Characterization of a hamster brain cell line persistently infected with measles virus

Molecular mechanisms of measles virus persistence

As measles virus causes subacute sclerosing panencephalitis and measles inclusion body encephalitis due to its ability to establish human persistent infection, without symptoms for the time between the acute infection and the onset of clinical symptoms, it has been the paradigm for a long term persistent as opposed to chronic infection by an RNA virus. We have reviewed the mechanisms of persistence of the virus and discuss specific mutations associated with CNS infection affecting the matrix and fusion protein genes. These are placed in the context of our current understanding of the viral replication cycle. We also consider the proposed mechanisms of persistence of the virus in replicating cell cultures and conclude that no general mechanistic model can be derived from our current state of knowledge. Finally, we indicate how reverse genetics approaches and the use of mouse models with specific knock-out and knock-in modifications can further our understanding of measles virus persistence.

Cell proteins bind to sites within the 3' noncoding region and the positive-strand leader sequence of measles virus RNA

The genomic 3' noncoding region (NCR) of nonsegmented negative-strand RNA viruses contains recognition site(s) for the polymerase complex, while the RNA plus-strand leader sequence (LS) is probably involved in RNA encapsidation. It is known that host-encoded factors play a role in transcription and replication of some of this group of viruses. Here we report that cellular proteins interact with the genomic 3' NCR and with the plus-strand LS RNA of an important human pathogen, measles virus (MV), a member of the family Paramyxoviridae. Using gel retardation assay and RNA footprinting analysis, we demonstrated that in Vero cells, host-encoded proteins bind specifically to domains within these two sequences. A polypeptide of about 20 kDa binding to the 3' NCR and two polypeptides of about 22 and 30 kDa interacting with plus-strand LS were detected by RNA-protein UV cross-linking. Different RNA-binding activities were found in cells differing in permissiveness to MV replication. The results suggest a role for host-encoded proteins in MV replication.

Relation of HVJ (Sendai virus) production to cell growth phase in persistently infected mouse 3T3 cells

Using 3T3 mouse fibroblasts persistently infected with temperature-sensitive HVJ (3T3-HVJ pi), the relationship between production of HVJ and cell growth was investigated. In these cells the highest virus release into the culture media occurred from 24 to 48 hours after seeding. The release gradually decreased as the cultures approached confluency, at which time it was reduced below 1-2 per cent of that on day 2 in parallel with the decrease of both cellular DNA and RNA synthesis rates. Comparative examination in growing and resting HVJ carrier 3T3 cells showed that amounts of nucleocapsids and rate of viral structural protein synthesis in the latter phase was reduced to 4-5 per cent of those in the former phase. In addition, viral replication and transcription rates in the resting phase were found to be suppressed to 8-9 per cent of levels detected in the growing phase. These results suggest that the reduced virus production in the resting HVJ carrier cells may be mainly due to the suppression of viral RNA synthesis.