Self-inhibition of synthesis reduces antigen presentation of the alcelaphine herpesvirus 1-encoded latency-associated protein, aLANA

Alcelalphine herpesvirus 1 (AlHV-1) persistently infects its natural host, the wildebeest, without inducing any clinical signs. However, cross-transmission to other ruminant species leads to the development of a deadly lymphoproliferative disease named malignant catarrhal fever (MCF). AlHV-1 ORF73 encodes the latency-associated nuclear antigen (LANA)-homolog protein termed aLANA. Similarly to other viral genome maintenance proteins encoded by gammaherpesviruses, aLANA has recently been shown to be essential for viral persistence and induction of MCF. Here we have investigated the self-inhibition of antigen presentation by aLANA and the potential role of such mechanism during the development of MCF. We showed that the GE-rich repeat domain of aLANA was sufficient to inhibit the presentation of an epitope linked to it. Though antigen presentation in absence of GE was dependent upon proteasomal degradation of aLANA, a lack of GE did not affect protein turnover. We further found that similarly to EBNA-1 GAr, aLANA GE downregulated protein self-synthesis. Likewise, such mechanism could be associated with reduced antigen presentation in vitro. In addition, in-frame insertion of GE repeat domain in a heterologous eGFP protein significantly down-regulated protein steady-state levels and self-antigen presentation. Next, we modified the AlHV-1 ORF73 gene sequence to reduce the purine bias in GE, without affecting the peptidic sequence. Such codon-modified aLANA GEm construct displayed increased antigen presentation. Finally, we generated an AlHV-1 recombinant strain expressing a GE-deficient aLANA protein and observed that viral growth was not affected in vitro by the absence of aLANA GE domain and MCF could be induced in rabbits irrespective of the expression of full-length aLANA or GE-deficient aLANA protein.