Figure 3.

STAT5a modulates chemoresistance in breast cancer by regulating the transcription of ABCB1. (A) Data from GSE87455 showed that the expression of ABCB1 was higher in the STAT5a-high group than in the STAT5a-low group in breast cancer, and the expression of STAT5a and ABCB1 was positively correlated. (B) Correlation between STAT5a expression and ABCB1 expression in breast cancer samples obtained from 67 patients. (C) Representative images of STAT5a and ABCB1 expression levels in breast cancer samples. (D, E) Representative images (D) and quantification (E) of the accumulation of DOX in MCF7/DOX cells transfected with scramble siRNA or STAT5a-targeting siRNA after treatment with DOX. (F) Expression levels of STAT5a and ABCB1 in MCF7 cells transfected with an empty vector or a STAT5a vector determined by Western blotting and MCF7/DOX cells transfected with scramble siRNA or STAT5a-targeting siRNA. (G, H) mRNA levels of STAT5a and ABCB1 in MCF7/DOX cells transfected with scramble siRNA or STAT5a-targeting siRNA (G) and in MCF7/DOX cells transfected with scramble siRNA or STAT5a-targeting siRNA (H) determined by qPCR. (I) Relative promoter activity in MCF7 cells transfected with the empty vector or STAT5a vector and in MCF7/DOX cells transfected with scramble siRNA or STAT5a-targeting siRNA. (J) Four pairs of primers were designed to detect sequences covering five predicted binding sites for STAT5a in the ABCB1 promoter region. (K) Binding between STAT5a and the ABCB1 promoter region in sequence 1 was determined by ChIP. (L) Levels of STAT5a and ABCB1 in MCF7 cells transfected with the indicated vector or siRNA and in MCF7/DOX cells transfected with the indicated targeting siRNA or vectors. (M, N) Survival rates and IC₅₀ of MCF7 (M) and MCF7/DOX (N) cells transfected with the indicated vector or siRNA after treatment with DOX for 48 h determined by a CCK8 assay. ns, p > 0.05; *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.