Nef-Mediated Enhancement of Virion Infectivity and Stimulation of Viral Replication Are Fundamental Properties of Primate Lentiviruses

Abstract

Nef is a multifunctional accessory protein of primate lentiviruses. Recently, it has been shown that the ability of Nef to downmodulate CD4, CD28, and class I major histocompatibility complex is highly conserved between most or all primate lentiviruses, whereas Nef-mediated downregulation of T-cell receptor-CD3 was lost in the lineage that gave rise to human immunodeficiency virus type 1 (HIV-1). Whether or not other Nef activities are preserved between different groups of primate lentiviruses remained to be determined. Here, we show that nef genes from a large variety of HIVs and simian immunodeficiency viruses (SIVs) enhance virion infectivity and stimulate viral replication in human cells and/or in ex vivo infected human lymphoid tissue (HLT). Notably, nef alleles from unpassaged SIVcpz and SIVsmm enhanced viral infectivity, replication, and cytopathicity in cell culture and in ex vivo infected HLT as efficiently as those from HIV-1 and HIV-2, their human counterparts. Furthermore, nef genes from several highly divergent SIVs that have not been found in humans were also highly active in human cells and/or tissues. Thus, most primate lentiviral Nefs enhance virion infectivity and stimulate viral replication. Moreover, our data show that SIVcpz and SIVsmm Nefs do not require adaptive changes to perform these functions in human cells or tissues and support the idea that nef alleles from other primate lentiviruses would also be capable of promoting efficient virus spread in humans.

Consequences of HLA-B*13-Associated Escape Mutations on HIV-1 Replication and Nef Function

“…Fourth, we assessed the impact of Nef-E24Q and/or Nef-Q107R on only three of Nef's in vitro functions (viral replication and CD4/HLA class I downregulation), but the impact of Nef-E24Q and Nef-Q107R on other Nef functions, including upregulation of HLA class II invariant chain (CD74) (61), enhancement of virion infectivity (62), and alteration of T cell receptor signaling (63), remains to be determined. Moreover, to evaluate the effect of Nef mutations on HLA downregulation and its consequences for T cell-mediated recognition of infected cells, we used HLA-A*02 and an FK10…”

The inability to disrupt the immunological synapse between infected human T cells and APCs distinguishes HIV-1 from most other primate lentiviruses

“…The group 2 nefs were derived from HIV-2 BEN, the SIVmac239 molecular clone, and SIVblu from a Blue monkey (Cercopithecus mitis). All 6 nef alleles have been characterized in previous studies (29,30,34,35) and were chosen because they are functionally active and represent the 2 human AIDS viruses (HIV-1 and HIV-2), their simian counterparts (SIVcpz and SIVmac), and a naturally SIV-infected small monkey species (SIVblu). The SIVmac239 and SIVblu Nefs were also selected because of the availability of specific mutants that are selectively active (mac tNef) or defective (SIVblu RR-AA; also referred to as bluRR) in TCR-CD3 modulation (30,36).…”

Efficient SIVcpz replication in human lymphoid tissue requires viral matrix protein adaptation

“…Virus stocks were generated by transient transfection of 293T cells, and infectivity assays were performed using TZM-bl indicator cells as described (60).…”