Ebola virus matrix protein trafficking and cellular innate immune response

Ebola virus (EBoV), a negative sense ssRNA virus (NSV) of family Filoviridae , causes severe hemorrhagic fever in humans, with case mortality rates up to 90%. Recent outbreak in 2014 of Ebola virus disease resulted in over 7500 deaths in West Africa. The viral matrix protein (VP40), is a structural protein involved in virus assembly and budding. Several studies have shown NSV matrix proteins are capable of nucleo-cytoplasmic shuttling (Newcastle disease, Nipah and Influenza) and modulate host innate immune response (Influenza and Marburg). Role of EBoV VP40 in disease pathogenesis remains elusive. Here, we analyzed the trafficking of VP40 and cellular innate immune response using wild type and mutant VP40 fused to EGFP. Our data shows that VP40 gets transiently localized to the nucleus at 6-10 h post-transfection with subsequent transport to the plasma membrane by 16-24 h. Blocking tyrosine phosphorylation by inhibiting phosphokinases or mutating tyrosine phosphorylation sites or blocking ubiquitination by a proteasome inhibitor prevent VP40 nuclear export, transport to the membrane and virus-like particle formation. We also found that VP40 expression lead to activation and nuclear translocation of pIRF3, STAT1 and NFkB (p50), and induced increased expression of LC3b at 24 h post-transfection. Our results suggest EBoV VP40 does not inhibit type I interferon pathway, and may have a potential role in disease pathogenesis by enhancing host inflammatory response and autophagy.