Cytoskeleton association and virion incorporation of the human immunodeficiency virus type 1 Vif protein

Abstract

The human immunodeficiency virus type 1 (HIV-1) Vif protein has an important role in the regulation of virus infectivity. This function of Vif is cell type specific, and virions produced in the absence of Vif in restrictive cells have greatly reduced infectivity. We show here that the intracellular localization of Vif is dependent on the presence of the intermediate filament vimentin. Fractionation of acutely infected T cells or transiently transfected HeLa cells demonstrates the existence of a soluble and a cytoskeletal form and to a lesser extent the presence of a detergent-extractable form of Vif. Confocal microscopy suggests that in HeLa cells, Vif is predominantly present in the cytoplasm and closely colocalizes with the intermediate filament vimentin. Treatment of cells with drugs affecting the structure of vimentin filaments affect the localization of Vif accordingly, indicating a close association of Vif with this cytoskeletal component. The association of Vif with vimentin can cause the collapse of the intermediate filament network into a perinuclear aggregate. In contrast, analysis of Vif in vimentin-negative cells reveals significant staining of the nucleus and the nuclear membrane in addition to diffuse cytoplasmic staining. In addition to the association of Vif with intermediate filaments, analyses of virion preparations demonstrate that Vif is incorporated into virus particles. In sucrose density gradients, Vif cosediments with capsid proteins even after detergent treatment of virus preparations, suggesting that Vif is associated with the inner core of HIV particles. We propose a model in which Vif has a crucial function as a virion component either by regulating virus maturation or following virus entry into a host cell possibly involving an interaction with the cellular cytoskeletal network.

Virus factories: associations of cell organelles for viral replication and morphogenesis

“…Confocal microscopy shows that these filaments change their distribution in infected cells, building a cage around the VV factory (Risco et al, 2002). A collapse of vimentin IFs around viral factories has also been observed for reoviruses (Sharpe et al, 1982), picornaviruses (Nédellec et al, 1998), iridoviruses (Murti and Goorha, 1983), ASFV (Heath et al, 2001) and human immunodeficiency virus (HIV) (Karczewski and Strebel, 1996). This collapse of vimentin resembles a constitutive cellular process known as aggresome formation that cells use to encapsulate potentially toxic aggregates of misfolded proteins (see below).…”

Association of Human Immunodeficiency Virus Nef Protein with Actin is Myristoylation Dependent and Influences its Subcellular Localization

“…Two other HIV gene products (Gag and Vif) are known to be incorporated into virions via their interaction with cytoskeletal components. Whereas Gag directly binds F-actin, thereby possibly contributing to virus assembly [56], Vif has been shown to bind vimentin [57]. Since actin is present in significant amounts in HIV particles [58,591, the interaction of HIV-1 Nef with actin might be of biological relevance for the incorporation of HIV-1 Nef into viral particles which is thought to increase viral infectivity [ 18,191, especially since infectivityenhancement as well as association with actin are myristoylation dependent.…”

Role of Vif in human immunodeficiency virus type 1 reverse transcription

“…The efficiency of viral DNA synthesis is determined by several factors, including those which directly affect the activity of the RT enzyme (i.e., divalent cations), the NC protein, the configuration of the RNA or DNA template, and the spatial organization of these components within the nucleoprotein complex. A small quantity of Vif may be incorporated into the virion core (22,26), raising the possibility that Vif itself might associate with a core component(s) and thereby might directly stimulate reverse transcription or preceding early postentry events. However, whether virion incorporation of Vif is specific or biologically important remains to be determined (5).…”

“…Electron microscopy of vif mutant virions demonstrates an abnormality in the structure of the virion core (19), suggesting that the effect of Vif on viral DNA synthesis may result indirectly from an effect on the nucleoprotein complex which contains the reverse transcription machinery. A small amount of Vif (between 10 and 50 molecules) is associated with the virus particle (3,5,22,26), raising the alternative possibility that Vif might directly stimulate reverse transcription or other early events.…”