Fig 2: HCP5 and BIRC3 shared a common miR‐219a‐5p binding site. A, Bioinformatics analysis revealed that HCP5 and BIRC3 shared a common miR‐219a‐5p binding site. B, MiR‐219a‐5p expression was lower in TNBC cell lines than in normal breast epithelial cell line MCF‐10A and other breast cancer cell lines. * P < 0.05 and ** P < 0.01. Two‐sided Student's t test; n = 3. C, A total of 58 basal‐like cases from TCGA database were enrolled and analyzed by Pearson correlation coefficient. The correlation between HCP5 and BIRC3 was positive in TNBC patients. And the correlations between miR‐219a‐5p and HCP5 or miR‐219a‐5p and BIRC3 were all negative. D, Luciferase activity in HEK293T cells cotransfected with miR‐219a‐5p mimics and luciferase reporters containing control vector, plasmids HCP5‐wt, HCP5‐mut, BIRC3‐wt, and BIRC3‐mut. MiR‐219a‐5p mimics reduced the luciferase activity of HCP5‐wt or BIRC3‐wt reporter vector but not that of HCP5‐mut or BIRC3‐mut reporter vector. * P < 0.05, two‐sided Student's t test; n = 3. E, QPCR was used to detect HCP5 in the sample pulled down by biotinylated miR‐219a‐5p. And qPCR was used to detect miR‐219a‐5p in the sample pulled down by biotinylated HCP5 probe. (n = 3, each group). ** P < 0.01

Fig 3: The rescue effects of miR‐219a‐5p and BIRC3 on breast cancer cells proliferation, migration and invasion. A, CCK8 assay to evaluate the rescue effect of miR‐219a‐5p inhibitor and BIRC3 on MDA‐MB‐468 cells proliferation after HCP5 knockdown and the rescue effect of miR‐219a‐5p mimics and BIRC3 siRNA on MDA‐MB‐231 cells proliferation after HCP5 overexpression. B, Transwell assay to detect the rescue effect of miR‐219a‐5p and BIRC3 on MDA‐MB‐468 or MDA‐MB‐231 cells migration and invasion after HCP5 knockdown or overexpression. * P < 0.05 and ** P < 0.01, compared with control group. Two‐sided Student's t test; n = 3

Fig 4: Knockdown of HCP5 activated apoptosis pathway. A and B, Representative picture of antibody array showed an obviously decreased expression of BIRC3 and increased expression of caspase‐3, IGFBP‐3 and TGF‐beta were obtained in HCP5 stable knockdown MDA‐MB‐231 cells. * P < 0.05, two‐sided Student's t test; n = 3. C, Western blot showed that the protein expression of BIRC3 was decreased while caspase‐3 was increased in HCP5 knockdown MDA‐MB‐231 and MDA‐MB‐468 cells