The N terminus of adenovirus type 12 E1A inhibits major histocompatibility complex class I expression by preventing phosphorylation of NF-kappaB p65 Ser276 through direct binding

• Published in: Journal of virology 2010-08, Vol.84 (15), p.7668-7674
• Main Authors: Jiao, Junfang, Guan, Hancheng, Lippa, Andrew M, Ricciardi, Robert P
• Format: Article
• Language: English
• Subjects: Adenovirus E1A Proteins - metabolism; Adenoviruses, Human - immunology; Adenoviruses, Human - pathogenicity; Animals; Cercopithecus aethiops; COS Cells; Gene Expression; Histocompatibility Antigens Class I - biosynthesis; Phosphorylation; Protein Binding; Protein Interaction Mapping; Transcription Factor RelA - metabolism; Virulence Factors - metabolism
• ISSN: 1098-5514
• DOI: 10.1128/JVI.02317-09

The immune-escape strategy employed by human oncogenic adenovirus type 12 (Ad12) involves downregulation of major histocompatibility complex class I (MHC-I) transcription by disabling the transactivator NF-kappaB (p50/p65). This is accomplished by the Ad12 E1A protein (E1A-12), which prevents NF-kappaB from becoming phosphorylated by the protein kinase A catalytic subunit (PKAc). In this study, we examined the interactions between E1A-12 and NF-kappaB. Our data show that an E1A-12 mutant retaining the N-terminal 66 amino acids was as effective as the wild-type E1A-12 protein (266 amino acids) in binding p65, preventing phosphorylation of p65-Ser(276), and inhibiting transactivation. In contrast, the nontumorigenic adenovirus type 5 E1A protein (E1A-5) and other E1A-12 mutants lacking the N-terminal regions were severely defective in these activities. Further studies revealed that an N-terminal peptide consisting of residues 1 to 40 of E1A-12 was able to associate directly with p65 in vitro and prevent PKAc from phosphorylating p65-Ser(276). In the absence of the N terminus, there is an almost complete loss of E1A-12 binding to p65. These findings provide solid evidence for the role of the E1A-12 N terminus as an NF-kappaB binding domain. Significantly, this study indicates that the E1A-12 N terminus prevents PKAc from gaining access to p65 to account for Ser(276) hypophosphorylation. The E1A-12 N terminus interaction with p65 serves as a key explanation of how Ad12 downregulates MHC-I transcription and contributes to oncogenesis by escaping cytotoxic T lymphocytes.