| Complete loss or deletion of the long arm of chromosome 5 is frequent in myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). The putative gene(s) deleted and responsible for the pathogenesis of these poor prognosis hematological disorders remain controversial. This study represents a comprehensive analysis of previously implicated and novel genes on 5q, exploring epigenetic inactivation of some genes in that region in AML and MDS. Through an examination of 146 AML cases, DNA methylation of CTNNA1 was discovered to be frequent, and more common in AML patients with 5q deletion (31%) than those without 5q deletion (14%), while no inactivation of other 5q genes was observed. In 31 MDS cases, CTNNA1 methylation was only found in high risk MDS (≥2AEB2), but not in low risk MDS (<RAEB2), suggesting that CTNNA1 methylation is important in the transformation of MDS to AML. CTNNA1 expression was lowest in AML/MDS patients with CTNNA1 methylation, although reduced expression occurred in some patients without promoter methylation. Repressive chromatin marks (H3K27me3) at the promoter were identified in CTNNA1-repressed AML cell lines and primary leukemias, with the most repressive state correlating with DNA methylation. We observed DNMT1 occupancy of the CTNNA1 promoter in a leukemia cell line with silenced and methylated CTNNA1, and also in cell lines with repressed, but unmethylated CTNNA1, where DNMT1 enrichment directly correlates with the level of CTNNA1 repression. This suggests that DNMT1 plays a critical role in initiating and/or maintaining DNA repression of CTNNA1 in AML cell lines, which is also consistent with the observed increase in expression of CTNNA1 following treatment with 5-aza-dC, a drug that depletes DNMT1 and thus reduces DNA methylation in dividing cells. Our study demonstrates progressive, acquired epigenetic inactivation at CTNNA1, including histone modifications and promoter CpG methylation, as a component of leukemia progression in patients with both 5q- and non 5q-myeloid malignancies. |
