High CFTR expression in Philadelphia chromosome-positive acute leukemia protects and maintains continuous activation of BCR-ABL and related signaling pathways in combination with PP2A

Abstract

Cystic fibrosis transmembrane conductance regulator (CFTR) is classified as an anion channel transporter of Cl⁻ and HCO3⁻. Through interactions with its PDZ domain, CFTR is capable of regulating other proteins, such as protein phosphatase 2A (PP2A). The aberrant expression and mutation of CFTR have been observed in several tumor, but not in philadelphia chromosome–positive(Ph⁺) acute leukemia, including Ph⁺ B cell acute lymphoblastic leukemia(Ph⁺ B-ALL) and chronic myelogenous leukemia blast crisis phases (CML-BC). In this study, we demonstrated the mean expression level of CFTR in Ph⁺ acute leukemia cells was markedly higher than that in Ph- B-ALL and CML-chronic phase cells. CFTRinh-172, a classic CFTR inhibitor, down-regulated the expression of CFTR, p-BCR-ABL and classical Wnt/β-catenin signaling in Ph⁺ acute leukemia cells, while imatinib had no effect on CFTR. Importantly, reduced efficacy of CFTRinh-172 was closely associated with elevated PP2A phosphatase activity. Furthermore, we confirmed an interaction between CFTR and the PP2AA subunit in K562 cells. In addition, we demonstrated CFTR and PP2AA interact in the cytosol, resulting in PP2_A complex inactivation and increased degradation of PP2_A substrates via the lysosomal/proteasome pathway. In conclusion, our results showed CFTR was highly expressed in Ph⁺ acute leukemia, which protected and maintained the continuous activation of BCR-ABL and the canonical Wnt/β-catenin signaling pathway by decreasing PP2A phosphatase activity. According to this working model of the CFTR-PP2A-BCR-ABL axis, targeting the CFTR protein will activate PP2A and may offer a new treatment strategy for Ph⁺ acute leukemia, especially for patients exhibiting high levels of CFTR expression.