Browsing by Issue Date, starting with "2019-08-07"
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- Alternative mechanisms of mRNA translationiInitiation in cellular stress response and cancerPublication . Lacerda, Rafaela; Menezes, Juliane; Candeias, Marco M.Throughout evolution, eukaryotic cells have devised different mechanisms to cope with stressful environments. When eukaryotic cells are exposed to stress stimuli, they activate adaptive pathways that allow them to restore cellular homeostasis. Most types of stress stimuli have been reported to induce a decrease in overall protein synthesis accompanied by induction of alternative mechanisms of mRNA translation initiation. Here, we present well-studied and recent examples of such stress responses and the alternative translation initiation mechanisms they induce, and discuss the consequences of such regulation for cell homeostasis and oncogenic transformation.
- The mRNA Metabolism in Human DiseasePublication . Romão, LuísaIntroduction: The eukaryotic gene expression pathway involves a number of interlinked steps, with messenger RNA (mRNA) being the key intermediate. The precursor mRNA is transcribed from DNA, processed by removal of introns and addition of the cap structure and the poly(A) tail. The mature mRNA is then exported to the cytoplasm where it is translated into protein and finally degraded. In this process, mRNA is associated with RNA-binding proteins forming ribonucleoprotein complexes, whose protein content evolves throughout the lifetime of the mRNA. While the complexity of eukaryotic gene expression allows the production of proteins to be controlled at many levels, it also makes the process vulnerable to errors. Although eukaryotic cells have evolved elaborate mRNA quality control mechanisms that ensure the fidelity of gene expression, some defects are not detected, thus affecting mRNA metabolism. This condition plays a fundamental role in the pathogenesis of several disease processes, such as neurodegeneration and oncogenesis. Besides, exciting recent data have shown that cellular RNAs can be modified post-transcriptionally via dynamic and reversible chemical modifications, the so-called epitranscriptome. These modifications can alter mRNA structure, being able to modulate different steps of the mRNA metabolism that can be associated with various human diseases, such as systemic lupus erythematosus and cancer. This book provides a collection of novel studies and hypotheses aimed to define the pathophysiological consequences of altered mRNA metabolism events in human cells, and is written for a wide spectrum of readers in the field of gene expression regulation. The last chapter highlights how the discovery of disease-causing defects (or modifications) in mRNA can provide a variety of therapeutic targets that can be used for the development of new RNA-based therapeutics. Hopefully, it may also contribute to inspire the drug-developing scientific community.
- The Implication of mRNA degradation disorders on human dISease: focus on DIS3 and DIS3-Like enzymesPublication . Saramago, Margarida; da Costa, Paulo J.; Viegas, Sandra C.; Arraiano, Cecília M.RNA degradation is considered a critical posttranscriptional regulatory checkpoint, maintaining the correct functioning of organisms. When a specific RNA transcript is no longer required in the cell, it is signaled for degradation through a number of highly regulated steps. Ribonucleases (or simply RNases) are key enzymes involved in the control of RNA stability. These enzymes can perform the RNA degradation alone or cooperate with other proteins in RNA degradation complexes. Important findings over the last years have shed light into eukaryotic RNA degradation by members of the RNase II/RNB family of enzymes. DIS3 enzyme belongs to this family and represents one of the catalytic subunits of the multiprotein complex exosome. This RNase has a diverse range of functions, mainly within nuclear RNA metabolism. Humans encode two other DIS3-like enzymes: DIS3L (DIS3L1) and DIS3L2. DIS3L1 also acts in association with the exosome but is strictly cytoplasmic. In contrast, DIS3L2 acts independently of the exosome and shows a distinctive preference for uridylated RNAs. These enzymes have been shown to be involved in important cellular processes, such as mitotic control, and associated with human disorders like cancer. This review shows how the impairment of function of each of these enzymes is implicated in human disease.
- Translational regulation by upstream open reading frames and human diseasesPublication . Silva, Joana; Fernandes, Rafael; Romão, LuísaShort upstream open reading frames (uORFs) are cis-acting elements located within the 5'-leader sequence of transcripts and are defined by an initiation codon in-frame with a termination codon located upstream or downstream of its main ORF (mORF) initiation codon. Recent genome-wide ribosome profiling studies have confirmed the widespread presence of uORFs and have shown that many uORFs can initiate with non-AUG codons. uORFs can impact gene expression of the downstream mORF by triggering mRNA decay or by regulating translation. Thus, disruption or creation of uORFs can elicit the development of several genetic diseases. Here, we review the mechanisms by which AUG- and non-AUG uORFs regulate translation. We also show some examples of uORF deregulation in human genetic diseases, focusing mainly on cancer. The knowledge of how uORF deregulation drives the onset of a disease, points out the need to screen the 5'-leader sequences of the transcripts in search for potential disease-related variants. This information will be relevant for the implementation of new diagnostic and/or therapeutic tools.
- Nonsense-Mediated mRNA decay in development, stress and cancerPublication . Fernandes, Rafael; Nogueira, Gonçalo; da Costa, Paulo J.; Pinto, Francisco; Romão, LuísaNonsense-mediated mRNA decay (NMD) is a well characterized eukaryotic mRNA degradation pathway, responsible for the identification and degradation of transcripts harboring translation termination codons in premature contexts. Transcriptome-wide studies revealed that NMD is not only an mRNA surveillance pathway as initially thought, but is also a post-transcriptional regulatory mechanism of gene expression, as it fine-tunes the transcript levels of many wild-type genes. Hence, NMD contributes to the regulation of many essential biological processes, including pathophysiological mechanisms. In this chapter we discuss the importance of NMD and of its regulation to organism development and its link to the cellular stress responses, like the unfolded protein response (UPR) and the integrated stress response (ISR). Additionally, we describe how tumor cells have explored both NMD functions to promote tumorigenesis. Using published data and databases, we have also performed a network-based approach that further supports the link between NMD and these (patho) physiological processes.