a-catenin Hypermethylation Correlates with AML Transformation in Patients with and without 5q Defects.

Interstitial loss of the long arm of chromosome(Ch) 5 or complete loss of Ch 5 is seen in de novo MDS and AML, and more frequently in MDS and AML arising after previous cancer treatments with alkylating agents or radiotherapy. The recurrent nature of these chromosomal deletions suggests that 5q contains tumor suppressor gene(s) important to hematological transformation. Although the common deleted 5q31 region has been delineated for some time, no genes have been identified that explain the poor prognosis of these patients. While tumor suppressor genes altered in solid tumors are infrequently mutated in MDS or AML, several studies indicate that epigenetic changes, including aberrant DNA methylation, can also play important roles in the progression of MDS or AML. Two demethylating agents have been approved by the FDA for the treatment of MDS, further providing support for the involvement of DNA methylation changes in this disease. In this work we have analyzed previously implicated Ch 5 tumor suppressor genes for epigenetic silencing in the myeloid malignancies. Genes analyzed for hypermethylation were a-catenin, Egr1, Smad5, and IRF1 within the minimally deleted 5q31 region, and NPM1 at 5q35.1. Methylation of a-catenin was found in myeloid cell lines associated with lack of gene expression and its expression restored with 5-aza-2′-deoxycytidine. No methylation of the other four 5q genes was detected in MDS and AML. No a-catenin methylation was found in mononuclear cells from 15 normal healthy individuals. In 27 MDS (15 with 5q deletion) and 140 AML cases tested (26 with 5q deletion), we found that methylation of a-catenin is common and more frequent in AML patients with 5q deletion (50%) than those without 5q deletion (16%), a-catenin methylation also occurs more frequently in MDS/AML patients (37%) than in AML patients without preexisting MDS (14%). Although methylation of a-catenin was found more frequently in AML patients with an unfavorable karyotype, secondary AML or in patients >60 years of age, in multivariate analysis only 5q deletion was associated with methylation of a-catenin. We also examined other hematological malignancies including CLL, CML, ALL. Methylation was observed only in two CLL patients of these 40 cases. Surprisingly, since a-catenin has been identified as under expressed in MDS (Liu et al., 2007), and 5q loss is a common occurrence in MDS, methylation of a-catenin was not found in 5q deletion or 5q intact MDS patients, with the exception of two case of RAEB-t (currently reclassified by WHO as AML). The methylation frequency of a-catenin was frequent in leukemia with p15 methylation, but and was also observed in those with CDH1 methylation, although these trends did not reach statistical significance. These results suggest that a-catenin methylation may be most important in promoting transformation from MDS to AML. Our data indicate that methylation of a-catenin is very common in AML patients with 5q deletion and in AML patients progressing from MDS. a-catenin methylation is correlated with unfavorable karyotype and poor prognosis. The accumulation of epigenetic events affecting genes which are involved in regulating cell cycle inhibition and cell adhesion may contribute to the progression of AML.