Internalization and intracellular retention of CD4 are two separate functions of the human immunodeficiency virus type 1 Nef protein.
The pathogenic Nef protein of the human immunodeficiency virus type 1 (HIV-1) downregulates CD4 by inducing its endocytosis and by inhibiting the transport of the receptor to the cell membrane. By means of in vivo-selected mutations, we show that L37, P78 and E177 residues of Nef are required for its effect on CD4 internalization and recycling but dispensable for Nef-induced retention and degradation of intracellular CD4. Of note, the function of Nef on the anterograde transport of newly synthesized CD4 molecules is irrelevant in cells with a slow constitutive CD4 turnover such as T cell lines. Moreover, we show that a mutated CD4 that is unresponsive to Nef-mediated endocytosis, CD4LL(144)AA, is retained intracellularly and degraded by Nef like wild-type CD4. Thus, Nef's abilities to enhance endocytosis and induce intracellular retention of CD4 are mediated by separate protein surfaces and occur through distinct mechanisms.
Giolo
Giorgia
G
Division of Immunology and Infectious Disease, Children's Hospital Bambino Gesù, 00165 Rome, Italy.
Neri
Francesca
F
Division of Immunology and Infectious Disease, Children's Hospital Bambino Gesù, 00165 Rome, Italy.
Casartelli
Nicoletta
N
Division of Immunology and Infectious Disease, Children's Hospital Bambino Gesù, 00165 Rome, Italy.
Potestà
Marina
M
Division of Immunology and Infectious Disease, Children's Hospital Bambino Gesù, 00165 Rome, Italy.
Belleudi
Francesca
F
Department of Experimental Medicine, 'La Sapienza' University of Rome, Italy.
Torrisi
Maria Rosaria
MR
Department of Experimental Medicine, 'La Sapienza' University of Rome, Italy.
Doria
Margherita
M
Division of Immunology and Infectious Disease, Children's Hospital Bambino Gesù, 00165 Rome, Italy.
D019943:Amino Acid Substitution / Q000235:genetics; D015704:CD4 Antigens / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000737:chemistry / Q000821:virology*; D015497:HIV-1 / Q000235:genetics / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D020125:Mutation, Missense; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000502:physiology*
D015704:CD4 Antigens; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1