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Holly A Saffran

Publications and source records attributed to Holly A Saffran.

4 recordsLinked to original sources
PubMed2006

Herpes simplex virus eliminates host mitochondrial DNA.

Mitochondria have crucial roles in the life and death of mammalian cells, and help to orchestrate host antiviral defences. Here, we show that the ubiquitous human pathogen herpes simplex virus (HSV) induces rapid and complete degradation of host mitochondrial DNA during productive infection of cultured mammalian cells. The depletion of mitochondrial DNA requires the viral UL12 gene, which encodes a conserved nuclease with orthologues in all herpesviruses. We show that an amino-terminally truncated UL12 isoform-UL12.5-localizes to mitochondria and triggers mitochondrial DNA depletion in the absence of other HSV gene products. By contrast, full-length UL12, a nuclear protein, has little or no effect on mitochondrial DNA levels. Our data document that HSV inflicts massive genetic damage to a crucial host organelle and show a novel mechanism of virus-induced shutoff of host functions, which is likely to contribute to the cell death and tissue damage caused by this widespread human pathogen.

Animals↗
PubMed2005

Herpes simplex virus infection stabilizes cellular IEX-1 mRNA.

Herpes simplex virus (HSV) virion host shutoff protein (vhs) destabilizes cellular and viral mRNAs. Previous work from several laboratories has indicated that vhs accelerates the turnover of most host mRNAs and provided evidence that at least some of these are degraded via endonucleolytic cleavage near regions of translational initiation followed by 5'-->3' decay. In contrast, several recent reports have argued that vhs is selective, preferentially targeting a subset of mRNAs including some that bear AU-rich instability elements (such as the stress-inducible IEX-1 mRNA). These reports concluded that vhs triggers deadenylation, 3' cleavage, and 3'-->5' decay of IEX-1 mRNA. However, we report here that HSV infection does not increase the rate of degradation of IEX-1 mRNA; rather, actinomycin D chase assays indicate that the transcript is stabilized relative to that in uninfected cells in both the presence and absence of functional vhs. Moreover, deadenylated but otherwise intact IEX-1 mRNA was readily detected in uninfected cells cultured under our experimental conditions, and its relative abundance did not increase following HSV type 1 (HSV-1) infection. We confirm that HSV infection increases the relative abundance of a discrete 0.75-kb 3'-truncated IEX-1 RNA species in a vhs-dependent manner. This truncated transcript was also detected (albeit at lower levels) in cells infected with vhs mutants and in uninfected cells, where it increased in abundance in response to tumor necrosis factor alpha, cycloheximide, and puromycin. We conclude that IEX-1 mRNA is not preferentially degraded during HSV-1 infection and that HSV-1 instead inhibits the normal turnover of this mRNA.

Apoptosis Regulatory Proteins↗
PubMed2004

Herpes simplex virus virion host shutoff protein is stimulated by translation initiation factors eIF4B and eIF4H.

The virion host shutoff protein (vhs) of herpes simplex virus triggers accelerated degradation of cellular and viral mRNAs while sparing other cytoplasmic RNA species. Previous work has shown that vhs forms a complex with translation initiation factor eIF4H, which displays detectable RNase activity in the absence of other viral or host proteins. However, the contributions of eIF4H and other host factors to the activity and mRNA targeting properties of vhs have not yet been directly examined. An earlier report from our laboratory demonstrated that rabbit reticulocyte lysate (RRL) contains one or more factors that strongly stimulate the RNase activity of vhs produced in Saccharomyces cerevisiae. We report here that such yeast extracts display significant vhs-dependent RNase activity in the absence of mammalian factors. This activity differs from that displayed by vhs generated in RRL in that it is not targeted to the encephalomyocarditis virus (EMCV) internal ribosome entry site (IRES). Activity was strongly enhanced by the addition of RRL, eIF4H, or the related translation factor eIF4B. RRL also reconstituted strong targeting to the EMCV IRES, resulting in a major change in the RNA cleavage pattern. In contrast, eIF4H and eIF4B did not reconstitute IRES-directed targeting. These data indicate that eIF4B and 4H stimulate the nuclease activity of vhs, and they provide evidence that additional mammalian factors are required for targeting to the EMCV IRES.

Amino Acid Sequence↗