PTPA and chronic myelogenous leukemia, BCR-ABL1 positive: Interestingly, in IM-resistant CML cells, the sphingosine kinase-1 (SK-1)/sphingosine 1-phosphate (S1P) activation enhances BCR–ABL1 stability through S1P receptor 2 (S1P2) signaling, which prevents BCR–ABL1 dephosphorylation and degradation through inhibition of PP2A (45).