IDENTIFICATION OF THE CHIMERIC PROTEIN PRODUCT OF THE CBFB-MYHII FUSION GENE IN INV(16) LEUKEMIA-CELLS

An expressed gene formed by fusion between the CBFB transcription fact or gene and the smooth muscle myosin heavy chain gene MYHI I is consis tently detected by reverse transcription polymerase chain reaction (RT -PCR) in patients who have acute myeloid leukemia (AML) subtype M4Eo w ith an inversion of chromosome I Ci, We have previously shown that a C BFB-MYHI I cDNA construct can produce a chimeric protein and transform NIH 3T3 cells. However, the presence of the chimeric protein in patie nt cells has not been demonstrated previously. Here, we show that such chimeric proteins can be identified in vivo, primarily in the nuclei of the leukemic cells, by use of antibodies against the C-terminus of the smooth muscle myosin heavy chain and the fusion junction peptide. A very high molecular weight protein/DNA complex is generated when nuc lear extracts from patient cells are used in electrophoretic mobility shift assays, as seen in NIH 3T3 cells transfected with the CBFB-MYHI I cDNA. Immunofluorescence staining shows that the proteins are organi zed in vivo into novel structures within cell nuclei, One isoform of t he transcript of the CBFB-MYHI I fusion gene, containing the MHC,,, C- terminus, was the predominant form in all five cases studied. (C) 1996 Wiley-Liss, Inc.