The nested open reading frame in the Epstein-Barr virus nuclear antigen-1 mRNA encodes a protein capable of inhibiting antigen presentation in cis.
Herpesviruses employ many mechanisms to evade the immune response, allowing them to persist life-long in their hosts. The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) and, more recently, the latency-associated nuclear antigen 1 (LANA-1) of the Kaposi Sarcoma Herpesvirus have been shown to function as in cis-acting inhibitors of antigen presentation. In both proteins, long simple repeat elements are responsible for the inhibition, but the sequences of these repeats are strongly dissimilar. Intriguingly, EBNA-1 mRNA contains a large nested open reading frame that codes for a 40.7kDa strongly acidic protein, in addition to the full-length EBNA-1. This protein, here called pGZr, has a 230 amino-acids long glycine, glutamine, and glutamic acid-rich repeat ('GZ' repeat), highly similar (65% amino-acid identity) to the acidic repeat of LANA-1. To evaluate if pGZr, like EBNA-1 and LANA-1, can inhibit antigen presentation in cis, we fused the nested ORF with the E. coli-derived LacZ gene encoding beta-galactosidase. Whereas cells producing the unmodified beta-galactosidase readily present the H-2L(d)-restricted CTL epitope TPHPARIGL, which resides in the C-terminal region of beta-galactosidase, cells producing the pGZr-beta-galactosidase fusion protein do not. Also shorter fragments of the repeat can inhibit peptide presentation. Even though the physiological function of pGZr remains to be elucidated, the GZ-repeat protein may be valuable as inhibitor of presentation of antigenic peptides derived from transgenes in gene therapy.
Ossevoort
Martine
M
Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands.
Zaldumbide
Arnaud
A
te Velthuis
Aartjan J W
AJ
Melchers
Mark
M
Ressing
Maaike E
ME
Wiertz
Emmanuel J H J
EJ
Hoeben
Rob C
RC
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D001483:Base Sequence; D002460:Cell Line; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics*; D010455:Peptides / Q000276:immunology; D012333:RNA, Messenger / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
D019309:Epstein-Barr Virus Nuclear Antigens; D010455:Peptides; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D001616:beta-Galactosidase; C417029:EBV-encoded nuclear antigen 1