Overexpressed EGFR could activate specifically and persistently STAT3
after the decrease TGF-beta signaling pathway . The key contribution of the present study is to provide a link between signaling via LMP1/EGFR and LMP1/STAT3, which is consistent with the previous learn more findings that EBV LMP1 could promote the expression of EGFR [58, 59]. The mechanism by which EBV LMP1 induces EGFR and STAT3 to enhance the promoter activity and expression of cyclin D1 involves physical and functional interaction between EGFR and STAT3. This observation is in agreement with other reports that nuclear EGFR interacts with transcription factors, such as STAT3, E2F1, STAT5 and TIF2 to induce the expression of some target genes in various cancers [31, 40, 60–63]. Nuclear EGFR-targeted genes including cyclin D1 [54, 64], iNOS, B-Myb, Aurora A and COX-2, have
been reported, yet these studies did not support cyclin D1 as the target gene co-regulated find more by EGFR and other transcription factors after the infection of EBV, such as in the work of EGFR and STAT3 co-affecting on iNOS and STAT1 in breast cancer [31, 57]. Together, these findings suggest the EGFR-STAT3 axis signaling pathway is critical in regulating cellular transcriptional and biologic properties in different carcinomas in response to diverse carcinogens such as virus infection. Our previous studies reported EBV LMP1 induces in both expression and phosphorylation of EGFR in a dose-dependent manner [21, 45], and Leukotriene-A4 hydrolase other authors demonstrated EGFR that accumulated in the nucleus of breast carcinoma cell lines and esophageal cancer tissues was highly tyrosine-phosphorylated [54, 65]. Meanwhile, we found EBV LMP1 expressing cells exhibited more nuclear accumulation of Tyr 705-phophorylated STAT3 (pY-STAT3) [35, 45]. EGFR physically interacts
and functionally cooperates with STAT3 at both the cytoplasmic and nuclear levels. As reported, EGFR and phosphorylated STAT3 were strongly expressed in the nucleus of cancer cells in surgical and biopsy specimens of nasopharyngeal tissues from NPC patients in southern China [35, 66], suggesting that EGFR- and STAT3-dependent mechanisms are important for carcinogenesis. It has been shown that LMP1 induces cyclin D1 expression through EGFR in NPC cells . The present study show that the promoter activity and mRNA expression level of cyclin D1 in LMP1-expressing cells could be decreased by co-transfecting the plasmids of mutated EGFR/STAT3 or siRNA for EGFR and siSTAT3. However, we did not find the cooperative effect of siEGFR and siSTAT3 at both mRNA and protein levels of cyclin D1. We provide the evidence showing cyclin D1 might be selleck screening library modulated by STAT3 induced by EBV LMP1, illustrating the importance of the JAK/STAT signaling pathway on EBV LMP1 induced cyclin D1 transcription and expression.