Previously, we demonstrated that PTH increases the level of cAMP, the activity of ornithine decarboxylase (ODC; EC 18.104.22.168; which is a rate-limiting enzyme in polyamine biosynthesis), and glycosaminoglycan (GAG) synthesis (which is characteristic of the chondrocyte phenotype) in rabbit costal chondrocytes in culture. These studies suggested that the accumulation of cAMP and the induction of ODC by PTH are good markers of the differentiated phenotype of cultured chondrocytes. In the present study, the biological effects of a series of bovine PTH (bPTH) fragments and analogs on these three parameters of PTH action were examined. bPTH- (1–34), [Nle8, Nle18, Tyr34]bPTH-(l–34) amide and bPTH-(l–27) amide increased cAMP levels, ODC activity, and GAG synthesis in a dose-dependent manner over the concentration range of 10−9–10−5 M. The order of decreasing potency was: BPTH-(l–34), [Nle8, Nle18, Tyr34]bPTH-(l–34) amide, and bPTH-(l–27) amide. On the other hand, [Nle8, Nle18, Tyr34]bPTH-(3–34) amide, bPTH-(5–27) amide, and [Tyr34]bPTH-(20–34) amide failed to increase cAMP levels, ODC activity, or GAG synthesis when present in concentrations up to 10−6 M. However, [Nle8, Nle18, Tyr34]bPTH-(3–34) amide, bPTH-(5–27) amide, and [Tyr34]bPTH-(20–34) amide inhibited bPTH-(1–34)-stimulated increases in cAMP and ODC activity. These results partially define the principal structural determinants within the PTH molecule required for biological activity and expression of the differentiated phenotype of chondrocytes.
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