RETROVIRUSES HIV AND MLV ARE ENRICHED IN PHOSPHOINOSITIDES.

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 HIV-1 and MLV. The results of this comprehensive survey found that the overall lipid content of these viruses mostly matched that of the plasma membrane, being considerably different from the total lipid content of the cells. However, several lipids are enriched in comparison to plasma membrane: 1) cholesterol, ceramide, and GM3; 2) 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, PI(4,5)P2, has been implicated in membrane binding by Gag. Consistent with this observation, we found PI(4,5)P2 to be 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)P2 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)P2 interactions for particle release from cells.