Different NFkB regulatory networks define Hodgkin's and Non-Hodgkin's Lymphomas

STELLA MARIS RANUNCOLO, BRIAN A. LEWIS.

Whistler, British Columbia.

Congreso; B Cells: new insights into normal versus dysregulated function.; 2011

Keystone Symposia on Molecular and Cellular Biology.

RELB-dependency uniquely distinguishes Hodgkin’s Lymphoma from Non-Hodgkin’s Lymphomas.  Stella M. Ranuncolo and Brian A. Lewis. Transcriptional Regulation and Biochemistry Unit, Metabolism Branch, Center for Cancer Research, NCI, NIH, Bethesda, MD 20892.   Despite considerable evidence supporting the role of the REL members in the immune system and lymphomagenesis, it is not clear whether specific NF-KB dimers control a particular set of target genes that account for the biological functions mediated by these TFs.  We performed loss of function experiments delivering specific shRNA to knock down each REL member in different lymphoma cell lines representing stages of germinal center (GC) B cell maturation: Mantle Cell Lymphoma, Diffuse Large B-Cell Lymphoma [DLBCL-including the three main molecular subtypes: ABC-Like (Activated B-Cell), GCB-Like (Germinal Center B-Cell), and PMBL (Primary Mediastinal B-cell Lymphoma)] and Hodgkin Lymphoma (HL) cell lines. All these lymphoma subsets showed a dependency on RELA and c-REL, but only HL cells were sensitive to RELB knock-down. ChIP-seq analysis uncovered an extensive NF-kB network in BJAB (GCB), HBL-1 (ABC), U-H01 (HL) and primary GC B cells. Microarray analysis of these cell lines following knock-down of RELA, RELB, or c-REL was merged with our ChIP-seq data. The overlap of RELB peaks and RELB shRNA downregulated targets suggested that RELB directly controlled regulators of the cell cycle, apoptosis, and DNA damage, including CCND3, CDK6 and BCL2.  Additionally, RELB maintains HL cell viability through BCL2 induction:  expression of a BCL2 cDNA rescued HL cell lines from the shRNA RELB toxicity. That CCND3, CDK6 and BCL2 are exclusively RELB targets in HL cells is supported by the lack of down-regulation of these genes following knock-down of c-REL. In summary, we found that HL is the only B-cell malignancy that depends on RELB for viability, and thus differentiates HL from non-Hodgkin lymphomas.  These data argue that each REL member has specific and unique functions and targets, as we predicted from the lack of similarities in their transactivation domains.  Furthermore, the specificity of the RELB for Hodgkin’s lymphoma makes RELB and the alternative NF-kB pathway an attractive therapeutic target.