Aberrant DNA Methylation and Epigenetic Inactivation of hMSH2 Decrease Overall Survival of Acute Lymphoblastic Leukemia Patients via Modulating Cell Cycle and Apoptosis

Objective: Altered regulation of many transcription factors has been shown to play important roles in thedevelopment of leukemia. hMSH2 can modulate the activity of some important transcription factors and is knownto be a regulator of hematopoietic differentiation. Herein, we investigated epigenetic regulation of hMSH2 and itsinfluence on cell growth and overall survival of acute lymphoblastic leukemia (ALL) patients.
Methods: hMSH2promoter methylation status was assessed by COBRA and pyrosequencing in 60 ALL patients and 30 healthyvolunteers. mRNA and protein expression levels of hMSH2, PCNA, CyclinD1, Bcl-2 and Bax were determinedby real time PCR and Western blotting, respectively. The influence of hMSH2 on cell proliferation and survivalwas assessed in transient and stable expression systems.
Results: mRNA and protein expression of hMSH2 andBcl-2 was decreased, and that of PCNA, CyclinD1 and Bax was increased in ALL patients as compared to healthyvolunteers (P<0.05). hMSH2 was inactivated in ALL patients through promoter hypermethylation. Furthermore,hMSH2 hypermethylation was found in relapsed ALL patients (85.7% of all cases). The median survival ofpatients with hMSH2 methylation was shorter than that of patients without hMSH2 methylation (log-rank test,P=0.0035). Over-expression of hMSH2 in cell lines resulted in a significant reduction in growth and inductionof apoptosis.
Conclusions: This study suggests that aberrant DNA methylation and epigenetic inactivation ofhMSH2 play an important role in the development of ALL through altering cell growth and survival.