Fig 2: Expression of SPIN1 in breast cancer cells and tissues. a The Adriamycin resistant breast cancer MCF-7/ADM cells displayed greater resistance to Adriamycin than MCF-7 cells (IC50: 29.17 vs 1.179). b SPIN1 was highly expressed in Adriamycin resistant MCF-7/ADM cells, and metastatic MDA-MB-231 and MDA-MB-468 cells, compared with MCF-7 cells (*P < 0.05). c-e Drug-resistant (d) tissues displayed higher SPIN1 protein levels than drug-sensitive (c) tissues (e, P = 0.0020, scale bar = 50 µm). f Receiver operating characteristic (ROC) curve analysis showed that SPIN1 could significantly distinguish drug-resistant tissues from drug-sensitive tissues (area under the curve (AUC) = 0.7025, P = 0.002096). g Data from GEO datasets GSE22513 showed that SPIN1 was highly expressed in non-pCR patients compared to pCR (pathologic complete response) patients. h Data from GSE18728 showed that SPIN1 expression was higher in non-responders than responders. i Analysis of the GEO dataset METABRIC showed that high expression of SPIN1 predicted poorer survival of breast cancer patients

Fig 3: miR-148a-3p, miR-148b-3p and miR-152-3p directly targeted SPIN1 and increased chemosensitivity in breast cancer cells. a The 3’-UTR element of SPIN1 mRNA is partially complementary to miR-148a-3p, miR-148b-3p and miR-152-3p. b The relative luciferase activity was significantly reduced in the miR-148a/148b/152-3p overexpressing cells (*P < 0.05) and these effects could be abolished by mutation of SPIN1 3’-UTR. c-d The SPIN1 protein expression was clearly reduced after the transfection of miR-148a-3p, miR-148b-3p or miR-152-3p. e The expression levels of miR-148a-3p, miR-148b-3p and miR-152-3p were lower in MCF-7/ADM cells than that in MCF-7 cells. f-g Transfection of miR-148a-3p, miR-148b-3p, miR-152-3p, or cotransfection of these three miRNAs significantly increased the miRNAs levels. h-i miR-148a-3p, miR-148b-3p and miR-152-3p decreased Adriamycin resistance in MCF-7/ADM and MCF-7 cells. In MCF-7 cells, miR-148a-3p or miR-152-3p (Adriamycin = 0.1 µM and 1 µM), and miR-152-3p (Adriamycin = 10 µM) could significantly reduce cell viability, compared with the negative control (NC) group (*P < 0.05, t-test). In MCF-7/ADM cells, miR-148a-3p or miR-152-3p (Adriamycin = 0.1 µM), and miR-148a-3p, miR-148b-3p or miR-152-3p (Adriamycin = 1 µM and 10 µM) could significantly decrease cell viability compared with NC (*P < 0.05, t-test). j-l Data from MIRUMIR and miRpower showed that breast cancer patients with low expression of miR-148a, miR-148b or miR-152 had shorter survival time than those with high expression

Fig 4: SPIN1 increased breast cancer resistance to Adriamycin in vitro and in vivo. a SPIN1 overexpression plasmid transfection increased, whereas SPIN1 siRNA transfection decreased, SPIN1 mRNA expression in breast cancer cells. b, d Overexpression of SPIN1 enhanced chemoresistance in MCF-7/ADM and MCF-7 cells. c, e Downregulation of SPIN1 increased chemosensitivity in MCF-7/ADM and MCF-7 cells. f Tumors originating from MCF-7/ADM cells expressing miRNA against SPIN1 (SPIN1-low) were significantly smaller in size than those originating from control (SPIN1-high) cells (**P < 0.01, ***P < 0.001)

Fig 5: The expression of ABCB4, CYP2C8, UGT2B4 and UGT2B17 was upregulated by SPIN1 in breast cancer cells. a Candidate SPIN1 targets from microarray were presented as a heat map. b-c The mRNA expression levels of ABCB4, CYP2C8, UGT2B4, and UGT2B17 were decreased after SPIN1 siRNA transfection. Accordingly, overexpression of SPIN1 led to upregulation of ABCB4, CYP2C8, UGT2B4, and UGT2B17 mRNA expression levels. d-e Western blot analysis confirmed that overexpression of SPIN1 upregulated ABCB4, CYP2C8, UGT2B4, and UGT2B17 protein levels, however, SPIN1 downregulation decreased the expression levels of these proteins. f-i Data from PPISURV (ABCB4 and UGT2B4) and GOBO (CYP2C8 and UGT2B17) revealed that patients with high expression of ABCB4, CYP2C8, UGT2B4 or UGT2B17 had poorer survival than those with low expression