To further confirm that both EGFR and STAT3 may be involved in the cyclin D1 protein, we detected the cyclin D1 protein level after we knocked down EGFR or STAT3 with siRNA. Data in Figure  6C showed that knockdown of EGFR and STAT3 with siRNA decreased the cyclin D1 protein level in CNE1-LMP1 cells. To further address how EGFR or STAT3 affects the cell cycle, we performed FACS analysis on the CNE1-LMP1 cells after knockdown of EGFR, STAT3 or Selleck Liproxstatin-1 both. Data in Figure  6D indicated that the depletion of EGFR, STAT3 or both proteins altered the cell cycle distribution especially at S phase with the stimulation of LMP1. Taken together, these findings demonstrate that both

EGFR and STAT3 are essential for cyclin D1 expression in the presence of LMP1. Figure 6 Cyclin D1 expression is reduced in CNE1-LMP1 cells after treatment with EGFR siRNA and STAT3 siRNA. (A) Dual luciferase-reporter assays were performed in CNE1-LMP1 cells after co-transfection with either control siRNA (siControl), EGFR siRNA (siEGFR), or STAT3 siRNA (siSTAT3) in addition to cyclin D1 promoter-reporter constructs and a Renilla AL3818 luciferase transfection control plasmid. Temozolomide clinical trial Firefly luciferase was measured and normalized to Renilla luciferase activity. The fold change in cyclin D1 expression by the indicated siRNA is displayed in each case. The control siRNA served as a non-targeting control. (mean ± SD, n =3, *p < 0.05)

(B) The cells were incubated with medium containing the indicated 6-phosphogluconolactonase siRNAs for 72 h. Total RNA was isolated from the cells and subjected to real-time PCR, using specific primers designed to amplify cyclin D1. β-actin mRNA served as an internal control. (mean ± SD, n =3, *p < 0.05, **p < 0.01). (C) Western Blot was performed in CNE1-LMP1 cells after co-transfection with the indicated siRNAs for 72 h. β-actin was served as an internal control. (D) FACS was performed

in CNE1 and CNE1-LMP1 cells after co-transfection with the indicated siRNAs for 72 h. The data are presented from three independent experiments. Discussion cyclin D1 over-expression is important in the development and progression of numerous cancers [48]. Regulation of the cyclin D1 protein level is one of the critical aspects in cell proliferation and tumor development [49], indicating that cyclin D1 may be regarded as a therapeutic target in cancer [50]. Cyclin D1 is upregulated expression in NPC [51]. Overexpressed cyclin D1 in NPC increases the risk of tumor formation and local disease recurrence [52]. Although cyclin D1 is known to be a target gene of EGFR and STAT3 [46, 53–56], its transcriptional regulation remains elusive after the infection of virus. Our previous study reported that LMP1 encoded by EBV could regulate the nuclear accumulation of EGFR and that nuclear EGFR could bind to the promoters of cyclin D1 and cyclin E to accelerate the G1/S phase transition.