Abstract: Objective The aim of this study was to investigate the effect of lncRNA NBAT1 on proliferation of human breast cancer cells by regulating the molecular axis of miR-3664-5p/Caspase 9.Methods The expression of lncRNA NBAT1 in breast cancer and normal breast tissues was compared by analyzing the TCGA(The Cancer Genome Atlas)database with online biological software.qRT-PCR was used to compare the expression of lncRNA NBAT1 in MCF-10A and MCF-7,MDA-MB-231 and MDA-MB-453 cells.Bioinformatics predicted the relationship between lncRNA NBAT1,miR-3664-5p,and Caspase 9,and further verified by the luciferase reporting system.lncRNA NBAT1 overexpression vectors were transfected into MCF-7 cells,RT-qPCR was used to detect the expression of lncRNA NBAT1,qPCR was used to detect the expression of miR-3664-5,and Western blot was used to detect the expression of Caspase 9 protein.The CCK-8 assay and clone formation test were used to detect the ability of cell proliferation.At the same time,lncRNA NBAT1 overexpression vector and mimics miR-3664-5p were transfected into MCF-7 cells,mimics miR-3664-5p was observed to alleviate lncRNA NBAT1′s ability to inhibit cell proliferation.Results The TCGA database analysis found that the expression of lncRNA NBAT1 in breast cancer tissues was significantly lower than that in normal tissues(P＜0.001).lncRNA NBAT1 was highest expressed in normal control MCF-10A cells(P＜0.001),low expressed in MDA-MB-231 and MDA-MB-453 cells(P＜0.001)and lowest expressed in MCF-7 cells(P＜0.001).It was predicted by bioinformatics that lncRNA NBAT1 could absorb miR-3664-5p,and Caspase 9 was the target gene of miR-3664-5p.These were further verified by the luciferase reporting system.LncRNA NBAT1 overexpression vectors were transfected into MCF-7 cells.The expression of lncRNA NBAT1 in the NBAT1 group was higher than that in the control group(P＜0.001),and the expression of miR-3664-5 was reduced in MCF-7 cells(P＜0.001).The expression of Caspase 9 protein in the NBAT1 group was higher than that in the control group(P＜0.001).The proliferative ability of MCF-7 cells in the NBAT1 group was lower than that of the control group(P＜0.001).At the same time,MCF-7 cells were transfected with lncRNA NBAT1 plasmids and mimics miR-3664-5p,mimics miR-3664-5p could alleviate the inhibitory effect of lncRNA NBAT1 on proliferation of MCF-7 cells(P＜0.001).Conclusion LncRNA NBAT1 can inhibit the proliferation of breast cancer cells by regulating the molecular axis of miR-3664-5p/Caspase 9,providing a new potential target for breast cancer treatment.

Key words: Breast cancer, Long non-coding RNAs, NBAT1, miR-3664-5p, Caspase 9, Proliferation