Avian sarcoma virus and human immunodeficiency virus, type 1 use different subsets of ESCRT proteins to facilitate the budding process.
Members of the Nedd4 family of E3 ubiquitin ligases bind the L domain in avian sarcoma virus (ASV) Gag and facilitate viral particle release. Translational fusion of ASV Gag with an L domain deletion (Deltap2b) to proteins that comprise ESCRT-I, -II, and -III (the endocytic sorting complexes required for transport) rescued both Gag ubiquitination and particle release from cells. The ESCRT-I factors Vps37C or Tsg101 were more effective in rescue of Gag/Deltap2b budding than the ESCRT-II factor Eap20 or the ESCRT-III component CHMP6. Thus ESCRT components can substitute for Nedd4 family members in ASV Gag release. Unlike wild type, ASV Gag/Deltap2b -ESCRT chimeras failed to co-immunoprecipitate with co-expressed hemagglutinin-tagged Nedd4, indicating that Nedd4 was not stably associated with these Gag fusions. Release of the Gag-ESCRT-I or -II fusions was inhibited by a dominant negative mutant of Vps4 ATPase similar to wild type ASV Gag. In contrast to ASV Gag, HIV-1 Gag containing an L domain inactivating mutation (P7L) was efficiently rescued by fusion to a component of ESCRT-III (Chmp6) but not ESCRT-II (Eap20). Depletion of the endogenous pool of Eap20 (ESCRT-II) had little effect on HIV-1 Gag release but blocked ASV Gag release. In contrast, depletion of the endogenous pool of Vps37C (ESCRT-I) had little effect on ASV but blocked HIV-1 Gag release. Furthermore, an N-terminal fragment of Chmp6 inhibited both HIV-1 and ASV Gag release in a dominant negative manner. Taken together, these results indicate that ASV and HIV-1 Gag utilize different combinations of ESCRT proteins to facilitate the budding process, although they share some common elements.
Pincetic
Andrew
A
Department of Microbiology and Immunology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois 60611, USA.
Medina
Gisselle
G
Carter
Carol
C
Leis
Jonathan
J
D001358:Avian Sarcoma Viruses / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D002460:Cell Line; D004705:Endocytosis; D015683:Gene Products, gag / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D025801:Ubiquitin / Q000737:chemistry; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000378:metabolism*
D015683:Gene Products, gag; D011993:Recombinant Fusion Proteins; D025801:Ubiquitin; D033921:Vesicular Transport Proteins