WNT5A, a putative tumour suppressor of lymphoid malignancies, is inactivated by aberrant methylation in acute lymphoblastic leukaemia

Abstract

Wnt5a is a member of the Wnt family of proteins that signals through the non-canonical Wnt/Ca(2+) pathway to suppress cyclin D1 expression and negatively regulate B cell proliferation suggesting that it acts as an tumour suppressor for lymphoid leukemogenesis. Although canonical Wnt pathway is a 'hot spot' for methylation in acute lymphoblastic leukaemia (ALL), the role of Wnt5a abnormalities has never been evaluated in this clinical setting. The methylation status of the WNT5A promoter was analysed by methylation-specific PCR (MSP) and sequencing in six ALL-derived cell lines (TOM-1, NALM-20, MY, LOUCY, JURKAT and TANOUE) and in 307 ALL patients. WNT5A and CYCLIN D1 expressions were assessed by quantitative RT-PCR. We observed WNT5A hypermethylation in all cell lines and in cells from 43% (132/307) of ALL patients. WNT5A methylation was associated with decreased WNT5A mRNA expression (P<0.001) and this expression was restored after exposure to the demethylating agent 5-Aza-2'-deoxycytidine. Moreover, WNT5A hypermethylation correlated with upregulation of CYCLIN D1 expression (P=0.002). Disease-free survival (DFS) and overall survival (OS) at 13 and 14 years, respectively, were 59% and 53% for unmethylated patients and 28% and 31% for hypermethylated patients (P=0.0003 and P=0.003). Multivariate analysis demonstrated that WNT5A methylation was an independent prognostic factor predicting DFS (P=0.003) and OS (P=0.04). We have demonstrated that WNT5A, a putative tumour suppressor gene in ALL, is silenced by methylation in this disease and that this epigenetic event is associated with upregulation of CYCLIN D1 expression and confers poor prognosis in this group of patients.