Showing papers by "Kotb Abdelmohsen published in 2013"

Scaffold function of long non-coding RNA HOTAIR in protein ubiquitination

Abstract: Although mammalian long non-coding (lnc)RNAs are best known for modulating transcription, their post-transcriptional influence on mRNA splicing, stability and translation is emerging. Here we report a post-translational function for the lncRNA HOTAIR as an inducer of ubiquitin-mediated proteolysis. HOTAIR associates with E3 ubiquitin ligases bearing RNA-binding domains, Dzip3 and Mex3b, as well as with their respective ubiquitination substrates, Ataxin-1 and Snurportin-1. In this manner, HOTAIR facilitates the ubiquitination of Ataxin-1 by Dzip3 and Snurportin-1 by Mex3b in cells and in vitro, and accelerates their degradation. HOTAIR levels are highly upregulated in senescent cells, causing rapid decay of targets Ataxin-1 and Snurportin-1, and preventing premature senescence. These results uncover a role for a lncRNA, HOTAIR, as a platform for protein ubiquitination.

Evidence for miR-181 involvement in neuroinflammatory responses of astrocytes

Abstract: Inflammation is a common component of acute injuries of the central nervous system (CNS) such as ischemia, and degenerative disorders such as Alzheimer's disease. Glial cells play important roles in local CNS inflammation, and an understanding of the roles for microRNAs in glial reactivity in injury and disease settings may therefore lead to the development of novel therapeutic interventions. Here, we show that the miR-181 family is developmentally regulated and present in high amounts in astrocytes compared to neurons. Overexpression of miR-181c in cultured astrocytes results in increased cell death when exposed to lipopolysaccharide (LPS). We show that miR-181 expression is altered by exposure to LPS, a model of inflammation, in both wild-type and transgenic mice lacking both receptors for the inflammatory cytokine TNF-α. Knockdown of miR-181 enhanced LPS-induced production of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, IL-8) and HMGB1, while overexpression of miR-181 resulted in a significant increase in the expression of the anti-inflammatory cytokine IL-10. To assess the effects of miR-181 on the astrocyte transcriptome, we performed gene array and pathway analysis on astrocytes with reduced levels of miR-181b/c. To examine the pool of potential miR-181 targets, we employed a biotin pull-down of miR-181c and gene array analysis. We validated the mRNAs encoding MeCP2 and X-linked inhibitor of apoptosis as targets of miR-181. These findings suggest that miR-181 plays important roles in the molecular responses of astrocytes in inflammatory settings. Further understanding of the role of miR-181 in inflammatory events and CNS injury could lead to novel approaches for the treatment of CNS disorders with an inflammatory component.

Senescence-associated lncRNAs: senescence-associated long noncoding RNAs

Abstract: Noncoding RNAs include small transcripts, such as microRNAs and piwi-interacting RNAs, and a wide range of long noncoding RNAs (lncRNAs). Although many lncRNAs have been identified, only a small number of lncRNAs have been characterized functionally. Here, we sought to identify lncRNAs differentially expressed during replicative senescence. We compared lncRNAs expressed in proliferating, early-passage, 'young' human diploid WI-38 fibroblasts [population doubling (PDL) 20] with those expressed in senescent, late-passage, 'old' fibroblasts (PDL 52) by RNA sequencing (RNA-Seq). Numerous transcripts in all lncRNA groups (antisense lncRNAs, pseudogene-encoded lncRNAs, previously described lncRNAs and novel lncRNAs) were validated using reverse transcription (RT) and real-time, quantitative (q)PCR. Among the novel senescence-associated lncRNAs (SAL-RNAs) showing lower abundance in senescent cells, SAL-RNA1 (XLOC_023166) was found to delay senescence, because reducing SAL-RNA1 levels enhanced the appearance of phenotypic traits of senescence, including an enlarged morphology, positive β-galactosidase activity, and heightened p53 levels. Our results reveal that the expression of known and novel lncRNAs changes with senescence and suggests that SAL-RNAs play direct regulatory roles in this important cellular process.

Age-associated miRNA Alterations in Skeletal Muscle from Rhesus Monkeys reversed by caloric restriction

Abstract: The levels of microRNAs (miRNAs) are altered under different conditions such as cancer, senescence, and aging. Here, we have identified differentially expressed miRNAs in skeletal muscle from young and old rhesus monkeys using RNA sequencing. In old muscle, several miRNAs were upregulated, including miR-451, miR-144, miR-18a and miR-15a, while a few miRNAs were downregulated, including miR-181a and miR-181b. A number of novel miRNAs were also identified, particularly in old muscle. We also examined the impact of caloric restriction (CR) on miRNA abundance by reverse transcription (RT) followed by real-time, quantitative (q)PCR analysis and found that CR rescued the levels of miR-181b and chr1:205580546, and also dampened the age-induced increase in miR-451 and miR-144 levels. Our results reveal that there are changes in expression of known and novel miRNAs with skeletal muscle aging and that CR may reverse some of these changes to a younger phenotype.

