Gastrin regulates the human histidine decarboxylase promoter through an AP-1-dependent mechanism

The histidine decarboxylase (HDC) gene is regulated transcriptionally by gastrin and phorbol 12-myristate 13-acetate (PMA) through a protein kinase C (PKC)-related pathway. To determine the role of AP-1 (fos/jun) in the regulation of the HDC promoter, gastric cancer (AGS-B) cells stably expressing the cholecystokinin-B/gastrin receptor and the 1.8-kb human (h) HDC-luciferase (luc) construct were cotransfected with constructs expressing c-fos and c-jun. Overexpression of c-fos and c-jun activated the HDC promoter in a dose-dependent fashion in 1.8-kb hHDC-luc/AGS-B cells as well as in transfected F9 embryonal carcinoma cells, which lack endogenous AP-1 activity. PMA was unable to activate the HDC promoter in F9 cells, which were not transfected with c-fos and c-jun. Gastrin stimulation increased c-fos and c-jun mRNA abundance and AP-1-dependent transcriptional activity, as assessed by a reporter construct in which the CAT reporter gene is under the control of a 12-O-tetradecanoylphorbol-13-acetate response element multimer. Gastrin- stimulated HDC promoter activity was blocked by transfection of c-fos antisense and dominant negative c-jun expression constructs. Finally, overexpression of c-fos and c-jun activated the hHDC promoter through a downstream cis-acting element (gastrin response element), which does not bind AP-1. In conclusion, activation of AP-1 is essential for gastrin-stimulated HDC transcription, but the mechanism appears to be indirect.