Diphthamide modification of eEF2 is required for gut tumor-like hyperplasia induced by oncogenic Ras

Diphthamide - a conserved modification of eEF2 with clinical relevance

Diphthamide, a complex modification on eukaryotic translation elongation factor 2 (eEF2), assures reading-frame fidelity during translation. Diphthamide and enzymes for its synthesis are conserved in eukaryotes and archaea. Originally identified as target for diphtheria toxin (DT) in humans, its clinical relevance now proves to be broader than the link to pathogenic bacteria. Diphthamide synthesis enzymes (DPH1 and DPH3) are associated with cancer, and DPH gene mutations can cause diphthamide deficiency syndrome (DDS). Finally, new analyses provide evidence that diphthamide may restrict propagation of viruses including SARS-CoV-2 and HIV-1, and that DPH enzymes are targeted by viruses for degradation to overcome this restriction. This review describes how diphthamide is synthesized and functions in translation, and covers its clinical relevance in human development, cancer, and infectious diseases.

Interaction of lncRNA Gm2044 and EEF2 promotes estradiol synthesis in ovarian follicular granulosa cells

The functions and molecular mechanisms of long noncoding RNA (lncRNA) in reproduction have been widely studied at present. However, lncRNA regulating hormone synthesis in ovarian follicular granulosa cells has not been sufficiently studied. Our previous research demonstrated that lncRNA Gm2044 could promote estradiol synthesis in follicular granulosa cells. In this study, we identified 21 binding proteins of lncRNA Gm2044 in ovarian follicles using comprehensive identification of RNA-binding proteins by mass spectrometry (ChIRP-MS). RNA immunoprecipitation (RNA IP) and reverse transcription PCR (RT-PCR) confirmed that lncRNA Gm2044 can interact with eukaryotic translation elongation factor 2 (EEF2) protein. Furthermore, we constructed lncRNA Gm2044 knockout mice using the CRISPR/Cas9 method. Although the follicular development and fertility of female lncRNA Gm2044 knockout mice were not affected, the serum estradiol concentration in female lncRNA Gm2044 knockout mice significantly decreased. Western blotting and ELISA revealed that lncRNA Gm2044 may promote the binding of EEF2 to Nr5a1 mRNA and then enhance the Nr5a1 mRNA translation, and the upregulated NR5A1 protein can strengthen estradiol synthesis. To determine the potential signaling pathway of lncRNA Gm2044 regulating estradiol synthesis, transcriptome sequencing was performed for ovaries of adult lncRNA Gm2044 knockout mice, which identified 565 significant up-regulated genes and 303 significant down-regulated genes, which were then analyzed with Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) and validated by molecular experiments. Understanding how lncRNA Gm2044/EEF2 protein regulates estradiol synthesis will help treat estrogen-related reproductive diseases.

Oncogenic stress-induced Netrin is a humoral signaling molecule that reprograms systemic metabolism in Drosophila

Cancer exerts pleiotropic, systemic effects on organisms, leading to health deterioration and eventually to organismal death. How cancer induces systemic effects on remote organs and the organism itself still remains elusive. Here we describe a role for NetrinB (NetB), a protein with a particularly well-characterized role as a tissue-level axon guidance cue, in mediating oncogenic stress-induced organismal, metabolic reprogramming as a systemic humoral factor. In Drosophila, Ras-induced dysplastic cells upregulate and secrete NetB. Inhibition of either NetB from the transformed tissue or its receptor in the fat body suppresses oncogenic stress-induced organismal death. NetB from the dysplastic tissue remotely suppresses carnitine biosynthesis in the fat body, which is critical for acetyl-CoA generation and systemic metabolism. Supplementation of carnitine or acetyl-CoA ameliorates organismal health under oncogenic stress. This is the first identification, to our knowledge, of a role for the Netrin molecule, which has been studied extensively for its role within tissues, in humorally mediating systemic effects of local oncogenic stress on remote organs and organismal metabolism.

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 have 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 let 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 hepatocytes-derived tumor and promotes periportal progenitors-associated liver tumors. This article is protected by copyright. All rights reserved.

A novel DPH5-related diphthamide-deficiency syndrome causing embryonic lethality or profound neurodevelopmental disorder

PURPOSE

Diphthamide is a post-translationally modified histidine essential for messenger RNA translation and ribosomal protein synthesis. We present evidence for DPH5 as a novel cause of embryonic lethality and profound neurodevelopmental delays (NDDs).

METHODS

Molecular testing was performed using exome or genome sequencing. A targeted Dph5 knockin mouse (C57BL/6Ncrl-Dph5^em1Mbp/Mmucd) was created for a DPH5 p.His260Arg homozygous variant identified in 1 family. Adenosine diphosphate-ribosylation assays in DPH5-knockout human and yeast cells and in silico modeling were performed for the identified DPH5 potential pathogenic variants.

RESULTS

DPH5 variants p.His260Arg (homozygous), p.Asn110Ser and p.Arg207Ter (heterozygous), and p.Asn174LysfsTer10 (homozygous) were identified in 3 unrelated families with distinct overlapping craniofacial features, profound NDDs, multisystem abnormalities, and miscarriages. Dph5 p.His260Arg homozygous knockin was embryonically lethal with only 1 subviable mouse exhibiting impaired growth, craniofacial dysmorphology, and multisystem dysfunction recapitulating the human phenotype. Adenosine diphosphate-ribosylation assays showed absent to decreased function in DPH5-knockout human and yeast cells. In silico modeling of the variants showed altered DPH5 structure and disruption of its interaction with eEF2.

CONCLUSION

We provide strong clinical, biochemical, and functional evidence for DPH5 as a novel cause of embryonic lethality or profound NDDs with multisystem involvement and expand diphthamide-deficiency syndromes and ribosomopathies.