Dominant Inhibition of Akt/Protein Kinase B Signaling by the Matrix Protein of a Negative-Strand RNA Virus

Abstract

Vesicular stomatitis virus (VSV) is a rhabdovirus that alters host nuclear and cytoplasmic function upon infection. We have investigated the effect of VSV infection on cellular signaling through the phosphatidylinositol-3 kinase (PI3k)/Akt signaling pathway. Akt phosphorylation at both threonine 308 (Thr308) and serine 473 (Ser473) was inhibited in cells infected with VSV. This inhibition was rapid (beginning within the first 2 to 3 h postinfection) and correlated with the dephosphorylation of downstream effectors of Akt, such as glycogen synthase kinase 3␤ (GSK3␤) and mammalian target of rapamycin (mTOR). The dephosphorylation of Akt occurred in the presence of growth factor stimulation and was not overcome through constitutive membrane targeting of Akt or high levels of phosphatidylinositol-3,4,5-triphosphate (PIP3) accumulation in the membrane. Akt dephosphorylation was not a result of alterations in PDK1 phosphorylation or activity, changes in phosphatase and tensin homologue deleted on chromosome 10 (PTEN) levels, or the downregulation of PI3k signaling. Inactivation of Akt was caused by the expression of the viral M protein in the absence of other viral components, and an M protein mutant that does not inhibit RNA polymerase II (Pol II) transcription and nuclear/cytoplasmic transport was also defective in inhibiting Akt phosphorylation. These data illustrate that VSV utilizes a novel mechanism to alter this central player in cell signaling and oncogenesis. It also suggests an inside-out model of signal transduction where VSV interruption of nuclear events has a rapid and significant effect on membrane signaling events.

The PI3K/Akt Pathway Contributes to Arenavirus Budding

“…To examine the effect of LY and BEZ-235 on LCMV GP-mediated cell entry we used a recombinant VSV (rVSV⌬G-GFP/LCMV-GP) whose cell entry is mediated by the GP of the Armstrong strain of LCMV (41). The rationale for using this rVSV was that multiplication of VSV was shown not to be affected by LY (10). Therefore, an effect of LY or BEZ-235 treatment on rVSV⌬G-GFP/LCMV-GP multiplication would reflect the drug's effect on LCMV GP-mediated cell entry.…”

“…Thus, recognition of cell surface receptors by a variety of virus surface glycoproteins can result in activation of the PI3K/Akt pathway to promote virus cell entry (34). In addition, some viral proteins like VSV M have been shown to downregulate PI3K/Akt signaling at an early stage of virus replication (10). Likewise, there is evidence that the PI3K/Akt pathway plays an important role in RNA replication of a variety of negative-stranded (NS) RNA viruses (38).…”

Varicella-Zoster Virus ORF12 Protein Activates the Phosphatidylinositol 3-Kinase/Akt Pathway To Regulate Cell Cycle Progression

“…In contrast, other viruses inhibit the Akt pathway to suppress host immune responses. For example, measles virus inactivates PI3K/Akt to induce T-cell unresponsiveness (17), and vesicular stomatitis virus (VSV) matrix protein inactivates Akt so that it might inhibit the interferon response that could otherwise inhibit virus replication (18).…”

Role for the Phosphatidylinositol 3-Kinase-Akt-TOR Pathway during Sindbis Virus Replication in Arthropods

“…The activation of RTK leads to the binding and, hence, activation of PI3K, which in turn leads to the conversion of phosphatidylinositol-4,5-bisphosphate (PIP2) to its phosphatidylinositol-3,4,5-triphosphate (PIP3) form. PIP3 recruits both Akt and phosphoinositide-dependent protein kinase 1 (PDK1) to the membrane and positions them such that PDK1 can phosphorylate Akt at Thr308, leading to Akt activation (5,13).…”