Tissue-Specific Replicating Capacity of a Chimeric Poliovirus That Carries the Internal Ribosome Entry Site of Hepatitis C Virus in a New Mouse Model Transgenic for the Human Poliovirus Receptor

Abstract

Nucleotides (nt) 108 to 742 of an infectious cDNA clone of poliovirus (PV) Mahoney strain, including the corresponding region of the internal ribosome entry site (IRES), was replaced by nt 28 to 710 of hepatitis C virus (HCV) cDNA corresponding to the whole HCV IRES. A chimeric PV (2A-369) was generated by transfecting mammalian cells with an RNA transcribed in vitro from the cDNA. To examine replicating capacity of virus 2A-369 in the brain and liver of a mouse model for poliomyelitis, a new mouse model (MPVRTg25-61) that is transgenic for human PV receptor (hPVR; CD155) was generated in order to obtain a higher expression level of hPVR in the liver than those of hPVRTg mouse lines generated by us so far. The transgene used was constructed by combining a putative regulatory region of the mouse PVR homolog and the whole structural region of the hPVR gene. Virus 2A-369 replicated well in the liver of MPVRTg25-61 but not in the brain, whereas control Mahoney virus replicated well both in the liver and in the brain. The data suggest that the HCV IRES works more efficiently in the liver than in the brain and that PV IRES works well both in the liver and in the brain. The results support the notion that tissue-specific activity of IRES may be reflected in tissue tropism of a virus whose specific translation initiation is driven by IRES, that is, an IRES-dependent virus tropism.Internal initiation of translation for eukaryotic mRNAs was first described for picornavirus RNAs such as poliovirus (PV) RNA (27) and encephalomyocarditis virus RNA (12). Since then, an internal ribosome entry site (IRES) has been discovered on many cellular mRNAs (37), as well as other viral RNAs, including hepatitis C virus (HCV) RNA (36, 38). Nucleotide sequences that serve as IRESs discovered thus far have a variety of lengths and predicted secondary structures, although all of them have similar functions in translation initiation. This observation suggests that individual IRESs require different sets of trans-acting cellular factors to initiate translation. In fact, the translation of PV RNA does not occur efficiently in a cell-free translation system of rabbit reticulocyte lysates (RRL), although other IRESs, such as the IRESs of encephalomyocarditis virus RNA (12) and HCV RNA (36), are highly functional in the RRL. The poor translation of PV RNA in RRL is markedly improved by the addition of factors from HeLa cells. Furthermore, it has been reported that PV IRES requires higher concentrations of La protein, one of the trans-acting cellular factors, than HCV IRES to display its activity in cell-free translation systems (11). These observations strongly support the notion that cellular factors required for IRES activity are different quantitatively and/or qualitatively in individual IRESs.PV is the causative agent of poliomyelitis, an acute disease of the central nervous system (CNS). Natural PV infection in humans begins with oral ingestion, and paralytic poliomyelitis occurs as a result of the destruction of neurons induced by the lytic...

Poliovirus tropism and attenuation are determined after internal ribosome entry

“…Previously, poliovirus dependent on the HCV IRES was reported to be cleared from the brain and spinal cord of adult mice without causing disease (13). These results led to the conclusion that the HCV IRES does not mediate translation initiation in the murine brain and spinal cord.…”

“…Viral replication could be regulated by organ-specific synthesis, localization, or modification of these cell proteins. Recombinant polioviruses dependent on the IRES of human rhinovirus 2 or hepatitis C virus (HCV) do not accumulate or cause disease in the brain and spinal cord of mice (12,13,20). These results have been interpreted as indicating that the IRESs of rhinovirus and HCV do not mediate translation initiation in the brain and spinal cord.…”

“…Although the poliovirus receptor is produced in a broad range of organs (17,18), viral replication and disease are limited to a few sites, including the brain, spinal cord, and alimentary tract. It has been proposed that this restriction is established at the step of IRES-mediated translation of the viral RNA (11)(12)(13)(14)47). This hypothesis cannot be tested in cell culture, because poliovirus replication occurs in cell lines derived from many organs that do not support viral replication (48).…”

Poliovirus proves IRES-istible in vivo

“…Additional studies confirmed the validity of these findings following inoculation of cynomolgus monkeys and suggested that interactions between specific stem-loop structures (V and VI) within the poliovirus IRES are a major determinant of neurovirulence in addition to the known attenuating lesion in stem-loop V (22). Recently, Nomoto and colleagues reported altered tissuespecific viral replication (in the transgenic mouse model) of a chimeric poliovirus that contains the IRES sequences from hepatitis C virus (HCV), further emphasizing the importance of these RNA sequences in poliovirus tropism and attenuation (23).…”

Poliovirus tropism and attenuation are determined after internal ribosome entry

“…It has been suggested that poliovirus tropism, defined as the organs where the virus replicates, is determined by cell type-specific differences in translation initiation by the poliovirus IRES (11)(12)(13)(14). Poliovirus replication is limited to the brain and spinal cord, oropharyngeal and intestinal mucosa, tonsils, Peyer's patches, and cervical and mesenteric lymph nodes (15).…”