Abstract: Objective·To investigate the effects of deSUMOylation of sirtuin 3（SIRT3） on the proliferation and chemotherapeutic drug resistance in breast cancer cells. Methods·In order to construct the MFC7-SIRT3 KO cell line, the CRISPR-Cas9 plasmid pX330-sgRNA targeting SIRT3 gene was designed. Then, this cell line was infected with SIRT3 K288 R（sumoylation modification site mutant）, SIRT3 WT（wild type） or Vector retrovirus to establish the SIRT3 SUMOylation site mutation and control cell lines. Cell counting and microscopic observation were used to determine the changes in tumor cell number and morphology under the same incubation condition. To detect the chemotherapeutic drug resistance of SIRT3 K288 R and the control cells, these cells were treated with different concentrations of adriamycin（ADM） for 24 h, 48 h and 72 h. Results·The MFC7-SIRT3 KO cell line was constructed successfully, and then SIRT3 K288 R, SIRT3 WT and Vector cell lines were established. The cell growth curves showed that the growth rate of SIRT3 K288 R cells was significantly slower than those of SIRT3 WT and Vector cells under the same incubation condition（P=0.000）. This phenotype was also observed under the microscope. The diameter of non-adherent breast cancer cell clumps of SIRT3 K288 R cells was smaller than those of the control cells. ADM resistance experiment showed that the activity of SIRT3 K288 R cells was significantly higher than those of Vector and SIRT3 WT cells treated with different concentrations of ADM（1.25 μg/mL, 2.5 μg/mL, 5 μg/mL and 10 μg/mL） for 24 h, 48 h and 72 h（P<0.05）, and the half maximal inhibitory concentration（IC50） of ADM in the SIRT3 K288 R cells was higher than those in the control cells. Conclusion·The SIRT3 SUMOylation deficiency inhibits the proliferation of breast cancer cells MCF7, while increases the drug resistance to ADM.

Key words: sirtuin 3（SIRT3）, SUMOylation, breast cancer, adriamycin（ADM）, drug resistance