Etiology-independent activation of the LTβ-LTβR-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-κB) signaling network consists of a canonical and a non-canonical branch. An activation of canonical NF-κB in HCC is documented. However, a functional and clinically relevant role of non-canonical NF-κB 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-κB signaling components and activating ligands. In vitro , NF-κB signaling, proliferation and cell death were measured, proving a pro-proliferative role of RELB activated via NIK. In vivo , Lymphotoxin beta (LTβ) 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 LTβ/LTβR/RELB axis in hepatocarcinogenesis. These observations may harbor broad implications for HCC, including possible clinical exploitation.