Genetic Determinants of Cell Type-Specific Poliovirus Propagation in HEK 293 Cells

Abstract

The ability of poliovirus to propagate in neuronal cells can be reduced by introducing appropriate nucleotide substitutions into the viral genome. Specific mutations scattered throughout the poliovirus genome yielded the live attenuated vaccine strains of poliovirus. Neuron-specific propagation deficits of the Sabin strains are partially encrypted within a confined region of the internal ribosomal entry site (IRES), which carries attenuating point mutations in all three serotypes. Recently, high levels of neurovirulence attenuation were achieved with genetically engineered polioviruses containing heterologous IRES elements. This is exemplified with poliovirus recombinants replicating under control of a human rhinovirus type 2 (HRV2) IRES element. We have carried out experiments delineating the genetic basis for neuronal IRES function. Neuronal dysfunction of the HRV2 IRES is determined mainly by IRES stem-loop domain V, the locus for attenuating point mutations within the Sabin strains. Neuronal incompetence associated with HRV2 IRES domain V is substantially more pronounced than that observed with the attenuating IRES point mutation of the Sabin serotype 1 vaccine strain. Mix-and-match recombination of polio and HRV2 IRES domain V suggests that the attenuation phenotype correlates with overall structural features rather than primary sequence. Our experiments have identified HEK 293 cells as a novel system for the study of neuron-specific replication phenotypes of poliovirus. This cell line, originally derived from embryonic human kidney, has recently been described to display neuronal characteristics. We report propagation properties in HEK 293 cells for poliovirus recombinants with attenuated neurovirulence in experimental animals that corroborate this observation.Poliovirus (PV), a positive-strand RNA virus of approximately 7,500 nucleotides (nt), is the prototypic member of the genus Enterovirus in the family Picornaviridae. PV is the causative agent of poliomyelitis, a paralytic condition complicating ϳ1% of all PV infections. The incidence of poliomyelitis has been drastically reduced since the introduction of two effective vaccines-the live attenuated (Sabin) strains and the formalininactivated (Salk) vaccine. Serial passage of wild-type (wt) PV in various culture systems yielded the serotype 1 and 3 Sabin strains, while serotype 2 is a naturally occurring variant with inherently reduced neurovirulence (48).It is generally assumed that the excellent safety record of the Sabin strains (the rate of vaccine-associated paralytic poliomyelitis [VAPP] is estimated at 0.14 per 1,000,000 doses) (60) is a direct reflection of tissue type-specific deficiencies that affect their propagation in the human central nervous system (CNS). Nevertheless, despite over 40 years of successful application, the molecular basis for neuroattenuation of the Sabin strains is not completely understood (16).Elucidation of the genomic sequences of PV type 1 (Sabin) [PV1(S)] (38) and PV3(S) (53, 58) and comparison to their wt progenitor...

Modification of the Untranslated Regions of Human Enterovirus 71 Impairs Growth in a Cell-Specific Manner

“…This, coupled with a large excess of positivestrand RNA production, may explain the recovery of viral growth at a later time in infection. In similar studies of poliovirus, in which the IRES was replaced with that of HRV2, no significant difference in virus growth or translation was observed in nonneuronal cells (6,17). We found that the PV1M 5= UTR was less efficient in controlling cap-independent translation than the HEV71 5= UTR in luciferase reporter assays (data not shown).…”

“…Although previous studies in animal models have succeeded in identifying genetic modifications that attenuate the virulence of enteroviruses, including coxsackieviruses and poliovirus (6,11), attempts to understand the underlying mechanism of virulence attenuation have not been undertaken. This is because the replication cycle of picornaviruses involves a series of complex overlapping processes.…”

“…Studies of related enteroviruses have indicated that the UTRs exert significant influence on tissue tropism and neurovirulence (13,17,27). However, the underlying biological mechanisms that contribute to the observed phenotypes have remained elusive (6,11). The aim of this study was to examine the role of the UTRs in regulating HEV71 translation and replication.…”

Breaking pseudo-twofold symmetry in the poliovirus 3'-UTR Y-stem by restoring Watson-Crick base pairs

“…In a comparable study Semler and co-workers deleted the entire 39-UTR of poliovirus and found only a minor defect in viral RNA replication in HeLa cells, but a major replication defect in neuroblastoma cells and a major neurovirulence attenuation in transgenic mice (Todd et al 1995(Todd et al , 1997Brown et al 2004). A cell-type-specific effect of 39-UTR mutations on virus propagation was also reported for HEK 293 cells by Gromeier and collaborators (Campbell et al 2005). A coxsackievirus mutant containing the rhinovirus IRES and a deletion of the Z-domain had wild-type growth characteristics in HeLA cells but was severely impaired in growth in neuroblastoma cells (Campbell et al 2005).…”

“…A cell-type-specific effect of 39-UTR mutations on virus propagation was also reported for HEK 293 cells by Gromeier and collaborators (Campbell et al 2005). A coxsackievirus mutant containing the rhinovirus IRES and a deletion of the Z-domain had wild-type growth characteristics in HeLA cells but was severely impaired in growth in neuroblastoma cells (Campbell et al 2005). We did not detect reduced growth of any mutant in neuroblastoma cells as well.…”