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The E3 CR1-gamma gene in human adenoviruses associated with epidemic keratoconjunctivitis.

ABSTRACT: Human adenovirus species D type 37 (HAdV-D37) is an important etiologic agent of epidemic keratoconjunctivitis. Annotation of the whole genome revealed an open reading frame (ORF) in the E3 transcription unit predicted to encode a 31.6kDa protein. This ORF, also known as CR1-?, is predicted to be an integral membrane protein containing N-terminal signal sequence, luminal, transmembrane, and cytoplasmic domains. HAdV-D19 (C), another viral pathogen causing epidemic keratoconjunctivitis, contains an ORF 100% identical to its HAdV-D37 homologue but only 66% identical to other HAdV-D homologues. Kinetics of RNA expression and confirmation of splicing to the adenovirus tripartite leader sequence suggest a role for the protein product of CR1-? in the late stages of the viral replication cycle. Confocal microscopy is consistent with expression in the cytoplasm. Sequence analysis reveals a hypervariable luminal domain and a conserved cytoplasmic domain. The luminal domain is predicted to contain multiple N-glycosylation sites. The cytoplasmic domain contains a putative protein kinase C phosphorylation site and potential YXX? and dileucine (LL) motifs suggesting a potential role in modification of host proteins.

SUBMITTER: Robinson CM

PROVIDER: S-EPMC3163711 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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The E3 CR1-gamma gene in human adenoviruses associated with epidemic keratoconjunctivitis.

Robinson Christopher M CM Rajaiya Jaya J Zhou Xiaohong X Singh Gurdeep G Dyer David W DW Chodosh James J

Virus research 20110612 1-2

Human adenovirus species D type 37 (HAdV-D37) is an important etiologic agent of epidemic keratoconjunctivitis. Annotation of the whole genome revealed an open reading frame (ORF) in the E3 transcription unit predicted to encode a 31.6kDa protein. This ORF, also known as CR1-γ, is predicted to be an integral membrane protein containing N-terminal signal sequence, luminal, transmembrane, and cytoplasmic domains. HAdV-D19 (C), another viral pathogen causing epidemic keratoconjunctivitis, contains ...[more]

PMID: 21683743

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Project description:Human adenoviruses (HAdV), species D in particular (HAdV-D), are frequently associated with epidemic keratoconjunctivitis (EKC). Although the infection originates at the ocular surface epithelium, the mechanisms by which HAdV-Ds bypass the membrane-associated mucin (MAM)-rich glycocalyx of the ocular surface epithelium to trigger infection and inflammation remain unknown. Here, we report that an EKC-causing adenovirus (HAdV-D37), but not a non-EKC-causing one (HAdV-D19p), induces ectodomain release of MUC16-a MAM with barrier functions at the ocular surface-from cultured human corneal and conjunctival epithelial cells. HAdV-D37, but not HAdV-D19p, is also found to decrease the glycocalyx barrier function of corneal epithelial cells, as determined by rose bengal dye penetrance assays. Furthermore, results from quantitative PCR (qPCR) amplification of viral genomic DNA using primers specific to a conserved region of the E1B gene show that, in comparison to infection by HAdV-D19p, infection by HAdV-D37 is significantly increased in corneal epithelial cells. Collectively, these results point to a MUC16 ectodomain release-dependent mechanism utilized by the EKC-causing HAdV-D37 to initiate infection at the ocular surface. These findings are important in terms of understanding the pathogenesis of adenoviral keratoconjunctivitis. Similar MAM ectodomain release mechanisms may be prevalent across other mucosal epithelia in the body (e.g., the airway epithelium) that are prone to adenoviral infection. IMPORTANCE Human adenoviruses (HAdVs) are double-stranded DNA viruses that cause infections across all mucosal tissues in the body. At the ocular surface, HAdVs cause keratoconjunctivitis (E. Ford, K. E. Nelson, and D. Warren, Epidemiol Rev 9:244-261, 1987, and C. M. Robinson, D. Seto, M. S. Jones, D. W. Dyer, and J. Chodosh, Infect Genet Evol 11:1208-1217, 2011, doi:10.1016/j.meegid.2011.04.031)-a highly contagious infection that accounts for nearly 60% of conjunctivitis cases in the United States (R. P. Sambursky, N. Fram, and E. J. Cohen, Optometry 78:236-239, 2007, doi:10.1016/j.optm.2006.11.012, and A. M. Pihos, J Optom 6:69-74, 2013, doi:10.1016/j.optom.2012.08.003). The infection begins with HAdV entry within ocular surface epithelial cells; however, the mechanisms used by HAdVs to transit the otherwise protective mucosal barrier of ocular surface epithelial cells prior to entry remain unknown. Here, we report that the highly virulent keratoconjunctivitis-causing HAdV-D37 induces release of the extracellular domain (ectodomain) of MUC16, a major component of the mucosal barrier of ocular surface epithelial cells, prior to infecting underlying cells. Currently, there is no specific treatment for controlling this infection. Understanding the early steps involved in the pathogenesis of keratoconjunctivitis and using this information to intercept adenoviral entry within cells may guide the development of novel strategies for controlling the infection.

Project description:Human adenoviruses (HAdVs) contain seven species (HAdV-A to -G), each associated with specific disease conditions. Among these, HAdV-D includes those viruses associated with epidemic keratoconjunctivitis (EKC), a severe ocular surface infection. The reasons for corneal tropism for some but not all HAdV-Ds are not known. The fiber protein is a major capsid protein; its C-terminal "knob" mediates binding with host cell receptors to facilitate subsequent viral entry. In a comprehensive phylogenetic analysis of HAdV-D capsid genes, fiber knob gene sequences of HAdV-D types associated with EKC formed a unique clade. By proteotyping analysis, EKC virus-associated fiber knobs were uniquely shared. Comparative structural modeling showed no distinct variations in fiber knobs of EKC types but did show variation among HAdV-Ds in a region overlapping with the known CD46 binding site in HAdV-B. We also found signature amino acid positions that distinguish EKC from non-EKC types, and by in vitro studies we showed that corneal epithelial cell tropism can be predicted by the presence of a lysine or alanine at residue 240. This same amino acid residue in EKC viruses shows evidence for positive selection, suggesting that evolutionary pressure enhances fitness in corneal infection, and may be a molecular determinant in EKC pathogenesis. IMPORTANCE:Viruses adapt various survival strategies to gain entry into target host cells. Human adenovirus (HAdV) types are associated with distinct disease conditions, yet evidence for connections between genotype and cellular tropism is generally lacking. Here, we provide a structural and evolutionary basis for the association between specific genotypes within HAdV species D and epidemic keratoconjunctivitis, a severe ocular surface infection. We find that HAdV-D fiber genes of major EKC pathogens, specifically the fiber knob gene region, share a distinct phylogenetic clade. Deeper analysis of the fiber gene revealed that evolutionary pressure at crucial amino acid sites has a significant impact on its structural conformation, which is likely important in host cell binding and entry. Specific amino acids in hot spot residues provide a link to ocular cell tropism and possibly to corneal pathogenesis.

Dataset Information

The E3 CR1-gamma gene in human adenoviruses associated with epidemic keratoconjunctivitis.

Publications

The E3 CR1-gamma gene in human adenoviruses associated with epidemic keratoconjunctivitis.

Similar Datasets

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