Context‐specific roles of diphthamide deficiency in hepatocellular carcinogenesis

Diphthamide biosynthesis protein 1 (DPH1) is biochemically involved in the first step of diphthamide biosynthesis, a post‐translational modification of eukaryotic elongation factor 2 (EEF2). Earlier studies showed that DPH1, also known as ovarian cancer‐associated gene 1 (OVCA1), is involved in ovarian carcinogenesis. However, the role of DPH1 in hepatocellular carcinoma (HCC) remains unclear. To investigate the impact of DPH1 in hepatocellular carcinogenesis, we performed data mining from The Cancer Genome Atlas Liver Hepatocellular Carcinoma (TCGA‐LIHC) dataset. We found that reduced DPH1 levels were associated with advanced stages and poor survival of patients with HCC. Also, we generated hepatocyte‐specific Dph1‐deficient mice and showed that diphthamide‐deficient EEF2 resulted in a reduced translation elongation rate in the hepatocytes and led to mild liver damage with fatty accumulation. After N‐diethylnitrosamine (DEN)‐induced acute liver injury, p53‐mediated pericentral hepatocyte death was increased, and compensatory proliferation was reduced in Dph1‐deficient mice. Consistent with these effects, Dph1 deficiency decreased the incidence of DEN‐induced pericentral‐derived HCC and revealed a protective effect against p53 loss. In contrast, Dph1 deficiency combined with Trp53‐ or Trp53/Pten‐deficient hepatocytes led to increased tumor loads associated with KRT19 (K19)‐positive periportal‐like cell expansion in mice. Further gene set enrichment analysis also revealed that HCC patients with lower levels of DPH1 and TP53 expression had enriched gene‐sets related to the cell cycle and K19‐upregulated HCC. Additionally, liver tumor organoids obtained from 6‐month‐old Pten/Trp53/Dph1‐triple‐mutant mice had a higher frequency of organoid re‐initiation cells and higher proliferative index compared with those of the Pten/Trp53‐double‐mutant. Pten/Trp53/Dph1‐triple‐mutant liver tumor organoids showed expression of genes associated with stem/progenitor phenotypes, including Krt19 and Prominin‐1 (Cd133) progenitor markers, combined with low hepatocyte‐expressed fibrinogen genes. These findings indicate that diphthamide deficiency differentially regulates hepatocellular carcinogenesis, which inhibits pericentral hepatocyte‐derived tumors and promotes periportal progenitor‐associated liver tumors. © 2022 The Pathological Society of Great Britain and Ireland.