The role of NSUN2-mediated mRNA 5-methylcytidine methylation in colorectal cancer initiation and progression
Tez Türü: Bütünleşik Doktora
Tezin Yürütüldüğü Kurum: University of Edinburgh, Institute of Genetics and Cancer, İngiltere
Tez Danışmanı: Dr. Kevin Myant
Tezin Onay Tarihi: 2024
Tezin Dili: İngilizce
Desteklendiği Program: Diğer
Özet:
Colorectal cancer (CRC), the second commonest cause of cancer mortality, initiates with the loss of the APC gene and progresses to cancer with additional mutations. APC is mutated in ~80% of CRC patients with Wnt signalling activation. Despite all treatment strategies, relapse still occurs. There are several reasons for the relapse: unsuccessful surgical removal, residual cancer stem cells (CSCs) after treatment, and poor knowledge or variability in molecular mechanisms. To improve these, an extensive understanding of cancer biology is crucial. A recent cancer hallmark phenomenon is “RNA modifications” or “Epitranscriptomics”. Of these, 5-methylcytidine (m5C) was the first modified nucleoside discovered in distinct RNA types and installed to distinct RNAs by NSUN2. m5C is well-characterized in tRNA and rRNA, but its functional importance in mRNA has been poorly understood. Moreover, NSUN2-mediated m5C has been previously investigated in other cancer types but its role in CRC initiation remains elusive. Along with the literature and our preliminary data, we hypothesised that NSUN2 and m5C-mRNAs mediate CRC initiation and progression. In my project, we observed elevated NSUN2 levels following Apc-loss in mouse intestines and CRC patient tumours. We also found higher Nsun2 and m5C levels in Lgr5-expressing intestinal stem cells. We next determined that NSUN2 functions through CSC regulation in Apc-loss organoids and intestinal crypts by modulating the phenotype and transcriptomic footprints. Convincingly, loss of NSUN2 in normal intestine did not affect intestinal architecture and overall transcriptome. Furthermore, NSUN2 also selectively affects metastatic CRC models depending on the mutational burden. In terms of NSUN2-mediated global RNA methylation, we found no change in the intestinal models. However, we identified specific epitranscriptomic footprints of mRNAs when we conducted mRNA whole transcriptomic bisulphite sequencing. Subsequently, two potential mechanisms could be behind NSUN2-mediated mRNA methylation in CRC initiation. The former is dysregulated mRNA methylation that drives transcriptional drift towards attenuation. The latter is dysregulated methylation and expression of Igfbp4 mRNA along with dysfunctional MAPK signalling that negatively affect Apc-deficient intestinal homeostasis. Collectively, my findings are the first reporting NSUN2/m5C -mediated CRC initiation through regulating CSCs. Therefore, NSUN2-m5C-mRNA axis has significant potential to investigate CRC initiation, tumour heterogeneity, and relapse.