O-GlcNAc transferase promotes fatty liver-associated liver cancer through inducing palmitic acid and activating endoplasmic reticulum stress

Abstract

Background & aims: O-GlcNAc transferase (OGT) is a unique glycosyltransferase involved in metabolic reprogramming. We investigated the functional role of OGT in non-alcoholic fatty liver disease-associated hepatocellular carcinoma (NAFLD-HCC).

Methods: The biological function of OGT in NAFLD-HCC was determined by gain- or loss- of OGT functional assays in vitro and in nude mice. OGT target factors and pathways were identified by liquid chromatography-tandem mass spectrometry (LC-MS), promoter luciferase assay, DNA binding activity assay and Western blot.

Results: OGT was upregulated in 12 out of 18 (66.7%) NAFLD-HCC tumor tissues by transcriptome sequencing, which was confirmed in additional NAFLD-HCC tumor tissues and cell lines. Biofunctional investigation demonstrated that OGT significantly increased cell growth (p<0.001), clonogenicity (p<0.01), migration and invasion (p<0.05) ability in vitro, and promoted xenograft tumor growth as well as lung metastasis in nude mice. The oncogenic effect of OGT was investigated, we found that OGT significantly induced palmitic acid production identified by LC-MS, which enhanced the protein expression of endoplasmic reticulum (ER) stress masters of glucose-regulated protein 78 and inositol-requiring enzyme 1α. Consequently, OGT significantly activated JNK/c-jun/AP-1 cascade by increasing protein expression of p-JNK, p-c-Jun and activation of AP-1; and induced NF-κB pathway through enhancing the protein levels of p-IKKα/ p-IKKβ, p-p65, p-p50 and the NF-κB DNA binding activity. Notably, OGT inhibition by its antagonist (ST045849) suppressed cell proliferation in vitro (p<0.001) and in xenograft mice models (p<0.05).

Conclusions: OGT plays an oncogenic role in NAFLD-associated HCC through regulating palmitic acid and inducing ER stress, consequently activating oncogenic JNK/c-jun/AP-1 and NF-κB cascades.

Lay summary: OGT, a unique glycosyltransferase enzyme, was identified to be upregulated in non-alcoholic fatty liver disease-associated hepatocellular carcinoma tissues by transcriptome sequencing. Here, we found that OGT plays a role in cancer by promoting tumor growth and metastasis in both cell models and animal models. This effect is mediated by the induction of palmitic acid.

Keywords: ER stress; NAFLD-HCC; NF-κB; O-GlcNAc transferase; Palmitic acid.