Suppressive activity of a viral histone H4 against two host chromatin remodelling factors: lysine demethylase and SWI/SNF

Abstract

Histone H4, a nucleosome subunit in eukaryotes, plays crucial roles in DNA package and regulation of gene expression through covalent modification. A viral histone H4 encoded in Cotesia plutellae bracovirus (CpBV), a polydnavirus, is called CpBV-H4. It is highly homologous to other histone H4 proteins excepting 38 extra amino acid residues in the N terminus. CpBV-H4 can form octamer with other histone subunits and alter host gene expression. In this study, CpBV-H4 was transiently expressed in a natural host (Plutella xylostella) and its suppressive activity on host gene expression was evaluated by the suppressive subtractive hybridization (SSH) technique. The SSH targets down-regulated by CpBV-H4 were read with the 454 pyrosequencing platform and annotated using the genome of P. xylostella. The down-regulated genes (610 contigs) were annotated in most functional categories based on gene ontology. Among these SSH targets, 115 genes were functionally distinct, including two chromatin remodelling factors: a lysine-specific demethylase (Px-KDM) and a chromatin remodelling complex [Px-SWI/SNF (SWItch/Sucrose Non-Fermentable)]. Px-KDM was highly expressed in all tested tissues during the entire larval period. Suppression of Px-KDM expression by specific RNA interference (RNAi) significantly (P<0.05) reduced haemocyte nodule formation in response to immune challenge and impaired both larval and pupal development. Px-SWI/SNF was expressed in all developmental stages. Suppression of Px-SWI/SNF expression by RNAi reduced cellular immune response and interfered with adult metamorphosis. These results suggest that CpBV-H4 can alter host gene expression by interfering with chromatin modification and remodelling factors in addition to its direct epigenetic control activity.

Characterization of joining sites of a viral histone H4 on host insect chromosomes

“…plutellae alters host gene expression via parasitic factors including CpBV-H4 which has been regarded as a regulator of host gene expression at transcriptional level by an epigenetic mode [14]. To determine genes regulated only by CpBV-H4, four RNA-Seq data (S1 Table) were compared in fragment per kilobase of transcript per million mapped reads (FPKM) levels: nonparasitized larvae (‘NP5’), parasitized larvae (‘P7’), nonparasitized larvae transiently expressing CpBV-H4 (‘vH4’), and truncated CpBV-H4 (‘vH4T’).…”

“…Recently, a cys-motif protein of CpBV has been reported to be able to suppress the translation of host mRNAs [24]. CpBV-H4 is known to be able to regulate host gene expression in transcriptional level by an epigenetic mode [14, 16]. Thus, parasitism of C .…”

“…xylostella larvae injected with CpBV also can suppress host gene expression [30]. Especially, an SSH analysis has shown that CpBV-H4 alone can inhibit the expression levels of at least 115 host genes at transcription level [14]. Thus, the 1,858 host genes regulated by C .…”

“…Furthermore, subtractive suppressive hybridization (SSH) analysis performed in natural host, P . xylostella , has shown that CpBV-H4 suppresses the expression of at least 115 genes, including chromatin remodeling factors that can subsequently alter other gene expression [14]. These previous results suggest that CpBV-H4 may have structural or DNA sequence specificity to joining sites.…”

“…CpBV-H4 suppresses host immunity by inhibiting gene expression of phenoloxidase and antimicrobial peptides [13]. CpBV-H4 expression also inhibits gene expression of insulin-like peptide of host larvae, leading to developmental retardation and hemolymph hypertrehalosemic conditions which are beneficial for symbiotic parasitoid development [14]. However, these physiological alterations by CpBV-H4 are completely lost when it loses its N-terminal extended tail [15].…”