OBJECTIVETo investigate the role of retinoic acid receptor beta (RARbeta) in mediating inhibitory effect of all-trans retinoic acid (ATRA) on activator protein-1 (AP-1) activity in gastric cancer cells.

METHODSTransient transfection and chloramphenicol acetyltransferase (CAT) assay, Nort hern blot, gene transfection, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, and anchorage independent growth assay were used.

RESULTSTransient transfection of RARbeta expression vector into MKN-45 cells resulted in the RARbeta concentration dependent repression of AP-1 activity induced by 12-o-tetradecanoylphorbol-13-acetate (TPA), regardless of the presence of ATRA. When the c-jun and c-fos expression vectors were cotransfected with the RARbeta expression vector into MKN-45 cells, AP-1 activity was also obviously repressed. The inhibitory effect, again, was RARbeta-concentration-dependent. The stable transfection of the RARbeta gene into MKN-45 cells led to cell growth inhibition and colony formation inhibition by ATRA. Furthermore, Cotransfection of both RARbeta/DNA binding domain (DBD) and reporter gene could not alter AP-1 activity, even in the presence of ATRA.However, when the cotransfection was substituted with the RARbeta/ligand binding domain (LBD), the inhibition was significantly enhanced by ATRA.

CONCLUSIONRARbeta might be required for anti-AP-1 activity, and contribute to growth inhibition of gastric cancer cells by ATRA.