The beta-chemokines MIP-1alpha, MIP-1beta and RANTES inhibit infection of CD4+ T cells by primary, non-syncytium-inducing (NSI) HIV-1 strains at the virus entry stage, and also block env-mediated cell-cell membrane fusion. CD4+ T cells from some HIV-1-exposed uninfected individuals cannot fuse with NSI HIV-1 strains and secrete high levels of beta-chemokines. Expression of the beta-chemokine receptor CC-CKR-5 in CD4+, non-permissive human and non-human cells renders them susceptible to infection by NSI strains, and allows env-mediated membrane fusion. CC-CKR-5 is a second receptor for NSI primary viruses.

Human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies are thought be distinguished from nonneutralizing antibodies by their ability to recognize functional gp120/gp41 envelope glycoprotein (Env) trimers. The antibody responses induced by natural HIV-1 infection or by vaccine candidates tested to date consist largely of nonneutralizing antibodies. One might have expected a more vigorous neutralizing response, particularly against virus particles that bear functional trimers. The recent surprising observation that nonneutralizing antibodies can specifically capture HIV-1 may provide a clue relating to this paradox. Specifically, it was suggested that forms of Env, to which nonneutralizing antibodies can bind, exist on virus surfaces. Here, we present evidence that HIV-1 particles bear nonfunctional gp120/gp41 monomers and gp120-depleted gp41 stumps. Using a native electrophoresis band shift assay, we show that antibody-trimer binding predicts neutralization and that the nonfunctional forms of Env may account for virus capture by nonneutralizing antibodies. We hypothesize that these nonfunctional forms of Env on particle surfaces serve to divert the antibody response, helping the virus to evade neutralization.

. Here we produced pseudovirions bearing the mutant envelope and a reporter gene to examine the mutant's infectious properties. These pseudovirions attach to cells expressing CD4 and coreceptor but infect only when triggered with reducing agent, implying that gp120-gp41 dissociation is necessary for infection. Further studies suggested that virus entry was arrested after CD4 and coreceptor engagement. By measuring the activities of various entry inhibitors against the arrested intermediate, we found that gp120-targeting inhibitors typically act prior to virus attachment, whereas gp41 inhibitors are able to act postattachment. Unexpectedly, a significant fraction of antibodies in HIV-1-positive sera neutralized virus postattachment, suggesting that downstream fusion events and structures figure prominently in the host immune response. Overall, this disulfide-shackled virus is a unique tool with potential utility in vaccine design, drug discovery, and elucidation of the HIV-1 entry process.Human immunodeficiency virus type 1 (HIV-1) enters susceptible target cells via a complex cascade of receptor-mediated events. A fine characterization of this process is complicated by the transient nature of the lipid and protein rearrangements involved. The envelope glycoprotein (Env) is responsible for viral attachment and fusion. Env consists of noncovalently associated trimers of heterodimers comprising gp120 surface and gp41 transmembrane glycoproteins (29, 39). During infection, gp120 attaches to the CD4 receptor and undergoes conformational changes that enable coreceptor binding (39). This leads to further changes in gp41 (22) to form a six-helix bundle consisting of three alpha-helical hairpins (7, 48) and culminates in lipid mixing and membrane fusion.The study of HIV-1 entry and the Env conformations involved has provided a rich source of targets for a new generation of antiretroviral therapies (6,16,18). The most clinically advanced HIV-1 entry inhibitor, the peptide T-20 (also known as DP178), blocks fusion at nanomolar concentrations (49) by binding to a structure known as the gp41 prehairpin intermediate that becomes available during the fusion process (22).Env represents the primary target for the neutralizing antibody response. Successful vaccines against many viral infections elicit neutralizing antibodies (4) but have been difficult to elicit against HIV-1. The virus evades host immunity by exposing hypervariable and heavily glycosylated regions on gp120, while the conserved domains that bind its cellular receptors are located in recessed cavities (29, 39). As a result, only a few monoclonal antibodies (MAbs) against Env isolated to date are both potently and broadly neutralizing (5,9,33,34,39,41,44,45,52). Since conserved domains and potential targets for neutralizing antibodies may become exposed after receptor binding, fusion intermediates may find utility in vaccine research (12,13,20,26,33,37,51).Until now, HIV-1 fusion intermediates have been generated by incubating virus or Env-expressing cells with tar...

Germline mutations in the breast and ovarian cancer susceptibility gene BRCA1 are responsible for the majority of cases involving hereditary breast and ovarian cancer. Whereas all truncating mutations are considered as functionally deleterious, most of the missense variants identified to date cannot be readily distinguished as either disease-associated mutations or benign polymorphisms. The C-terminal domain of BRCA1 displays an intrinsic transactivation activity, and mutations linked to disease predisposition have been shown to confer loss of such activity in yeast and mammalian cells. In an attempt to clarify the functional importance of the BRCA1 C-terminus as a transcription activator in cancer predisposition, we have characterized the effect of C-terminal germline variants identified in Scandinavian breast and ovarian cancer families. Missense variants A1669S, C1697R, R1699W, R1699Q, A1708E, S1715R and G1738E and a truncating mutation, W1837X, were characterized using yeast- and mammalian-based transcription assays. In addition, four additional missense variants (V1665M, D1692N, S1715N and D1733G) and one in-frame deletion (V1688del) were included in the study. Our findings demonstrate that transactivation activity may reflect a tumor-suppressing function of BRCA1 and further support the role of BRCA1 missense mutations in disease predisposition. We also report a discrepancy between results from yeast- and mammalian-based assays, indicating that it may not be possible to unambiguously characterize variants with the yeast assay alone. We show that transcription-based assays can aid in the characterization of deleterious mutations in the C-terminal part of BRCA1 and may form the basis of a functional assay.