Background: Nonsteroidal antiinflammatory drugs (NSAIDs) such as acetylsalicylic acid (ASA, aspirin) are well known chemotherapeutic agents of cancers; however, the signaling molecules involved remain unclear. The aim of this study is to investigate the possible existence of a putative p53-dependent pathway underlying the ASA-induced apoptosis in OC2 cells, a human oral cancer cell line. Materials and Methods: The MTT (methyl tetrazolium) assay was employed to quantify differences in cell viability. DNA ladder formation on agarose electrophoresis was used as apoptosis assay. The expression levels of several master regulatory molecules controlling various signal pathways were monitored using the immunoblotting techniques. Flow cytometry was used to confirm the effect of ASA on cell cycle. Patterns of changes in expression were scanned and analyzed using the NIH image 1.56 software. All the data were analyzed by ANOVA. Results: ASA reduced cell viability and presence of internucleosomal DNA fragmentation. In the meanwhile, phosphorylation of p53 at serine 15, accumulation of p53 and increased the expression of its downstream target genes, p21 and Bax induced by ASA. The expression of COX-2 was suppressed. Disruption of p53-MDM2 (murine double minute-2) complex formation resulted in increasing the expression of MDM2 60 kd cleavage fragment. Inhibited the activation of p42/p44 MAPK (mitogen-activated protein kinase ) by PD98059, a specific inhibitor of ERK (extracellular regulatory kinase), significantly decreased cell viability and enhanced the expression of p53 induced by ASA. The result of cell cycle analysis showed that ASA and PD98059 induced the cell cycle arrested at G0/G1 phase and resulted in apoptosis. Conclusion: NSAIDs inhibit cyclooxygenase is not the only or even the most important mechanism of inhibition. Our study presents evidences that activation of p53 signaling involved in apoptosis induced by ASA. Furthermore, the apoptotic effect was enhanced by blocking the activation of p42/p44 MAPK in response to treatment with ASA, thus indicating a negative role for p42/p44 MAPK.
