Background: Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous aggressive non-Hodgkin lymphoma and can be classified into GCB or ABC DLBCL. Aberrant activation of NF-κB has been associated with tumor proliferation and survival ABC-DLBCL. The “canonical” pathway of NF-κB activation involves activities of IκB kinase IKK2, which lead to degradation of NF-κB inhibitors IκBα/β/ϵ and nuclear translocation of p50/p65 and p50/c-Rel dimers from the cytoplasm.
Objective: To investigate the common mechanisms for c-Rel activation and function, and to evaluate the prognostic significance of c-Rel in a large group of DLBCL patients (n = 460).
Results: Nuclear c-Rel expression (c-Rel+) was observed in 29.6% of DLBCL patients and correlated with higher expression levels of p50 (P = 0.12), p52 (P = 0.724E-8), p65 (P = 0.073), RelB (P = 0.013). Coimmunoprecipitation analysis using nuclear extract purified from primary GCB and ABC cells showed that in addition to the known p50 to form dimers with c-Rel, p65, p52 and RelB could also form dimers with c-Rel in some cell lines.
A unique function of c-Rel in terminating NF-κB as negative feedback of IKK2 activation was suggested by the significantly upregulated genes encoding IκBα/β/ϵ, A20 and TNIP1 at the mRNA level in either GCB- or ABC-DLBCL. The B-cell receptor signaling (BCR) appeared most relevant for c-Rel activation in GCB-DLBCL, with upreglated B-cell receptors (CD19, CD20, CD79A) and downstream LYN, SYK, CARD11, MALT1, BLNK, TAK1.
The role of c-Rel in cytokine production was validated in our study cohort, showing significant correlation between c-Rel+ and mRNA levels of IL1, IL3, IL6, IL10, IL12, IL21 and chemokine receptor CXCR4, mostly in GCB-DLBCL. GEP analysis showed enrichment in cytokine, growth factors, inflammation, gene expression, metabolism, actin, collagen, cell morphology and adhesion.
c-Rel did not correlate with prognosis in overall DLBCL. However, c-Rel+ patients with MUT-p53 had significantly worse survival compared with other MUT-p53 DLBCL patients, especially in in ABC-DLBCL, in which c-Rel+ was associated with upregulated MUT-TP53 transcription (P = 0.0087). Conversely, MUT-p53 expression was associated significantly with upregulated REL mRNA expression (P = 0.0021), predominantly in the ABC-DLBCL subtype (P = 0.0047).
Furthermore, the lack of c-Rel prognostic impact is likely due to the antagonism of p63, whose expression was correlated with c-Rel nuclear expression, and significantly better OS and PFS in ABC-DLBCL.
Conclusions: Unique function and upstream activation regulation of c-Rel was suggested by analysis in 460 DLBCLs. TP53 mutation status appears to a critical determinant for c-Rel prognostic impact. p63 is another tumor suppressor for the c-Rel oncogenic function.
Citation Format: Zijun Y. Xu-Monette, Ken H. Young. Distinct expression, activity, regulation and gene expression signature of NF-κB subunit c-Rel and the prognostic impact of crosstalk between p53, p63 and c-Rel in different subsets of diffuse large B-cell lymphoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5308. doi:10.1158/1538-7445.AM2015-5308