The N-terminal region of
parathyroid hormone (PTH) and PTH-related
protein (
PTHrP) interacts with a common
PTH/PTHrP receptor in osteoblasts. These cells synthesize
PTHrP, but its role in bone turnover is unclear. Intermittent treatment with N-terminal
PTHrP or PTH stimulates bone growth in vivo, possibly by increasing local bone factors. In addition, C-terminal
PTHrP (107-139), which does not bind to the
PTH/PTHrP receptor, appears to affect
bone resorption in vivo and in vitro, although its effect on bone formation in vivo remains controversial. Bone angiogenesis is an often overlooked but critical event in the process of bone remodeling. Recently, PTH (1-34) has been shown to induce gene expression of
vascular endothelial growth factor (
VEGF), a potent
angiogenic factor, by osteoblastic cells. However, no data are available on the effect of
PTHrP (107-139) on
VEGF expression in these cells. Using semiquantitative reverse transcription followed by PCR, we found that
PTHrP (107-139), between 10 nM and 1 pM, increased
VEGF mRNA in human osteoblastic (hOB) cells from trabecular bone. This effect of this agonist,
at 10 nM, was maximal (fivefold for
VEGF(165), and twofold for
VEGF(121), compared to control) within 1 to 4 h. This effect was similar to that induced by
PTHrP (1-34) in these cells, as well as in human
osteosarcoma MG-63 cells, using Northern blot analysis. Moreover, the effect of both
peptides, added together at 100 pM, was not higher than that observed with each
peptide alone in hOB cells. The effects of
PTHrP (107-139) and that of
PTHrP (1-34) were abolished by
actinomycin D in hOB cells. In these cells, the
protein kinase C inhibitor
staurosporine, but not the
protein kinase A inhibitor H89, inhibited the increase in
VEGF mRNA induced by 10 nM
PTHrP (107-139).
PTHrP (107-139),
at 10 nM, also stimulated cytosolic
VEGF immunostaining in hOB cells, and
VEGF secretion into the
medium conditioned by hOB or MG-63 cells for 24 h, which was (ng/mg
protein): 10 +/- 1 or 5 +/- 3 (control), respectively, and 21 +/- 1 or 11 +/- 2 (
PTHrP [107-139]-stimulated), respectively. Furthermore,
medium conditioned by these cells for 24 h in the presence of 10 nM
PTHrP (107-139), with or without 10 nM
PTHrP (1-34), increased about 30% bovine aortic endothelial cell (BAEC) growth at 48 h. This effect was inhibited by adding a specific anti-
VEGF antibody to the BAEC incubation medium. These findings demonstrate that the C-terminal domain of
PTHrP induces expression and secretion of
VEGF, a main
angiogenic factor, in hOB cells and MG-63 cells. This relationship between
PTHrP and
VEGF has potential implications for both bone vascularization and bone formation, and neoangiogenesis in
PTHrP-producing
tumors.