Evaluation of signal transduction mechanisms for the mitogenic effects of prostaglandin E2 in normal human bone cells in vitro
✍ Scribed by Timothy M. Baylink; Subburaman Mohan; Robert J. Fitzsimmons; David J. Baylink
- Publisher
- American Society for Bone and Mineral Research
- Year
- 2009
- Tongue
- English
- Weight
- 580 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0884-0431
No coin nor oath required. For personal study only.
✦ Synopsis
Prostaglandin E, (PGE,) is one of the most potent stimulators of bone formation in vivo. In these studies, we investigated the mechanism(s) underlying PGE, effects on human bone formation by evaluating the effects of PGE, on normal human bone cell (HBC) proliferation in vitro. Cell proliferation of normal HBCs was increased by PGE, as measured by increased r3H] thymidine incorporation after 18 h and increased cell number after 48 h of treatment. The effect of PGE, to stimulate cell proliferation was biphasic, with a maximum stimulation between 0.01 and 1.0 nM PGE, in different experiments. At higher concentrations of PGE, (0.1 pM), HBC proliferation was inhibited. Signal transduction for PGE, has been reported to include both protein kinase A (PKA) and protein kinase C (PKC) pathways. In these studies, concentrations of PGE, which stimulated cell proliferation did not increase cyclic adenosine monophosphate (CAMP) production. However, higher concentrations of PGE, increased CAMP production (7-to 12-fold at 1-10 pM) and inhibited cell proliferation. Because stimulators of PKC, such as phorbol esters, have been reported to stimulate cell proliferation, the action of PKC inhibitors were tested. Both staurosporine and sangivamysin (PKC inhibitors) totally abrogated the effect of PGE, to stimulate cell proliferation. Additional studies revealed that PGE, increased 45Ca uptake in a dose-dependent manner with a peak response occuring between 1 and 10 nM PGE, concentrations in different experiments. Furthermore, when the calcium channel blocker, verapamil, was added to HBC cultures treated with PGE,, the stimulation of 45Ca uptake and cell proliferation by PGE, was completely blocked. These data suggest that PGE, increases cell proliferation through activation of a verapamil-sensitive calcium channel. In conclusion, these data are consistent with a model in which stimulation of HBC proliferation by low doses of PGE, is mediated by an enhancement of phospholipase C, which results in both an increase in PKC activity and an increase in intracellular calcium influx. (