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- Is Antisense Oligonucleotide-Mediated Exon Skipping a Potential Therapeutic Approach for Mucolipidosis II?Publication . Gonçalves, Mariana; Moreira, Luciana; Encarnação, Marisa; Duarte, Ana Joana; Gaspar, Paulo; Santos, Juliana Inês; Coutinho Maria Francisca; Prata, Maria João; Omidi, Maryam; Pohl, Sandra; Silva, Frederico; Oliveira, Paula; Matos, Liliana; Alves, SandraIntridution: Mucolipidosis II (ML II) is a Lysosomal Storage Disorder caused by N-acetylglucosamine-1-phosphotransferase (GlcNAc-PT) deficiency, which impairs lysosomal hydrolases trafficking. Here, we explored an innovative therapeutic strategy based on the use of antisense oligonucleotides (ASOs) to promote targeted skipping of GNPTAB exon 19, which harbors c.3503_3504del, the most frequent disease-causing variant. Previously, in ML II patients’ fibroblasts, we tested ASOs to induce exon 19 skipping, successfully generating an in-frame mRNA1. Now, our aim is to determine if this in-frame transcript leads to increased GlcNAc-PT levels. Methodology: First, the GlcNAc-PT activity was measured in fibroblasts, but activity levels were similar in ML II and control fibroblasts (treated/non-treated) showing that the assay is not proper to measure endogenous levels. To overcome this, we designed 3 constructs: a WT (full GNPTAB cDNA), a del_ex19 (without exon 19) and a mutant (with the mutation c.3503_3504del) that were transfected in HEK293T cells. Then GlcNAc-PT expression was analyzed by Western Blot (WB). Also, we measured the activity of several hydrolases and evaluated the expression of α-galactosidase A (α-Gal) by WB after ASO treatment. To further validate this therapy we also generated a novel GlcNAc-PT antibody in rabbits. Results: Our results showed that HEK293T cells were able to express all the constructs. The WB of both WT and del_ex19 constructs showed bands corresponding to the α/β precursor. However, only the WT construct expressed the β-subunit, suggesting that there is no GlcNAc-PT activity in the absence of exon 19. As expected, in the delTC construct WB no α/β precursor band was detected. We also observed a slight increase in the activity of various lysosomal hydrolases in ML II fibroblasts after treatment. However, only the α-Gal values were statistically significant, but the WB analysis for this enzyme did not reveal any band in ASO-treated ML II cells. We also developed a novel antibody for GlcNAc-PT. Preliminary results showed a β-subunit band both in control and patient fibroblasts (unexpected), but in overexpression both WT and del_ex19 constructs presented α/β precursor bands. So, further assays are needed to assess its specificity. Conclusion: Our ASO-based approach effectively promotes exon 19 skipping. However, this strategy, as far as we have been able to prove, is not able to restore any GlcNAc-PT enzymatic activity. Further validation, including co-localization studies are planned to clarify these findings.
- The role of UPF1 cap-independent translation in colorectal cancerPublication . Lacerda, Rafaela; Menezes,Juliane; Elias, Adriana; Sousa, Sofia de; Romão, LuísaColorectal cancer (CRC) is one of the deadliest diseases worldwide with projections pointing towards an increase for the next two decades. Translation dysregulation of many genes contributes to CRC development, and here we are studying the role of translation dysregulation of up-frameshift 1 (UPF1) in CRC. This protein is involved in many cellular mechanisms such as nonsense-mediated mRNA decay, cell cycle progression, or telomere maintenance and homeostasis. It also works as a tumour suppressor protein in most cancers but not in CRC, in which UPF1 plays an oncogenic role. We used the Xena platform to perform in silico analyses that revealed UPF1 protein overexpressed in CRC, contrary to several other analysed cancers. Besides, UPF1 protein levels are increased in CRC compared to the counterpart normal tissues. Experimentally, we confirmed that UPF1 protein expression is maintained in different CRC cell lines under normal conditions or endoplasmic reticulum (ER) stress. To understand the mechanism underlying such maintenance, we used a bicistronic reporter construct to test whether UPF1 5’ untranslated region (UTR) can mediate alternative translation initiation and we concluded that such sequence drives cap-independent translation initiation, in both normal and stress conditions. Deletional and mutational analyses of UPF1 5’UTR showed that nucleotides 1–100 [stem-loop (SL) I] and 151–275 (SL III) — out of 275 nucleotides — are the minimal required sequences for the cap-independent translation initiation mechanism to work properly. Using RNA antisense oligonucleotides (ASOs) targeting UPF1 SL I and III, we observed a reduced UPF1 expression in HCT116 (CRC) cells, supporting the functional role of SL I and SL III in mediating cap-independent translation. Altogether, these results highlight the importance of cap-independent translation initiation in UPF1 expression regulation, in conditions that mimic the tumour microenvironment, and this might be used as a therapeutic target.