Guanosine-7 tRNA methylation regulates Prostate Cancer progression through protein reprogramming via tRNA-derived fragments biogenesis

Resumen

Prostate Cancer (PCa) is the most common tumour and the third cause of death by cancer in European men. Although important advances have been made in early stages of the disease and most of the tumours respond to hormone deprivation therapy, many patients develop Castration Resistant Prostate Cancer (CRPC) which lacks effective therapeutic options. One of the major drawbacks for PCa treatment is the high intratumoural heterogeneity and the lack of reliable biomarkers of disease progression. During the last years, several studies have highlighted the importance of RNA chemical modifications in the progression and therapy response of several tumours. Thus, manipulation of the epitranscriptome might be a potential therapeutic target to specifically eliminate those cancer cell resistant to conventional treatments. Thereby, this thesis focuses in deciphering the epitranscriptomic landscape of PCa in order to identify altered epitranscriptomic regulators that may control tumour proliferation and survival capacities. In silico analysis demonstrated that the tRNA methyltransferase METTL1 was overexpressed in primary and advanced PCa tumours, being increased expression correlated with poor prognosis. Altered expression of the methyltransferase was confirmed in primary tumours samples from both patients and from PtenKO PCa mouse model. For functional characterization of METTL1 molecular role, cells over-expressing, silenced and knocked out for the methyltransferase were generated in distinct PCa cell lines. In consequence, lack of METTL1 resulted in accumulation of 5’TOG tRNA derived fragments, which lead not only to a global inhibition of protein synthesis but also to an alteration of the translational programme. As a result, METTL1 deletion resulted in impaired cell proliferation and self-renewal capacity in cell cultures and reduced tumour formation and proliferation in both xenografted and PtenKO PCa in vivo murine models. Impaired self-renewal capacity is observed in a human PDXs-derived model upon the enzyme depletion. In addition, cells lacking METTL1 exhibited impaired autophagy termination, which lead to accumulation of protein aggregates, ROS and DNA damage, resulting in an hypersensitivity to stress conditions. Altogether, this thesis demonstrates that METTL1 regulates tumoural cells capacity to respond to stress stimuli and inhibition of its methyltransferase activity ultimately leads to an increase sensitivity to traditional therapeutic agents. This study concludes that METTL1 is overexpressed in PCa and higher expression correlates with poor prognosis. METTL1 is essential for 7-guanine methylation in tRNAs and lack of the methylation results in protein synthesis alterations, which results in a deregulation of essential cellular processes as proliferation and self-renewal. Whether METTL1 can be used as a therapeutical target needs further validation.