Showing papers by "Fumihiko Urano published in 2012"

Position-dependent FUS-RNA interactions regulate alternative splicing events and transcriptions

Abstract: FUS is an RNA-binding protein that regulates transcription, alternative splicing, and mRNA transport. Aberrations of FUS are causally associated with familial and sporadic ALS/FTLD. We analyzed FUS-mediated transcriptions and alternative splicing events in mouse primary cortical neurons using exon arrays. We also characterized FUS-binding RNA sites in the mouse cerebrum with HITS-CLIP. We found that FUS-binding sites tend to form stable secondary structures. Analysis of position-dependence of FUS-binding sites disclosed scattered binding of FUS to and around the alternatively spliced exons including those associated with neurodegeneration such as Mapt, Camk2a, and Fmr1. We also found that FUS is often bound to the antisense RNA strand at the promoter regions. Global analysis of these FUS-tags and the expression profiles disclosed that binding of FUS to the promoter antisense strand downregulates transcriptions of the coding strand. Our analysis revealed that FUS regulates alternative splicing events and transcriptions in a position-dependent manner.

Wolfram syndrome 1 and adenylyl cyclase 8 interact at the plasma membrane to regulate insulin production and secretion

Abstract: Persistent ER stress in pancreatic β-cells contributes to the pathogenesis of type 2 diabetes. Fonseca and colleagues show that the ER membrane glycoprotein WFS1, which is mutated in people with Wolfram syndrome, has a known role in the ER stress response. It regulates insulin production and secretion in β-cells by associating with adenylyl cyclase 8 at the plasma membrane and generating cAMP. ER stress prevents WFS1 plasma membrane localization, attenuating cAMP production and insulin secretion.

ER Stress as a Trigger for β-Cell Dysfunction and Autoimmunity in Type 1 Diabetes

Abstract: Type 1 diabetes is an autoimmune disease characterized by the destruction of pancreatic β-cells and an absolute deficiency of insulin. Patients with type 1 diabetes are insulin dependent for life and require multiple daily insulin injections or the use of an insulin pump. It has been considered that β-cell dysfunction and death in type 1 diabetes results from a combination of inflammation, autoimmunity, β-cell stress, and insulin resistance (1–5). Clinical and experimental evidence has indicated that defects in β-cell function precede the massive death of β-cells by severe infiltration of T cells into the islets and the clinical onset of type 1 diabetes (6–9). However, the mechanisms involved in β-cell dysfunction before the onset of clinical type 1 diabetes are unclear. In this issue of Diabetes , Tersey et al. (10) add a new dimension to the progression of type 1 diabetes by demonstrating that endoplasmic reticulum (ER) stress in β-cells precedes the clinical onset of type 1 diabetes. The ER performs a number of important cellular tasks, including protein folding, calcium regulation, redox regulation, and life or death decisions (11,12). Within the β-cell, insulin production and secretion depend on the processing capacity of the …

Cytoplasmic Polyadenylation Element Binding Protein Deficiency Stimulates PTEN and Stat3 mRNA Translation and Induces Hepatic Insulin Resistance

Abstract: The cytoplasmic polyadenylation element binding protein CPEB1 (CPEB) regulates germ cell development, synaptic plasticity, and cellular senescence. A microarray analysis of mRNAs regulated by CPEB unexpectedly showed that several encoded proteins are involved in insulin signaling. An investigation of Cpeb1 knockout mice revealed that the expression of two particular negative regulators of insulin action, PTEN and Stat3, were aberrantly increased. Insulin signaling to Akt was attenuated in livers of CPEB–deficient mice, suggesting that they might be defective in regulating glucose homeostasis. Indeed, when the Cpeb1 knockout mice were fed a high-fat diet, their livers became insulin-resistant. Analysis of HepG2 cells, a human liver cell line, depleted of CPEB demonstrated that this protein directly regulates the translation of PTEN and Stat3 mRNAs. Our results show that CPEB regulated translation is a key process involved in insulin signaling.

