Endocrinology, Vol 125, 2806-2811, Copyright © 1989 by Endocrine Society

ARTICLES

Glucocorticoid and 1,25-dihydroxyvitamin D modulate the degree of adenosine 3',5'-monophosphate-dependent protein kinase isoenzyme I and II activation by parathyroid hormone in rat osteosarcoma cells

L Titus, JE Rubin, MS Nanes and BD Catherwood
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia.

Glucocorticoid increases and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] decreases PTH activation of adenylate cyclase and cAMP-dependent protein kinase in rat osteosarcoma cells (ROS 17/2.8). Since selective cAMP-dependent protein kinase isoenzyme activation may account for specific physiological hormonal responses, we investigated steroid effects on activation of isoenzymes I and II in response to PTH using a new ion exchange separation procedure. Pretreatment of cells for 2 days with the glucocorticoid triamcinolone acetonide (TRM) or 1,25-(OH)2D3 altered the degree of cAMP-dependent protein kinase isoenzyme activation by PTH in accordance with their modulation of intracellular cAMP accumulation, but did not alter the amount of each isoenzyme present or the order in which isoenzymes I and II were activated. In all treatment groups isoenzyme I was preferentially activated by low doses of PTH, while high concentrations activated both isoenzymes, as predicted by the relative affinities of each isoenzyme for cAMP. Glucocorticoid reduced the concentration of bovine PTH-(1-34) required for maximal activation of isoenzyme I from 1 to 0.05 ng/ml and that required for activation of isoenzyme II from 10 to 1 ng/ml. This effect was abolished by simultaneous treatment of cells with 1,25-(OH)2D3. At doses of PTH that caused partial activation (0.05-0.1 ng/ml for isoenzyme I; 1 ng/ml for isoenzyme II), 1,25-(OH)2D3 treatment attenuated this activation. In all groups both isoenzymes were fully activated by 100 ng/ml PTH. Control experiments demonstrated that isoenzyme activation is not a result of cell disruption over the range of PTH doses that regulation by steroid hormone was observed. These results extend our studies on modulation of the cAMP pathway by steroid hormones and make it feasible to correlate selective isoenzyme activation with specific responses to PTH.

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