Higher levels of expression of BCL-2 and BCL-XL in poor prognosis monosomy 5 and monosomy 7} acute myeloid leukemia (AML) cells than in good prognosis (inversion 16 and translocation 8;21) aml cells

Specific cytogenetic abnormalities found in AML cells are associated with susceptibility or resistance to chemotherapeutic regimens. We attempted to test whether these cytogenetic subsets associated with presence or absence of responsiveness to chemotherapy is associated with any distinct pattern of expression of individual members of the bcl-2 gene family. We examined the expression of bcl-2 gene family members in poor prognosis subsets and good prognosis subtypes of AML. Oligonucleotide primers representing the BH1 and BH₂ domains, which are conserved among all members of the gene family, were used to amplify the region between these domains. The PCR products were cloned. The identity of the inserts were determined by blotting of individual bacterial colonies and hybridization with radioactive probes specific to bcl-2, bcl-x or bax. The bcl-2 was found to be the predominant member expressed in poor prognosis (monosomy 5 or 7) AML samples, whereas bcl-x is expressed more than bcl-2 in the good prognosis samples [inversion 16, translocation (8;21)J. No differences of bax expression in the poor versus good prognosis subsets of AML were detected. To test the expression level of the two isoforms of bcl-x, i.e. bcl-x long (bcl-xl), which protects, and bcl-x short (bcl-xs), which promotes cell death, we carried out RT-PCR with a pair of primers specific to bcl-x followed by separation of the PCR products on agarose gels. Bcl-xl and bcl-xs appeared as bands of different molecular mass and were visualized by ethidium bromide staining or Southern blot analysis with bcl-x specific probe. We found that the ratio of bcl-xl to bcl-xs was higher in the poor prognosis AML samples than in the good prognosis samples. The bcl-xs product was obtained at equal or higher amounts than the bcl-xl product from chemosensitive invlo and t(8;21) samples. This pattern of expression was observed in over 10 AML patients. The experiments showed that differences in expression of the bcl-2 family members are associated with altered sensitivity of AML to chemotherapeutic reagents. Those unidentified products are being analyzed for possible new members of the bcl-2 family.