Differential regulation of placental and germ cell alkaline phosphatases by glucocorticoid and sodium butyrate in human gastric carcinoma cell line TMK-1

The expression and regulation of alkaline phosphatase (AP) was studied in t he human gastric cancer cell line TMK-1. Biochemical analysis, reverse tran scription-polymerase chain reaction, and Northern blot analysis demonstrate d that the cells express placental, germ cell, and intestinal AP isozymes c onstitutively. Dexamethasone (Dex), a synthetic glucocorticoid, was shown t o specifically induce the placental AP activity to about 10-fold and sodium butyrate (NaBu) induced germ cell AP activity to about 4-fold, respectivel y. In contrast, these two agents showed little effect on the level of intes tinal isozymes. Dex and NaBu also differentially induced the mRNA levels of the placental and germ cell APs. Northern blot analysis of the placental A P transcript in the presence of the transcription inhibitor, 5, 6 dichloro- 1-beta -D-ribofuranosyl benzimidazole, revealed that the half-life of place ntal AP mRNA is about 27 h for both the Dex-treated and untreated cells. Nu clear run-on transcription analysis indicated an apparent increase in the r ate of placental AP gene transcription in Dex-treated cells. These results indicated that the effect of Dex occurred primarily by activation of the pl acental AP gene transcription in the cells. In order to study the direct De x and NaBu effect on AP gene expression, the proximal promoter regions of A P genes were fused to luciferase reporter vectors. Despite the high similar ity in nucleotide sequences of these two genes, transient transfection anal ysis demonstrated that Dex and NaBu exerted a specific stimulation only thr ough the respective placental and germ cell AP gene promoter. Taken togethe r, this study indicates that the expression of PAP and GCAP isozymes have s pecific regulatory mechanisms that can be differentially controlled by sign als including glucocorticoid and NaBu. (C) 2001 Academic Press.