effect of insulin and gonadotropin-releasing hormone is also evident in increased activation of cap-dependent translation. In contrast, co-stimulation attenuates Akt/Protein Kinase B activation. Our results show that both gonadotropin-releasing hormone and insulin are capable of mutually altering their respective regulatory signaling cascades. We suggest that this provides a mechanism to integrate neuropeptide and energy homeostatic signals to modulate reproductive function.

FOXO1 Transcription Factor Inhibits Luteinizing Hormone β Gene Expression in Pituitary Gonadotrope Cells

“…We then investigated whether FOXO1 is a target of insulin signaling in gonadotropes, as previously reported for IRS1/2 and AKT (24,27). Our results showed that insulin treatment of L␤T2 cells increased FOXO1 serine 256 phosphorylation and cytoplasmic localization.…”

CREB Binding Protein (CBP) Activation Is Required for Luteinizing Hormone Beta Expression and Normal Fertility in Mice

“…Phosphorylation of CBP via insulin results in dissociation of CBP from the CREB-CBP-TORC2 complex, and in gonadotrophs, it results in recruitment to the Lhb promoter and activation of Lhb gene expression. We and others have shown that insulin can increase GNRH-mediated Lhb expression and secretion with some evidence of a costimulatory effect of insulin and GNRH in L␤T2 cells via activation of AKT and extracellular signal-regulated kinase (ERK) (1,4,10,31,40). This suggests that energy-homeostatic information can be integrated at the level of the pituitary gland, possibly through CBP, to modulate reproductive function.…”

Heifers express G-protein coupled receptor 61 in anterior pituitary gonadotrophs in stage-dependent manner

“…GnRHRs are present in gonadotroph plasma membrane lipid rafts (Navratil et al 2009;Wehmeyer et al 2014;Kadokawa et al 2014), which are distinct, relatively insoluble regions that have lower density and are less fluid than surrounding membrane (Simons and Tooter, 2000;Head et al 2014). Lipid rafts facilitate signaling by allowing colocalization of membrane receptors and their downstream signaling components (Simons and Tooter, 2000;Head et al, 2014); as such, they are important pharmacological targets in human medicine (Jaffrès, 2016).…”

“…Lipid rafts containing GnRHR also harbor insulin receptor (Navratil et al 2009) and glucocorticoid receptor (Wehmeyer et al 2014) in the LβT2 clonal murine gonadotroph cell line, thus providing a potential means of integrating neuropeptide and energy homeostasis signals to modulate reproductive function. However, gonadotroph lipid rafts containing GnRHR are also likely to contain other types of receptor that have yet to be identified.…”