Promoter Hypermethylation of BANK1 Supports a Tumor Suppressor Role in Hodgkin Lymphomas
Jiong Yan, Taotao Zhang, Kui Nie, Sonam Prakash, Daniel M Knowles, Attilio Orazi, Wayne Tam. Weill Cornell Medical College, New York, NY
Background: BANK1 (B-cell scaffold protein with ankyrin repeats 1) is a B-cell-specific adaptor with a negative regulatory function on CD40-mediated signaling. We recently identified BANK1 as a novel IgH translocation partner in a case of polymorphic post-transplant lymphoproliferative disorder, in which BANK1 appears inactivated rather than over-expressed by the translocation. Initial expression analyses on cell lines and primary lymphomas suggest that it may act as a tumor suppressor (TS) gene. We investigate whether BANK1 is inactivated by epigenetic mechanisms in lymphomas.
Design: 23 B lymphoma cell lines, including 8 Burkitt lymphoma, 9 diffuse large B cell lymphoma, 3 primary effusion lymphoma (PEL), 3 classical Hodgkin lymphoma (cHL), were bisulfite sequenced to assess the methylation status of 37 CpG dinucleotides in a 436 base-pair region at the 5' end of BANK1. Methylation statuses of 17 of these 37 CpGs were assessed in 23 cHL, 5 nodular lymphocyte predominant HL (NLPHL) and 1 T-cell/histiocyte rich large B-cell lymphoma (THRLBCL) cases using en bloc formalin-fixed, paraffin-embedded (FFPE) materials and also laser-capture microdissected Hodgkin/Reed-Sternberg (HRS) cells (in 2 cHL cases). Normal tonsil tissues served as controls. Immunohistochemistry (IHC) with a polyclonal BANK1 antibody (Sigma) was performed on FFPE tissues of 29 cHL, 7 NLPHL and 4 THRLBCL.
Results: Hypermethylation (>60% methylation) was seen in all 3 cHL cell lines and in 2/3 PEL cell lines, which correlated with a virtually silent BANK1. There was evidence of BANK1 hypermethylation in the tumor cells in 9 of 23 cHL, 4 of 5 NLPHL, and 1 of 1 THRLBCL cases analyzed when en bloc analysis was performed. Tumor cell specificity of BANK1 hypermethylation was further confirmed in 2 cHL cases using microdissected HRS cells. Tonsils showed no BANK1 hypermethylation. HRS cells were negative for BANK1 in 28 of 29 cHL cases examined. All 7 NLPHL cases demonstrated weak BANK1 expression in variable (20 to 100%) proportions of tumor cells. Three of 4 THRLBCL showed BANK1 positivity in ∼100% of tumor cells and one showed partial (20%) positivity, with slightly stronger intensities compared to NLPHL.
Conclusions: BANK1 is likely downregulated by promoter methylation in cHL, NLPHL and THRLBCL, albeit to different extents. Our study supports a TS role of BANK1 in HLs and THRLBCL, and illustrates a potential clinical application of BANK1 IHC for differentiating cHL from NLPHL and THRLBCL.
Monday, March 4, 2013 2:30 PM
Proffered Papers: Section C, Monday Afternoon