The stress-inducible immediate-early responsive gene IEX-1 is activated in cells infected with herpes simplex virus 1, but several viral mechanisms, including 3' degradation of its RNA, preclude expression of the gene.

Abstract

The accumulation of cellular transcripts from cells infected with herpes simplex virus 1 (HSV-1) as measured with the aid of Affymetrix microchips has been reported elsewhere. Among these transcripts were genes that respond to stress and that could have a noxious effect on viral replication. We have selected the stress-inducible cellular gene encoding the immediate-early response protein IEX-1 to verify and determine the significance of the accumulation of these transcripts in infected cells. We report that we verified the increase in accumulation of IEX-1 transcripts after infection by Northern analyses and real-time PCR. These transcripts reach peak levels between 3 and 7 h after infection and decrease thereafter. However, IEX-1 protein was detected in cells 1 h after infection but not at later intervals. Studies designed to elucidate the failure of IEX-1 protein to be synthesized revealed the following points. (i) IEX-1 RNA transported to the cytoplasm after 1 h of infection consisted of at least two populations, a partially degraded population and a population consisting of unspliced IEX-1 RNA. Neither of these RNAs could translate the authentic IEX-1 protein. (ii) The partially degraded IEX-1 RNA was not detected in the cytoplasm of cells infected with a mutant virus lacking the U(L)41 gene encoding the virion host shutoff protein (vhs). Although degradation of RNA mediated by vhs was reported to be 5' to 3', the partially degraded IEX-1 RNA lacked the 3' sequences rather than the 5' sequences. (iii) The unspliced pre-RNA form containing the IEX-1 intron sequences was detected in the cytoplasm of cell infected with wild-type virus but not in those infected with a mutant lacking the alpha27 gene encoding the infected cell protein No. 27. (iv) Overexpression of IEX-1 protein by transduction of the gene prior to infection with 1 PFU of HSV-1 per cell had no effect on the accumulation of late genes and virus yield. We conclude that the failure of IEX-1 to express its protein reflects the numerous mechanisms by which the virus thwarts the cells from expressing its genes after infection.