Dexamethasone increases expression and hormone-stimulated phospholipase c activity in umr106-01 cells. Mitchell, Jane, and Atul Bansal. Department of Pharmacology, University of Toronto, Toronto, M5S 1A8, Canada
APStracts 4:0124E, 1997.
Glucocorticoids regulate responsiveness of many cells to hormones that bind to G protein-coupled receptors. We examined the effect of glucocorticoids on parathyroid hormone (PTH) activation of two G protein-activated signal transduction pathways, phospholipase C (PLC) and adenylyl cyclase, in osteosarcoma UMR 106-01 cells. Dexamethasone (100 nM) increased PTH-stimulatedand NaF-stimulated PLC activity by more than 100 percent over four days (223 +/- 8 and 293 +/- 8.2 percent of control after 4 days for PTH and NaF-stimulated activity, respectively). The increase in PTH-stimulated adenylyl cyclase response in the same cells was more modest (162 +/- 5.4 and 171 +/- 6.8 percent of control after 4 days for PTH and NaF-stimulated activity, respectively). PTH activation of PLC was blocked by antisera to Gq/11[alpha] and activation of adenylyl cyclase by Gs[alpha] antisera. Quantification of these G protein subunits in control and dexamethasone-treated cells showed a 78% increase in Gq/11[alpha] (from 18.1 +/- 1.2 to 32.2 +/- 1.5 pmol/mg), while Gs[alpha] was increased only 34% (from 6.2 +/- 0.5 to 8.2 +/- 0.3 pmol/mg) and G[beta] subunits were increased 40% (from 54 +/- 2.3 to 75.2 +/- 3.8 pmol/mg). These results suggest that glucocorticoids are more potent regulators of PLC activity than adenylyl cyclase activity in UMR cells and this is mediated, at least in part, by differential increases in Gq/11[alpha] proteins. 

Received 1997 March 4; accepted in final form 1995 May 20
APS Manuscript Number E099-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997