title: Differential control of CXCR4 and CD4 downregulation by HIV-1 Gag.
abstract: BACKGROUND
  The ESCRT (endosomal sorting complex required for transport) machinery functions to sort cellular receptors into the lumen of the multivesicular body (MVB) prior to lysosomal degradation. ESCRT components can also be recruited by enveloped viruses to sites of viral assembly where they have been proposed to mediate viral egress. For example, HIV-1 budding is dependent on Gag-mediated recruitment of the cellular ESCRTs-I, -III, AIP1/Alix and Vps4 proteins. Viral recruitment of ESCRT proteins could therefore impact on host cell processes such as receptor downregulation.
  
  
  RESULTS
  Here we show that downregulation of the HIV-1 co-receptor, CXCR4, by its ligand SDF-1, is ESCRT-I dependent. Expression of HIV-1 Gag attenuated downregulation of CXCR4, resulting in accumulation of undegraded receptors within intracellular compartments. The effect of Gag was dependent on an ESCRT-I interacting motif within the C-terminal p6 region of Gag. In contrast, PMA-induced downregulation of the HIV-1 receptor CD4 was independent of ESCRT-I and Vps4; HIV-1 Gag had no effect on this process.
  
  
  CONCLUSIONS
  These results establish that the HIV-1 receptor, CD4, and co-receptor, CXCR4 are differentially regulated by ESCRT proteins. HIV-1 Gag selectively modulates protein sorting at the MVB, interfering with ESCRT-I dependent but not ESCRT-I independent processes.
authors.affiliation: Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, USA. rrv@umich.edu
authors.forename: Rajeshwari R
authors.initials: RR
authors.lastname: Valiathan
authors.forename: Marilyn D
authors.initials: MD
authors.lastname: Resh
mesh_terms: D015704:CD4 Antigens / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D015536:Down-Regulation; D011992:Endosomes / Q000235:genetics / Q000378:metabolism; D015750:Genes, gag; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000378:metabolism*; D022161:Transport Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000502:physiology*
chemical_list: D015704:CD4 Antigens; D046912:Multiprotein Complexes; D019718:Receptors, CXCR4; D033921:Vesicular Transport Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus