Gene Expression in Chronic Myeloid Leukemia Patients at Time ofDiagnosis

Overview

Background.
The new technologies that have the DNA laboratory over recent years and the general progress inknowledge of the human genome, have allowed the simultaneous observation of the activity of a large number ofgenes. Chronic myeloid leukemia is characterized with abnormal tyrosine kinase activity of the fused bcr/abl gene,which is most often product of translocation between chromosomes 9 an 22. It is as yet unknown whether this isthe only and sufficient cause of the disease, or whether other supporting and co-active abnormalities exist. It is alsonot yet clear whether an increase of proliferating activity or reduced programmed cell death plays the dominant role.The aim of this study was to make further steps in resolving the question as to which of these hypotheses fits better.Methods and Results. Membrane macroarrays (Clontech 7742-1: Human Cancer cDNA Expression Array with588 gene probes) were used throughout the study, on which cDNA reverse-transcribed from total RNA in turn isolatedfrom peripheral white blood cells and labelled with32P was hybridized. Cells obtained from 5 patients with confirmeddiagnoses by cytogenetic and molecular (bcr/abl) analyses, but who had not yet been treated by chemotherapy, werethe source of the material. In some cases mononuclears and granulocytes were also isolated by Ficoll-Paquecentrifugation. Radioactivity was detected by autoradiography or by a Phosphorimager (Fujifilm FLA-2000).Comparison with normal gene expression (healthy donor) was made by subtraction using Clontech AtlaImage 1.5software. Although changes of expression of identical genes were not observed in all of patients examined, themajority of them were concordant. Values at least double those of the controls applied to the activity of c-junN-terminal kinase, MMP-8, MMP-9, integrin a E, integrin b and PDGF, whereas the expression of ZAP-70, IRF1,MCL-1, STAT 5B, RARA, CDC25B, RPSA, TNFR decreased. Increases of PCNA, MMP-17, CD59, rho G, CRAF1and PIG7 or decreases of notch, caspase 8, caspase 4, interleukin 6 receptor, rho B and TIMP1 were observed onlyin some cell samples.Conclusions. It seems that some maturation processes and transmembrane signalling are blocked, as well as theeffectors of apoptosis. On the other hand, the reduced activity of ZAP-70, IRF1 and MCL-1 also indicated thatproliferation breaks were weakened. The involvement of both processes-released replication and ineffective apoptosis- was evident; the problem of bcr/abl gene fusion being the necessary first and sufficient step on the way towardsdeveloping chronic myeloid leukemia, however, remained unresolved.

Key words:
membrane macroarrays, gene expression, chronic myeloid leukemia.