M-Sec promotes the production of infectious HIV-1 virus through the exocyst complex

We have demonstrated that the cellular protein M-Sec promotes the transmission of human immunodeficiency virus type 1 (HIV-1). However, the underlying mechanism is not fully understood. Here, we report that M-Sec promotes the production of infectious HIV-1 virus. The major viral structural protein Gag distributed as many puncta in infected cells, which is one of the indicators of viral particle formation. The knockdown of M-Sec hindered the Gag puncta formation and co-localization of Gag with the viral envelope protein Env in cells, and reduced the amount of Env and infectivity of the produced virus. Consistent with these results, the over-expression of M-Sec induced the accumulation of Gag puncta, Gag/Env co-localization, and Env incorporation into virus and viral infectivity. M-Sec is known to bind phosphatidylinositol 4,5-bisphosphate (PIP2) and a small GTPase Ral, both of which were required for the M-Sec-mediated HIV-1 regulation. The exocyst complex, which is the downstream effector of Ral, was also required for the M-Sec-mediated HIV-1 regulation. Because PIP2, Ral and the exocyst complex are important for the M-Sec-mediated formation of the long plasma membrane protrusions, the present study suggests that M-Sec promotes HIV-1 transmission by acting on both cell structures and viral production through these overlapping components. Author SummaryDespite an effective anti-retroviral therapy, human immunodeficiency virus type 1 (HIV-1) persists in a fraction of infected cells, which is an obstacle to cure. HIV-1 exploits the cell-to-cell infection for its transmission, which is more efficient than infection by cell-free virus. Thus, it is important to fully understand the process of cell-to-cell infection towards the HIV-1 cure. We previously identified M-Sec as the cellular protein that potentiates the cell-to-cell infection of HIV-1. However, the underlying mechanism is not fully explained. In this study, we discovered that M-Sec promotes the production of infectious HIV-1 particles. Mechanistically, M-Sec affects the intracellular dynamics of the major viral structural protein Gag, which leads to an efficient incorporation of the viral envelope protein Env into viral particles. This activity of M-Sec depends on PIP2 (the phosphoinositide), Ral (the small GTPase), and the exocyst complex (the downstream effector of Ral), all of which are involved in vesicular trafficking. Thus, the present study identifies M-Sec and related molecular components as potential targets of anti-HIV-1 strategies.