Activation of OASIS family, ER stress transducers, is dependent on its stabilization

Abstract: Endoplasmic reticulum (ER) stress transducers transduce signals from the ER to the cytoplasm and nucleus when unfolded proteins accumulate in the ER. BBF2 human homolog on chromosome 7 (BBF2H7) and old astrocyte specifically induced substance (OASIS), ER-resident transmembrane proteins, have recently been identified as novel ER stress transducers that have roles in chondrogenesis and osteogenesis, respectively. However, the molecular mechanisms that regulate the activation of BBF2H7 and OASIS under ER stress conditions remain unresolved. Here, we showed that BBF2H7 and OASIS are notably unstable proteins that are easily degraded via the ubiquitin-proteasome pathway under normal conditions. ER stress conditions enhanced the stability of BBF2H7 and OASIS, and promoted transcription of their target genes. HMG-CoA reductase degradation 1 (HRD1), an ER-resident E3 ubiquitin ligase, ubiquitinated BBF2H7 and OASIS under normal conditions, whereas ER stress conditions dissociated the interaction between HRD1 and BBF2H7 or OASIS. The stabilization of OASIS in Hrd1−/− cells enhanced the expression of collagen fibers during osteoblast differentiation, whereas a knockdown of OASIS in Hrd1−/− cells suppressed the production of collagen fibers. These findings suggest that ER stress stabilizes OASIS family members and this is a novel molecular mechanism for the activation of ER stress transducers.

c-Abl Inhibition Delays Motor Neuron Degeneration in the G93A Mouse, an Animal Model of Amyotrophic Lateral Sclerosis

Abstract: Background Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive death of motor neurons. Although the pathogenesis of ALS remains unclear, several cellular processes are known to be involved, including apoptosis. A previous study revealed the apoptosis-related gene c-Abl to be upregulated in sporadic ALS motor neurons. Methodology/Findings We investigated the possibility that c-Abl activation is involved in the progression of ALS and that c-Abl inhibition is potentially a therapeutic strategy for ALS. Using a mouse motor neuron cell line, we found that mutation of Cu/Zn-superoxide dismutase-1 (SOD1), which is one of the causative genes of familial ALS, induced the upregulation of c-Abl and decreased cell viability, and that the c-Abl inhibitor dasatinib inhibited cytotoxicity. Activation of c-Abl with a concomitant increase in activated caspase-3 was observed in the lumbar spine of G93A-SOD1 transgenic mice (G93A mice), a widely used model of ALS. The survival of G93A mice was improved by oral administration of dasatinib, which also decreased c-Abl phosphorylation, inactivated caspase-3, and improved the innervation status of neuromuscular junctions. In addition, c-Abl expression in postmortem spinal cord tissues from sporadic ALS patients was increased by 3-fold compared with non-ALS patients. Conclusions/Significance The present results suggest that c-Abl is a potential therapeutic target for ALS and that the c-Abl inhibitor dasatinib has neuroprotective properties in vitro and in vivo.

Pathological ER Stress in β Cells

Abstract: Diabetes mellitus is a global chronic disease, major cause of morbidity and mortality, and significantly decreases both quality of life and life expectancy. The reduction in functional β cell mass due to increased β cell apoptosis and decreased β cell proliferation is a crucial factor in the pathogenesis of diabetes mellitus. Mounting clinical and experimental research findings suggest that endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) play fundamental roles in the diminution of functional β cell mass during the prediabetic phase. In this chapter, the physiological purpose of ER stress in the pancreatic β cell is reviewed and the pathological features of chronic ER stress and unwarranted UPR activation in the progression to β cell dysfunction and diabetes progression are described. The molecular pathways activated during the transition from physiological to pathological UPR and proapoptotic signaling in a variety of environmental and genetic diabetic conditions are addressed. In addition, therapeutic approaches to modulate the level of β cell ER stress and mitigate UPR activation are discussed. Finally, we propose that the identification of clinical biomarkers for detection of overt ER stress and UPR activation would herald ER stress and the UPR as viable targets in the prevention of diabetes progression or treatment of established diabetes.

Role of ER Stress in Dysfunction of the Nervous System

Abstract: Recent clinical, genetic and experimental evidence indicates that dysregulation of endoplasmic reticulum (ER) homeostasis plays an important role in the pathogenesis of neurodegenerative diseases and psychiatric illness. Protein flux through the ER must be carefully monitored to prevent dysregulation of ER homeostasis and stress. ER stress elicits a signaling cascade known as the unfolded protein response (UPR) which functions in influencing both cellular life and death decisions. In this chapter, we address the transition from the physiological ER stress response to the pathological response and explore the mechanisms of ER stress-mediated dysfunction and death of neurons during the progression of neurodegenerative diseases and psychiatric illness.