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 LI M-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 P hiladelphia chromosome (H.-K. Wu et al., 1996, Oncogene 12, 1205-1212) . To elucidate the mechanism of hLH-2 transcriptional activation, we s tudied the methylation status of hLH-2 in normal bone marrow and CML c ells. When blots containing genomic DNA digested with Hpa II or Msp I were hybridized with full-length cDNA probe, it was discovered that hL H-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 w ere heavily hypomethylated. Furthermore, using a sensitive RT-PCR tech nique, 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 fa iled to identify a consistent expression pattern in the cell lines tes ted. 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 ge nerally ape transcribed more efficiently than hypermethylated genes, t he 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. (C) 19 97 Academic Press.