Pim-1 and Pim-2 kinases are required for efficient pre-B-cell transformation by v-Abl oncogene

The precise mechanisms by which AN oncogenes transform hernatopoietic cells are unknown. We have examined the role of Pim kinases in v-AbI-mediated transformation. In v-AbI transformants, expression of Pim-1 and Pim-2, but not Pim-3, is dependent on AbI kinase activity. Transformation assays demonstrate that v-AbI cannot efficiently transform bone marrow cells derived from Pim-1(-/-)/Pim-2(-/-) mice. Ectopic expression of either Pim-1 or Pim-2 in Pim-1(-/-)/Pim-2(-/-) cells restores transformation by v-AbI, strongly suggesting that either Pim-1 or Pim-2 is required for v-AbI-mediated tumorigenesis. Interestingly, the combined deficiency of Pim-1, Pim-2, and Suppressor of Cytokine Signalling (SOCS)-1 resulted in partial restoration of v-AbI transformation efficiency. In addition, Pim kinases are involved in modification of SOCS-1 and in regulating SOCS-1 protein levels in v-AbI-transformed cells. Furthermore, Pim kinases regulate the proapoptotic proteins Bcl-XS and BAD. Pim kinases inhibit the expression of Bcl-XS. Pim deficiency decreases the phosphorylation levels of BAD, whereas ectopic expression of Pim-1 increases the amount of phospho-BAD. This correlates with an increased protection from apoptosis in AbI transformants expressing Pim kinases. Together, these data suggest that Pim kinases play a key role in the v-AbI transformation, possibly via participating in modulation of SOCS-1 and via regulating the apoptotic signaling.