| Resumo: | Up-frameshift 1 (UPF1) is the key factor in nonsense-mediated mRNA decay (NMD, a mechanism that degrades transcripts carrying premature translation termination codons. Besides its role in NMD, UPF1 has also a role in other mechanisms, such as cell cycle progression, being crucial for the G1/S transition, and in telomere maintenance and homeostasis. Furthermore, it has also been identified as having tumour suppressor activity in different cancers, such as hepatocellular carcinoma. Our data supports the existence of an IRES within the human UPF1 5’ untranslated region (UTR). In fact, using a bicistronic reporter system, we observed that UPF1 5’UTR can mediate internal translation in a 5’ cap-independent manner, both in normal and under stress conditions. We concluded that the first 100 nucleotides and the last 125 (out of a total of 275) are the minimal sequences essential for the identified IRES activity. According to the in silico predicted secondary structure, these two segments correspond to two stem-loops. Now, we are experimentally confirming this predicted secondary structure, and understanding the physiological role of this IRES-mediated activity in the NMD process. Also, we are testing its importance for UPF1 function as a tumour suppressor. For that, we are using custom-made antisense oligonucleotides that specifically target those stem-loops and see to what extent they inhibit UPF1 IRES-mediated activity and how such inhibition will play a role in the cell and the functions in which UPF1 participates. Also, we are testing some hallmarks of cancer, such as proliferation, invasion, and apoptosis inhibition when the UPF1 IRES is impaired. With this work, we wish to unravel a new layer of knowledge in gene expression regulation of UPF1.
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