HuR counteracts miR-330 to promote STAT3 translation during inflammation-induced muscle wasting.

Debilitating cancer-induced muscle wasting, a syndrome known as cachexia, is lethal. Here we report a posttranscriptional pathway involving the RNA-binding protein HuR as a key player in the onset of this syndrome. Under these conditions, HuR switches its function from a promoter of muscle fiber formation to become an inducer of muscle loss. HuR binds to the STAT3 (signal transducer and activator of transcription 3) mRNA, which encodes one of the main effectors of this condition, promoting its expression both in vitro and in vivo. While HuR does not affect the stability and the cellular movement of this transcript, HuR promotes the translation of the STAT3 mRNA by preventing miR-330 (microRNA 330)-mediated translation inhibition. To achieve this effect, HuR directly binds to a U-rich element in the STAT3 mRNA-3'untranslated region (UTR) located within the vicinity of the miR-330 seed element. Even though the binding sites of HuR and miR-330 do not overlap, the recruitment of either one of them to the STAT3-3'UTR negatively impacts the binding and the function of the other factor. Therefore, together, our data establish the competitive interplay between HuR and miR-330 as a mechanism via which muscle fibers modulate, in part, STAT3 expression to determine their fate in response to promoters of muscle wasting.

Neuroinflammation, mitochondrial defects and neurodegeneration in mucopolysaccharidosis III type C mouse model.

Severe progressive neurological paediatric disease mucopolysaccharidosis III type C is caused by mutations in the HGSNAT gene leading to deficiency of acetyl-CoA: α-glucosaminide N-acetyltransferase involved in the lysosomal catabolism of heparan sulphate. To understand the pathophysiology of the disease we generated a mouse model of mucopolysaccharidosis III type C by germline inactivation of the Hgsnat gene. At 6-8 months mice showed hyperactivity, and reduced anxiety. Cognitive memory decline was detected at 10 months and at 12-13 months mice showed signs of unbalanced hesitant walk and urinary retention. Lysosomal accumulation of heparan sulphate was observed in hepatocytes, splenic sinus endothelium, cerebral microglia, liver Kupffer cells, fibroblasts and pericytes. Starting from 5 months, brain neurons showed enlarged, structurally abnormal mitochondria, impaired mitochondrial energy metabolism, and storage of densely packed autofluorescent material, gangliosides, lysozyme, phosphorylated tau, and amyloid-ß. Taken together, our data demonstrate for the first time that deficiency of acetyl-CoA: α-glucosaminide N-acetyltransferase causes lysosomal accumulation of heparan sulphate in microglial cells followed by their activation and cytokine release. They also show mitochondrial dysfunction in the neurons and neuronal loss explaining why mucopolysaccharidosis III type C manifests primarily as a neurodegenerative disease.

Planning your every move: the role of ß-actin and its post-transcriptional regulation in cell motility.

Cell motility is a tightly regulated process that involves the polymerization of actin subunits. The formation of actin filaments is controlled through a variety of protein factors that accelerate or perturb the polymerization process. As is the case for most biological events, cell movement is also controlled at the level of gene expression. Growing research explains how the ß-actin isoform of actin is particularly regulated through post-transcriptional events. This includes the discovery of multiple sites in the 3' untranslated region of ß-actin mRNA to which RNA-binding proteins can associate. The control such proteins have on ß-actin expression, and as a result, cell migration, continues to develop, and presents a thorough process that involves guiding an mRNA out of the nucleus, to a specific cytosolic destination, and then controlling the translation and decay of this message. In this review we will provide an overview on the recent progress regarding the mechanisms by which actin polymerization modulates cell movement and invasion and we will discuss the importance of post-transcriptional regulatory events in ß-actin mediated effects on these processes.

Assessment of correlation between p16INK4a staining, specific subtype of human papillomavirus, and progression of LSIL/CIN1 lesions: first comparative study.

