Maintenance of Syncytium-Inducing Phenotype of HIV Type 1 Is Associated with Positively Charged Residues in the HIV Type 1 gp120 V2 Domain without Fixed Positions, Elongation, or RelocatedN-Linked Glycosylation Sites

Abstract

The prevalence of HIV-1 sequences of the envelope domains V1V2 and V3 was analyzed by RT-PCR amplification. Two distinct biological phenotypes of HIV-1 have been described: the nonsyncytium-inducing (NSI) phenotype, best characterized by the inability to infect MT-2 cells, and the syncytium-inducing phenotype (SI), with the ability to infect MT-2 cells. Viral phenotype SI has been associated with HIV pathogenesis. The presence of positively charged amino acids at position 306 and 320 in the V3 domain of gp120 has been shown to be required for the support of the SI phenotype. In addition, V2 elongation and relocation of N-glycosylation sites were postulated to herald an NSI to SI phenotype switch. The present study was designed to assess the stability of an elongated V2 region with relocated N-glycosylation sites observed in SI isolates compared to NSI isolates. Eleven isolates with the SI phenotype and 19 isolates with the NSI phenotype were included in the study. Nine of the SI and 1 of the NSI isolates had a positively charged residue at position 306 or 320 (p < 0.001) in the V3 domain as assessed by direct sequencing of the viral RNA. In contrast, elongation and/or relocation of N-glycosylation sites of the V2 variable region were not found to be a consistent genetic feature of the SI phenotype. However, SI isolates had more positively charged amino acid residues in the hypervariable V2 region compared with NSI isolates. In one of the two SI isolates lacking positively charged amino acids at positions 306 or 320 in the V3 loop an elongation of 26 amino acids with 4 additional N-linked glycosylation sites was observed in the V2 region. This is consistent with the theory that elongation of V2 may be transiently required for SI conversion. These results suggest that maintenance of the SI phenotype requires positively charged amino acids in V3 in the majority of the virus population, but not an elongated V2 region with added or relocated N-linked glycosylation sites. Although increased charged residues in the V2 region may contribute.

Structural Analysis of Histo-Blood Group Antigen Binding Specificity in a Norovirus GII.4 Epidemic Variant: Implications for Epochal Evolution

“…The changes in the surface electrostatic potential, resulting from immunological pressure, could affect the manner by which NoVs interact with the cell surface receptors through avidity effects. The modulation of cell binding due to alterations of the surface charge was noted previously in the cases of influenza virus (14) and HIV (8). This may explain the results of elegant surrogate HBGA blockade assays, used in lieu of neutralization assays, that showed different binding activities of pre-and postepidemic antisera (23).…”

HIV/SIV glycoproteins: structure-function relationships

“…Overall, amino acid changes throughout the region have been shown to be important in terms of structure, function and antibody-mediated neutralisation . More recently it has been demonstrated that SI isolates carry more positive charge in V2 compared to NSI isolates (Cornelissen et al, 1995) and that the V1-V2 region can de®ne both tropism and cytopathicity independently of the V3 sequence (Palmer et al, 1996). For the prototype strain HIV-1HXB2, removal of a glycosylation site (213 to 215; Figure 3) results in a non-viable virus and length differences in V2 modulate exposure of the CD4-binding site and the immunoreactivity of SU (Fox et al, 1997).…”

Syncytium formation induced by human immunodeficiency virus type 1 isolates correlates with affinity for CD4.

“…Previously published data on the role of the V3 loop in the formation of syncytia, as well as its role in the determination of tropism in strains of HIV-1, suggested that the dominant effect of the V3 loop was, in fact, on cellular tropism (Harrowe & Cheng-Meyer, 1995 ;Cann et al, 1992 ;Carrillo et al, 1993 ;Chesebro et al, 1991Chesebro et al, , 1992Hwang et al, 1991 ;Shoida et al, 1991 ;O'Brien et al, 1990), while the ability to induce the formation of syncytia in the host cells could be influenced by regions of Env outside V3 (Groenink et al, 1992 ;Forte et al, 1994 ;Todd et al, 1995 ;Holm-Hansen et al, 1995 ;Cornelissen et al, 1995 ;Andeweg et al, 1993Andeweg et al, , 1995Sullivan et al, 1993). These observations suggested to us that chimera J, containing the HIV-1 HXB# V3 loop in the HIV-1 Ba-L env, might be able to replicate in T-cell lines with more restricted support for HIV-1 replication than Sup-T1 and PM-1.…”

“…Several investigators have also pointed out the correlation between the ability of different strains of HIV-1 to induce syncytia, and their ability to replicate in the T-cell lines used to assess syncytium formation (Fouchier et al, 1995 ;De Jong et al, 1992 ;Schuitemaker et al, 1991). In addition, there have been recent reports of involvement of the V2 region of gp120 in the determination of the syncytium-forming phenotype (Andeweg et al, 1993(Andeweg et al, , 1995Cornelissen et al, 1995 ;Sullivan et al, 1993), and some reports of V3 loop phenotype not correlating with SI\NSI phenotype (Forte et al, 1994 ;Todd et al, 1995 ;HolmHansen et al, 1995 ;Cornelissen et al, 1995). In this study, we have used cell lines that not only support syncytium formation, but which also support the replication of a wide variety of strains of HIV-1.…”

“…This has led to a situation in which the ability of HIV-1 strains to form syncytia has been defined simply as the ability to replicate in the target cell line (Fouchier et al, 1995 ;De Jong et al, 1992 ;Schuitemaker et al, 1991). Recently, some reports have noted that the correlation between V3 loop sequence and SI phenotype is not absolute (Groenink et al, 1992 ;Forte et al, 1994 ;Todd et al, 1995 ;Holm-Hansen et al, 1995 ;Cornelissen et al, 1995). In addition, several reports have demonstrated that the sequence of the V2 region of the HIV-1 envelope can influence the determination of SI or NSI phenotype (Andeweg et al, 1993(Andeweg et al, , 1995Cornelissen et al, 1995 ;Sullivan et al, 1993).…”