Pituitary homeobox 2 (PITX2) protects renal cancer cell lines against doxorubicin toxicity by transcriptional activation of the multidrug transporter ABCB1

摘要

The multidrug resistance (MDR) P-glycoprotein ABCB1 plays a major role in MDR of malignant cells and is regulated by various transcription factors, including Wnt/β-catenin/TCF4. The transcription factor PITX2 (Pituitary homeobox-2) is essential for embryonic development. PITX2 operates by recruiting and interacting with β-catenin to increase the expression of growth-regulating genes, such as cyclin D1/2 and c-Myc. The importance of PITX2 in malignancy is not yet known. Here we demonstrate that in the renal cancer cell lines ACHN and A498, the level of ABCB1 expression and function correlate with nuclear PITX2 localization and PITX2-luciferase reporter gene activity (A498 ACHN). In A498 cells, doxorubicin toxicity is augmented by the ABCB1 inhibitor, PSC833. PITX2 overexpression increases ABCB1 expression and cell survival in ACHN cells. Silencing of PITX2 by siRNA downregulates ABCB1 and induces a greater chemotherapeutic response to doxorubicin in A498 cells, as determined by MTT cell viability and clonogenic survival assays. Two PITX2 binding sequences were identified in the ABCB1 promoter sequence. PITX2 binding was confirmed by chromatin immunoprecipitation. β-Catenin is not required for PITX2 upregulation of ABCB1 because ABCB1 mRNA increased and doxorubicin toxicity decreased upon PITX2 overexpression in β-catenin-/- cells. The data show for the first time that ABCB1 is a target gene of PITX2 transcriptional activity, promoting MDR and cell survival of cancer cells. What's new? Pituitary homeobox-2 (PITX2) is an essential transcription factor in embryonic development. While PITX2 is overexpressed in some cancers, its importance in tumorigenesis remains unclear. Here the authors investigate the role of PITX2 in regulating the expression of ABCB1, a P-glycoprotein that plays a major role in the multidrug resistance of malignant cells. Using human renal cancer cell lines, they show for the first time that cell survival in the presence of doxorubicin is caused by up-regulation of ABCB1 as a downstream target of PITX2, in a β-catenin-independent mechanism. PITX2 is a putative target for cancer therapy in drug-resistant renal carcinoma.