OBJECTIVES: To study and compare the effectiveness of p16(INK4a) staining and specific human papillomavirus (HPV) subtypes as a prognostic marker in cervical intraepithelial neoplasia grade 1 (CIN1; low-grade squamous intraepithelial lesions). METHODS: Sixty-four cervical samples diagnosed as CIN1 and stained with p16(INK4a), with HPV status assessed by polymerase chain reaction-direct sequencing. RESULTS: Of the 34 p16(INK4a)-negative biopsy specimens, 26 regressed, seven persisted, and one progressed. Of the 20 p16(INK4a) diffusely positive biopsy specimens, seven regressed, eight persisted, and five progressed. Ten biopsy specimens stained positive only in the lower one-third of the sample, of which seven regressed and three persisted. p16(INK4a) diffusely positive CIN1 lesions were associated with only high-risk HPV subtypes, with the exception of one HPV-negative biopsy specimen. Three different high-risk HPV subtypes and one low-risk HPV subtype (HPV66) were identified in the six CIN1 lesions that progressed. CONCLUSIONS: There is a significant relationship between p16(INK4a) immunostaining and follow-up (P = .002). p16(INK4a)-negative specimens or positivity in the lower one-third of CIN1 lesions seldom progress to a CIN2-3 lesion.

Destabilization of nucleophosmin mRNA by the HuR/KSRP complex is required for muscle fibre formation.

HuR promotes myogenesis by stabilizing the MyoD, myogenin and p21 mRNAs during the fusion of muscle cells to form myotubes. Here we show that HuR, via a novel mRNA destabilizing activity, promotes the early steps of myogenesis by reducing the expression of the cell cycle promoter nucleophosmin (NPM). Depletion of HuR stabilizes the NPM mRNA, increases NPM protein levels and inhibits myogenesis, while its overexpression elicits the opposite effects. NPM mRNA destabilization involves the association of HuR with the decay factor KSRP as well as the ribonuclease PARN and the exosome. The C terminus of HuR mediates the formation of the HuR-KSRP complex and is sufficient for maintaining a low level of the NPM mRNA as well as promoting the commitment of muscle cells to myogenesis. We therefore propose a model whereby the downregulation of the NPM mRNA, mediated by HuR, KSRP and its associated ribonucleases, is required for proper myogenesis.

HuR and miR-1192 regulate myogenesis by modulating the translation of HMGB1 mRNA.

Upon muscle injury, the high mobility group box 1 (HMGB1) protein is upregulated and secreted to initiate reparative responses. Here we show that HMGB1 controls myogenesis both in vitro and in vivo during development and after adult muscle injury. HMGB1 expression in muscle cells is regulated at the translational level: the miRNA miR-1192 inhibits HMGB1 translation and the RNA-binding protein HuR promotes it. HuR binds to a cis-element, HuR binding sites (HuRBS), located in the 3'UTR of the HMGB1 transcript, and at the same time miR-1192 is recruited to an adjacent seed element. The binding of HuR to the HuRBS prevents the recruitment of Argonaute 2 (Ago2), overriding miR-1192-mediated translation inhibition. Depleting HuR reduces myoblast fusion and silencing miR-1192 re-establishes the fusion potential of HuR-depleted cells. We propose that HuR promotes the commitment of myoblasts to myogenesis by enhancing the translation of HMGB1 and suppressing the translation inhibition mediated by miR-1192.

The RNA-binding protein Unr prevents mouse embryonic stem cells differentiation toward the primitive endoderm lineage.

The maintenance of embryonic stem cells (ESCs) pluripotency depends on key transcription factors, chromatin remodeling proteins, and microRNAs. The roles of RNA-binding proteins are however poorly understood. We report that the cytoplasmic RNA-binding protein Unr prevents the differentiation of ESCs into primitive endoderm (PrE). We show that unr knockout (unr(-/-) ) ESCs spontaneously differentiate into PrE, and that Unr re-expression in unr(-/-) ESCs reverses this phenotype. Nevertheless, unr(-/-) ESCs retain pluripotency, producing differentiated teratomas, and the differentiated unr(-/-) ESCs coexpress the PrE inducer Gata6 and the pluripotency factors Oct4, Nanog, and Sox2. Interestingly, in the differentiated unr(-/-) ESCs, Nanog and Sox2 exhibit a dual nuclear and cytoplasmic localization. This situation, that has never been reported, likely reflects an early differentiation state toward PrE. Finally, we show that Unr destabilizes Gata6 mRNAs and we propose that the post-transcriptional repression of Gata6 expression by Unr contributes to the stabilization of the ESCs pluripotent state.

FasL expression in activated T lymphocytes involves HuR-mediated stabilization.

