Expression and regulation of alkaline phosphatases in XXXX @entity0 MCF-7 cells.

@entity1 @entity0 @entity3927 @entity619 @entity72756 @entity1968
The effect of @entity1968 and @entity619 on alkaline phosphatase (AP) expression was investigated in @entity1 @entity0 MCF-7 cells. Cellular AP activity was induced significantly by @entity1968 or @entity619 in a time-dependent and dose-dependent fashion. A marked synergistic induction of AP activity was observed when the cells were incubated with both agents simultaneously. Two AP isozymes, tissue-nonspecific ( @entity72756 ) and intestinal (IAP), were shown to be expressed in MCF-7 cells as confirmed by the differential rate of thermal inactivation of these isozymes and RT-PCR. Based on the two-isozyme thermal-inactivation model, the specific activities for @entity72756 and IAP in each sample were analyzed. @entity72756 activity was induced only by @entity1968 and IAP activity was induced only by @entity619 . Whereas @entity619 conferred no significant effect on @entity72756 activity, @entity1968 was shown to inhibit IAP activity by approximately 50%. Interestingly, @entity72756 was found to be the only isozyme activity superinduced when the cells were costimulated with @entity1968 and @entity619 . Northern blot and RT-PCR analysis were then used to demonstrate that the steady-state @entity72756 mRNA level was also superinduced, which indicates that the superinduction is regulated at the transcriptional or post-transcriptional levels. In the presence of the glucocorticoid receptor antagonist @entity3927 , the @entity619 -mediated induction of IAP activity was blocked completely as expected. However, the ability of @entity3927 to antagonize the action of glucocorticoid was greatly compromised in @entity619 -mediated superinduction of @entity72756 activity. Furthermore, in the presence of @entity1968 , @entity3927 behaved as an agonist, and conferred superinduction of @entity72756 gene expression in the same way as @entity619 . Taken together, these observations suggest that the induction of IAP activity by @entity619 and the superinduction of @entity72756 by @entity619 were mediated through distinct regulatory pathways. In addition, @entity1968 plays an essential role in the superinduction of @entity72756 gene expression by enabling @entity619 to exert its agonist activity, which otherwise has no effect.
