PKR has been shown to play an essential role against VSV infection by phosphorylating eIF2alpha leading to the inhibition of protein synthesis. Through this capacity PKR is thought to be a mediator of the anti-viral and anti-proliferative actions of IFNs. In addition to translational control, PKR has been shown to modulate the transcriptional activities of NF-kappaB, Stats and p53. However, experiments with two different PKR-/- mouse models have failed to verify many of the biological functions attributed to PKR. Here, we show that the two PKR-/- MEFs express different PKR truncated proteins suggesting that both PKR-/- models are incomplete knockouts. The expression of the PKR variants may account for the significant signaling differences between cells from the two PKR-/- mice. / We also demonstrate that another eIF2alpha kinase, PERK contributes to cellular resistance towards VSV infection. We demonstrate that PERK -/- MEFs are more susceptible to VSV-mediated apoptosis than PERK +/+ MEFs. The higher replication capacity of VSV in PERK-/- MEFs results from their inability to attenuate viral protein synthesis due to an impaired eIF2alpha phosphorylation. We also show that VSV-infected PERK-/- MEFs are unable to fully activate PKR suggesting a cross-talk between the two eIF2alpha kinases in virus infected cells. These findings further implicate PERK in virus infection, and provide evidence that the anti-viral and anti-apoptosic roles of PERK are mediated, at least in part, via the activation of PKR. / Despite the translational control function of eIF2alpha kinases, we demonstrate their implications in p53 inactivation. Specifically, we show that PERK activation is responsible for the proteasomal degradation of p53 in a manner that is independent of translational control. This role is not specific for PERK, since the PKR also promotes p53 degradation in response to dsRNA transfection. We established that activation of eIF2alpha kinases leads to the activation of GSK3beta thus promoting the Mdm2-dependent degradation of p53. That is, induction of eIF2alpha kinases leads to the nuclear localization of GSK3beta, and the nuclear export and proteasomal degradation of p53. Our findings establish a novel cross-talk between the eIF2alpha kinases and p53 with significant implications in stress responses that control cell proliferation and tumorigenesis.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.103021 |
| Date | January 2007 |
| Creators | Baltzis, Dionissios. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | © Dionissios Baltzis, 2007 |
| Relation | alephsysno: 002598860, proquestno: AAINR32292, Theses scanned by UMI/ProQuest. |
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