The effect of prostaglandin E2 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 vitamin D action may be interrelated. To test this hypothesis, we examined the effect of PGE(2) on rat costochondral resting zone and growth zone cartilage cells and determined whether the effects of PGE(2) are mediated by changes in the level of cAMP and/or PKC activity, whether there is a relationship between cAMP production and PKC activity, and whether cell maturation-specific effects are involved. Confluent, fourth passage resting zone and growth zone cartilage cell cultures were incubated in DMED containing 10% FBS, 50 mu g/ml vitamin C, and 1% antibiotics. The PGE(2) caused a dose-dependent increase in cell number and [H-3]thymidine incorporation and stimulated alkaline phosphatase specific activity. These effects were comparable in resting zone and growth zone cartilage cells at the same PGE(2) concentrations. At higher concentrations, PGE(2) caused a general increase in the synthesis of collagenase-digestible protein and noncollagenase-digestible protein in resting zone cartilage cells and of collagenase-digestible protein in growth zone cartilage cells, resulting in a net increase in the percent collagen synthesis for both cell types. cAMP production was increased over the entire range of chondrocyte response. Prevention of cAMP metabolism with the protein kinase A inhibitors H-8 and H-89 blocked the PGE(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. These results suggest that low levels of PHE2 promote differentiation, whereas high doses promote and anabolic response; PGE(2) increases cAMP production and PKC activity in a cell maturation-dependent manner; PGE(2) exerts its effects via cAMP production and PKC activity; and regulation of PGE(2)-dependent PKC is via cAMP.