Role Of Pygopus2and FoxO1Activation In MDR1Expression In Breast Cancer Cells

【Background and Objective】 Breast cancer is a serious threat to women’slives and health. The incidence of breast cancer in the world has increased year byyear. The main reason of treatment failure attributed to tumor cells resistance.Drugresistance is derived from the MDR1gene overexpressed (multidrug resistance1).MDR1gene can activate a variety of different kinds of mechanisms, leading to cellsresistance. Wnt signaling pathway is a highly conserved which is widely exists ineukaryotic cells. It is involved in early embryonic development, cells differentiation,proliferation and growth regulation. It is found that Wnt signaling pathway regulatesthe expression of MDR1in breast cancer cells. Pygopus2(Pygo2) is one of the maineffect proteins in Wnt signaling pathways. Pygopus2can promote β-catenin toraise the transcriptional activation of Wnt target gene and participate in the occurrenceand development of a variety of human diseases, especially tumor diseases. Therefore,Pygopus2, for breast cancer, has certain research value. FoxO1(forkhead boxtranscription factor O1, FoxO1) can combine FoxO binding sites on MDR1promoter,then has the effect on the transcriptional regulation. FoxO through acombination of β-catenin, and then to the inhibition of Wnt signaling pathway. Toinvestigate the roles of Pygopus2, a key protein in Wnt signaling pathway, regulatethe MDR1gene expression in breast cancer cells, and reveal possibility ofPygopus2to be become a treatment target and detection index in the breast cancer.Further, through the building FoxO1fragments, it is found that FoxO1associated withexpression of Pygopus2and MDR1.【Methods】 TO structure the dnFoxO1-A, dnFoxO1-B, dnFoxO1-Cplasmids.ForLentiviruses transfection, pLL3.7-hPygo2-KD、 pGL3.3-contol、HA-hPygo2、Pcmv-HA、dnTCF4、dnFoxO1are respectively tansfected into MCF-7and MCF/ADRcells. Infection efficiency are obtained by the expression of GFP, and maintained as a pool population. Expression of pygopus2and MDR1are detected by Realtime-PCRand Western bloting.【Results】1.Western bloting ing and Realtime-PCR have been used todemonstrate that Pygopus2and MDR1are both expressed in MCF-7cells andMCF/ADR cells. The expression level of Pygopus2in MCF/ADR cells issignificantly higher than in MCF-7cells.2. By lentiviral vectors overexpressed Pygopus2, MDR1expression is detectedhigher than untransfected; while, the expression of MDR1is lower when Pygopus2isknocked down.3. Morever, dnTCF4, dnFoxO1plasmids have been constructed in the experiment.HA-pygo2, dnTCF4, and dnFoxO1plasmids are been cotransfected in MCF-7celllines. Pygopus2can both bind at the FoxO-binding site and the nearestTCF/LEF-binding site to transactive the expression of the MDR1. Pygopus2mightthrough β-catenin/TCF in Wnt signaling pathway and β-catenin/FoxO in Wntsignaling pathway regulate MDR1gene expression, resulting in increased activity ofWnt signaling.【Conclutions】1. It is a correlation between Pygopus2expression and multidrugresistance in breast cancer.2. Pygopus2might regulate the expression of MDR1. There is correlation between theexpression of Pygopus2and MDR1in the breast cancer cell lines. The MDR1bothmRNA and protein are increased or decrease with Pygopus2changed.3. It is a relationship between Pygopus2and TCF/LEF and FoxO1. Pygopus2mightthrough β-catenin/TCF and β-catenin/FoxO in Wnt signaling pathway involved intranscriptional regulation of MDR1in the WNT signal.