Transcriptional activation of human LIM-HOX gene, hLH-2, in chronic myelogenous leukemia is due to a cis-acting effect of Bcr-Abl.
DNA methylation plays an important role in gene regulation. A human LIM-HOX gene, namely hLH-2, was highly expressed in chronic myelogenous leukemia (CML) and located on chromosome 9q33-34.1, in the same region as the reciprocal translocation that creates the Bcr-Abl chimera of Philadelphia chromosome (H.-K. Wu et al., 1996, Oncogene 12, 1205-1212). To elucidate the mechanism of hLH-2 transcriptional activation, we studied the methylation status of hLH-2 in normal bone marrow and CML cells. When blots containing genomic DNA digested with Hpa II or Msp I were hybridized with full-length cDNA probe, it was discovered that hLH-2 was methylated in normal bone marrow cells in which hLH-2 was not expressed; in contrast, both alleles of the hLH-2 locus in CML cells were heavily hypomethylated. Furthermore, using a sensitive RT-PCR technique, we examined the expression of LH-2 in mouse x human hybrids and a wide array of mouse cell lines containing Abl or Bcr-Abl, and we failed to identify a consistent expression pattern in the cell lines tested. These results suggest that the transcriptional activation of hLH-2 in CML is likely due to a cis-acting effect, but not a trans-acting effect, of the Bcr-Abl fusion protein. Because hypomethylated genes generally are transcribed more efficiently than hypermethylated genes, the high level of hLH-2 mRNA in CML cells probably is a consequence of the low level of methylation of the gene in the leukemic cells.
Wu
H K
HK
Department of Medicine, Ontario Cancer Institute/Princess Margaret Hospital, Faculty of Medicine, University of Toronto, Canada.
Minden
M D
MD
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D019175:DNA Methylation; D017931:DNA Primers / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D016044:Fusion Proteins, bcr-abl / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D006822:Hybrid Cells; D060850:LIM-Homeodomain Proteins; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D009857:Oncogenes; D016133:Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation; D014162:Transfection
D017931:DNA Primers; D004273:DNA, Neoplasm; D018398:Homeodomain Proteins; C489783:LHX2 protein, human; D060850:LIM-Homeodomain Proteins; C086922:LIM-homeodomain protein LH-2; C489784:Lhx2 protein, mouse; D014157:Transcription Factors; D016044:Fusion Proteins, bcr-abl