Abstract
Growth hormone (GH) is a key modulator of growth and GH over-secretion can lead to gigantism. One form is X-linked acrogigantism (X-LAG), in which infants develop GH-secreting pituitary tumors over-expressing the orphan G-protein coupled receptor, GPR101. The role of GPR101 in GH secretion remains obscure. We studied GPR101 signaling pathways and their effects in HEK293 and rat pituitary GH3 cell lines, human tumors and in transgenic mice with elevated somatotrope Gpr101 expression driven by the rat Ghrhr promoter (GhrhrGpr101). Here, we report that Gpr101 causes elevated GH/prolactin secretion in transgenic GhrhrGpr101 mice but without hyperplasia/tumorigenesis. We show that GPR101 constitutively activates not only Gs, but also Gq/11 and G12/13, which leads to GH secretion but not proliferation. These signatures of GPR101 signaling, notably PKC activation, are also present in human pituitary tumors with high GPR101 expression. These results underline a role for GPR101 in the regulation of somatotrope axis function.
Highlights
Growth hormone (GH) is a key modulator of growth and GH over-secretion can lead to gigantism
To investigate the impact of GPR101 signaling on somatotrope function, we generated a mouse model (GhrhrGpr101) expressing Gpr[101] under the control of the rat Ghrhr promoter, which drives expression in terminally differentiated somatotropes and somatomammototropes of the POU1F1/positive transcription factor 1 (Pit-1) lineage[14,15,17,18]
We confirmed by Western Blot the direct stimulation of Protein kinase A (PKA) and Protein kinase C (PKC) by GPR101 (Fig. 5h) and we found with siRNA depletion of Gα subunits that only Gs contributed to PKA activation while both Gs and Gq/11 played a role in PKC activation (Fig. 5i, j)
Summary
Growth hormone (GH) is a key modulator of growth and GH over-secretion can lead to gigantism. Chronic GH/IGF-1 hypersecretion in transgenic mice associates with classical metabolic effects of elevated glucose levels, decreased fat mass and increased lean mass[16] This GH hypersecretion occurs in the absence of pituitary hyperplasia or tumorigenesis, indicating that the role of Gpr[101] in the pituitary enhances secretion rather than enhancing proliferation. We find that GPR101-induced GH secretion is dependent on Gs and Gq/11 pathways, notably through the activation of Protein kinase A (PKA) and Protein kinase C (PKC) We validate these findings in transgenic mice and observe that the pituitary adenomas of X-LAG patients, that are characterized by high expression levels of GPR1017, have an increase of PKC activity compared to other GH-secreting tumors. GPR101 is a constitutively active GPCR coupled to multiple G proteins that acts via Gs- and Gq/11-dependent pathways to promote hormonal activity of the somatotrope axis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
