HIV-1 Nef Limits Communication between Linker of Activated T Cells and SLP-76 To Reduce Formation of SLP-76–Signaling Microclusters following TCR Stimulation

Human immunodeficiency virus type 1 (HIV-1) particles assemble at the plasma membrane, which is lined by a dense network of filamentous actin (F-actin). Large amounts of actin have been detected in HIV- IMPORTANCEHIV-1 particles assemble at the plasma membrane of virus-producing cells. This membrane is lined by a dense network of actin filaments that might either present a physical obstacle to the formation of virus particles or generate force promoting the assembly process. Drug-mediated interference with the actin cytoskeleton showed different results for the formation of retroviral particles in different studies, likely due to general effects on the cell upon prolonged drug treatment. Here, we characterized the effect of actin-interfering compounds on the HIV-1 assembly process by direct observation of virus formation in live cells, which allowed us to measure assembly rate constants directly upon drug addition. Virus assembly proceeded with normal rates when actin filaments were either disrupted or stabilized. Taken together with the absence of characteristic actin filament patterns at viral budding sites in our analyses, this indicates that the actin network is dispensable for HIV-1 assembly.

Section: Methodsmentioning

confidence: 99%

Investigating the Role of F-Actin in Human Immunodeficiency Virus Assembly by Live-Cell Microscopy

Rahman

Koch

Weichsel

et al. 2014

“…HIV-1 Nef also alters the response of CD4 T lymphocytes to stimulation via the T cell receptor (TCR), and modulation of the resulting cellular signaling pathways is thought to increase virus replication in the infected host (11)(12)(13)(14)(15)(16)(17). This involves the retargeting of the TCR-proximal Src kinase Lck from the plasma membrane to the trans-Golgi network (12,14,18) as well as the inhibition of actin reorganization induced upon TCR engagement (19,20). Inhibition of host cell actin remodeling by Nef also occurs upon chemokine stimulation of T lymphocytes and translates into a potent block to cell migration (21)(22)(23)(24).…”

mentioning

confidence: 99%

The Antagonism of HIV-1 Nef to SERINC5 Particle Infectivity Restriction Involves the Counteraction of Virion-Associated Pools of the Restriction Factor

Trautz

Pierini

Wombacher

et al. 2016

Self Cite

SERINC3 (serine incorporator 3) and SERINC5 are recently identified host cell inhibitors of HIV-1 particle infectivity that are counteracted by the viral pathogenesis factor Nef. Here we confirm that HIV-1 Nef, but not HIV-1 Vpu, antagonizes the particle infectivity restriction of SERINC5. SERINC5 antagonism occurred in parallel with other Nef activities, including cell surface receptor downregulation, trans-Golgi network targeting of Lck, and inhibition of host cell actin dynamics. Interaction motifs with host cell endocytic machinery and the Nef-associated kinase complex, as well as CD4 cytoplasmic tail/HIV-1 protease, were identified as essential Nef determinants for SERINC5 antagonism. Characterization of antagonism-deficient Nef mutants revealed that counteraction of SERINC5 occurs in the absence of retargeting of the restriction factor to intracellular compartments and reduction of SERINC5 cell surface density is insufficient for antagonism. Consistent with virion incorporation of SERINC5 being a prerequisite for its antiviral activity, the infectivity of HIV-1 particles produced in the absence of a SERINC5 antagonist decreased with increasing amounts of virion SERINC5. At low levels of SERINC5 expression, enhancement of virion infectivity by Nef was associated with reduced virion incorporation of SERINC5 and antagonism-defective Nef mutants failed to exclude SERINC5 from virions. However, at elevated levels of SERINC5 expression, Nef maintained infectious HIV particles, despite significant virion incorporation of the restriction factor. These results suggest that in addition to virion exclusion, Nef employs a cryptic mechanism to antagonize virion-associated SERINC5. The involvement of common determinants suggests that the antagonism of Nef to SERINC5 and the downregulation of cell surface CD4 by Nef involve related molecular mechanisms. IMPORTANCEHIV-1 Nef critically determines virus spread and disease progression in infected individuals by incompletely defined mechanisms. SERINC3 and SERINC5 were recently identified as potent inhibitors of HIV particle infectivity whose antiviral activity is antagonized by HIV-1 Nef. To address the mechanism of SERINC5 antagonism, we identified four molecular determinants of Nef antagonism that are all linked to the mechanism by which Nef downregulates cell surface CD4. Functional characterization of these mutants revealed that endosomal targeting and cell surface downregulation of SERINC5 are dispensable and insufficient for antagonism, respectively. In contrast, virion exclusion and antagonism of SERINC5 were correlated; however, Nef was also able to enhance the infectivity of virions that incorporated robust levels of SERINC5. These results suggest that the antagonism of HIV-1 Nef to SERINC5 restriction of virion infectivity is mediated by a dual mechanism that is related to CD4 downregulation. Nef is a myristoylated 25-to 34-kDa protein that, in addition to human immunodeficiency virus type 1 (HIV-1), is encoded by HIV-2 and simian immunodeficiency virus (S...

“…These activities presumably optimize viral spread by balancing between unfavorable, premature, activation-induced cell death and specific lymphocyte activation required for efficient HIV-1 replication. This is achieved via a block of early TCR-triggered signaling events such as actin remodeling, tyrosine phosphorylation, and the formation of signaling microclusters (34)(35)(36). Simultaneously, a specific TCR-distal signaling cascade is initiated by the Src family kinase Lck, which is retargeted by Nef from the plasma membrane (PM) to recycling endosomes (REs) and the trans-Golgi network (TGN) (35,37,38).…”

mentioning

confidence: 99%

HIV-1 Nef and Vpu Are Functionally Redundant Broad-Spectrum Modulators of Cell Surface Receptors, Including Tetraspanins

Haller

Müller

Fritz

et al. 2014

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IMPORTANCEIn this paper, we define that HIV-1 Nef and Vpu display a surprising functional overlap and affect the cell surface exposure of a previously unexpected breadth of cellular receptors. Our analyses furthermore identify the tetraspanin protein family as a previously unrecognized target of Nef and Vpu activity. These findings have implications for the interpretation of effects detected for these accessory gene products on individual host cell receptors and illustrate the coevolution of Nef and Vpu function.