Abstract
Endosomal sorting complex required for transport-I (ESCRT-I) is one of three defined protein complexes in the class E vacuolar protein sorting (VPS) pathway required for the sorting of ubiquitinated transmembrane proteins into internal vesicles of multivesicular bodies. In yeast, ESCRT-I is composed of three proteins, VSP23, VPS28, and VPS37, whereas in mammals only Tsg101(VPS23) and VPS28 were originally identified as ESCRT-I components. Using yeast two-hybrid screens, we identified one of a family of human proteins (VPS37C) as a Tsg101-binding protein. VPS37C can form a ternary complex with Tsg101 and VPS28 by binding to a domain situated toward the carboxyl terminus of Tsg101 and binds to another class E VPS factor, namely Hrs. In addition, VPS37C is recruited to aberrant endosomes induced by overexpression of Tsg101, Hrs, or dominant negative form of the class E VPS ATPase, VPS4. Enveloped viruses that encode PTAP motifs to facilitate budding exploit ESCRT-I as an interface with the class E VPS pathway, and accordingly, VPS37C is recruited to the plasma membrane along with Tsg101 by human immunodeficiency virus, type 1 (HIV-1) Gag. Moreover, direct fusion of VPS37C to HIV-1 Gag obviates the requirement for a PTAP motif to induce virion release. Depletion of VPS37C from cells does not inhibit murine leukemia virus budding, which is not mediated by ESCRT-I, however, if murine leukemia virus budding is engineered to be ESCRT-I-dependent, then it is inhibited by VPS37C depletion, and this inhibition is accentuated if VPS37B is simultaneously depleted. Thus, this study identifies VPS37C as a functional component of mammalian ESCRT-I.
Highlights
Endosomal sorting complex required for transport-I (ESCRT-I) is one of three defined protein complexes in the class E vacuolar protein sorting (VPS) pathway required for the sorting of ubiquitinated transmembrane proteins into internal vesicles of multivesicular bodies
Depletion of VPS37C from cells does not inhibit murine leukemia virus budding, which is not mediated by ESCRT-I, if murine leukemia virus budding is engineered to be ESCRT-I-dependent, it is inhibited by VPS37C depletion, and this inhibition is accentuated if VPS37B is simultaneously depleted
Because we have previously shown that VPS28 is recruited to viral budding sites in a p6- and Tsg101-dependent manner (27), we conclude from this analysis that it is likely that viral proteins that make use of a PTAP-type L domain likely recruit the entire ESCRT-I complex
Summary
Endosomal sorting complex required for transport-I (ESCRT-I) is one of three defined protein complexes in the class E vacuolar protein sorting (VPS) pathway required for the sorting of ubiquitinated transmembrane proteins into internal vesicles of multivesicular bodies. Enveloped viruses that encode PTAP motifs to facilitate budding exploit ESCRT-I as an interface with the class E VPS pathway, and VPS37C is recruited to the plasma membrane along with Tsg101 by human immunodeficiency virus, type 1 (HIV-1) Gag. direct fusion of VPS37C to HIV-1 Gag obviates the requirement for a PTAP motif to induce virion release.
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