Novel MicroRNA Reporter Uncovers Repression of Let-7 by GSK-3β.

Abstract: Several members of the let-7 microRNA family are downregulated in ovarian and other cancers. They are thought to act as tumor suppressors by lowering growth-promoting and anti-apoptotic proteins. In order to measure cellular let-7 levels systematically, we have developed a highly sensitive let-7 reporter assay system based on the expression of a chimeric mRNA that contains the luciferase coding region and a 3′-untranslated region (UTR) bearing two let-7-binding sites. In cells expressing the reporter construct, termed pmirGLO-let7, luciferase activity was high when let-7 was absent, while luciferase activity was low when let-7 levels were elevated. The ovarian cancer cell lines BG-1 and UCI-101 were transfected with the let-7 reporter and surveyed with a library of kinase inhibitors in order to identify pathways affecting let-7 activity. Among the inhibitors causing changes in endogenous let-7 abundance, the lowering of glycogen synthase kinase 3 (GSK-3)β function specifically increased let-7 levels and lowered luciferase activity. Similarly, silencing GSK-3β increased both mature and primary-let-7 levels in BG-1 cells, and decreased BG-1 cell survival. Further studies identified p53 as a downstream effector of the GSK-3β-mediated repression of let-7 biosynthesis. Our studies highlight GSK-3β as a novel therapeutic target in ovarian tumorigenesis.

Modulation of cancer traits by tumor suppressor microRNAs.

Abstract: MicroRNAs (miRNAs) are potent post-transcriptional regulators of gene expression. In mammalian cells, miRNAs typically suppress mRNA stability and/or translation through partial complementarity with target mRNAs. Each miRNA can regulate a wide range of mRNAs, and a single mRNA can be regulated by multiple miRNAs. Through these complex regulatory interactions, miRNAs participate in many cellular processes, including carcinogenesis. By altering gene expression patterns, cancer cells can develop specific phenotypes that allow them to proliferate, survive, secure oxygen and nutrients, evade immune recognition, invade other tissues and metastasize. At the same time, cancer cells acquire miRNA signature patterns distinct from those of normal cells; the differentially expressed miRNAs contribute to enabling the cancer traits. Over the past decade, several miRNAs have been identified, which functioned as oncogenic miRNAs (oncomiRs) or tumor-suppressive miRNAs (TS-miRNAs). In this review, we focus specifically on TS-miRNAs and their effects on well-established cancer traits. We also discuss the rising interest in TS-miRNAs in cancer therapy.

Posttranscriptional Regulation of Insulin Family Ligands and Receptors

Abstract: Insulin system including ligands (insulin and IGFs) and their shared receptors (IR and IGFR) are critical regulators of insulin signaling and glucose homeostasis. Altered insulin system is associated with major pathological conditions like diabetes and cancer. The mRNAs encoding for these ligands and their receptors are posttranscriptionally controlled by three major groups of regulators; (i) alternative splicing regulatory factors; (ii) turnover and translation regulator RNA-binding proteins (TTR-RBPs); and (iii) non-coding RNAs including miRNAs and long non-coding RNAs (lncRNAs). In this review, we discuss the influence of these regulators on alternative splicing, mRNA stability and translation. Due to the pathological impacts of insulin system, we also discussed the possibilities of discovering new potential regulators which will improve understanding of insulin system and associated diseases.

CORRIGENDUM: SRT1720 improves survival and healthspan of obese mice.

Abstract: Sirt1 is an NAD+-dependent deacetylase that extends lifespan in lower organisms and improves metabolism and delays the onset of age-related diseases in mammals. Here we show that SRT1720, a synthetic compound that was identified for its ability to activate Sirt1 in vitro, extends both mean and maximum lifespan of adult mice fed a high-fat diet. This lifespan extension is accompanied by health benefits including reduced liver steatosis, increased insulin sensitivity, enhanced locomotor activity and normalization of gene expression profiles and markers of inflammation and apoptosis, all in the absence of any observable toxicity. Using a conditional SIRT1 knockout mouse and specific gene knockdowns we show SRT1720 affects mitochondrial respiration in a Sirt1- and PGC-1α-dependent manner. These findings indicate that SRT1720 has long-term benefits and demonstrate for the first time the feasibility of designing novel molecules that are safe and effective in promoting longevity and preventing multiple age-related diseases in mammals.