Mutation of the ATP cassette binding transporter A1 (ABCA1) C-terminus disrupts HIV-1 Nef binding but does not block the Nef enhancement of ABCA1 protein degradation.
HIV-1 infection and antiretroviral therapy are associated with a dyslipidemia marked by low levels of high-density lipoprotein and increased cardiovascular disease, but it is unclear whether virion replication plays a causative role in these changes. The HIV-1 Nef protein can impair ATP cassette binding transporter A1 (ABCA1) cholesterol efflux from macrophages, a potentially pro-atherosclerotic effect. This viral inhibition of efflux was correlated with a direct interaction between ABCA1 and Nef. Here, we defined the ABCA1 domain required for the Nef-ABCA1 protein-protein interaction and determined whether this interaction mediates the ability of Nef to downregulate ABCA1. Nef expressed in HEK 293 cells strongly inhibited ABCA1 efflux and protein levels but did not alter levels of cMIR, another transmembrane protein. Analysis of a panel of ABCA1 C-terminal mutants showed Nef binding required the ABCA1 C-terminal amino acids between positions 2225 and 2231. However, the binding of Nef to ABCA1 was not required for inhibition because the C-terminal ABCA1 mutants that did not bind Nef were still downregulated by Nef. Given this discordance, the mechanism of downregulation was investigated and was found to involve the acceleration of ABCA1 protein degradation but did not to depend upon the ABCA1 PEST sequence, which mediates the calpain proteolysis of ABCA1. Furthermore, it did not associate with a Nef-dependent induction of signaling through the unfolded protein response but was significantly dependent upon proteasomal function and could act on an ABCA1 mutant that fails to exit the endoplasmic reticulum. In summary, we show that Nef downregulates ABCA1 function by a post-translational mechanism that stimulates ABCA1 degradation but does not require the ability of Nef to bind ABCA1.
Mujawar
Zahedi
Z
Lipid Metabolism Unit, Center for Computational and Integrative Biology, Richard B. Simches Research Center, Massachusetts General Hospital, 185 Cambridge Street, 7th Floor #7150, Boston, Massachusetts 02114, USA.
Tamehiro
Norimasa
N
Grant
Angela
A
Sviridov
Dmitri
D
Bukrinsky
Michael
M
Fitzgerald
Michael L
ML
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000235:genetics; D002460:Cell Line; D015536:Down-Regulation; D008075:Lipoproteins, HDL / Q000235:genetics / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009154:Mutation; D056811:Unfolded Protein Response; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D008075:Lipoproteins, HDL; D026901:Membrane Transport Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1