Browsing by Author "Matos, Paulo"
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- Activation of RAC1/PAK1 axis potentiates transcriptional upregulation of DNA damage response genes via the BCL6/STAT5 switchPublication . Barros, Patrícia; Amaral, Andreia; Abrantes, Leonor; Oliveira, Tiago; Lourio, Henriqueta; Silva, Maria João; Jordan, Peter; Gama-Carvalho, Margarida; Matos, PauloColorectal cancer is one of the most prevalent types of cancer worldwide. The GTPase RAC1 and its effector PAK1 have been found overexpressed or hyperactivated in colorectal cancers, particularly those with more aggressive and invasive features, leading to unfavourable clinical prognosis, often resulting from chemoresistance.
- Adherens Junction Integrity Is a Critical Determinant of Sodium Iodide Symporter Residency at the Plasma Membrane of Thyroid CellsPublication . Faria, Márcia; Vareda, José; Miranda, Micaella; Bugalho, Maria João; Silva, Ana Luísa; Matos, PauloWhile most cases of differentiated thyroid carcinoma (DTC) are associated with a good prognosis, a significant number progress to advanced disease exhibiting aggressive clinical characteristics and often becoming refractory to radioactive iodine (RAI) treatment, the current gold-standard therapeutic option for metastatic disease. RAI-refractoriness is caused by defective functional expression of the sodium-iodide symporter (NIS), which is responsible for the active transport of iodide across the plasma membrane (PM) into thyroid follicles. NIS deficiency in these tumors often reflects a transcriptional impairment, but also its defective targeting and retention at the cells’ PM. Using proteomics, we previously characterized an intracellular signaling pathway derived from SRC kinase that acts through the small GTPase RAC1 to recruit and bind the actin-anchoring adaptor EZRIN to NIS, regulating its retention at the PM of both non-transformed and cancer thyroid cells. Here, we describe how by reanalyzing the proteomics data, we identified cell–cell adhesion as the molecular event upstream the pathway involved in the anchoring and retention at the PM. We show that by interacting with NIS at the PM, adherens junction (AJ)-associated P120-catenin recruits and is phosphorylated by SRC, allowing it to recruit RAC1 to the complex. This enables SRC-phosphorylated VAV2 exchange factor to activate RAC1 GTPase, inducing NIS retention at the PM, thus increasing its abundance and function at the surface of thyroid cells. Our findings indicate that the loss of epithelial cell–cell adhesion may contribute to RAI refractoriness, indicating that in addition to stimulating NIS expression, successful resensitization therapies might require the employment of agents that improve cell–cell adhesion and NIS PM retention in refractory TC cells.
- Adverse Outcome Pathways Associated with the Ingestion of Titanium Dioxide Nanoparticles - A Systematic ReviewPublication . Rolo, Dora; Assunção, Ricardo; Ventura, Célia; Alvito, Paula; Gonçalves, Lídia; Martins, Carla; Bettencourt, Ana; Jordan, Peter; Vital, Nádia; Pereira, Joana; Pinto, Fátima; Matos, Paulo; Silva, Maria João; Louro, HenriquetaTitanium dioxide nanoparticles (TiO2-NPs) are widely used, and humans are exposed through food (E171), cosmetics (e.g., toothpaste), and pharmaceuticals. The oral and gastrointestinal (GIT) tract are the first contact sites, but it may be systemically distributed. However, a robust adverse outcome pathway (AOP) has not been developed upon GIT exposure to TiO2-NPs. The aim of this review was to provide an integrative analysis of the published data on cellular and molecular mechanisms triggered after the ingestion of TiO2-NPs, proposing plausible AOPs that may drive policy decisions. A systematic review according to Prisma Methodology was performed in three databases of peer-reviewed literature: Pubmed, Scopus, and Web of Science. A total of 787 records were identified, screened in title/abstract, being 185 used for data extraction. The main endpoints identified were oxidative stress, cytotoxicity/apoptosis/cell death, inflammation, cellular and systemic uptake, genotoxicity, and carcinogenicity. From the results, AOPs were proposed where colorectal cancer, liver injury, reproductive toxicity, cardiac and kidney damage, as well as hematological effects stand out as possible adverse outcomes. The recent transgenerational studies also point to concerns with regard to population effects. Overall, the findings further support a limitation of the use of TiO2-NPs in food, announced by the European Food Safety Authority (EFSA).
