Nef Proteins from Simian Immunodeficiency Virus-Infected Chimpanzees Interact with p21-Activated Kinase 2 and Modulate Cell Surface Expression of Various Human Receptors

Abstract

The accessory Nef protein allows human immunodeficiency virus type 1 (HIV-1) to persist at high levels and to cause AIDS in infected humans. The function of HIV-1 group M subtype B nef alleles has been extensively studied, and a variety of in vitro activities believed to be important for viral pathogenesis have been established. However, the function of nef alleles derived from naturally simian immunodeficiency virus (SIV)-infected chimpanzees, the original host of HIV-1, or from the HIV-1 N and O groups resulting from independent zoonotic transmissions remains to be investigated. In the present study we demonstrate that SIVcpz and HIV-1 group N or O nef alleles down-modulate CD4, CD28, and class I or II MHC molecules and up-regulate surface expression of the invariant chain (Ii) associated with immature major histocompatibility complex (MHC) class II. Furthermore, the ability of Nef to interact with the p21-activated kinase 2 was generally conserved. The functional activity of HIV-1 group N and O nef genes did not differ significantly from group M nef alleles. However, SIVcpz nef genes as a group showed a 1.8-and 2.0-fold-higher activity in modulating CD28 (P ‫؍‬ 0.0002) and Ii (P ‫؍‬ 0.016) surface expression, respectively, but were 1.7-fold less active in down-regulating MHC class II molecules (P ‫؍‬ 0.006) compared to HIV-1 M nef genes. Our finding that primary SIVcpz nef alleles derived from naturally infected chimpanzees modulate the surface expression of various human cellular receptors involved in T-cell activation and antigen presentation suggests that functional nef genes helped the chimpanzee virus to persist efficiently in infected humans immediately after zoonotic transmission.

Nef Associates with p21-Activated Kinase 2 in a p21-GTPase-Dependent Dynamic Activation Complex within Lipid Rafts

“…The requirement of NL4-3 Nef to precipitate NAK activity in the absence of Cdc42 V12 or an appropriate activating mutation in PAK2 suggested that this Nef allele was unable to stimulate PAK2 activity in the transfected cells. However, since previous studies have reported PAK activation by certain Nef alleles, such as SF2 (1) been recently extensively characterized for their functionality, and all were shown to be able to associate with PAK2 if cotransfected with Cdc42 V12 (15). As can be seen from Fig.…”

“…pEBB-NL4-3-Nef R71 has been described previously (29). All divergent Nef alleles were cloned into pCG plasmid, and they are described elsewhere (15), except for HIV-2 cbl and SIV SYK51. HIV-2 cbl Nef was amplified from an HIV-2-infected culture obtained through the NIH AIDS Research and Reference Reagent Program.…”

Lysine 144, a Ubiquitin Attachment Site in HIV-1 Nef, Is Required for Nef-Mediated CD4 Down-Regulation

“…K144 and the sequence surrounding K144 (FK 144 LVP) are conserved between all HIV-1 and SIVcpz sequences (55). The FKLVP motif we identified is located in a ␤-sheet secondary structure (␤4) that is exposed to the surface (54,78,79).…”

“…1 results indicate that K144 is required for Nef-mediated CD4 downregulation (Table I). In this regard, it is worthy of note that K144 as well as the motif K 144 LPV are conserved in all sequenced HIV-1 and SIVcpz Nef strains (55).…”

Activation of p21-activated Kinase 2 and Its Association with Nef Are Conserved in Murine Cells but Are Not Sufficient to Induce an AIDS-like Disease in CD4C/HIV Transgenic Mice

“…The Nef-NAK association has also been implicated in increased virion infectivity (56). This interaction of PAK with Nef is a highly conserved feature of primary HIV-1 and SIV Nef alleles (57,58), suggesting that this association is important for Nef functions. Moreover, targeting Nef to the plasma membrane is critical to allow NAK association and its autophosphorylation (59 -61).…”