Extracellular calcium-sensing receptor (CaR) expression and its potential role in parathyroid hormone-related peptide (PTHrP) secretion in the H-500 rat Leydig cell model of humoral hypercalcemia of malignancy.
Humoral hypercalcemia of malignancy (HHM) occurs when secretion of parathyroid hormone-related peptide (PTHrP) by cancer cells causes hypercalcemia in the absence of skeletal metastases. High extracellular calcium (Ca(2+)(o)) increases secretion of PTH-like bioactivity by rat H-500 leydig cells, a transplantable model of HHM, an action potentially mediated by the Ca(2+)(o)-sensing receptor (CaR). In this study we investigated whether H-500 cells express the CaR and, if so, whether CaR agonists modulate PTHrP secretion. Northern blot analysis and RT-PCR revealed bona fide CaR transcript(s), and immunocytochemistry and Western analysis with a specific anti-CaR antiserum demonstrated CaR protein expression in H-500 cells. Furthermore, high Ca(2+)(o) and neomycin stimulated PTHrP secretion dose-dependently with maximal 2.7- and 3.3-fold increases at 5 mM Ca(2+)(o) and 300 microM neomycin, respectively. Thus in HHM caused by H-500 cells, the CaR could participate in a vicious cycle whereby PTHrP-induced increases in Ca(2+)(o) further stimulate PTHrP release and exacerbate hypercalcemia.
Sanders
J L
JL
Endocrine-Hypertension Division, Harvard Medical School, Boston, Massachusetts, 02115, USA. jsanders@rics.bwh.harvard.edu
Chattopadhyay
N
N
Kifor
O
O
Yamaguchi
T
T
Brown
E M
EM
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D005110:Extracellular Space / Q000378:metabolism; D006934:Hypercalcemia / Q000150:complications*; D007150:Immunohistochemistry; D007985:Leydig Cells / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D009374:Neoplasms, Experimental / Q000150:complications*; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; C473605:extracellular calcium cation-sensing receptor, rat