Regulation of adenosine 3 ',5 '-cyclic monophosphate (cAMP) accumulation in UMR-106 osteoblast-like cells: Role of cAMP-phosphodiesterase and cAMP efflux

The present study aimed to define the role of adenosine 3',5'-cyclic monoph osphate (cAMP)-phosphodiesterase (PDE) activity and the possible involvemen t of cAMP efflux on parathyroid hormone (PTH) stimulated intracellular cAMP accumulation in cultured osteoblast like UMR-106 cells. Treatment of the c ells with 10 nM PTH (1-84) rapidly increased the level of intracellular cAM P. PTH stimulation also increased the cAMP efflux rate. The efflux of cAMP could only account for a minor part of the decrease in intracellular cAMP. Six peaks of cAMP-hydrolyzing PDE activity were separated by Q-Sepharose ch romatography The first peak to elute was stimulated by Ca2+/calmodulin and provided less than 2% of the total eluted cAMP-PDE activity. The second pea k, providing less than 4% of the cAMP-PDE activity, was stimulated 3-fold b y 4 mu M cyclic GMP (cCMP) and was sensitive to the PDE2 isoenzyme-selectiv e inhibitor erythro 9-(2-hydroxy-3-nonyl) adenine (EHNA). The third peak, p roviding less than 10% of the cAMP-PDE activity, was insensitive to rolipra m, EHNA, Ca2+/calmodulin, and cGMP. Peaks 4, 5 and 6 were sensitive to roli pram (IC50 < 0.1 mu M) and provided approximately 85% of the total cAMP-hyd rolyzing activity. It is concluded that cAMP PDE activity in UMR-106 cells plays a major role in the control of intracellular cAMP accumulation, where as only moderate amounts of cAMP are extruded from the cells through cAMP e fflux. The main cAMP-hydrolyzing PDE isozyme is cAMP-specific/rolipram-sens itive. Ca2+/calmodulin-stimulated PDE, cGMP stimulated PDE, and presently u nidentified cAMP-specific/rolipram- insensitive PDE are also present in UMR -106 cells. (C) 1999 Elsevier Science Inc.