Etiology-independent activation of the LT-LTR-RELB axis drives aggressiveness and predicts poor prognosis in Hepatocellular carcinoma

Background & Aims: Hepatocellular carcinoma (HCC) is the most common primary liver tumor with an increasing incidence worldwide. HCC is a heterogeneous malignancy and develops usually in a chronically injured liver. The nuclear factor kappa B (NF-kappa B) signaling network consists of a canonical and a non-canonical branch. An activation of canonical NF-kappa B in HCC is documented. However, a functional and clinically relevant role of non-canonical NF-kappa B and its downstream effectors is not established.Approach & Results: Four human HCC cohorts (total n=1,462) and four mouse HCC models were assessed for expression and localization of NF-kappa B signaling components and activating ligands. In vitro, NF-kappa B signaling, proliferation and cell death were measured, proving a pro-proliferative role of RELB activated via NIK. In vivo, Lymphotoxin beta (LT beta) was identified as predominant inducer of RELB activation. Importantly, hepatocyte-specific RELB knockout in a murine HCC model led to a lower incidence compared to controls and lower maximal tumor diameters. In silico, RELB activity and RELB directed transcriptomics were validated on the TCGA HCC cohort using inferred protein activity and Gene Set Enrichment Analysis (GSEA). In RELB-active HCC, pathways mediating proliferation were significantly activated. In contrast to RELA, nuclear enrichment of non-canonical RELB expression identified patients with a poor prognosis in an etiology-independent manner. Moreover, RELB activation was associated with malignant features metastasis and recurrence.Conclusions: This study demonstrates a prognostically relevant, etiology-independent and cross-species consistent activation of a LT beta/LT beta R/RELB axis in hepatocarcinogenesis. These observations may harbor broad implications for HCC, including possible clinical exploitation.