Abstract
Recently, human parathyroid hormone-related peptide (hPTHrP) has been purified and its amino acid sequence determined. Within the amino-terminal 13 residues of hPTHrP, 8 amino acids were found homologous between hPTHrP and human PTH (hPTH). This peptide was reported to stimulate cyclic AMP (cAMP) production in osteoblastic cell lines (UMR106 and ROS17/2.8), However, whether or not this peptide affects another second messenger, i.e., cytosolic free calcium ([Ca 2+] i), in osteoblasts has not yet been determined. Therefore, in the present study, we examined the effects of synthetic aminoterminal fragments of hPTHrP (Tyr 40hPTHrP1-40 and hPTHrP1-34) on intracellular cAMP production and [Ca 2+] i in an osteoblastic cell line (MC3T3-E1) and compared them with those of hPTH1-34. Human PTHrP1-34, Tyr 40hPTHrP1-40 and hPTH1-34 stimulated cAMP production in an equipotent manner at concentrations ranging from 2.5 × 10 −10 to 1.3 × 10 −6 M. Human PTH1-34 at concentrations from 2.5 × 10 −7 to 1.3 × 10 −6 M significantly ( P < 0.05) increased [Ca 2+] i, but hPTHrP1-34 and Tyr 40PTHrP1-40 at the same concentrations did not. These results suggest a different receptor-mediated mechanism for [Ca 2+] i increase between hPTHrP and hPTH, although these two peptides appear to share the same receptor site(s) which is coupled to the cAMP system in MC3T3-E1.
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