THE EFFECT OF PROSTAGLANDIN E-2 ON COSTOCHONDRAL CHONDROCYTE DIFFERENTIATION IS MEDIATED BY CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE AND PROTEIN-KINASE-C

Recent studies indicate that vitamin D metabolites exert rapid effects on growth plat chondrocytes via changes in PG production and protein kinase C (PKC) activity. This suggests that these two products of vita min D action may be interrelated. To test this hypothesis, we examined the effect of PGE(2) on rat costochondral resting zone and growth zon e cartilage cells and determined whether the effects of PGE(2) are med iated by changes in the level of cAMP and/or PKC activity, whether the re is a relationship between cAMP production and PKC activity, and whe ther cell maturation-specific effects are involved. Confluent, fourth passage resting zone and growth zone cartilage cell cultures were incu bated in DMED containing 10% FBS, 50 mu g/ml vitamin C, and 1% antibio tics. The PGE(2) caused a dose-dependent increase in cell number and [ H-3]thymidine incorporation and stimulated alkaline phosphatase specif ic activity. These effects were comparable in resting zone and growth zone cartilage cells at the same PGE(2) concentrations. At higher conc entrations, PGE(2) caused a general increase in the synthesis of colla genase-digestible protein and noncollagenase-digestible protein in res ting zone cartilage cells and of collagenase-digestible protein in gro wth zone cartilage cells, resulting in a net increase in the percent c ollagen synthesis for both cell types. cAMP production was increased o ver the entire range of chondrocyte response. Prevention of cAMP metab olism with the protein kinase A inhibitors H-8 and H-89 blocked the PG E(2)-dependent inhibition of PKC in resting zone cartilage cells in a dose-dependent manner. H-8 alone had no effect on PKC in resting zone cartilage cells, but stimulated PKC activity in growth zone cartilage; H-89 alone stimulated PKC activity in resting zone cartilage cells. T hese results suggest that low levels of PHE2 promote differentiation, whereas high doses promote and anabolic response; PGE(2) increases cAM P production and PKC activity in a cell maturation-dependent manner; P GE(2) exerts its effects via cAMP production and PKC activity; and reg ulation of PGE(2)-dependent PKC is via cAMP.