The role of mRNA capping enzyme CMTR1 in hepatocellular carcinoma and the innate immune response

Brett, Natasha June Maria (2025) The role of mRNA capping enzyme CMTR1 in hepatocellular carcinoma and the innate immune response. PhD thesis, University of Glasgow.

Abstract

mRNA capping of is essential for the efficient translation and processing of transcripts generated by RNA polymerase II (RNAPII) in eukaryotes. Cap methyltransferase 1 (CMTR1) is responsible for the generation of the mature Cap-1 structure (m7G(5’)ppp(5’)Nm, by the addition of a methyl group at the 2’-O-ribose position of the first transcribed nucleotide. This modification acts as a means for the innate immune system to differentiate “self” and “non-self” RNA species and appears to regulate the expression of specific genes implicated in proliferation, ribosomal biogenesis and histone synthesis. In murine models of liver cancer, where oncogenes Ctnnb1 and MYC were dysregulated, conditional knock out of CMTR1 accelerated tumorigenesis. To enrich understanding of the role of CMTR1 in Hepatocellular carcinoma (HCC), characterisation of CMTR1 and relevant binding partners was undertaken in mouse models and Huh-7 cell lines. Following this, the CMTR1 interactome was analysed in wild type (WT) and Ctnnb1ex3/WT; R26-LSL-Myc mouse liver to determine if CMTR1 interacting proteins influence the role of this capping enzyme in liver cancer. Of the proteins identified as potential interacting partners of CMTR1, Argininosuccinate synthetase (ASS1) and PGAM family member 5, mitochondrial serine/threonine protein phosphatase (PGAM5) were selected for validation. This has laid initial foundations for further investigation into the biological ramifications of these interactions, particularly in regard to hepatocellular carcinoma.

CMTR1 is phosphorylated at 15 sites within the N-terminus of the protein, which promotes binding between CMTR1 and RNAPII to enhance capping activity. CMTR1 has been previously identified as an interferon stimulated gene (ISG) and promotes expression of fellow ISGs, in part by preventing Interferon induced proteins with tetratricopeptide repeats (IFIT) mediated translational inhibition. To determine the role of CMTR1 phosphorylation in the innate immune response mouse embryonic fibroblasts (MEFs) expressing WT CMTR1 and a phosphodeficient mutant were treated with immunostimulatory agents, followed by analysis of ISG expression. In the absence of CMTR1 phosphorylation expression of various ISGs was attenuated, particularly at earlier stages of the interferon response. Despite this, follow up experiments involving infection of MEF cells with Influenza A virus (IAV) uncovered that CMTR1 phosphorylation promotes IAV infection.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: R Medicine > RC Internal medicine > RC0254 Neoplasms. Tumors. Oncology (including Cancer)
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Supervisor's Name: Cowling, Professor Victoria
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-84921
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 25 Feb 2025 15:56
• Last Modified: 25 Feb 2025 16:44
• Thesis DOI: 10.5525/gla.thesis.84921
• URI: https://theses.gla.ac.uk/id/eprint/84921