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.

Pten Haplodeficiency Accelerates Liver Tumor Growth in miR-122a-Null Mice via Expansion of Periportal Hepatocyte-Like Cells.

This study aimed to shed light on the molecular and cellular mechanisms responsible for initiation and progression of liver malignancies by examining the role of phosphatase and tensin homolog on chromosome 10 (Pten) in liver tumor progression in miR-122a (Mir122a)-null mice. We generated and monitored liver tumor initiation in Mir122a-null Pten heterozygous (Mir122a-/-;Pten+/- and Mir122a-/-;Alb-Cre;Ptenfx/+) mice and compared the results with those in Mir122a-/- mice. Both Mir122a-/-;Pten+/- and Mir122a-/-;Alb-Cre;Ptenfx/+ mice developed visible liver tumor nodules at 6 months of age. In premalignant livers of Mir122a-/-;Pten+/- mice, decreased PTEN and increased phosphorylated AKT were specifically observed in periportal cells, associated with inflammatory and fibrotic microenvironments. Furthermore, IL-1ß and tumor necrosis factor-α levels significantly increased in Mir122a-/-;Pten+/- premalignant livers at 6 months of age. Oval cells expressing A6, epithelial cell adhesion molecule, keratin (K) 8, K19, and SRY (sex determining region Y)-box 9 (SOX9) were present in both Mir122a-/- and Mir122a-/-;Pten+/- livers. Interestingly, a hybrid hepatocyte-like population with intermediate levels of K8, HNF4α, and SOX9 was located proximally to the oval cells in Mir122a-/-;Pten+/- livers. Lineage-tracing experiments revealed that these intermediate levels of K8 hepatocyte-like cells may be the cells of origin for Mir122a-/-;Pten+/- liver tumors. These findings suggest that inflammatory microenvironments in the periportal area of Mir122a-null mice may locally cause Pten down-regulation and expand tumor-initiating cells, causing hepatocellular carcinoma.