Murine myeloid leukemias with aberrant myb loci show heterogeneous expression of novel myb proteins

Using a panel of anti-myb antibodies, we have examined the c-myb proteins present in the NFS-60 and ABPL-1, ABPL-2, and ABPl-4 tumor cell lines, all of which have an altered myb locus due to viral insertional mutagenesis. As predicted from previous DNA and RNA analysis, NFS-60 cells produce myb protein with a truncated C-terminus and a normal N-terminus. The three ABPL tumor cell lines studied here were previously shown to have undergone similar rearrangements towards the 5' end of myb locus and were expected to synthesize identical myb RNAs and proteins. These cell lines were found to produce myb proteins with N-terminal modifications. Surprisingly, however, the three cell lines were found to synthesize a heterogenous array of myb proteins of different sizes. These observations suggest that oncogenic activation of Myb in ABPL tumors may involve additional changes in the coding region in addition to those occurring at the N-terminus.