The nucleocapsid protein of Crimean–Congo hemorrhagic fever virus interacts with eIF4A to promote the translation of viral mRNA in cells

Crimean–Congo hemorrhagic fever virus (CCHFV), a tick-borne nairovirus of the Bunyavirales order, differs from many viruses in that it does not suppress host cell protein synthesis. This raises the question of how the virus’s mRNAs are able to be efficiently translated despite competition from host transcripts. This study demonstrates that the CCHFV nucleocapsid protein (N protein) boosts the translation of luciferase reporter mRNA, but only when assisted by the viral S-segment mRNA-derived 5’ untranslated region (5’ UTR). Inhibiting eIF4E, a typical cap-binding factor, did not disrupt this enhanced translation. However, when eIF4G was cleaved or eIF4A was chemically inhibited, the N protein’s ability to promote translation was lost. These results reveal that both eIF4A and eIF4G are essential for N protein-driven translation, and this process specifically relies on the viral mRNA 5’ UTR. If the 5’ UTR was randomized, the translation efficiency of the viral S-segment mRNA dropped sharply. Wild-type (WT) S-segment mRNA was found to strongly associate with ribosomes, while the N protein remained bound to the WT 5’ UTR, likely helping ribosomes load repeatedly, encouraging polysome formation and thus enhancing protein synthesis. In contrast, the randomized UTR version of the S-segment mRNA was mostly not associated with ribosomes, leading to reduced protein output. The data indicate that the N protein physically interacts with eIF4A and probably sequesters eIF4A–eIF4G complexes for dedicated use in translating viral S-segment mRNAs, thereby giving viral RNA an advantage over cellular mRNAs for access to the host translation machinery.
(MKO)