Abstract
Doxorubicin also termed adriamycin has been applied in the treatments of various malignant cancers. Critical concerns of using this drug in chemotherapy are its fatal cardiac toxicity and resistance in cancers. Many therapeutic chemicals possess the ability to activate the p38 mitogen-activated protein kinase (MAPK) signaling and thereby affect the fate of cellular survival or apoptosis. Our recent studies in a non-small cell lung carcinoma cell line CL3 indicate that the activated p38 MAPK may counteract apoptosis after doxorubicin treatment. In this thesis, I continued to investigate whether the p38 MAPK signaling regulates caspase-3 activation through linkage to Bcl-2 and p53 in CL3 cells. Immunoblot analysis showed that doxorubicin could activate the p38 MAPK signaling during exposure for 4-12 h with a peak level at 8 h, yet the signaling disappears after a 24 h treatment. Doxorubicin could induce the amounts of cleaved caspase-3 and also the anti-apoptotic protein Bcl-2. By using immuno-kinase assay, I found that SB202190 could block the kinase activity of p38 MAPK and significantly enhanced the caspase-3 induction by doxorubicin. Similarly, depletion of p38□ using specific small interfering RNA (si-p38□) further confirmed that p38 MAPK is necessary for preventing caspase-3 induction and increasing Bcl-2 by doxorubicin in CL3 cells. Conversely, depletion of Bcl-2 could further enhance the activation of p38 MAPK by doxorubicin with limitation to increase caspase-3 activation. Furthermore, doxorubicin significantly induced the level of tumor suppressor p53 that could be lowered by SB202190 or si-p38□ but not by depletion of Bcl-2. Knockdown of p53 significantly reduced the doxorubicin-induced caspase-3, Bcl-2 and p38 MAPK activation. In summary, in doxorubicin-treated CL3 cells p38 MAPK may facilitate Bcl-2 to prevent caspase-3 induction and thus assists the survival of cells; however, p38 MAPK may also regulate p53 induction to promote apoptosis. This thesis reveals the crosstalk among p38 MAPK, Bcl-2, and p53 in the regulation of cellular survival or apoptosis following doxorubicin that may provide a novel aspect on improving the efficacy of this drug during chemotherapy.