APOBEC1-Mediated Editing and Attenuation of Herpes Simplex Virus 1 DNA Indicate That Neurons Have an Antiviral Role during Herpes Simplex Encephalitis

Abstract

APOBEC1 (A1) is a cytidine deaminase involved in the regulation of lipids in the small intestine. Herpes simplex virus 1 (HSV-1) is a ubiquitous pathogen that is capable of infecting neurons in the brain, causing encephalitis. Here, we show that A1 is induced during encephalitis in neurons of rats infected with HSV-1. In cells stably expressing A1, HSV-1 infection resulted in significantly reduced virus replication compared to that in control cells. Infectivity could be restored to levels comparable to those observed for control cells if A1 expression was silenced by specific A1 short hairpin RNAs (shRNA). Moreover, cytidine deaminase activity appeared to be essential for this inhibition and led to an impaired accumulation of viral mRNA transcripts and DNA copy numbers. The sequencing of viral gene UL54 DNA, extracted from infected A1-expressing cells, revealed G-to-A and C-to-T transitions, indicating that A1 associates with HSV-1 DNA. Taken together, our results demonstrate a model in which A1 induction during encephalitis in neurons may aid in thwarting HSV-1 infection.The human apolipoprotein B-editing catalytic polypeptide (ABOBEC) family is a group of zinc-dependent DNA and RNA cytidine deaminases and consists of AID, APOBEC1 (A1), APOBEC2 (A2), seven APOBEC3s (APOBEC3A [A3A] to A3H), and APOBEC4 (A4). A1, the first APOBEC to be discovered, is known to introduce a premature stop codon into host apolipoprotein B mRNA in the gastrointestinal tract, an event critical for lipid metabolism (17,40,61). The editing by A1 is highly precise and specifically converts C to U at position 6666 of the apolipoprotein B mRNA substrate (46). Along with APOBEC1 complementation factor (ACF), these two proteins constitute the minimal required components necessary for the editing of apolipoprotein B mRNA in vitro (37).Cytidine deaminases first came into the limelight as antiviral factors after A3G was identified as a cellular restriction factor capable of inhibiting HIV-1 dissemination in the absence of HIV-1 virus infectivity factor (Vif) (56). This molecule was later shown to inhibit retrovirus infection by inducing a massive hypermutation of the murine leukemia virus (MLV) genome (23). Further detailed studies revealed that APOBEC molecules are packaged into HIV-1 virions in virus producer cells via a specific interaction with Gag and viral RNA and then exert their deaminase activity in subsequent target cells on a single-stranded DNA (ssDNA) intermediate synthesized by reverse transcriptase (3, 28, 55). Editing can lead to nonsynonymous mutations, such as premature stop codons, in critical proteins (e.g., reverse transcriptase) necessary for virus replication and infectivity, severely impairing the next round of infection (54,64). Extensive studies to assess the antiviral nature of these APOBEC enzymes have been performed across a broad range of retroviruses and hepatitis B virus (HBV) (7,35,36,42,43,50,56,58).Herpes simplex virus (HSV) is an enveloped, double-stranded DNA (dsDNA) virus and a member of the genus Alphaherpe...

The RNA editing enzyme APOBEC1 induces somatic mutations and a compatible mutational signature is present in esophageal adenocarcinomas

“…On the other hand, APOBEC1 can also target DNA in bacteria and in vitro [15][16][17]. Based on this activity, other roles have been suggested, from controlling DNA methylation [18,19], to being part of a restriction pathway against retroviruses and mobile elements, similar to the APOBEC3s [20][21][22][23][24][25].…”

The genetic basis for individual differences in mRNA splicing and APOBEC1 editing activity in murine macrophages

“…AS and mRNA editing, pervasive in eukaryotic transcripts, are known to contribute to a variety of mammalian phenotypes (Caceres and Kornblihtt 2002;Dhir and Buratti 2010;Gee et al 2011;Burns et al 2013). However, despite the unequivocal characterization of the cellular factors that mediate these events, the genetic features that delimit individual differences for these tightly regulated mRNA biogenesis processes are largely understudied.…”

Changes in neural network homeostasis trigger neuropsychiatric symptoms

“…In fact, members of the APOBEC family of C-to-U RNAediting enzymes are expressed in principal neurons and possibly also in interneurons (47,48). Whether spatiotemporal regulation governs GlyR C-to-U RNA editing in vivo is presently unclear, but an interesting possibility is that principal neurons and interneurons alternate in GlyR RNA editing and thereby contribute to alternating episodes of cognitive dysfunction during epileptic seizures and interictal anxiety, which is a well-known psychiatric comorbidity of epilepsy (ref.…”

“…Ectopic GlyR α3L 185L expression has several advantages: (a) It more closely matches the situation in patients with epilepsy, because RNA-edited and nonedited GlyRs coexist in neurons due to the enzymatic nature of RNA editing; (b) replacement of the Glra3 gene with the GlyR HA-3L 185L knockin cassette would knock out Glra3 gene function, yield a fraction of total RNA-edited Glra3 mRNA, and considerably overrepresent GlyR α3L 185L function; (c) Glra3 gene replacement with our cDNA copy of GlyR α3L 185L would reflect Glra3 gene promoter regulation and preclude analysis of the spatiotemporal (neuron type-specific) effects of RNA-edited GlyR α3L, which depends on the regulation of neuronal C-to-U RNA-editing enzymes (47,48).…”