PTBP1 and chronic myelogenous leukemia, BCR-ABL1 positive: Consistent with our hypothesis, the downregulation of PTBP1 diminished imatinib-induced apoptosis in the K562 CML cell line, as indicated by the reduced expression of apoptotic markers like cleaved poly (ADP-ribose) polymerase (PARP) and cleaved caspase 3 (Fig. 9A).