Switching of G-protein usage by the calcium-sensing receptor reverses its effect on parathyroid hormone-related protein secretion in normal versus malignant breast cells.
The calcium-sensing receptor (CaR) is a G-protein-coupled receptor that signals in response to extracellular calcium and regulates parathyroid hormone secretion. The CaR is also expressed on normal mammary epithelial cells (MMECs), where it has been shown to inhibit secretion of parathyroid hormone-related protein (PTHrP) and participate in the regulation of calcium and bone metabolism during lactation. In contrast to normal breast cells, the CaR has been reported to stimulate PTHrP production by breast cancer cells. In this study, we confirmed that the CaR inhibits PTHrP production by MMECs but stimulates PTHrP production by Comma-D cells (immortalized murine mammary cells) and MCF-7 human breast cancer cells. We found that changes in intracellular cAMP, but not phospholipase C or MAPK signaling, correlated with the opposing effects of the CaR on PTHrP production. Pharmacologic stimulation of cAMP accumulation increased PTHrP production by normal and transformed breast cells. Inhibition of protein kinase A activity mimicked the effects of CaR activation on inhibiting PTHrP secretion by MMECs and blocked the effects of the CaR on stimulating PTHrP production in Comma-D and MCF-7 cells. We found that the CaR coupled to Galphai in MMECs but coupled to Galphas in Comma-D and MCF-7 cells. Thus, the opposing effects of the CaR on PTHrP production are because of alternate G-protein coupling of the receptor in normal versus transformed breast cells. Because PTHrP contributes to hypercalcemia and bone metastases, switching of G-protein usage by the CaR may contribute to the pathogenesis of breast cancer.
Mamillapalli
Ramanaiah
R
Section of Endocrinology and Metabolism, Department of Internal Medicine, School of Medicine, Yale University, New Haven, Connecticut 06520, USA.
VanHouten
Joshua
J
Zawalich
Walter
W
Wysolmerski
John
J
D000818:Animals; D001859:Bone Neoplasms / Q000378:metabolism / Q000473:pathology / Q000556:secondary; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005260:Female; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism*; D006801:Humans; D006934:Hypercalcemia; D007774:Lactation / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008321:Mammary Glands, Animal / Q000378:metabolism* / Q000473:pathology; D015674:Mammary Neoplasms, Animal / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D009362:Neoplasm Metastasis; D009363:Neoplasm Proteins / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein / Q000378:metabolism*; D011247:Pregnancy; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
D044385:GTP-Binding Protein alpha Subunits; D009363:Neoplasm Proteins; D044162:Parathyroid Hormone-Related Protein; D044169:Receptors, Calcium-Sensing; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010738:Type C Phospholipases