Fig 2: Involvement of AURKB in the regulation of exocrine secretion and PTX efflux in breast cancer cells. a Transmission electron micrographs of exosomes derived from MDA-MB-231 and MDA-MB-231/PTX cells. b Detection of related marker proteins in exosomes using Western blot. c Histogram of the relative exosome concentrations of MDA-MB-231 and MDA-MB-231/PTX cells after measurement of the relative exosome concentrations of MDA-MB-231 and MDA-MB-231/PTX cells by nanoparticle tracking analysis (NTA) and normalization with the number of cells. d Detection of the relative exocrine concentration in MDA-MB-231/PTX cells treated with BIM and transfected with RAB27B expression plasmid for 24 h; the sphingomyelinase inhibitor GW4869 was used as a positive control of inhibiting exosome secretion. e Measurement of the content of PTX in exosomes by HPLC–MS after the extraction of exosomes from the same culture supernatant when MDA-MB-231/PTX were treated with BIM and transfected with RAB27B expression plasmid for 24 h, and then treated by PTX (0.5 µM) for 2 h

Fig 3: Correlation analysis of AURKB and RAB27B expression. a Correlation analysis between AURKB mRNA and RAB27B mRNA expression using online tool UALCAN to collect breast cancer data in TCGA. b, c Analysis of RAB27B mRNA and protein expression differences in breast cancer cells MDA-MB-231 and corresponding PTX-resistant MDA-MB-231/PTX cells using quantitative PCR and Western blot. d, e Analysis of the mRNA and protein expression of RAB27B using PCR and Western blot after the transfection with wild-type or mutant-type AURKB expression plasmids in 231/PTX-A cells with stable AURKB knockdown, and simultaneous treatment with DMSO or Bisindolylmaleimide I (1 µM) for 24 h. One-way ANOVA with Tukey post hoc analysis. *P < 0.05 and **P < 0.01

Fig 4: Analysis of the expression of other RAB-GTPases. (A)—RAB27B and RAB35 expressions were analyzed by RT-qPCR assays in both HCT-116 and U87-MG cell lines. RAB35 was not detected in the U87-MG cell line. The Mann–Whitney test was performed on three independent experiments; * p < 0.05; ** p < 0.01; *** p < 0.001. (B)—RAB27B and RAB35 expressions were assessed by Western blot in both HCT-116 and U87-MG cell lines. RAB35 failed to be detected in U87-MG. The Mann–Whitney test was performed in three independent experiments; ** p < 0.01; *** p < 0.001. (C)—RAB11 expression was analyzed by Western blot in both HCT-116 and U87-MG cell lines. The Mann–Whitney test was performed on three independent experiments.

Fig 5: Interaction between AURKB and RAB27B. a Detection of the interaction between AURKB and RAB27B by immunoprecipitation assay using DDK-labeled antibody after the transfection with wild-type or mutant-type AURKB expression plasmids in 231/PTX-A cells with stable AURKB knockdown. b Detection of the relative content of RAB27B protein at different time points after the transfection of 231/PTX-A with wild-type or mutant-type AURKB expression plasmid for 24 h, and subsequent treatment with Cycloheximide (100 µg/mL). c Quantification of RAB27B protein levels (normalized to ß-actin) at different time points. One-way ANOVA with Tukey post hoc analysis. *P < 0.05 and **P < 0.01