Nef increases infectivity of HIV via lipid rafts

Lipid rafts, also known as detergent-resistant membranes (DRM), are microdo mains in the plasma membrane enriched in sphingolipids and cholesterol (rev iewed in [1, 2]), Human immunodeficiency virus 1 (HIV) buds via lipid rafts [3, 4], However, the targeting of viral structural components to DRM and i ts consequences for viral replication are not understood. Moreover, the neg ative factor Nef from HIV increases viral infectivity (reviewed in [5, 6]), With no apparent differences in structural components and morphology betwe en wild-type and Delta Nef virons, the latter viruses display less efficien t reverse transcription in target cells. As Nef is expressed abundantly ear ly in the viral replicative cycle [7], we hypothesized that Nef could affec t viral morphogenesis and budding to render viruses more infectious, In thi s report, we demonstrated first that Nef increases viral budding from lipid rafts, Second, in the presence of Nef, viral envelopes contain more gangli oside (GM1), which is a major component of lipid rafts. This finding correl ated directly with the increased infectivity of HIV, Finally, the depletion of exogenous and endogenous cholesterol biochemically and genetically, whi ch disrupted lipid rafts, decreased viral infectivity only in the presence of Nef. Importantly, HIV lacking the nef gene remained unaffected by these manipulations. We conclude that lipids in virions are essential for viral i nfectivity, Thus, HIV becomes more infectious when it buds from lipid rafts , and Nef plays a major role in this process.