cREL and Rel-B hierarchies define a DNA-binding network in Non-Hodgking and Hodgking Lymphoma respectively.

GAMBOA-CEDEÑO, ANGÉLICA; XIAO, WEIMING; WALDMANN, THOMAS; RANUNCOLO, STELLA MARIS

CABA

Congreso; Reunión Conjunta de las Sociedades de Biociencias 2017; 2017

SAIC-SAI-SAB-SAH

NFkB is a pleitropic family of transcription factors (TFs) known to play major roles in diverse cell processes such as proliferation, apoptosis and inflammation. It is comprised of hetero or homo dimeric combinations of five members: RELA, RELB, cREL, NFKB1 and NFkB2. Despite considerable evidence supporting the role of the REL members in the immune system and lymphomagenesis, it is not clear whether specific NFKB dimers control a particular set of target genes that account for the biological functions mediated by these TFs. Furthermore, it is not established whether NFkB controls different targets in distinct subsets of germinal center (GC) B cell derived lymphomas. As a first approach to address this issue we performed ChIP-Seq analysis for each REL member in different lymphoma cell lines model of Non-Hodgkin Lymphoma: BJAB, HBL1 and UH01 representing respectively GCB-Like and ABC-Like, the two molecular subtypes of Diffuse Large B-Cell Lymphoma (DLBCL) and Hodgkin Lymphoma (HL), as well as in primary human centroblasts isolated from tonsils. This analysis uncovered an extensive NFkB gene network. Microarray analysis of these cell lines following knockdown of RELA, RELB, or cREL was merged with our ChIP-Seq data. The overlap of RELA, cREL and RELB peaks and the corresponding shRNA downregulated targets suggested that these factors directly controlled regulators of the cell cycle, apoptosis, GC B cell TFs and DNA repair among other gene signatures. Strikingly there was a switch from alternative pathway hierarchy gene controlled in HL cells to canonical pathway hierarchy in NHL cells. For example, out of 4,581 genes that had relB binding (+/- 2kB TSS) in HL cells, more than 70% were only relB targets in HL. This data shaped two network architectures: a RelB hierarchical network in HL and a cREL hierarchy in NHL. 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. 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 cREL.