Calcium-sensing receptor induces proliferation through p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase but not extracellularly regulated kinase in a model of humoral hypercalcemia of malignancy.
Using H-500 rat Leydig cancer cells as a model of humoral hypercalcemia of malignancy (HHM), we previously showed that high Ca(2+) induces PTH-related peptide (PTHrP) secretion via the calcium-sensing receptor (CaR) and mitogen- and stress-activated kinases, e.g. MAPK kinase 1 (MEK1), p38 MAPK, and stress-activated protein kinase 1/c-Jun N-terminal kinase. Because cellular proliferation is a hallmark of malignancy, we studied the role of the CaR in regulating the proliferation of H-500 cells. Elevated Ca(2+) has a mitogenic effect on these cells that is mediated by the CaR, because the calcimimetic NPS R-467 also induced proliferation. Inhibition of phosphatidylinositol 3-kinase (PI3K) and p38 MAPK but not MEK1 abolished the mitogenic effect. Activation of PI3K by elevated Ca(2+) was documented by phosphorylation of its downstream kinase, protein kinase B. Because protein kinase B activation promotes cell survival, we speculated that elevated Ca(2+) might protect H-500 cells against apoptosis. Using terminal uridine deoxynucleotidyl nick end labeling staining, we demonstrated that high Ca(2+) (7.5 mM) and NPS R-467 indeed protect cells against apoptosis induced by serum withdrawal compared with low Ca(2+) (0.5 mM). Because the CaR induces PTHrP secretion, it is possible that the mitogenic and antiapoptotic effects of elevated Ca(2+) could be indirect and mediated via PTHrP. However, blocking the type 1 PTH receptor with PTH (7-34) peptide did not alter either high Ca(2+)-induced proliferation or protection against apoptosis. Taken together, our data show that activation of PI3K and p38 MAPK but not of MEK1/ERK by the CaR promotes proliferation of H-500 cells as well as affords protection against apoptosis. These effects are likely direct without the involvement of PTHrP in an autocrine mode.
Tfelt-Hansen
J
J
Division of Endocrinology, Diabetes and Hypertension, Department of Medicine and Membrane Biology Program, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA. jtfelt@rics.bwh.harvard.ed
Chattopadhyay
N
N
Yano
S
S
Kanuparthi
D
D
Rooney
P
P
Schwarz
P
P
Brown
E M
EM
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D006801:Humans; D006934:Hypercalcemia / Q000209:etiology / Q000378:metabolism*; D007984:Leydig Cell Tumor / Q000150:complications / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009368:Neoplasm Transplantation; D044162:Parathyroid Hormone-Related Protein / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D013736:Testicular Neoplasms / Q000150:complications / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
D044162:Parathyroid Hormone-Related Protein; D044169:Receptors, Calcium-Sensing; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D002118:Calcium