Effects of N-terminal, midregion, and C-terminal parathyroid hormone-related peptides on adenosine 3',5'-monophosphate and cytoplasmic free calcium in rat aortic smooth muscle cells and UMR-106 osteoblast-like cells.
N-Terminal analogs of PTH-related protein (PTHrP) and PTH bind to a common receptor and exhibit similar biological properties. However, recent studies suggest that certain midregion and C-terminal PTHrP peptides have activities distinct from those of PTH in the placenta and in osteoclasts, respectively. In this study we determined the biological activities of full-length recombinant PTHrP-(1-141) and several synthetic N-terminal, midregion, and C-terminal PTHrP fragments in two PTHrP-producing cell types. Peptides were tested for their ability to stimulate cAMP production and raise intracellular free calcium ([Ca2+]i) in primary rat aortic smooth muscle cells (VSMC) and UMR-106 rat osteoblast-like (UMR) cells. In UMR cells PTHrP-(1-34)NH2, PTHrP-(1-141), and bovine PTH-(1-34) all increased cAMP (approximately 50 fold) and [Ca2+]i (180 nM). By contrast, in VSMC, these N-terminal peptides increased cAMP (3-fold) but had no detectable effect on [Ca2+]i. PTHrP-(1-34) and PTHrP-(1-141) significantly blunted the angiotensin II-induced rise in cAMP (but not the calcium signal) consistent with the concept that PTHrP opposes angiotensin II activity in VSMC. PTHrP-(67-86)NH2, PTHrP-(107-138)NH2, and PTHrP-(107-111)NH2 had no effect on either cAMP or [Ca2+]i in either cell type. VSMC and UMR-106 cells both expressed a 2.5-kilobase PTH/PTHrP receptor messenger RNA (mRNA) transcript. However, high affinity specific binding of 125I-labeled [Tyr36] PTHrP-(1-36)NH2 was detected in UMR cells but not in VSMC. We conclude that the PTH-like, N terminus of the PTHrP molecule is critical in induction of cAMP and [Ca2+]i pathways in UMR cells, and for cAMP stimulation in VSMC. In addition, PTHrP, like other established vasodilators, signals in VSMC mainly (if not exclusively) by increasing the production of cAMP.
Wu
S
S
Department of Medicine, Cedars-Sinai Research Institute, Cedars-Sinai Medical Center, Los Angeles, California.
Pirola
C J
CJ
Green
J
J
Yamaguchi
D T
DT
Okano
K
K
Jueppner
H
H
Forrester
J S
JS
Fagin
J A
JA
Clemens
T L
TL
D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D010006:Osteoblasts / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000494:pharmacology; D011506:Proteins / Q000494:pharmacology*; D051381:Rats; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism
D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D011506:Proteins; D018016:Receptors, Parathyroid Hormone; D000242:Cyclic AMP; D002118:Calcium