The infection of human fetal foreskin fibroblasts (HFFF2) with human cytomegalovirus (HCMV) resulted in the induction of autophagy. This was demonstrated by the increased lipidation of microtubule-associated protein 1 light chain 3 (LC3), a hallmark of autophagy, and by the visualization of characteristic vesicles within infected cells. The response was detected first at 2 h postinfection and persisted for at least 3 days. De novo protein synthesis was not required for the effect, since HCMV that was irradiated with UV light also elicited the response, and furthermore the continuous presence of cycloheximide did not prevent induction. Infection with herpes simplex virus type 1 (HSV-1) under conditions that inhibited viral gene expression provoked autophagy, whereas UV-irradiated respiratory syncytial virus did not. The induction of autophagy occurred when cells were infected with HCMV or HSV-1 that was gradient purified, but HCMV dense bodies and HSV-1 light particles, each of which lack nucleocapsids and genomes, were inactive. The depletion of regulatory proteins Atg5 and Atg7, which are required for autophagy, reduced LC3 modification in response to infection but did not result in any detectable difference in viral or cellular gene expression at early times after infection. The electroporation of DNA into HFFF2 cultures induced the lipidation of LC3 but double-stranded RNA did not, even though both agents stimulated an innate immune response. The results show a novel, early cellular response to the presence of the incoming virion and additionally demonstrate that autophagy can be induced by the presence of foreign DNA within cells.Autophagy is a process by which cellular organelles and abnormal proteins are degraded (recently reviewed in references 16, 43, and 75). It is an important mechanism for maintaining cell viability in times of starvation and stress, as it recycles cell components to provide nutrients. In addition, autophagy provides a means to eliminate toxic protein aggregates or damaged organelles from the cell. Three types of autophagy are recognized, named macroautophagy, microautophagy, and chaperone-mediated autophagy, and the term autophagy used here will refer only to macroautophagy. Studies of yeast first defined a number of proteins, given the prefix Atg, that control autophagy, and mammalian orthologs have been described for most of these. A simplified schematic of autophagy is shown in Fig. 1. The process is initiated by the formation of a phagophore, a double-membraned structure that can be visualized as crescent shaped by electron microscopy. The initiation of the phagophore requires the activities of two multiprotein complexes, the ULK1/2 and Beclin 1 complexes. The phagophore undergoes elongation, a stage that requires the modification of microtubule-associated protein 1 light chain 3 (LC3) by the conjugation of phosphatidylethanolamine, and the activity of a complex consisting of Atg5, Atg12, and Atg16L. The extended phagophore proceeds to engulf cell material or toxic proteins and c...

The cellular protein hypoxia-inducible factor 1 alpha (HIF-1α) was induced after infection of human fibroblasts with human cytomegalovirus (HCMV). HCMV irradiated with ultraviolet light (uv-HCMV) also elicited the effect, demonstrating that the response was provoked by interaction of the infecting virion with the cell and that viral gene expression was not required. Although induction of HIF-1α was initiated by an early event, accumulation of the protein was not detected until 9 hours post infection, with levels increasing thereafter. Infection with uv-HCMV resulted in increased abundance of HIF-1α-specific RNA, indicating stimulation of transcription. In addition, greater phosphorylation of the protein kinase Akt was observed, and the activity of this enzyme was required for induction of HIF-1α to occur. HIF-1α controls the expression of many cellular gene products; therefore the findings reveal new ways in which interaction of the HCMV particle with the host cell may cause significant alterations to cellular physiology.

All of the UL82 homolog proteins analysed activated gene expression, but surprising differences in other aspects of their properties were revealed. The results provide new information on early events in infection with cytomegaloviruses.