Comparison of inhibition by a @entity5 promoter ( @entity864 ) of expression of the differentiated phenotype of chondrocytes in @entity95 costal chondrocytes in culture with inhibition by XXXX .

@entity4878 @entity5 @entity44225 @entity95 @entity7222 @entity1919 @entity865 @entity4664 @entity864 @entity1968 @entity5393
Both @entity4878 and the @entity5 promoter @entity864 ( @entity865 ) inhibit expression of the differentiated phenotype by @entity95 costal chondrocytes in culture, as judged by morphological changes and decreased sulfation of glycosaminoglycans (GAG). However, the inhibition of the differentiated phenotype of chondrocytes in @entity865 -treated cells is restored by parathyroid hormone ( @entity44225 ), while the inhibition by @entity4878 is not [Takigawa et al. (1982) Mol. Cell. Biochem. 42, 145-153; Takigawa et al. (1983) Cell Differ. 13, 283-291]. In the present study, we examined the difference between @entity865 -treated chondrocytes and @entity1968 -treated chondrocytes to determine the mechanism of the restoration of the differentiated phenotype in de-differentiated cells treated with @entity865 . @entity44225 increased the activity of @entity7222 decarboxylase [ODC; EC 4.1.1.17], a rate limiting enzyme of @entity4664 biosynthesis, and proteoglycan synthesis in chondrocytes pretreated with @entity865 as well as in normal chondrocytes. The maximal stimulations of ODC activity and GAG synthesis were observed 4 h and 24-36 h, respectively, after addition of @entity44225 . The dose-response curve for ODC induction by @entity44225 was parallel to that of @entity44225 -stimulated proteoglycan synthesis both in @entity865 -treated chondrocytes and in normal chondrocytes. @entity44225 also increased the intracellular @entity1919 level after 2 min in @entity865 -treated cells as in normal cells. Addition of @entity5393 ( @entity5393 ) induced ODC and restored proteoglycan synthesis in @entity865 -treated cells. The dose-response curve for induction of ODC by @entity5393 was parallel to that of @entity5393 -stimulated proteoglycan synthesis in both @entity865 -treated chondrocytes and normal chondrocytes. On the other hand, the increases by @entity44225 in the intracellular @entity1919 level, ODC activity, and proteoglycan synthesis were inhibited in chondrocytes pretreated with a combination of @entity865 and @entity1968 as well as in those pretreated with @entity1968 alone. @entity865 stimulated the syntheses of DNA and RNA in chondrocytes but did not increase the @entity1919 level or ODC activity. @entity44225 and @entity5393 inhibited the syntheses of DNA and RNA both in @entity865 -treated cells and in normal cells. These results suggest that ODC induction mediated by elevation of @entity1919 plays an important role in re-differentiation of de-differentiated cells pretreated with these agents.
