ObjectiveTo investigate the molecular mechanisms of plasmacytoma variant translocation 1 (PVT1) downregulation on the cell proliferation of nasopharyngeal carcinoma (NPC).MethodsRecombinant lentivirus that encoded PVT1 shRNA (LV/shRNA PVT1) was prepared. The NPC C6661 cells were transduced with LV/shRNA PVT1 and then the expression of Smad4 was detected. Twentyfour hours after transduction, the C6661 cells were transfected with Smad4 siRNA or control siRNA following the manufacturer’s protocol. And then cytometry, tetramethylazolazolam (MTT) method, and flow cytometry were adopted to detect the effects of silence of Smad4 on the cell growth and cell cycle of PVT1induced C6661 cells as well as the expressions of cell cycle regulators.ResultsThe PVT1 expression was reduced while the Smad4 expression was increased after LV/shRNA PVT1 transduction. Transfection of Smad4 siRNA into C6661 cells reduced the level of Smad4 expression and caused a significant blockage on the downregulation of PVT1induced cell growth inhibition. Compared with the control cells, the number of S and G2phase cells was significantly increased and that of G1phase cells was reduced with significant increase in the expression of CDK4, CDK6 and cmyc in the PVT1induced C6661 cells.ConclusionDownregulation of PVT1 can inhibit the cell growth and increase the expression of Smad4. Silence of Smad4 may block the PVT1induced cell growth inhibition. All these suggest that Smad4 maybe a downstream target gene of PVT1 and downregulation of PVT1 expression may inhibit the cell growth via Smad4.