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 [Wu et al. (1996) Oncogene 12, 1205]. 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 hLH-2 locus in CML cells were heavily hypomethylated. Furthermore, using the 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 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; D001853:Bone Marrow / Q000378:metabolism; D001854:Bone Marrow Cells; D002461:Cell Line, Transformed; D019175:DNA Methylation; D016044:Fusion Proteins, bcr-abl / Q000235:genetics* / Q000378:metabolism; D018398:Homeodomain Proteins; D006801:Humans; D006822:Hybrid Cells; D060850:LIM-Homeodomain Proteins; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics*; D051379:Mice; D008809:Mice, Inbred C3H; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D014157:Transcription Factors; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D018398:Homeodomain Proteins; C489783:LHX2 protein, human; D060850:LIM-Homeodomain Proteins; C489784:Lhx2 protein, mouse; D012333:RNA, Messenger; D014157:Transcription Factors; D016044:Fusion Proteins, bcr-abl