A prolonged activation of the immune system is one of the main causes of hyperproliferation of lymphocytes leading to defects in immune tolerance and autoimmune diseases. Fas ligand (FasL), a member of the TNF superfamily, plays a crucial role in controlling this excessive lymphoproliferation by inducing apoptosis in T cells leading to their rapid elimination. Here, we establish that posttranscriptional regulation is part of the molecular mechanisms that modulate FasL expression, and we show that in activated T cells FasL mRNA is stable. Our sequence analysis indicates that the FasL 3'-untranslated region (UTR) contains two AU-rich elements (AREs) that are similar in sequence and structure to those present in the 3'-UTR of TNFα mRNA. Through these AREs, the FasL mRNA forms a complex with the RNA-binding protein HuR both in vitro and ex vivo. Knocking down HuR in HEK 293 cells prevented the phorbol 12-myristate 13-acetate-induced expression of a GFP reporter construct fused to the FasL 3'-UTR. Collectively, our data demonstrate that the posttranscriptional regulation of FasL mRNA by HuR represents a novel mechanism that could play a key role in the maintenance and proper functioning of the immune system.

The Elav-like protein HuR exerts translational control of viral internal ribosome entry sites.

The human embryonic-lethal abnormal vision (ELAV)-like protein, HuR, has been recently found to be involved in the regulation of protein synthesis. In this study we show that HuR participates in the translational control of the HIV-1 and HCV IRES elements. HuR functions as a repressor of HIV-1 IRES activity and acts as an activator of the HCV IRES. The effect of HuR was evaluated in three independent experimental systems, rabbit reticulocyte lysate, HeLa cells, and Xenopus laevis oocytes, using both overexpression and knockdown approaches. Furthermore, results suggest that HuR mediated regulation of HIV-1 and HCV IRESes does not require direct binding of the protein to the RNA nor does it need the nuclear translocation of the IRES-containing RNAs. Finally, we show that HuR has a negative impact on post-integration steps of the HIV-1 replication cycle. Thus, our observations yield novel insights into the role of HuR in the post-transcriptional regulation of HCV and HIV-1 gene expression.

The RNA-binding protein HuR promotes cell migration and cell invasion by stabilizing the beta-actin mRNA in a U-rich-element-dependent manner.

A high expression level of the beta-actin protein is required for important biological mechanisms, such as maintaining cell shape, growth, and motility. Although the elevated cellular level of the beta-actin protein is directly linked to the long half-life of its mRNA, the molecular mechanisms responsible for this effect are unknown. Here we show that the RNA-binding protein HuR stabilizes the beta-actin mRNA by associating with a uridine-rich element within its 3' untranslated region. Using RNA interference to knock down the expression of HuR in HeLa cells, we demonstrate that HuR plays an important role in the stabilization but not in the nuclear/cytoplasmic distribution of the beta-actin mRNA. HuR depletion in HeLa cells alters key beta-actin-based cytoskeleton functions, such as cell adhesion, migration, and invasion, and these defects correlate with a loss of the actin stress fiber network. Together our data establish that the posttranscriptional event involving HuR-mediated beta-actin mRNA stabilization could be a part of the regulatory mechanisms responsible for maintaining cell integrity, which is a prerequisite for avoiding transformation and tumor formation.

Regulation of Unr expression by 5'- and 3'-untranslated regions of its mRNA through modulation of stability and IRES mediated translation.

Unr (upstream of N-ras) is a cytoplasmic RNA-binding protein that can act as a regulator of mRNA stability and IRES-mediated translation. Unr, a member of the cold-shock domain (CSD) protein super-family, is ubiquitously expressed, with variable abundance, in different tissues or during embryonic development. Prokaryotic and eukaryotic cold-shock protein expression is highly regulated at both the transcriptional and post-transcriptional levels. Here we analyzed the role of the 5'- and 3'-untranslated regions (UTR) of unr mRNA in post-transcriptional regulation of Unr expression. We show that, in vitro, unr 3'-UTR specifically destabilizes unr transcripts. Accordingly, in vivo, the half-life of unr messages deleted of noncoding regions is increased by approximately 3.6 fold, resulting in an enhanced steady-state level of Unr protein. We also show that the 5'-UTR exhibits IRES activity both when translated in vitro and in transiently transfected cells. This IRES activity displays cell type specificity with a higher efficiency in HeLa and HuH7 than in ES cells. Moreover, Unr IRES activity was higher in unr(-/-) than in unr(+/+) ES cells, indicating that Unr negatively regulates its own IRES activity. Our studies further reveal that Unr specifically interacts with its own mRNAs in vivo. These results suggest that a feedback control of mRNA translation is involved in regulating Unr expression.