MAPK Signal-integrating Kinase Controls Cap-independent Translation and Cell Type-specific Cytotoxicity of an Oncolytic Poliovirus

Abstract

Many animal viruses exhibit proficient growth in transformed cells, a property that has been harnessed for the development of novel therapies against cancer. Despite overwhelming evidence for this phenomenon, understanding of the molecular mechanisms enabling tumor-cell killing is rudimentary for most viruses. We report here that growth and cytotoxicity of the prototype oncolytic poliovirus (PV), PVSRIPO, in glioblastoma multiforme (GBM) is promoted by mitogen-activated protein kinases (MAPKs) converging on the MAPK signal-integrating kinase 1 (Mnk1) and its primary substrate, the eukaryotic initiation factor (eIF) 4E. Inducing Mnk1-catalyzed eIF4E phosphorylation through expression of oncogenic Ras substantially enhanced PVSRIPO translation, replication, and cytotoxicity in resistant cells. This effect was mimicked by expression of constitutively active forms of Mnk1 and correlated with enhanced translation of subgenomic reporter RNAs. Our findings implicate Mnk1 activity in stimulation of PVSRIPO cap-independent translation, an effect that can be synergistically enhanced by inhibition of the phosphoinositide-3 kinase (PI3K).

Attenuation of Neurovirulence, Biodistribution, and Shedding of a Poliovirus:Rhinovirus Chimera after Intrathalamic Inoculation in Macaca fascicularis

“…Phosphorylation of eIF4G(Ser1186) and activation of Erk1/2 MAPKs induces MAPK signal integrating kinase 1 (Mnk1) binding to eIF4G (38), which is required for phosphorylation of eIF4E by Mnk1 (35). We showed that signaling through Erk1/2 to MAPK signal integrating kinase 1 (Mnk1) determines PVS-RIPO translation and cytotoxicity in GBM (14). Accordingly, providing constitutively active Mnk1 in neuron-like cells stimulates viral, HRV2 IRES-mediated translation and reverses the CNS deficit of PVS-RIPO (14).…”

“…We showed that signaling through Erk1/2 to MAPK signal integrating kinase 1 (Mnk1) determines PVS-RIPO translation and cytotoxicity in GBM (14). Accordingly, providing constitutively active Mnk1 in neuron-like cells stimulates viral, HRV2 IRES-mediated translation and reverses the CNS deficit of PVS-RIPO (14). MAPK signal transduction to protein synthesis machinery may favor viral cap-independent translation by stimulating the formation of translation-competent RNPs via recruitment of eIF4G to the IRES.…”

“…PVS-RIPO shedding studies included the analysis of stool samples from animals in the high-dose group (A09163, A08813, A09165, and A10103; Table 3) at study days 3,10,12,14,15,18,21,25,28,35,43,49, and 56 (Table 1). Analysis of stool samples by TCID 50 assay, plaque assay, and qRT-PCR at all study intervals did not indicate the presence of PVS-RIPO in stool samples from any animal enrolled in the study.…”

“…Insertion of the HRV2 IRES into wt PV1, yielding PV1-RIPO, reduced neuronal competence below the levels of PV1-S, evident as poor replication potential in neuroblastoid cell lines, e.g., Sk-N-Mc (15) or HEK-293 (5,14). Accordingly, PV1-RIPO lacked neurovirulence in the World Health Organization (WHO) standard neurovirulence test after intraspinal inoculation in Macaca fascicularis (16).…”

Oncolytic viruses: From bench to bedside with a focus on safety

“…106 Overexpression of CD155 has also been shown in (neuro) ectodermal tumors, and transcriptional upregulation has been linked to signaling pathways commonly affected in malignancy, including Raf-Erk-Mnk signaling. 107, 108 The neuropathogenicity of PV is dependent on the neuronal cell-type-specific function of its IRES element, which assures initiation of translation in a 5' end-and cap-independent manner. Mutations in the IRES genomic region or exchange with other viral IRES counterparts result in markedly neuro-attenuation in CD155-transgenic mice and non-human primates, without reducing the cytopathogenicity in malignant cell types that express CD155.…”