The means of three independent determinations ?s.d.To further evaluate
The means of three independent determinations ?s.d.To further evaluate the relative contribution of TCF transcription factor to the regulation of ABCB1 promoter activity, we performed transient transfection assays using K562 and Lucena cells with constructions containing TCF binding sites (Figure 9A). These constructions wereCorr et al. BMC Cancer 2012, 12:303 http://www.biomedcentral.com/1471-2407/12/Page 8 ofFigure 8 Expression of ABCB1 mRNA levels after -catenin depletion in CML cell lines. (A) -catenin siRNA in K562 and Lucena cells. (B) Analysis of ABCB1 mRNA levels after -catenin depletion. Total RNA was isolated and used in RT-qPCR analysis to determine changes in ABCB1 mRNA levels after normalization to -actin expression. All data were presented as fold inductions relative to control group expression (scrambled). Values represent the means of three independent determinations ?s.d.Discussion Resistance to chemotherapy is a recurrent issue in all cancer types. Because CML has the propensity to evolve from the CP to the AP and BC, with different responses to targeted therapy such as TK inhibitors, the molecular understanding of the mechanism of resistance in this neoplasia is advancing rapidly. IM was the first molecularly targeted therapy rationally designed to specifically inhibit BCR-ABL TK activity [38]. However, despite the effectiveness and good tolerEPZ-5676 cancer ability of IM, drug resistance does emerge. Although a hematological response is observed in over 95 of CP patients, primary resistant can occur [39]. Otherwise, AP patients initially respond to IM but inevitably relapse with treatment-refractory disease because they acquire other mutations in addition to BCR-ABL amplification or kinase domain mutations [40-42].Since the demonstration that IM could be extruded from CML cells through Pgp action [43,44], ABCB1 has become an interesting subject in IM resistance studies. Our previous results indicated that ABCB1 is overexpressed in CML patients with intrinsic and acquired resistance to IM therapy compared to its expression in IM-responsive patients and healthy bone marrow donors see reference [30]. This finding contrasts the idea that only individuals in the BC stage can exhibit ABCB1 overexpression, as suggested in the literature. Even though we PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/27196668 have analyzed a small cohort of patients, our results corroborate those of Vasconcelos and colleagues see reference [24], ratifying the importance of ABCB1/Pgp in CML. Interestingly, in CML, Jamieson and colleagues demonstrated that the granulocyte-macrophage progenitor pools from patients in BC and IM-resistant patients exhibited elevated levels of nuclear -catenin compared with those in granulocyte-macrophage progenitors from healthy donors. Moreover, these progenitors acquired self-renewal ability [45]. These data indicated the important role of the Wnt/-catenin pathway in the selfrenewal of CML progenitors and the acquisition of resistance. Wnt signaling involvement in TK inhibitor resistance was also demonstrated through its noncanonical pathway by Gregory and colleagues [46]. Their results indicated that Wnt/Ca2+/NFAT signaling maintains the survival of Ph+ leukemic cells under BCR-ABL inhibition. Altogether, we can speculate that the deregulation of Wnt signaling leads to key modifications in the biology of cells, allowing them to become intrinsically more resistant to drug therapy. However, a link between TK inhibitor resistance, Wnt signaling and drug efflux mechanisms such as MDR.