Characterisation of the cellular response to defective translational termination

Enzymatic hydroxylation of varied cellular substrates is catalyzed by the 2-oxoglutarate and Fe(II) dependent 2-oxoglutrate (OG) oxygenase group of proteins. These enzymes control gene expression, from epigenetics to splicing and translation. The 2OG oxygenase JMJD4 has been shown to catalyse the hydroxylation of the eukaryotic omnipotent termination factor 1 (eRF1), and is essential for optimal translational termination. In this thesis, we expand on previous work by examining two further potential binding partners of JMJD4, GTF2I and TCP1-γ. Subsequently, we find that depletion of JMJD4 and eRF1 is associated with growth reduction in cancer cell lines in 2D and 3D. The transcriptomic changes in response to eRF1 depletion are then assessed by RNA-Seq. Among the potential pathways identified, downstream targets of the transcription factor ATF4 were most prominent. Upregulation of ATF4 and its downstream targets was validated in an eRF1 rescue system and the contribution of specific subdomains of eRF1 to the transcriptional response assessed, indicating multiple arms of the unfolded protein response being upregulated downstream of defective translational termination. The implications of our findings and their relevance in wider biological and disease contexts, including cancer, is finally discussed

Tumour hypoxia causes DNA hypermethylation by reducing TET activity

Hypermethylation of the promoters of tumour suppressor genes represses transcription of these genes, conferring growth advantages to cancer cells. How these changes arise is poorly understood. Here we show that the activity of oxygen-dependent ten-eleven translocation (TET) enzymes is reduced by tumour hypoxia in human and mouse cells. TET enzymes catalyse DNA demethylation through 5-methylcytosine oxidation. This reduction in activity occurs independently of hypoxia-associated alterations in TET expression, proliferation, metabolism, hypoxia-inducible factor activity or reactive oxygen species, and depends directly on oxygen shortage. Hypoxia-induced loss of TET activity increases hypermethylation at gene promoters in vitro. In patients, tumour suppressor gene promoters are markedly more methylated in hypoxic tumour tissue, independent of proliferation, stromal cell infiltration and tumour characteristics. Our data suggest that up to half of hypermethylation events are due to hypoxia, with these events conferring a selective advantage. Accordingly, increased hypoxia in mouse breast tumours increases hypermethylation, while restoration of tumour oxygenation abrogates this effect. Tumour hypoxia therefore acts as a novel regulator of DNA methylatio

Tumour hypoxia causes DNA hypermethylation by reducing TET activity

Hypermethylation of the promoters of tumour suppressor genes represses transcription of these genes, conferring growth advantages to cancer cells. How these changes arise is poorly understood. Here we show that the activity of oxygen-dependent ten-eleven translocation (TET) enzymes is reduced by tumour hypoxia in human and mouse cells. TET enzymes catalyse DNA demethylation through 5-methylcytosine oxidation. This reduction in activity occurs independently of hypoxia-associated alterations in TET expression, proliferation, metabolism, hypoxia-inducible factor activity or reactive oxygen species, and depends directly on oxygen shortage. Hypoxia-induced loss of TET activity increases hypermethylation at gene promoters in vitro. In patients, tumour suppressor gene promoters are markedly more methylated in hypoxic tumour tissue, independent of proliferation, stromal cell infiltration and tumour characteristics. Our data suggest that up to half of hypermethylation events are due to hypoxia, with these events conferring a selective advantage. Accordingly, increased hypoxia in mouse breast tumours increases hypermethylation, while restoration of tumour oxygenation abrogates this effect. Tumour hypoxia therefore acts as a novel regulator of DNA methylation.status: publishe