Biomedical subjects

Marie-Eve Bordeleau

Publications and source records attributed to Marie-Eve Bordeleau.

7 recordsLinked to original sources

PubMed2006

Inhibition of ribosome recruitment induces stress granule formation independently of eukaryotic initiation factor 2alpha phosphorylation.

Cytoplasmic aggregates known as stress granules (SGs) arise as a consequence of cellular stress and contain stalled translation preinitiation complexes. These foci are thought to serve as sites of mRNA storage or triage during the cell stress response. SG formation has been shown to require induction of eukaryotic initiation factor (eIF)2alpha phosphorylation. Herein, we investigate the potential role of other initiation factors in this process and demonstrate that interfering with eIF4A activity, an RNA helicase required for the ribosome recruitment phase of translation initiation, induces SG formation and that this event is not dependent on eIF2alpha phosphorylation. We also show that inhibition of eIF4A activity does not impair the ability of eIF2alpha to be phosphorylated under stress conditions. Furthermore, we observed SG assembly upon inhibition of cap-dependent translation after poliovirus infection. We propose that SG modeling can occur via both eIF2alpha phosphorylation-dependent and -independent pathways that target translation initiation.

Antigens, Surface↗

PubMed2006

Caliciviruses differ in their functional requirements for eIF4F components.

Two classes of viruses, namely members of the Potyviridae and Caliciviridae, use a novel mechanism for the initiation of protein synthesis that involves the interaction of translation initiation factors with a viral protein covalently linked to the viral RNA, known as VPg. The calicivirus VPg proteins can interact directly with the initiation factors eIF4E and eIF3. Translation initiation on feline calicivirus (FCV) RNA requires eIF4E because it is inhibited by recombinant 4E-BP1. However, to date, there have been no functional studies carried out with respect to norovirus translation initiation, because of a lack of a suitable source of VPg-linked viral RNA. We have now used the recently identified murine norovirus (MNV) as a model system for norovirus translation and have extended our previous studies with FCV RNA to examine the role of the other eIF4F components in translation initiation. We now demonstrate that, as with FCV, MNV VPg interacts directly with eIF4E, although, unlike FCV RNA, translation of MNV RNA is not sensitive to 4E-BP1, eIF4E depletion, or foot-and-mouth disease virus Lb protease-mediated cleavage of eIF4G. We also demonstrate that both FCV and MNV RNA translation require the RNA helicase component of the eIF4F complex, namely eIF4A, because translation was sensitive (albeit to different degrees) to a dominant negative form and to a small molecule inhibitor of eIF4A (hippuristanol). These results suggest that calicivirus RNAs differ with respect to their requirements for the components of the eIF4F translation initiation complex.

Animals↗

PubMed2006

Functional characterization of IRESes by an inhibitor of the RNA helicase eIF4A.

RNA helicases are molecular motors that are involved in virtually all aspects of RNA metabolism. Eukaryotic initiation factor (eIF) 4A is the prototypical member of the DEAD-box family of RNA helicases. It is thought to use energy from ATP hydrolysis to unwind mRNA structure and, in conjunction with other translation factors, it prepares mRNA templates for ribosome recruitment during translation initiation. In screening marine extracts for new eukaryotic translation initiation inhibitors, we identified the natural product hippuristanol. We show here that this compound is a selective and potent inhibitor of eIF4A RNA-binding activity that can be used to distinguish between eIF4A-dependent and -independent modes of translation initiation in vitro and in vivo. We also show that poliovirus replication is delayed when infected cells are exposed to hippuristanol. Our study demonstrates the feasibility of selectively targeting members of the DEAD-box helicase family with small-molecule inhibitors.

Adenosine Triphosphate↗

PubMed2006

Short RNAs repress translation after initiation in mammalian cells.

MicroRNAs (miRNAs) are predicted to regulate 30% of mammalian protein-encoding genes by interactions with their 3' untranslated regions (UTRs). We use partially complementary siRNAs to investigate the mechanism by which miRNAs mediate translational repression in human cells. Repressed mRNAs are associated with polyribosomes that are engaged in translation elongation, as shown by puromycin sensitivity. The inhibition appears to be postinitiation because translation driven by the cap-independent processes of HCV IRES and CrPV IRES is repressed by short RNAs. Further, metabolic labeling suggests that silencing occurs before completion of the nascent polypeptide chain. In addition, silencing by short RNAs causes a decrease in translational readthrough at a stop codon, and ribosomes on repressed mRNAs dissociate more rapidly after a block of initiation of translation than those on control mRNAs. These results suggest that repression by short RNAs, and thus probably miRNAs, is primarily due to ribosome drop off during elongation of translation.

Animals↗

PubMed2006

RNA-mediated sequestration of the RNA helicase eIF4A by Pateamine A inhibits translation initiation.

Eukaryotic initiation factor 4A (eIF4A) is a member of the DEAD-box family of putative RNA helicases whose members are involved in many aspects of RNA metabolism. eIF4A is thought to facilitate binding of 43S preinitiation complexes to mRNAs by unwinding secondary structures present in the 5' untranslated region. Pateamine A, a small-molecule inhibitor of translation initiation, acts in an unusual manner by stimulating eIF4A activity. Herein, we report the elucidation of pateamine's mode of action. We demonstrate that Pateamine A is a chemical inducer of dimerization that forces an engagement between eIF4A and RNA and prevents eIF4A from participating in the ribosome-recruitment step of translation initiation.

Dimerization↗

PubMed2006

Hepatitis C virus-related internal ribosome entry sites are found in multiple genera of the family Picornaviridae.

The internal ribosome entry site (IRES) elements from porcine enterovirus 8 and simian virus 2, two members of a proposed new genus within the family Picornaviridae, were characterized. These IRES elements, in common with the porcine teschovirus 1 IRES, were found to be related functionally and structurally to the IRES element from Hepatitis C virus, a member of the family Flaviviridae. Partial secondary structure predictions were derived and functional assays demonstrated that these IRES elements continued to be active when eIF4G was cleaved and when the activity of eIF4A was blocked.

5' Untranslated Regions↗

PubMed2005

Stimulation of mammalian translation initiation factor eIF4A activity by a small molecule inhibitor of eukaryotic translation.

RNA helicases are the largest group of enzymes in eukaryotic RNA metabolism. The DEXD/H-box putative RNA helicases form the helicase superfamily II, whose members are defined by seven highly conserved amino acid motifs, making specific targeting of selected members a challenging pharmacological problem. The translation initiation factor eIF4A is the prototypical DEAD-box RNA helicase that works in conjunction with eIF4B and eIF4H and as a subunit of eIF4F to prepare the mRNA template for ribosome binding, possibly by unwinding the secondary structure proximal to the 5' m7GpppN cap structure. We report the identification and characterization of a small molecule inhibitor of eukaryotic translation initiation that acts in an unusual manner by stimulating eIF4A-associated activities. Our results suggest that proper control of eIF4A helicase activity is necessary for efficient ribosome binding and demonstrate the feasibility of selectively targeting DEAD-box RNA helicases with small molecules.

Animals↗