- Alternative Splicing at the Crossroad of Inflammatory Bowel Diseases and Colitis-Associated Colon CancerPublication . Matos, Paulo; Jordan, PeterSimple Summary: Patients with ulcerative colitis (UC) face a higher risk of developing colorectal cancer (CRC) due to chronic inflammation, a known promoter of tumour growth. Here, we review the molecular differences between colitis-associated cancer (CAC) and sporadic CRC, with a focus on “alternative splicing”, a mechanism by which the same gene can produce various protein forms. We explore how inflammation triggers changes in this process, increasing cancer risk for UC patients. The revised data emphasize that additional research into these molecular changes could help identify new biomarkers (molecules that indicate disease progression) and pave the way for innovative treatments targeting these alterations. Such advances would improve outcomes and quality of life for patients while contributing to cancer prevention and care.
- Alternative splicing of tumour-related Rac1b in colorectal cells is regulated by protein phosphorylation of splicing factor SRSF1Publication . Gonçalves, Vânia; Henriques, Andreia; Pereira, Joana; Neves-Costa, Ana; Moyer, Pat; Ferreira Moita, Luís; Gama-Carvalho, Margarida; Matos, Paulo; Jordan, PeterThe pre-messenger RNA of the majority of human genes can generate various transcripts through alternative splicing, and different tissues or disease states show specific patterns of splicing variants. These patterns depend on the relative concentrations of the splicing factors present in the cell nucleus, either as a consequence of their expression levels or of post-translational modifications such as protein phosphorylation, which are determined by signal transduction pathways. Here we analyzed the contribution of protein kinases to the regulation of alternative splicing variant Rac1b that is overexpressed in certain tumor types. In colorectal cells we found that depletion of AKT2, AKT3, GSK3β and SRPK1 significantly decreased endogenous Rac1b levels. Whereas knockdown of AKT2 and AKT3 affected only Rac1b protein levels suggesting a post-splicing effect, the depletion of GSK3β or SRPK1 decreased Rac1b alternative splicing, an effect mediated through changes in splicing factor SRSF1. In particular, the knockdown of SRPK1 or inhibition of its catalytic activity reduced phosphorylation and subsequent translocation of SRSF1 to the nucleus, limiting its availability to promote the inclusion of alternative exon 3b into the Rac1 pre-mRNA. Altogether, the data identify SRSF1 as a prime regulator of Rac1b expression in colorectal cells and provide further mechanistic insights into how the regulation of alternative splicing events by protein kinases can contribute to sustain tumor cell survival.
- Alternative splicing of tumour-related Rac1b is regulated by upstream signalling pathwaysPublication . Gonçalves, Vânia; Matos, Paulo; Jordan, PeterThe small GTPase Rac1 regulates signalling pathways controlling actin-dependent cell motility as well as gene transcription. An alternative splicing variant Rac1b is overexpressed in a subset of colorectal tumours and cooperates with mutant B-Raf to sustain tumour cell viability. The alternative splicing mechanism regulating Rac1b expression involves two antagonistic splicing factors, ASF/SF2 and SRp20. Using a Rac1 minigene approach and siRNA-mediated depletion, we identified ASF/SF2 as an enhancer of endogenous Rac1b splicing whereas SRp20 acts as a silencer. Inhibition of the PI3-kinase pathway increased protein levels of ASF/SF2 and promoted Rac1b generation. By contrast, depletion of endogenous protein kinase SRPK1 led to decreased Rac1b expression. Together, these data indicate that altered upstream signaling pathways in colorectal cancer cells will target splicing factors that regulate alternative splicing of the small GTPase Rac1.
