Herein, we report that c-Jun protein, a component of AP-1, was elevated in the carcinoma cells by tylophorine treatment and the c-Jun phosphorylation was mainly through activated JNK. Moreover, ectopically overexpressed c-Jun significantly facilitated G1 arrest in the presence of tylophorine analyzed by flow cytometry analysis. Ultimately, the participation of c-Jun in downregulated cyclin A2 by tylophorine in carcinoma cells was dissected by ChIP and element reporter assays. Upon increase in binding of c-Jun to the deregulation AP-1 site and decrease in binding to up-regulation ATF site in c-Jun promoter, the tylophorine elevated c-Jun downregulated cyclin A2 promoter activity and thus its expression thereby leading to G1 arrest. Further biochemical studies using pharmacological inhibitors and RNA silencing approaches demonstrated that tylophorine elevated the c-Jun protein level is mainly through two discrete prolonged signaling pathways: 1) a prolonged activation of NF-kB_PKC?_(MKK4)_JNK cascade to phosphorylate c-Jun and increase its stability; 2) a prolonged activated PI3K_PDK1_PP2A_eEF2 cascade to sustain eEF2 activity and thus the c-Jun protein translation.
