Data from our in vitro studies using

Data from our in vitro studies using BEAS-2B cells showed a biphasic response of cells to NNK. The initial phase of decrease in CRM1 expression in NNK-exposed cells was observed in our previous study. In this study, we further showed that p-p53 (Thr55) expression was also decreased during this initial phase that may correspond to an adaptive response for cellular repair of NNK-induced DNA damage. Indeed, we have previously observed that following the exposure of BEAS-2B cells with NNK there was an accumulation of p53 in the nucleus and activation of p21 that is important for the process of GSK 0660 arrest to allow repair of DNA damage. Therefore, decrease in both CRM1 and p-p53 at Thr55 would lead to a decrease in export of p53 and a nuclear accumulation of p53 during the early phase of NNK exposure. Different from this early phase of cellular response to the tobacco carcinogen NNK, in which CRM1 was decreased and concomitantly p53 accumulated in the nucleus probably as a result of an adaptive response to DNA damage repair, we further demonstrated in this study that in the later stage of NNK exposure, there were increased expression levels of CRM1 and p-p53 at Thr55 in both BEAS-2BNNK cells and lung tumors. It has been proposed that a shared complex regulatory loop may exist between CRM1 and p53, and p53 could repress CRM1 promoter activity by interfering with the transcription factor, nuclear factor Y. Although our results suggest that NNK-mediated p53 phosphorylation at Thr55 works in parallel with CRM1 expression not only in early phase of NNK exposure but also in NNK-induced cellular transformation, the underlining mechanisms are not clear. On the other hand, the data from our transfection experiments indicate that exogenous CRM1 modulation by either overexpression in BEAS-2B or knockdown in A549 did not significantly alter expression of p-p53 at Thr55 (data not shown). Therefore, p53 may directly affect CRM1 in NNK-induced carcinogenesis but not vice versa, and further study is needed to elucidate this possibility. Cisplatin is commonly used to treat various types of cancers, including lung cancer. In our study, significant alterations in the expression of genes from protein kinases, cell cycle, transcription factors, and apoptosis were found in A549 cells treated with cisplatin. However, drug resistance in cisplatin-containing regimens is a major issue that prevents better response rates. As cisplatin constitutes a major therapeutic option in clinical settings, the development of chemosensitization strategies for cisplatin has important clinical implications. In this study, blocking CRM1 expression significantly improves cancer cell sensitization to Cis as revealed by the fact that the drug was more potent in A549CRM1- cells than in A549 cells and that CRM1 inhibition by a co-treatment with Cis + LMB further improved the efficacy of cisplatin in suppressing lung cancer cell proliferation. Thus, combined chemotherapy could be an effective and clinically practical strategy for interfering with chemoresistance. Genes, such as survivin, BAX, BCL2, p53, NF-κB, and ERBB2 are frequently involved in the pathways that sustain cisplatin resistance., In lines with these findings, we observed in this study an increased expression of NF-κB after treatment with Cisplatin alone while a decreased NF-kB expression in the Cis + LMB treatment. Moreover, p21 and survivin are well known to play a critical role in cell cycle and survival signaling., Accordingly, we observed a significant dose-dependent increase in p21 and decrease in survivin expression in cells treated with Cis alone and a more pronounced decrease in survivin in Cis + LMB, compared with Cis treatment alone. In fact, NF-κB is a transcription factor that regulates the expression of numerous genes that are critical for survival, for instance, survivin. NF-κB could be activated by various stimuli such as proinflammatory cytokines, cellular stress, as well as chemotherapeutic agents. Therefore, the inhibition of NF-κB by Cis + LMB leading to a further decrease in survivin compared with Cis alone could be partially responsible for the synergistic effect in A549 lung cancer cells. Finally, the observed changes of other genes such as RHOA, GRB2, and PARP2 in cells treated with Cis + LMB, compared with cells treated with Cis alone, could result in enhancing the sensitization of A549 cells to Cis + LMB treatment on cell proliferation.44, 45, 46