Rab27a regulates Gag trafficking and HIV assembly

CABRINI, MERCEDES; PEREYRA GERBER, PEHUEN; DUETTE, GABRIEL; PHILIPPE BENAROCH; FREED, ERIC; GEFFNER, JORGE; MATIAS OSTROWSKI

Cold Spring Harbor

Simposio; Col Spring Harbor Meeting on REtroviruses; 2013

Cold Spring Harbor Laboratory

The last stages of the HIV-1 replication cycle, including viral assembly, budding and release, are driven by the viral protein Gag. Following its synthesis, Gag must traverse the cytosol to reach the site of HIV assembly. Despite the fact that numerous proteins from the endosomal pathway have been implicated in Gag trafficking and HIV release, many phases of the itinerary followed by Gag to reach the plasma membrane are still elusive, particularly in primary cells. In this study we show that the small GTPase Rab27a is required for HIV production both in primary macrophages and CD4+ T lymphocytes, the main targets of HIV-1 infection in vivo. Rab27a has previously been shown to control the trafficking of lysosome-related organelles and we now show that it also regulates HIV assembly. The association of Gag with the plasma membrane is severely abrogated in Rab27a-deficient cells and, consequently, Gag acquires a primarily cytosolic distribution. The characteristic polarized Gag localization at points of cell-cell contact is also impaired in Rab27a-deficient macrophages and CD4+ T lymphocytes. Accordingly, cell-to-cell transmission of HIV is reduced. We show that the lack of association between Gag and the plasma membrane is due, at least partially, to a reduction in the levels of the phosphoinositide PI(4,5)P2 at the plasma membrane of Rab27a-deficient cells. Moreover, the HIV-induced recruitment of the tetraspanin CD81 towards the sites of HIV assembly is also impaired upon Rab27a silencing. Overall, we postulate that by regulating PI(4,5)P2 levels and controlling the traffic of CD81, Rab27a coordinates the formation of HIV assembly platforms required for HIV production both in macrophages and CD4+ T lymphocytes.