The Calcium-sensing Receptor Couples to Galpha(s) and Regulates PTHrP and ACTH Secretion in Pituitary Cells

The calcium-sensing receptor (CaR or CASR as listed in the MGI Database) is a G protein-coupled receptor that binds and signals in response to extracellular calcium and other polycations. It is highly expressed on parathyroid and kidney cells, where it participates in the regulation of systemic calcium homeostasis. It is also expressed on many other cell types and is involved in a wide array of biological functions such as cell growth and differentiation, ion transport, and hormone secretion. It has been described to couple to several different G proteins including Galpha(i/0), Galpha(q/11), and Galpha(12/13). Recently, it has also been shown to stimulate cAMP production by coupling to Galpha(s) in immortalized or malignant breast cells. The CaR is expressed on cells in the anterior pituitary and had previously been described to stimulate cAMP production in these cells. In this report, we examined signaling from the CaR in murine pituitary corticotroph-derived, AtT-20 cells. We found that CaR activation led to the stimulation of cAMP production, and PTH-related protein (PTHrP or PTHLH as listed in the MGI Database) and ACTH secretion from these cells. Furthermore, manipulation of cAMP levels was able to modulate PTHrP and ACTH secretion independent of changes in extracellular calcium. Finally, we demonstrated that the CaR couples to Galpha(s) in AtT-20 cells. Therefore, in pituitary corticotroph-like cells, as in breast cancer cells, the CaR utilizes Galpha(s) and activates cAMP production to stimulate hormone secretion.