Objective To investigate the role of retinoic acid receptor β (RARβ) in mediating inhibitory effect of all-trans retinoic acid (ATRA) on activator protein-1 (AP-1) activity in gastric cancer cells. Methods Transient...
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Objective To investigate the role of retinoic acid receptor β (RARβ) in mediating inhibitory effect of all-trans retinoic acid (ATRA) on activator protein-1 (AP-1) activity in gastric cancer cells. Methods Transient transfection and chloramphenicol acetyltransferase (CAT) assay, Northern blot, gene transfection, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, and anchorage-independent growth assay were *** Transient transfection of RARβ expression vector into MKN-45 cells resulted in the RARβ 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 RARβ expression vector into MKN-45 cells, AP-1 activity was also obviously repressed. The inhibitory effect, again, was RARβ-concentration-dependent. The stable transfection of the RARβ gene into MKN-45 cells led to cell growth inhibition and colony formation inhibition by ATRA. Furthermore, Cotransfection of both RARβ/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 RARβ/ligand binding domain (LBD), the inhibition was significantly enhanced by ATRA. Conclusion RARβ might be required for anti-AP-1 activity, and contribute to growth inhibition of gastric cancer cells by ATRA.
Objective To investigate the mechanism of all-trans retinoic acid (ATRA) on the regulation of the cell cycle in gastric cancer cells. Methods The protein level was detected by Western blot. Immunoprecipitation was u...
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Objective To investigate the mechanism of all-trans retinoic acid (ATRA) on the regulation of the cell cycle in gastric cancer cells. Methods The protein level was detected by Western blot. Immunoprecipitation was used in protein kinase activity determination. Cell growth and cell cycle phase were examined by MTT assay and flow-cytometric analysis, *** ATRA could effectively induce G0/G1 arrest and inhibit cell growth in certain human gastric cancer cell lines. ATRA might induce p21WAF1/CIP1 expression in ATRA-sensitive cell lines through p53-dependent and p53-independent pathways. Induction of p21WAF1/CIP1 caused decrease in CDK4 and CDK2 activities independent of CDK4 and CDK2 protein expression levels. In addition, the dephosphorylated form of Rb protein increased because of the down-regulation of CDK4 and CDK2 activities by ATRA. Conclusions Growth inhibition on gastric cancer cells by ATRA occurs through the regulation of relevant proteins leading to the arrest of cell cycle progression.
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