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Human heat stable alkaline phosphatases are encoded by two closely related genes: the PAP, which specifies the term placental enzyme, and the GCAP, which is expressed primarily in germ cells. In the human gastric cancer cell line TMK-1 cells, glucocorticoid induced the accumulation of the mRNA of PAP, while sodium butyrate induced the expression of GCAP transcripts only. In order to study the mechanism underlying the differential regulation by glucocorticoid and sodium butyrate, PAP and GCAP promoters were fused to luciferase gene and trans fection were carried out in TMK-1 cells. Dexamethasone confers about 10 fold of induction in luciferase activity in PAP promoter. Despite that the PAP and GCAP promoters differ only by few bases, the GCAP promoter directs a very low level of response to dexamethasone. The dexamethasone response region in PAP promoter was identified between -296 to -375, though there is no discernible canonical glucocorticoid response element in this region. Detailed studies in the this region , demonstrated that the dexamethasone response region in placental alkaline phosphatase (PAP) promoter was identified between -296 to -331 which contains an NF-like and an imperfect glucocorticoid response element (GRE). Inhibition studies, using the glucocorticoid receptor antagonist RU486, protein kinase C inhibitor H7, and protein kinase A inhibitor HA1004, demonstrated that RU 486 blocked about 80% and H7 blocked about 40% of dexamethasone-mediated induction of PAP promoter activity. The sodium butyrate-induced GCAP activity can be blocked by H7 and HA1004 but not by RU486. These results suggest that in TMK-1 cells, the dexamethasone exerts its inductive effect on PAP through both of glucocorticoid receptor and the protein kinase C pathways.
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