PTBP2 promotes cell survival and autophagy in chronic myeloid leukemia by stabilizing BNIP3

Polypyrimidine tract binding protein 2 (PTBP2) regulates alternative splicing in neuronal, muscle, and Sertoli cells. PTBP2 and its paralog, PTBP1, which plays a role in B-cell development, was found to be expressed aberrantly in myeloid leukemia. Genetic ablation of Ptbp2 in the cells resulted in decreased cellular proliferation and repopulating ability, decreased reactive oxygen species (ROS), and altered mitochondrial morphology. RNA immunoprecipitation followed by sequencing (RIP-seq) and functional assays confirmed that PTBP2 binds to Bcl-2 Interacting Protein 3 (Bnip3)-3'UTR and stabilizes its expression. Our study also suggests that PTBP2 promotes autophagy, as evidenced by the low levels of LC3-II expression in Ptbp2-knockout cells treated with Bafilomycin A1. This effect was restored upon overexpression of Bnip3 in the knockout cells. Notably, when KCL22-NTC cells were subcutaneously injected into the flanks of mice, they gave rise to malignant tumors, unlike Ptbp2-KO-KCL22 cells. Also, transplantation of KCL22 cells through the tail vein in NOD/SCID mice resulted in higher cell engraftment and increased infiltration of malignant cells in the extramedullary organs. Our study underscores the role of PTBP2 in promoting cell proliferation and tumor formation while enhancing autophagy through Bnip3, thereby supporting the role of PTBP2 as an oncogene in CML.