• Characterizing the Signaling, Crosstalk, and Trafficking of Adhesion G Protein-Coupled Receptor G2 and the Calcium-Sensing Receptor in Parathyroid Adenoma Models

      Gad, Abanoub; Balenga, Nariman; Olson, John A. Jr.; 0000-0002-8225-5298 (2022)
      The parathyroid glands sense serum calcium levels and release parathyroid hormone (PTH) in response to hypocalcemia. PTH acts at bone, intestine, and kidney to increase serum calcium. Primary hyperparathyroidism (PHPT) is an endocrine disorder characterized by neoplasia of one or more glands, dysregulated PTH release, and hypercalcemia. The mechanisms of dysregulated calcium-sensing in parathyroid adenomas are not well understood. The literature suggests that the expression of the calcium-sensing receptor (CaSR) is diminished in parathyroid adenomas. We have found that a subset of PHPT patients do not show a significant change in CaSR expression. Therefore, we hypothesized that other molecules that modify the action of CaSR might inhibit its ability to sense calcium properly. We identified ADGRG2, an adhesion G protein-coupled receptor (aGPCR), in a transcriptome screen of parathyroid tissue and hypothesized that it might serve as a modifier of CaSR function. A transgenic mouse with parathyroid-restricted ADGRG2 overexpression develops parathyroid neoplasia, hypercalcemia, and hyperparathyroidism. To understand crosstalk mechanisms between ADGRG2 and CaSR, we developed a double-expressing ADGRG2-CaSR stable cell line (FL-CaSR). Activation of ADGRG2 in this novel cell line completely ablated the Gαi and Gαq signaling pathways downstream of CaSR. We also developed a SNAP and CLIP tag system to ascertain changes in receptor trafficking. Live cell imaging studies showed that in cells expressing both ADGRG2 and CaSR, co-stimulation caused the receptors to remain on the cell surface and not traffic into the early endosome. Given the important role that the ADGRG2 plays in inhibiting CaSR activity we sought to identify targetable