To investigate the effect of circRNA_0044556 on the resistance of triple-negative breast cancer (TNBC) to paclitaxel (PTX) and the mechanism of drug resistance.

PTX resistant TNBC cells (MDA-MB-231/PTX) were obtained by exposing the human TNBC cell (MDA-MB-231) to increasing concentrations of PTX. MDA-MB-231 and MDA-MB-231/PTX cells in logarithmic growth phase were treated with circRNA_0044556 short hairpin RNA (sh-circRNA_0044556) and negative control (sh-NC), respectively. The groups were finally divided into MDA-MB-231-NC, MDA-MB-231-circRNA_0044556, MDA-MB-231/PTX-NC and MDA-MB-231/PTX-circRNA_0044556 groups. The expression level of circRNA_0044556 in cells was determined by real-time quantitative polymerase chain reaction (RT-qPCR); methyl thiazolyl tetrazolium assay and colony formation assay were used to observe cell proliferation; flow cytometry was used to observe cell apoptosisand; Western blot was used to observe the expression of cell proliferation and apoptosis-related proteins.

The relative expression levels of circRNA_0044556 in MDA-MB-231/PTX, MDA-MB-231 and MCF-10A cells were 6.08±0.59, 3.36±0.11 and 1.00±0.02, respectively, and the differences were statistically significant (all P<0.001). Proliferation rates of MDA-MB-231-NC and MDA-MB-231-circRNA_0044556 groups were (100.00±0.84)% and (54.38±1.20)%; the apoptosis rates were (2.41±0.34)% and (21.65±0.29)%, respectively, and the differences were statistically significant (all P<0.001). The proliferation rates of MDA-MB-231/PTX-NC and MDA-MB-231/PTX-circRNA_0044556 groups were (112.29±1.19)% and (61.33±1.24)%; the apoptosis rates were (2.08±0.07)% and (14.38±0.16)%, respectively, the differences were all statistically significant (all P<0.001). The relative protein expression level of Ki-67 in MDA-MB-231-NC and MDA-MB-231-circRNA_0044556 groups were 1.00±0.02 and 0.67±0.02; the relative protein expression of Bcl-2-associated X protein (Bax) were 1.00±0.02 and 1.46±0.03; and the differences were statistically significant (all P<0.05). The relative relative protein expression levels of Ki-67 in MDA-MB-231/PTX-NC group and MDA-MB-231/PTX-circRNA_0044556 group were 1.00±0.03 and 0.81±0.01, respectively; the relative expression levels of Bax protein were 1.00±0.02 and 1.55±0.02, respectively; the relative expression levels of Bcl-2 protein were 1.00±0.03 and 0.79±0.01, respectively. The above indexes in MDA-MB-231/PTX-NC group were significantly different from those in MDA-MB-231/PTX-circRNA_0044556 group (all P<0.05).

Knocking down the expression of circRNA_0044556 can inhibit the malignant progression and PTX resistance of TNBC cells.