Deciphering the role of guanine-7 tRNA methylation in Prostate Cancer progression

Abstract

Prostate cancer (PCa) is the most prevalent cancer and the third cause of death by cancer in European men. Although most of the patients respond to hormone deprivation therapy, this disease presents a high relapse rate and many patients develop castration resistant prostate cancer (CRPC) with limited treatment options. This progression is due to the existence of preexisting cancer cell sub-populations resistant to conventional treatments and with high capacity to self-renew, leading to tumour regeneration and therapy resistance. Recent evidence has indicated that self-renewal and stress resistance are controlled by epitranscriptomic marks or RNA modifications, and manipulation of the epitranscriptome may be a potential therapeutic target to specifically eliminate those cancer cells resistant to conventional treatments. By using genomic screenings, transcriptomic and epitranscriptomic tools, CRISPR/Cas9 technology, chemistry, proteomics, cell and mouse models and patient samples we aim to decipher the epitranscriptome in prostate cancer in order to implement novel therapeutics strategies to eliminate cancer cells with high survival and self-renewal capacity. The expression of RNA modifying enzymes was analysed in sequencing data from pre-existing studies including TCGA. We found that the transfer-RNA (tRNAs) methyltransferase METTL1 was overexpressed in primary and advanced tumours and increased expression correlated with poor prognosis. Altered expression of the methyltransferase was confirmed by qPCR and WB of primary tumours samples from patients from Basurto University Hospital. In addition, we further confirmed overexpression of the enzyme in a mouse model of PCa, where PTEN is deleted in the prostatic epithelium. For functional characterization of METTL1 role, cells over-expressing, silenced or knocked out for METTL1 using CRISPR/Cas9 were generated in prostate cancer cell lines. In vitro analysis showed that METTL1 overexpression led to enhanced proliferation in adherent and suspension conditions. METTL1 deletion resulted in impaired cell proliferation and migration in prostate cancer cell lines, reduced self-renewal capacity in cell cultures in self-renewal conditions and reduced tumour formation capacity in xenografted models. Mechanistically, METTL1 deletion in cells lead to a reduction of 7-methylguanosine (m7G) in tRNAs and codon usage alterations favouring translation of proteins enriched in m7G-unmethylated codons. Our study concludes that METTL1 is over-expressed in PCa and higher expression correlates with poor prognosis. Depletion of METTL1 leads to a reduction of m7G levels in tRNAs and protein synthesis alterations, which results in a deregulation of essential cellular processes such as proliferation, migration and self-renewal. Whether METTL1 implies a new possible therapeutic approach in PCa treatment needs further evaluation.