INTRACELLULAR COMPLEXES OF VIRAL SPIKE AND CELLULAR RECEPTOR ACCUMULATE DURING CYTOPATHIC MURINE CORONAVIRUS INFECTIONS

Murine hepatitis virus (MHV) infections exhibit remarkable variability in cytopathology ranging from acutely cytolytic to essentially asympt omatic levels, In this report, we assess the role of the MHV receptor (MHVR) in controlling this variable virus-induced cytopathology, We de veloped human (HeLa) cell lines in which the MHVR was produced in a re gulated fashion by placing MHVR cDNA under the control of an inducible promoter, Depending on the extent of induction, MHVR levels ranged fr om less than similar to 1,500 molecules per cell (designated R-lo) to similar to 300,000 molecules per cell (designated R-hi). Throughout th is range, the otherwise MHV-resistant HeLa cells were rendered suscept ible to infection. However, infection in the R-lo cells occurred witho ut any overt evidence of cytopathology, while the corresponding R-hi c ells died within 14 h after infection. When the HeLa-MHVR cells were i nfected with vaccinia virus recombinants encoding MHV spike (S) protei ns, the R-hi cells succumbed within 12 h postinfection; R-lo cells inf ected in parallel were intact, as judged by trypan blue exclusion. Thi s acute cytopathology was not due solely to syncytium formation betwee n the cells producing S and MHVR, because fusion-blocking antiviral an tibodies did not prevent it. These findings raised the possibility of an intracellular interaction between S and MHVR in the acute cell deat h. Indeed, we identified intracellular complexes of S and MHVR via coi mmunoprecipitation of endoglycosidase H-sensitive forms of the two pro teins. We suggest that MHV infections can become acutely cytopathic on ce these intracellular complexes rise above a critical threshold level .