γ2-Adaptin is functioning in the late endosomal sorting pathway and interacts with ESCRT-I and -III subunits.

γ2-Adaptin is a clathrin adaptor-related protein with unclear physiological function. Previous studies indicated that γ2-adaptin might act within the multivesicular body (MVB) protein-sorting pathway that is central to receptor down-regulation, lysosome biogenesis, and budding of enveloped viruses. Here, we have analyzed the effects of excess and deficit γ2-adaptin on exogenous and endogenous MVB cargoes and on the MVB machinery itself. Foreign cargoes, like retroviral Gags, are entrapped by overexpressed γ2-adaptin in detergent-insoluble polymers and blocked in budding. When viral budding involves MVB/endosomal structures, excess γ2-adaptin acts by accelerating lysosomal Gag destruction. Consistently, depletion of γ2-adaptin avoids Gag routing to the lysosome and increases viral production. Functional studies with natural MVB cargoes support a role of γ2-adaptin in MVB-to-lysosome transition. Furthermore, we show that different members of the endosomal sorting complex required for transport (ESCRT) that drive sorting from endosomes to lysosomes are sequestered upon γ2-adaptin overexpression. If sequestered irreversibly, they are targeted to enhanced lysosomal degradation. The participation of γ2-adaptin in MVB sorting is further suggested by our finding that it specifically interacts with the ESCRT subunits Vps28 and CHMP2A. These observations identify γ2-adaptin as a critical factor in MVB trafficking, which likely is involved in endosome-to-lysosome maturation.

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