RETROVIRAL INSERTIONAL ACTIVATION OF THE EVI1 ONCOGENE DOES NOT PREVENT G-CSF-INDUCED MATURATION OF THE MURINE PLURIPOTENT MYELOID CELL-LINE 32DCL3

Evil is a myeloid-specific protooncogene that encodes 145 kDa and 88 k Da proteins via alternative splicing, Overexpression of the gene via r etroviral insertion in murine tumors or chromosomal rearrangement in h uman tumors is associated with myeloid leukemias and myelodysplasias; however, the mechanism by which such overexpression leads to transform ation is not clear, It has been postulated that overexpression of evil acts to block normal myelopoiesis. In attempts to assess the effect o f overexpression of evil on myelopoiesis, we chose to utilize the IL-3 -dependent murine 32Dcl3 cell line, which has been shown to differenti ate in culture in response to G-CSP. Previous experiments with this ce ll line, which Ne have confirmed, showed that overexpression of evil, mediated by retroviral vector transfer, caused a block to G-CSF-induce d cell survival and differentiation, We report here that the naive 32D cl3 cell line contains a rearrangement of the evil locus and constitut ively overexpresses evil mRNA and protein; this expression is downregu lated only slightly during G-CSF-induced myeloid maturation, The stead y state levels, molecular weight and DNA binding characteristics of th e EVI1 protein in these cells is comparable to that seen in NFS 58, a myeloid leukemia cell line with retroviral insertion at evil, The obse rved ability of the murine 32Dcl3 cells to fully differentiate in the presence of G-CSF while evil continues to be expressed indicates that, at the levels expressed in naive 32Dcl3, evil does not block G-CSF-in duced survival and differentiation, Thus, retroviral insertions at evi l may have been selected for in 32Dcl3 cells due to effects other than that on G-CSF-induced cell survival.