Overexpression of TGEV cell receptor impairs the production of virus particles.

The porcine aminopeptidase-N (pAPN) is the cellular receptor for the transmissible gastroenteritis virus (TGEV) due to the specific binding of the spike protein S to APN. In the present study, we performed both biological and biochemical experiments to analyze how the level of expression of a virus receptor can influence the viral protein biosynthesis and the virus production. We generated two swine testis cell clones overexpressing pAPN (ST-APN clones). These clones produced 10(4) less infectious virus than control ST cells. Plaque assays revealed a four-fold reduction of the diameter of the plaques in ST-APN cells compared to ST cells. Pulse-chase experiments revealed that S transport from the endoplasmic reticulum to the Golgi apparatus was not affected in ST-APN cells. Additionally, an anti-APN antibody was able to increase the virus released in the supernatant of ST-APN cells. Likewise, BHK clones expressing variable amounts of pAPN were shown to acquire TGEV susceptibility and to produce infectious particles as an inverse function of their level of pAPN expression. In contrast, MDCK clones expressing low or large amounts of pAPN failed to produce infectious particles. Taken together, these studies strongly suggest that overexpression of receptor, but also other(s) undetermined factor(s), can impair the production of viral particles.