Reciprocal regulation of AKT and MAP kinase dictates virus-host cell fusion.

Viruses of the Paramyxoviridae family bind to their host cells by using hemagglutinin-neuraminidase (HN), which enhances fusion protein (F)-mediated membrane fusion. Although respiratory syncytial virus and parainfluenza virus 5 of this family are suggested to trigger host cell signaling during infection, the virus-induced intracellular signals dictating virus-cell fusion await elucidation. Using an F- or HN-F-containing reconstituted envelope of Sendai virus, another paramyxovirus, we revealed the role and regulation of AKT1 and Raf/MEK/ERK cascades during viral fusion with liver cells. Our observation that extracellular signal-regulated kinase (ERK) activation promotes viral fusion via ezrin-mediated cytoskeletal rearrangements, whereas AKT1 attenuates fusion by promoting phosphorylation of F protein, indicates a counteractive regulation of viral fusion by reciprocal activation of AKT1 and mitogen-activated protein kinase (MAPK) cascades, establishing a novel conceptual framework for a therapeutic strategy.