Structural organization of BCR-ABL gene in chronic phase and blast transformation in chronic myeloid leukemia...

We studied 36 DNA samples of 18 patients affected with chronic myeloid leukemia (CML) for the presence of mutations in the first exon of the BCR gene was divided into four regions amplified by polymerase chain reaction (PCR). By single strand conformation polymorphism analysis (SSCP) and direct sequencing of amplified fragments, we found different banding profiles in 9 out of 18 patients in the PCR fragment spanning nucleotide 506-826. In one patient, sequence analysis revealed the presence of a point mutation at nucleotide 669 (A-T; Gln-Leu). No difference was found between DNA samples collected during the chronic phase and the blastic transformation. No different mobility shifts of single stranded PCR products were found in the other amplified fragments. The activation of BCR-ABL involves direct interaction between BCR first exon sequences and the tyrosine kinase regulatory domains of ABL. In the first BCR exon, and around the mutated sequences two SH-2-binding sites, are retained. These domains are essential for BCR-ABL-mediated transformation. Our results demonstrate the presence of point mutation in this regulatory region, which may suggest a role for the altered BCR sequence in activation of the BCR-ABL oncogene.