Ed cell proliferation in NSCLC cells and clinical specimens. With all findings taken together, we hypothesized that WT1 potentially plays an oncogenic role in promoting carcinogenesis and progression of NSCLC. WT1 was originally identified as a tumor suppressor gene in Wilm’s tumor, and was subsequently found to be overexpressed in a variety of solid tumors [19]. However, the relationship between expression and carcinogenesis of WT1 in NSCLC remains controversial. Oji et al. suggested that WT1 might disturb the growth and differentiation of normal lung cells and contribute to oncogenesis of lung cancer [11]. More recently, Hayashi S et al reported that low WT1 gene expression in NSCLC tumors was a negative prognostic sign and was also associated with lymph node metastasis [20]. Moreover, it was demonstrated that WT1 loss induced senescence and decreased proliferation of lung cancer cells downstream of oncogenic KRAS signalling [21].STAT3 is constitutively activated in many human tumors such as prostate, lung, brain, breast and pancreatic cancer [13,15,22,23]. The downstream genes including Title Loaded From File Cyclin D1, c-myc, and Bcl-xL of STAT3, are potentially up-regulated by phosphorylated STAT3. Cyclin D1 is a cell-cycle regulator that promotes cells from G1phase to S-phase, and phosphorylates pRb protein [24], which is a nuclear phosphoprotein that regulates cell growth in G1-phase. Hypophosphorylated pRb on S780 then releases E2F from an inhibitory complex and enables it to promote the transcription necessary for progression into late G1-phase and S-phase [24?6]. It has been reported that Cyclin D1 and cyclin-depended-kinase 4 (CDK4) phosphorylated pRb and that pRb lost its ability to bind to E2F [27]. Thus, when Cyclin D1 is up-regulated by STAT3 it can phosphorylate pRb and promote cell growth by releasing E2F. Rong et al has reported that the function of WT1 as tumor suppressor or oncogene was primarily dependent upon the activities of STAT3. Consequently when STAT3 was activated, WT1 functioned as a tumor suppressor, but when STAT3 was deactivated, WT1 functioned as an oncoprotein [18]. They also proposed that WT1 and STAT3 synergistically promoted cell proliferation by up-regulating genes such as Cyclin D1 and Bcl-xL. Based on these results, we hypothesized that WT1 could function as an oncogene in NSCLC. In this study, we demonstrated that WT1 was overexpressed in NSCLC tissues compared with adjacent tissues. WT1 exhibited an effect on the proliferation of NSCLC cells in vitro and vivo: overexpression of WT1 promoted cell growth whereas downregulation inhibited the proliferation of NSCLC cells. We also detected expression of STAT3 in NSCLC specimens and cells, in line with Fernandes et al who found STAT3 overexpressed in lung cancer tissues [23]. Our results Title Loaded From File showed that WT1 accelerated Sphase cell entry; thus, we assessed the cell cycle regulator genes such as Cyclin D1 and p-pRb and we found that the expression of Cyclin D1 and p-pRb was indeed up-regulated as shown in Figure 3D. Taking into consideration our results and the previous findings of Rong et al, we found that WT1 and STAT3 synergistically promote the growth of NSCLC cells by upregulating the cell cycle regulators Cyclin D1 and p-pRb. Additionally, we found that WT1 expression was associated both with lymph node metastasis and tumor stage. This result indicates that WT1 expression may be relevant to tumor invasion and metastasis. Epithelial to mesenchymal transition (EMT) is consid.Ed cell proliferation in NSCLC cells and clinical specimens. With all findings taken together, we hypothesized that WT1 potentially plays an oncogenic role in promoting carcinogenesis and progression of NSCLC. WT1 was originally identified as a tumor suppressor gene in Wilm’s tumor, and was subsequently found to be overexpressed in a variety of solid tumors [19]. However, the relationship between expression and carcinogenesis of WT1 in NSCLC remains controversial. Oji et al. suggested that WT1 might disturb the growth and differentiation of normal lung cells and contribute to oncogenesis of lung cancer [11]. More recently, Hayashi S et al reported that low WT1 gene expression in NSCLC tumors was a negative prognostic sign and was also associated with lymph node metastasis [20]. Moreover, it was demonstrated that WT1 loss induced senescence and decreased proliferation of lung cancer cells downstream of oncogenic KRAS signalling [21].STAT3 is constitutively activated in many human tumors such as prostate, lung, brain, breast and pancreatic cancer [13,15,22,23]. The downstream genes including Cyclin D1, c-myc, and Bcl-xL of STAT3, are potentially up-regulated by phosphorylated STAT3. Cyclin D1 is a cell-cycle regulator that promotes cells from G1phase to S-phase, and phosphorylates pRb protein [24], which is a nuclear phosphoprotein that regulates cell growth in G1-phase. Hypophosphorylated pRb on S780 then releases E2F from an inhibitory complex and enables it to promote the transcription necessary for progression into late G1-phase and S-phase [24?6]. It has been reported that Cyclin D1 and cyclin-depended-kinase 4 (CDK4) phosphorylated pRb and that pRb lost its ability to bind to E2F [27]. Thus, when Cyclin D1 is up-regulated by STAT3 it can phosphorylate pRb and promote cell growth by releasing E2F. Rong et al has reported that the function of WT1 as tumor suppressor or oncogene was primarily dependent upon the activities of STAT3. Consequently when STAT3 was activated, WT1 functioned as a tumor suppressor, but when STAT3 was deactivated, WT1 functioned as an oncoprotein [18]. They also proposed that WT1 and STAT3 synergistically promoted cell proliferation by up-regulating genes such as Cyclin D1 and Bcl-xL. Based on these results, we hypothesized that WT1 could function as an oncogene in NSCLC. In this study, we demonstrated that WT1 was overexpressed in NSCLC tissues compared with adjacent tissues. WT1 exhibited an effect on the proliferation of NSCLC cells in vitro and vivo: overexpression of WT1 promoted cell growth whereas downregulation inhibited the proliferation of NSCLC cells. We also detected expression of STAT3 in NSCLC specimens and cells, in line with Fernandes et al who found STAT3 overexpressed in lung cancer tissues [23]. Our results showed that WT1 accelerated Sphase cell entry; thus, we assessed the cell cycle regulator genes such as Cyclin D1 and p-pRb and we found that the expression of Cyclin D1 and p-pRb was indeed up-regulated as shown in Figure 3D. Taking into consideration our results and the previous findings of Rong et al, we found that WT1 and STAT3 synergistically promote the growth of NSCLC cells by upregulating the cell cycle regulators Cyclin D1 and p-pRb. Additionally, we found that WT1 expression was associated both with lymph node metastasis and tumor stage. This result indicates that WT1 expression may be relevant to tumor invasion and metastasis. Epithelial to mesenchymal transition (EMT) is consid.