Fig 2: PTPRZ1 activated the NF-?B pathway in breast cancer cells following treatment with Dox. a RT-PCR analyses of the expression of NF-?B pathway components, including IKKa, IKKß, I?Ba, p65 and p50, in MDA-MB-231 cells transfected with PTPRZ1, siPTPRZ1 or scrambled siRNA (vector) and then treated with Dox (1 µg/ml) for 24 h are shown, n = 3, Student’s t-test, *p < 0.05, **p < 0.01, ***p < 0.001. b The phosphorylation of NF-?B pathway components was detected by western blotting; NF-?B activation was investigated by assessing the phosphorylation of IKKa/ß (Ser176), I?Ba (Ser32) and p65(Ser536). c Proposed model for mechanisms of CDKN1A/PTN/PTPRZ1-induced chemoresistance in breast cancer cells

Fig 3: PTN/PTPRZ1 are involved in breast cancer cell chemoresistance. MDA-MB-231 cells, which were transfected with siPTPRZ1, PTPRZ1, or siPTN to regulate endogenous protein, or added exogenous protein (rhPTN) in the cell culture medium to increase PTN levels, were treated with different concentrations of Dox or DDP. a, b Cell viability was determined with a CCK8 assay. c Cell growth was measured by colony formation assays. The data are shown as the mean ± s.e.m. of three independent experiments. The statistical significance of the between-group differences was evaluated with a Student’s t-test, *p < 0.05, **p < 0.01, n.s. means not significant. d Apoptosis was measured by flow cytometry based on Annexin V/PI double staining. The data are shown as the mean ± s.e.m. of three independent experiments. The statistical significance of the between-group differences was evaluated with a Student’s t-test, *p < 0.05, **p < 0.01

Fig 4: Dox upregulated the expression of PTN and its receptor PTPRZ1 in breast cancer cells. a, b RT-PCR analyses of the expression of PTN and PTPRZ1 in the MCF-7/ADR, MCF-7, MDA-MB-231, HCC-1937, and MDA-MB-453 cell lines. The data are shown as the mean ± s.e.m., n = 5, **p < 0.01, Student’s t-test. Immunoblot analyses of the expression of PTN and PTPRZ1 in MDA-MB-231 cells treated with different concentrations of Dox (c), rhPTN (d), scrambled siRNA (siCtrl) or empty vector plasmid (vector) (e), and PTPRZ1 knockdown (siRNA) or overexpression (PTPRZ1) were performed. (f). The representative blots are shown in the upper panel, and the summary densitometry measurements are shown in the lower panel. Data are shown as the mean ± s.e.m., n = 5, *p < 0.05, ***p < 0.001, Student’s t-test. g The chemotherapy-driven increases in PTN and PTPRZ1 expression levels create a positive feedback loop. h Immunofluorescent staining for PTPRZ1 (in red) in MDA-MB-231 cells treated with Dox, rhPTN or Dox + rhPTN is shown

Fig 5: CDKN1A is transcriptionally regulated by Dox and affects the expression of PTN in breast cancer cells. a MDA-MB-231 cells were treated with Dox (1 μg/ml) or PBS for 24 h, and a heatmap of the 20 genes that showed the largest changes in gene expression between the two groups determined by microarray analysis is shown. b The correlation analyses of PTN and CDKN1A expression in breast cancer specimens with or without chemotherapy from the GEO database are shown, n = 69, Pearson’s r test. c The paired expression data of CDKN1A in breast cancer specimens before and after adjuvant chemotherapy were obtained from the GEO database, n = 69, t-test, ***p < 0.001. d, e, f Immunoblot analyses of the expression of CDKN1A, PTN, and PTPRZ1 in MDA-MB-231 cells undergoing treatment with Dox and knockdown or increasing the expression of CDKN1A by siRNA treatment or plasmid overexpression, respectively, are shown. Representative blots are shown in the upper panel, and summary densitometry measurements are shown in the lower panel. The data are shown as the mean ± s.e.m., n = 5, *p < 0.05, n.s. means not significant, Student’s t-test