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Translational and transcriptional control of Sp1 against ischaemia through a hydrogen peroxide-activated internal ribosomal entry site pathway.

ABSTRACT: The exact mechanism underlying increases in Sp1 and the physiological consequences thereafter remains unknown. In rat primary cortical neurons, oxygen-glucose deprivation (OGD) causes an increase in H(2)O(2) as well as Sp1 in early ischaemia but apparently does not change mRNA level or Sp1 stability. We hereby identified a longer 5'-UTR in Sp1 mRNA that contains an internal ribosome entry site (IRES) that regulates rapid and efficient translation of existing mRNAs. By using polysomal fragmentation and bicistronic luciferase assays, we found that H(2)O(2) activates IRES-dependent translation. Thus, H(2)O(2) or tempol, a superoxide dismutase-mimetic, increases Sp1 levels in OGD-treated neurons. Further, early-expressed Sp1 binds to Sp1 promoter to cause a late rise in Sp1 in a feed-forward manner. Short hairpin RNA against Sp1 exacerbates OGD-induced apoptosis in primary neurons. While Sp1 levels increase in the cortex in a rat model of stroke, inhibition of Sp1 binding leads to enhanced apoptosis and cortical injury. These results demonstrate that neurons can use H(2)O(2) as a signalling molecule to quickly induce Sp1 translation through an IRES-dependent translation pathway that, in cooperation with a late rise in Sp1 via feed-forward transcriptional activation, protects neurons against ischaemic damage.

SUBMITTER: Yeh SH

PROVIDER: S-EPMC3141265 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Translational and transcriptional control of Sp1 against ischaemia through a hydrogen peroxide-activated internal ribosomal entry site pathway.

Yeh Shiu Hwa SH Yang Wen Bin WB Gean Po Wu PW Hsu Chung Yi CY Tseng Joseph T JT Su Tsung Ping TP Chang Wen Chang WC Hung Jan Jong JJ

Nucleic acids research 20110325 13

The exact mechanism underlying increases in Sp1 and the physiological consequences thereafter remains unknown. In rat primary cortical neurons, oxygen-glucose deprivation (OGD) causes an increase in H(2)O(2) as well as Sp1 in early ischaemia but apparently does not change mRNA level or Sp1 stability. We hereby identified a longer 5'-UTR in Sp1 mRNA that contains an internal ribosome entry site (IRES) that regulates rapid and efficient translation of existing mRNAs. By using polysomal fragmentati ...[more]

PMID: 21441538

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Project description:All viruses must usurp host ribosomes for viral protein synthesis. Dicistroviruses utilize an intergenic region internal ribosome entry site (IGR IRES) to directly recruit ribosomes and mediate translation initiation from a non-AUG start codon. The IGR IRES adopts a three-pseudoknot structure that comprises a ribosome binding domain of pseudoknot II and III (PKII and PKIII), and a tRNA-like anticodon domain (PKI) connected via a short, one to three nucleotide hinge region. Recent cryo-EM structural analysis of the dicistrovirus Taura syndrome virus (TSV) IGR IRES bound to the ribosome suggests that the hinge region may facilitate translocation of the IRES from the ribosomal A to P site. In this study, we provide mechanistic and functional insights into the role of the hinge region in IGR IRES translation. Using the honeybee dicistrovirus, Israeli acute paralysis virus (IAPV), as a model, we demonstrate that mutations of the hinge region resulted in decreased IRES-dependent translation in vitro. Toeprinting primer extension analysis of mutant IRESs bound to purified ribosomes and in rabbit reticulocyte lysates showed defects in the initial ribosome positioning on the IRES. Finally, using a hybrid dicistrovirus clone, mutations in the hinge region of the IAPV IRES resulted in decreased viral yield. Our work reveals an unexpected role of the hinge region of the dicistrovirus IGR IRES coordinating the two independently folded domains of the IRES to properly position the ribosome to start translation. IMPORTANCE Viruses must use the host cell machinery to direct viral protein expression for productive infection. One such mechanism is an internal ribosome entry site that can directly recruit host cell machinery. In this study, we have identified a novel sequence in an IRES that provides insight into the mechanism of viral gene expression. Specifically, this novel sequence promotes viral IRES activity by directly guiding the host cell machinery to start gene expression at a specific site.

Dataset Information

Translational and transcriptional control of Sp1 against ischaemia through a hydrogen peroxide-activated internal ribosomal entry site pathway.

Publications

Translational and transcriptional control of Sp1 against ischaemia through a hydrogen peroxide-activated internal ribosomal entry site pathway.

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