三阴性乳腺癌细胞对磷脂酰肌醇3激酶抑制剂产生抗药性的分子机制

Molecular mechanisms of resistance to phosphatidyl inositol 3-kinase inhibitors in triple-negative breast cancer cells

目的 探讨三阴性乳腺癌（TNBC）细胞对磷脂酰肌醇3激酶（PI3K）抑制剂产生抗药性的分子机制。方法 运用脂质体2000试剂盒将siFZD7、siWANT5B或siGSK3转染TNBC细胞HCC70，Western blot法测定WNT/β-连环蛋白（WNT/β-catenin）和磷脂酰肌醇3激酶/苏氨酸激酶/雷帕霉素靶蛋白（PI3K/AKT/mTOR）信号通路关键蛋白的表达。将PI3K/AKT/mTOR通路抑制剂作用TNBC细胞HCC70、雌激素受体（ER）阳性乳腺癌细胞MCF-7和人表皮生长因子受体2（HER2）阳性乳腺癌细胞SK-BR3，采用四甲基偶氮唑蓝（MTT）法检测细胞增殖抑制率，并计算半数抑制浓度（IC50）；Western blot和荧光素酶报告基因实验检测WNT/β-catenin和PI3K/AKT/mTOR信号通路的活性变化对乳腺癌细胞增殖的影响；免疫荧光实验检测β-catenin蛋白核转位。将BKM120处理的乳腺癌细胞皮下注入裸鼠体内，观察其致瘤能力，采用免疫组化法检测肿瘤组织中磷酸化肺耐药相关蛋白6（p-LRP6）、磷酸化eIF4E结合蛋白1（p-4EBP1）和β-catenin蛋白的表达。结果 siRNA转染的HCC70细胞中，卷曲蛋白7（FZD7）、细胞外因子5B （WANT5B）、糖原合成酶激酶3（GSK3）表达显著降低，WNT/β-catenin活性升高，PI3K/AKT/mTOR活性降低。PI3K/AKT/mTOR通路抑制剂能抑制MCF-7和SK-BR3细胞的增殖，GDC-094、BKM120、XL147、perifosine、everolimus、BEZ235对MCF-7细胞的IC50分别为0.46 mmol/L、1.44 mmol/L、4.34 mmol/L、11.35 μmol/L、53.71 μmol/L和12.87 μmol/L，对SK-BR3细胞的IC50分别为0.63 mmol/L、0.58 mmol/L、3.74 mmol/L、13.22 μmol/L、60.00 μmol/L和11.38 μmol/L。荧光素酶报告基因检测显示，经BKM120处理后，HCC70、MCF-7和SK-BR3细胞中的荧光素酶活性分别为1.75±0.05、1.13±0.02和0.43±0.01，对照组的荧光素酶活性为1.00±0.02，HCC70、SK-BR3细胞中的荧光素酶活性与对照组差异有统计学意义（P〈0.05）。BKM120能抑制mTOR的活性，提高WNT/β-catenin活性能解除BKM120对mTOR活性的抑制。BKM120能抑制MCF-7和SK-BR3细胞的体内致瘤能力，但对HCC70细胞的致瘤能力无影响。免疫组化检测显示，BKM120处理的HCC70细胞接种于裸鼠后，肿瘤组织中β-catenin蛋白发生核转位，p-LRP6蛋白表达增加，p-4EBP1蛋白表达无变化；BKM120处理的MCF-7细胞接种于裸鼠后，肿瘤组织中β-catenin蛋白未发生核转位，p-LRP6和p-4EBP1蛋白表达降低。结论 HCC70细胞对PI3K抑制剂具有抗药性，WNT/β-catenin信号通路可调节PI3K/AKT/mTOR信号通路，从而诱导TNBC细胞对PI3K抑制剂的抗药性。

Objective To explore the molecular mechanisms of resistance to phosphatidyl inositol 3- kinase （PI3K） inhibitors in triple-negative breast cancer （TNBC） cells. Methods HCC70 cells （TNBC） were transfected with siFZD7, siWANT5B or siGSK3 using lipofeetamine 2000 transfection reagent. The expression levels of key proteins of WNT/β-catenin and PI3K/AKT/mTOR pathways were determined by Western blot analysis. After HCC70, MCF-7 （ER-positive） and SK-BR3 （HER2-positive） cells were treated with PI3K/AKT/mTOR inhibitors, the inhibition rates of cell proliferation were measured by MTT assay, and half maximal inhibitory concentrations （ IC50 ） were calculated. The altered activities of WNT/β- eatenin and PI3K/AKT/mTOR proteins were detected by Western blot and luciferase report gene assay, respectively. The nuclear translocation of β-catenin protein was examined by immunofluorescence assay. Xenograft nude mouse model was used to evaluate the tumorigenicity of breast cancer cells treated with BKM120 in vivo. The expression levels of p-LRP6, p-4EBP1 and β-catenin proteins in the tumor tissues were determined by immunohistochemical staining. Results The expression levels of FZD7, WANT5B and GSK3 proteins were significantly reduced in the HCC70 cells transfected with the target siRNAs. Meanwhile, the activity of WNT/β-catenin was enhanced and PI3K/AKT/mTOR pathway was inhibited. PI3K/AKT/ mTOR inhibitors suppressed MCF-7 and SK-BR3 cell proliferation. The IC50 of GDC-094, BKMI20, XL147, perifosine, everolimus, and BEZ235 in MCF-7 cells were 0.46 mmol/L, 1.44 mmol/L, 4.34 mmol/L, 11.35 μmol/L, 53.71 μmol/L and 12.87 μmol/L respectively, and 0.63 mmol/L, 0.58 mmol/L, 3.74 mmol/L, 13.22 μmol/L, 60.00 μmoL/L and 11.38 μmol/L in the SK-BR3 cells, respectively. The results of luciferase report gene assay showed that the luciferase activities in HCC70, MCF-7 and SK-BR3 cells treated with BKM120 were 1.75±0.05, 1.13±0.02 and 0.43±0.01, respectively. The luciferase activities in HCC70 and SK-BR3 cells were significantly different from that of the control cells （ 1.00±0.02, P 〈 0.05 ）. The immunohistoehemical analysis showed that BKMI20 inhibited mTOR activity, and the enhanced WNT/β- catenin activity reversed the phenotype of inhibitory mTOR induced by BKM120. BKM120 suppressed the tumorigenic ability of MCF-7 and SK-BR3 cells in vivo, but had no effect on cultured HCC70 cells. The immunohistoehemieal analysis showed nuclear transloeation of β-catenin protein and increased expression level of p-LRP-6 protein in transplanted tumor tissues from HCC70 cells treated with BKM120, increased the level of p-LRP-6 protein, and no changes of p-4EBP1 protein expression. However, no nuclear translocation of β-catenin protein and no decrease of p-LRP6 and p-4EBP1 protein levels in the transplanted tumor tissue of MCF-7 cells after treatment with BKM120. Conclusions The triple-negative breast cancer HCC70 cells have drugs-resistance to PI3K inhibitors. The WNT/β-catenin signaling pathway may regulate the PI3K/ AKT/mTOR pathway, therefore, inducing the drng-resistance of TNBC cells to PI3K inhibitors.