Human immunodeficiency virus type 1 Vif- mutant particles from restrictive cells: role of Vif in correct particle assembly and infectivity

Abstract

Disruption of the vif gene of human immunodeficiency virus (HIV) type 1 affects virus infectivity to various degrees, depending on the T-cell line used.We have concentrated our studies on true phenotypic Vif ؊ mutant particles produced from CEMx174 or H9 cells. In a single round of infection, Vif ؊ virus is approximately 25 (from CEMx174 cells) to 100 (from H9 cells) times less infectious than wild-type virus produced from these cells or than the Vif ؊ mutant produced from HeLa cells. Vif ؊ virions recovered from restrictive cells, but not from permissive cells, are abnormal both in terms of morphology and viral protein content. Notably, they contain much reduced quantities of envelope proteins and altered quantities of Gag and Pol proteins. Although wild-type and Vif ؊ virions from restrictive cells contain similar quantities of viral RNA, no viral DNA synthesis was detectable after acute infection of target cells with phenotypically Vif ؊ virions. To examine the possible role of Vif in viral entry, attempts were made to rescue the Vif ؊ defect in H9 cells by pseudotyping Vif ؉ and Vif ؊ HIV particles with amphotropic murine leukemia virus envelope. Vif ؊ particles produced in the presence of HIV envelope could not be propagated when pseudotyped. In contrast, when only the murine leukemia virus envelope was present, significant propagation of Vif ؊ HIV particles could be detected. These results demonstrate that Vif is required for proper assembly of the viral particle and for efficient HIV Env-mediated infection of target cells.

Role of Vif in human immunodeficiency virus type 1 reverse transcription

“…Our results ( Fig. 5 and 6) and previous studies suggest that Vif does not affect viral RNA encapsidation (3,40), dimerization, or the stability of the RNA dimer linkage. Altered Gag processing has been demonstrated in vif mutant virions (3,34), raising the possibility that Vif might affect the NC protein, p24 Gag, or the spatial organization of Gag proteins within the nucleoprotein complex and thereby influence reverse transcription.…”

“…The Vif protein of human immunodeficiency virus type 1 (HIV-1) is important for virion infectivity (10,36,38). vif mutant HIV-1 virions are defective in their ability to synthesize proviral DNA in vivo (3,7,37,40). Whether this reflects an intrinsic defect in reverse transcription or an abnormality in a preceding early event(s) such as virus entry or uncoating is unknown.…”

“…Whether this reflects an intrinsic defect in reverse transcription or an abnormality in a preceding early event(s) such as virus entry or uncoating is unknown. Peripheral blood mononuclear cells (PBMC) and some cell lines such as H9 require Vif to produce infectious HIV-1 virus particles, whereas other cell lines such as COS-1 and SupT1 do not (3,7,9,14,15,33,40). vif mutant virions produced in some nonpermissive cell lines can initiate reverse transcription but are defective in their ability to complete proviral DNA synthesis after acute infection (35,37,40).…”

“…vif mutant virions produced in some nonpermissive cell lines can initiate reverse transcription but are defective in their ability to complete proviral DNA synthesis after acute infection (35,37,40). However, when vif mutant virions are produced in PBMC or CEMx174 cells, the synthesis of initial reverse transcripts is undetectable (3,7). 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.…”

“…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.…”