The interaction of HIV with cellular trafficking pathways

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Abstract

HIV-1 hijacks cellular trafficking pathways in order to transport newly synthesised viral subunits, such as the structural polyprotein Gag, to virion assembly sites. HIV-1 Gag has been reported to interact with clathrin adaptor proteins (AP) 1-3, which function to assist clathrin mediated cargo transport. AP-1 and AP-3 assist viral particle release, whereas AP-2 inhibits viral particle release. How these APs facilitate HIV protein trafficking and particle assembly, and the consequences of HIV infection on the function of these trafficking pathways, has not been elucidated. The interaction of these pathways with the closely related virus, HIV-2, has also not been defined.

Confocal immunofluorescence microscopy revealed HIV-1 and HIV-2 Gag have different intracellular localisations; HIV-1 displayed a mainly diffuse cytoplasmic location, whereas HIV-2 predominantly localised to intracellular compartments. Further investigation through microscopy found that HIV-2, unlike HIV-1, heavily colocalised with AP-3, which functions in endosomal cargo trafficking. siRNA mediated knockdown of the APs also deduced that HIV-2 is more dependent on AP-3 than AP-1 to facilitate particle assembly, whereas HIV-1 had similar dependencies on both. HIV-2 also strongly colocalised with, and redistributed clathrin.

Initial investigation of adaptor protein dependent trafficking pathways deduced that HIV-2 interrupted the trafficking of Diphtheria toxin, which traffics in an AP-3 dependent manner through endosomal compartments, to a greater extent than HIV-1. Taken together, these results suggested that these viruses adopt different pathways to reach assembly sites, and that particle assembly likely occurs at different localisations between these viruses; the plasma membrane, via an endosomal intermediate, for HIV-1, and predominantly intracellular compartments for HIV-2. Furthermore, it was found that the matrix domain of Gag, which contains AP binding sites, was not sufficient to drive this different Gag localisation in mutant chimeric viruses.

Finally, the interruption of AP dependent trafficking pathways was investigated in astrocytes. HIV-1 displayed a striking perturbation of vesicle endocytosis events, indicating a global negative effect on these AP dependent pathways and suggesting a putative mechanism for the development of neurological symptoms, in particular short-term memory loss, during HIV infection.

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