Abstract： Objective:To investigate the effect of MicroRNA (miR) -19b-3p on expression, proliferation and apoptosis activities of pancreatic cancer PANC-1 cells via targeting murine double microsome 4 (MDM4) , a proto-oncogene.Methods:The liposome transfection method was used to transfect the human PANC-1 cells with micrON rno-19b-3p (mimic group) , micrOFF mmu-miR-19b-3p inhibitor (suppresion group) and Lipofectamine 2000 (negative group) . Normally growing PANC-1 cells without special treatment were used as blank groups. The real-time quantitative PCR was used to detect the miR-19b-3p transcription level to determine the effect of transfection. MTT assay was used to detect cell proliferation activity at 24, 48 and 72 h after transfection. The contents of miR-19b-3p and MDM4 was detected by real-time quantitative PCR at 24, 48 and 72 h after transfection. Annexin V-FITC/PI dual staining was used to detect the apoptosis of PANC-1 cells 72 h after transfection. Western blotting was used to detect the expression of MDM4 protein in each group of PANC-1 cells at 72 h after transfection.Results:At 48 h after transfection, all four groups showed obvious green fluorescence, and the transfection efficiency of microRNA-19b-3p into PANC-1 cells was 72.1%. At 24, 48, and 72 h after transfection, the proliferation activity of PANC-1 cells, the expression levels of microRNA-19b-3p mRNA, FL-MDM4, and S-MDM4 in the mimic group were all higher than those in the blank group, negative group and the suppression group (all P<0.05) , and were the lowest in the suppression group compared with the blank group, negative group and mimic groups (all P<0.05) . There were no significant differences in cell proliferation activity and expression levels of microRNA-19b-3p mRNA, FL-MDM4, and S-MDM4 between the blank and negative groups (all P>0.05) . The PANC-1 cell proliferation activity ( r=0.629, 0.582, 0.524, 0.472) and expression levels of miR-19b-3p mRNA ( r=0.449, 0.475, 0.501, 0.399) , FL-MDM4 ( r=0.504, 0.423, 0.447, 0.431) , and S-MDM4 ( r=0.472, 0.428, 0.414, 0.408) in the blank, negative and mimic and suppression groups showed a time-correlated manner (all P<0.05) . At 72 h after transfection, the apoptosis level in the mimic group was lower those in the blank, negative group, and suppression groups [ (2.02±0.48) % vs (3.48±0.63) %, (3.52±0.52) %, and (8.23±0.82) %, all P<0.05], and that in the suppression group was higher than those in the blank, negative and mimic groups, with statistically significant differences (all P<0.05) . At 72 h after transfection, the expression level of MDM4 protein in the mimic group was higher than those in the blank, negative and suppression groups [ (1.162±0.114) vs (0.749±0.126) , (0.663±0.137) , and (0.347±0.092) , all P<0.05], and that in the suppression group was lower than those in the blank and negative groups, with statistically significant differences (all P<0.05) . Conclusion:miR-19b-3p may affect the expression of MDM4 and then the activity of p53 gene to promote the proliferation of pancreatic cancer, and therefore can be a new target for the treatment of pancreatic cancer.