Methylation of miR-155-3p in mantle cell lymphoma and other non-Hodgkin’s lymphomas

// Rita Lh Yim 1 , Kwan Yeung Wong 1 , Yok Lam Kwong 1 , Florence Loong 2 , Chung Ying Leung 3 , Raymond Chu 4 , William Wai Lung Lam 5 , Pak Kwan Hui 6 , Raymond Lai 7 , Chor Sang Chim 1 1 Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong 2 Department of Pathology, Queen Mary Hospital, Hong Kong 3 Department of Pathology, United Christian Hospital, Hong Kong 4 Department of Pathology, Pamela Youde Nethersole Eastern Hospital, Hong Kong 5 Department of Pathology, Princess Margaret Hospital, Hong Kong 6 Department of Pathology, Kwong Wah Hospital, Hong Kong 7 Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Canada Correspondence to: Chor-Sang Chim, e-mail: jcschim@hku.hk Key Words: tumor suppressive microRNA, hypermethylation, miR-155-3p, mantle cell lymphoma, non-Hodgkin’s lymphoma Received: July 08, 2014      Accepted: August 23, 2014      Published: November 11, 2014 ABSTRACT Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin’s lymphoma (NHL). In cancers, tumor suppressive microRNAs may be silenced by DNA hypermethylation. By microRNA profiling of representative EBV-negative MCL cell lines before and after demethylation treatment, miR-155-3p was found significantly restored. Methylation-specific PCR, verified by pyrosequencing, showed complete methylation of miR-155-3p in one MCL cell line (REC-1). 5-aza-2′-deoxycytidine treatment of REC-1 led to demethylation and re-expression of miR-155-3p . Over-expression of miR-155-3p led to increased sub-G1 apoptotic cells and reduced cellular viability, demonstrating its tumor suppressive properties. By luciferase assay, lymphotoxin-beta (LT-β) was validated as a miR-155-3p target. In 31 primary MCL, miR-155-3p was found hypermethylated in 6(19%) cases. To test if methylation of miR-155-3p was MCL-specific, miR-155-3p methylation was tested in an additional 191 B-cell, T-cell and NK-cell NHLs, yielding miR-155-3p methylation in 66(34.6%) including 36(27%) non-MCL B-cell, 24(53%) T-cell and 6(46%) of NK-cell lymphoma. Moreover, in 72 primary NHL samples with RNA, miR-155-3p methylation correlated with miR-155-3p downregulation (p=0.024), and LT-β upregulation (p=0.043). Collectively, miR-155-3p is a potential tumor suppressive microRNA hypermethylated in MCL and other NHL subtypes. As miR-155-3p targets LT-β , which is an upstream activator of the non-canonical NF-kB signaling, miR-155-3p methylation is potentially important in lymphomagenesis.