- Alternative splicing of tumour-related rac1b is regulated by upstream signalling pathwaysPublication . Gonçalves, Vânia; Matos, Paulo; Jordan, PeterThe small GTPase Rac1 regulates signalling pathways controlling actin-dependent cell motility as well as gene transcription. Analternative splicing variant Rac1b is overexpressed in a subset of colorectal tumours and cooperates with mutant B-Raf to sustain tumour cellviability. The alternative splicing mechanism regulating Rac1b expression involves two antagonistic splicing factors, ASF/SF2 and SRp20. Using aRac1 minigene approach and siRNA-mediated depletion, we identified ASF/SF2 as an enhancer of endogenous Rac1b splicing whereas SRp20 actsas a silencer. Inhibition of the PI3-kinase pathway increased protein levels of ASF/SF2 and promoted Rac1b generation. By contrast, depletion ofendogenous protein kinase SRPK1 led to decreased Rac1b expression. Together, these data indicate that altered upstream signaling pathways incolorectal cancer cells will target splicing factors that regulate alternative splicing of the small GTPase Rac1.
- Alternative Splicing: Expanding the Landscape of Cancer Biomarkers and TherapeuticsPublication . Bessa, Cláudia; Matos, Paulo; Jordan, Peter; Gonçalves, VâniaAlternative splicing (AS) is a critical post-transcriptional regulatory mechanism used by more than 95% of transcribed human genes and responsible for structural transcript variation and proteome diversity. In the past decade, genome-wide transcriptome sequencing has revealed that AS is tightly regulated in a tissue- and developmental stage-specific manner, and also frequently dysregulated in multiple human cancer types. It is currently recognized that splicing defects, including genetic alterations in the spliced gene, altered expression of both core components or regulators of the precursor messenger RNA (pre-mRNA) splicing machinery, or both, are major drivers of tumorigenesis. Hence, in this review we provide an overview of our current understanding of splicing alterations in cancer, and emphasize the need to further explore the cancer-specific splicing programs in order to obtain new insights in oncology. Furthermore, we also discuss the recent advances in the identification of dysregulated splicing signatures on a genome-wide scale and their potential use as biomarkers. Finally, we highlight the therapeutic opportunities arising from dysregulated splicing and summarize the current approaches to therapeutically target AS in cancer.
- Análise de coortes genómicas públicas de larga escala revelam BCL6 como marcador de prognóstico no cancro da mama Luminal APublication . Barros, Patrícia; Jordan, Peter; Matos, PauloO cancro da mama (CM) é a neoplasia maligna mais comum entre mulheres a nível mundial, constituindo uma das principais causas de mortalidade oncológica. Representa uma doença heterogénea, agrupada em subtipos moleculares com implicações prognósticas e terapêuticas distintas. O subtipo Luminal A é o mais prevalente e caracteriza-se por elevada expressão de recetores hormonais (estrogénio e progesterona), baixa taxa de proliferação e prognóstico geralmente favorável. No entanto, há evidências consistentes de risco significativo de recorrência tardia e de novos eventos neoplásicos, o que continua a levantar desafios na definição das estratégias de seguimento clínico. Neste estudo, analisámos dados genómicos da coorte de CM da base de dados pública TCGA (n=1247) para avaliar o valor prognóstico do gene BCL6, um regulador transcricional previamente implicado na progressão tumoral. Foram recolhidos dados de expressão de BCL6, subtipagem molecular (PAM50) e sobrevivência global (OS). Observou-se que, apesar da expressão de BCL6 estar globalmente diminuída nos tumores em comparação com o tecido normal, esta era significativamente mais elevada nos tumores Luminal A do que nos restantes subtipos, com um subgrupo (44%) a manter níveis semelhantes aos do tecido normal. Verificámos ainda que, exclusivamente neste subtipo, a expressão elevada de BCL6 se associava a pior sobrevivência (p=0,041). Estes resultados apontam para o potencial de BCL6 como biomarcador de estratificação de risco dentro do subtipo Luminal A, com possíveis implicações na definição da intensidade e duração do seguimento clínico a longo prazo