Frequent Epigenetic Inactivation of MSX2 In Acute Myeloid Leukemia

Abstract 4645

DNA hypermethylation has been implicated in the tumorigenesis and prognosis in acute myeloid leukemia (AML). To identify and validate relevant methylated genes in AML, we have compared expression levels and methylation status of 26 candidate genes. One of the interesting candidates identified in our study is MSX2. MSX2 is a member of muscle segment homeobox gene family. MSX2 plays a role in promoting cell growth under certain conditions and may be an important target for RAS signaling pathways. However, the mechanism of transcriptional regulation and functional role of MSX2 in hematological malignancies, especially AML, are poorly understood. In our study, we determined the methylation status, and analyzed the expression levels of MSX2 in AML cell lines and primary AML cells using RT-PCR and/or Taqman real-time PCR. MSX2 mRNA expression was robust in the normal granulocytes and blasts of human bone-marrow, but was either absent or significantly diminished in 6 of 9 (66.7%) AML cell lines. The expression levels of MSX2 in those 6 AML cell lines were restored after treatment of 5-aza 2′-deoxycytidine. In addition, COBRA (Combined Bisulfite Restriction) analysis demonstrated hypermethylation of MSX2 in those AML cell lines (6 of 9, 66.7%), and partial methylation in 3 of 9 AML cell lines. The methylation status was inversely correlated with the mRNA expression levels of MSX2 in those cell lines. Furthermore, the expression levels and methylation status of MSX2 in human primary AML cells were evaluated. COBRA analysis demonstrated frequent hypermethylation of MSX2 in primary AML patient samples (19 of 32, 59.3%). Importantly, the mRNA expression levels of MSX2 as shown by Taqman real-time PCR in those 19 primary AML patient samples were inversely correlated with the methylation status of MSX2. These findings confirmed the role of frequent DNA hypermethylation in silencing MSX2 in AML. We are in the process of determining the functional role of MSX2 in the pathogenesis of AML. In addition, diagnostic and prognostic values of MSX2 in AML are being pursued.