GPR101 drives growth hormone hypersecretion and gigantism in mice via constitutive activation of Gs and Gq/11

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). We report that Gpr101 causes elevated GH/prolactin secretion in transgenic GhrhrGpr101 mice. We also show that GPR101 promotes GH secretion through the activation of not only Gs, but also Gq/11, in a PKA and PKC-dependent manner, respectively. Interestingly, in stark contrast with other Gs-coupled receptors, GPR101 activation did not lead to the proliferation of somatotrope cells. These signatures of GPR101 signaling, notably PKC activation, are also present in human X-LAG pituitary tumors with high GPR101 expression. These results underline a role for GPR101 in the regulation of somatotrope axis function.