Retroviruses Human Immunodeficiency Virus and Murine Leukemia Virus Are Enriched in Phosphoinositides

Abstract

Retroviruses acquire a lipid envelope during budding from the membrane of their hosts. Therefore, the composition of this envelope can provide important information about the budding process and its location. Here, we present mass spectrometry analysis of the lipid content of human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MLV). The results of this comprehensive survey found that the overall lipid content of these viruses mostly matched that of the plasma membrane, which was considerably different from the total lipid content of the cells. However, several lipids are enriched in comparison to the composition of the plasma membrane: (i) cholesterol, ceramide, and GM3; and (ii) phosphoinositides, phosphorylated derivatives of phosphatidylinositol. Interestingly, microvesicles, which are similar in size to viruses and are also released from the cell periphery, lack phosphoinositides, suggesting a different budding mechanism/ location for these particles than for retroviruses. One phosphoinositide, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P 2 ], has been implicated in membrane binding by HIV Gag. Consistent with this observation, we found that PI(4,5)P 2 was enriched in HIV-1 and that depleting this molecule in cells reduced HIV-1 budding. Analysis of mutant virions mapped the enrichment of PI(4,5)P 2 to the matrix domain of HIV Gag. Overall, these results suggest that HIV-1 and other retroviruses bud from cholesterol-rich regions of the plasma membrane and exploit matrix/PI(4,5)P 2 interactions for particle release from cells.Retroviruses rely on their host for many essential parts of the viral replication cycle. Biochemical and antibody-based analyses of the replication cycle and proteins found in the virions have revealed many details of the molecular interactions between human immunodeficiency virus (HIV) and its host (20). In contrast, the role of lipids has been less well studied. With the increasing recognition that lipids play an important role in cellular signaling, it is no coincidence that lipid factors are slowly gaining prominence in our understanding of retroviral replication.Retroviruses, including HIV and murine leukemia virus (MLV), acquire their lipid coats by budding through host plasma membranes. Two important issues arise when considering the roles of lipids in retrovirus assembly and budding. First, the idea that HIV and other retroviruses bud from lipid rafts has gained widespread acceptance (39, 45). Lipid rafts are liquid ordered domains that exist within the liquid disordered phase of the bulk cell membrane. These dynamic lipid-protein assemblies are characterized by high levels of cholesterol, sphingolipids, saturated glycerophospholipids, and raft proteins. Because the half-lives for lipid rafts are extremely short (50), the assignment of HIV to lipid rafts is commonly established through the colocalization of HIV proteins with putative raft proteins and the preponderance of raft lipids, including cholesterol, sphingomyelin (SM), dihydrosphingomyelin (dhSM), ce...

HIV-1 incorporation of host-cell–derived glycosphingolipid GM3 allows for capture by mature dendritic cells

“…Whereas previous studies have demonstrated that HIV-1 particles incorporate both α2-3 NeuNAc-linked GM1 and GM3 gangliosides (12,18), a recent report suggests that assembly of HIV-1 Gag occurs at GM1-deficient lipid rafts (23). Our results support this recent finding and demonstrate that although GM1 can mediate mDC capture when added exogenously to virions (Fig.…”

“…Because depletion of α2-3-linked gangliosides from the virion results in particles that are deficient for mDC capture, we predicted that enrichment of the virion with α2-3-linked gangliosides would result in enhanced mDC capture. Our analyses focused on GM3 and GM1, because both α2-3-linked gangliosides were previously reported to populate lipid rafts (13) and HIV-1 particles (12,18). We used three independent strategies to test this hypothesis: exogenous addition of lipid, artificial liposomes, and ganglioside up-regulation during monocyte activation or differentiation into a macrophage.…”

“…Intriguingly, exomsomes can also mediate cross-presentation by entering mDCs, limiting exposure to endosomal acidification (31), and ultimately presenting antigen to T cells in the absence of any fusion events. Because exosomes directly compete with HIV-1 for mDC capture (15) and both are enriched for GM3 (18,32), we postulate that both types of particles bind to mDCs through GM3 and that this interaction leads to trans-dissemination (exosomes) or trans-infection (HIV). This trans-dissemination pathway, thus appears to be an intrinsic mechanism of mDCs that HIV has parasitized for facilitating its dissemination, while avoiding recognition as an agent that should be targeted for degradation.…”

Order of lipid phases in model and plasma membranes

“…This high membrane order can be related to two causes. First, as cholesterol concentration is more than 40% in plasma membranes (40,41), not only the ordered but also the disordered phase of GPMVs likely contains considerable amounts of cholesterol, increasing the packing in the membrane. In addition, both phases are above the order of the unseparated GPMVs at 20°C (Fig.…”

Rigid amphipathic fusion inhibitors, small molecule antiviral compounds against enveloped viruses

“…Only binding and rearrangements of virion glycoproteins releases energy to overcome the requirements for the formation of the negative curvature essential for fusion (19)(20)(21)(22). Furthermore, outer leaflets of virion envelopes are commonly enriched in glycolipids with relatively large hydrophilic heads, such as gangliosides, which favor positive curvature (23,24).…”