Biomedical subjects

Andrew Mehle

Publications and source records attributed to Andrew Mehle.

5 recordsLinked to original sources

PubMed2006

A zinc-binding region in Vif binds Cul5 and determines cullin selection.

Human immunodeficiency virus-1 (HIV-1) Vif overcomes the anti-viral activity of APOBEC3G by targeting it for ubiquitination via a Cullin 5-ElonginB-ElonginC (Cul5-EloBC) E3 ligase. Vif associates with Cul5-EloBC through a BC-box motif that binds EloC, but the mechanism by which Vif selectively recruits Cul5 is poorly understood. Here we report that a region of Vif (residues 100-142) upstream of the BC-box binds selectively to Cul5 in the absence of EloC. This region contains a zinc coordination site HX5CX17-18CX3-5H (HCCH), with His/Cys residues at positions 108, 114, 133, and 139 coordinating one zinc ion. The HCCH zinc coordination site, which is conserved among primate lentivirus Vif proteins, does not correspond to any known class of zinc-binding motif. Mutations of His/Cys residues in the HCCH motif impair zinc coordination, Cul5 binding, and APOBEC3G degradation. Mutations of conserved hydrophobic residues (Ile-120, Ala-123, and Leu-124) located between the two Cys residues in the HCCH motif disrupt binding of the zinc-coordinating region to Cul5 and inhibit APOBEC3G degradation. The Vif binding site maps to the first cullin repeat in the N terminus of Cul5. These data suggest that the zinc-binding region in Vif is a novel cullin interaction domain that mediates selective binding to Cul5. We propose that the HCCH zinc-binding motif facilitates Vif-Cul5 binding by playing a structural role in positioning hydrophobic residues for direct contact with Cul5.

APOBEC Deaminases↗

PubMed2004

Phosphorylation of a novel SOCS-box regulates assembly of the HIV-1 Vif-Cul5 complex that promotes APOBEC3G degradation.

HIV-1 Vif (viral infectivity factor) protein overcomes the antiviral activity of the DNA deaminase APOBEC3G by targeting it for proteasomal degradation. We report here that Vif targets APOBEC3G for degradation by forming an SCF-like E3 ubiquitin ligase containing Cullin 5 and Elongins B and C (Cul5-EloB-EloC) through a novel SOCS (suppressor of cytokine signaling)-box that binds EloC. Vif binding to EloC is negatively regulated by serine phosphorylation in the BC-box motif of the SOCS-box. Vif ubiquitination is promoted by Cul5 in vitro and in vivo, and requires an intact SOCS-box. Thus, autoubiquitination of Vif occurs within the assembled Vif-Cul5 complex, analogous to F-box proteins that are autoubiquitinated within their SCF (Skp1-Cullin-F-box) complex. These findings suggest mechanisms that regulate the assembly and activity of Cul5 E3 complexes through phosphorylation or autoubiquitination of the SOCS-box protein, and identify interactions between Vif and host cell proteins that may be therapeutic targets.

APOBEC-3G Deaminase↗

PubMed2003

Vif overcomes the innate antiviral activity of APOBEC3G by promoting its degradation in the ubiquitin-proteasome pathway.

Viruses must overcome diverse intracellular defense mechanisms to establish infection. The Vif (virion infectivity factor) protein of human immunodeficiency virus 1 (HIV-1) acts by overcoming the antiviral activity of APOBEC3G (CEM15), a cytidine deaminase that induces G to A hypermutation in newly synthesized viral DNA. In the absence of Vif, APOBEC3G incorporation into virions renders HIV-1 non-infectious. We report here that Vif counteracts the antiviral activity of APOBEC3G by targeting it for destruction by the ubiquitin-proteasome pathway. Vif forms a complex with APOBEC3G and enhances APOBEC3G ubiquitination, resulting in reduced steady-state APOBEC3G levels and a decrease in protein half-life. Furthermore, Vif-dependent degradation of APOBEC3G is blocked by proteasome inhibitors or ubiquitin mutant K48R. A mutation of highly conserved cysteines or the deletion of a conserved SLQ(Y/F)LA motif in Vif results in mutants that fail to induce APOBEC3G degradation and produce non-infectious HIV-1; however, mutations of conserved phosphorylation sites in Vif that impair viral replication do not affect APOBEC3G degradation, suggesting that Vif is important for other functions in addition to inducing proteasomal degradation of APOBEC3G. Vif is monoubiquitinated in the absence of APOBEC3G but is polyubiquitinated and rapidly degraded when APOBEC3G is coexpressed, suggesting that coexpression accelerates the degradation of both proteins. These results suggest that Vif functions by targeting APOBEC3G for degradation via the ubiquitin-proteasome pathway and implicate the proteasome as a site of dynamic interplay between microbial and cellular defenses.

APOBEC-3G Deaminase↗

PubMed2003

Fractalkine preferentially mediates arrest and migration of CD16+ monocytes.

CD16+ monocytes represent 5-10% of peripheral blood monocytes in normal individuals and are dramatically expanded in several pathological conditions including sepsis, human immunodeficiency virus 1 infection, and cancer. CD16+ monocytes produce high levels of proinflammatory cytokines and may represent dendritic cell precursors in vivo. The mechanisms that mediate the recruitment of CD16+ monocytes into tissues remain unknown. Here we investigate molecular mechanisms of CD16+ monocyte trafficking and show that migration of CD16+ and CD16- monocytes is mediated by distinct combinations of adhesion molecules and chemokine receptors. In contrast to CD16- monocytes, CD16+ monocytes expressed high CX3CR1 and CXCR4 but low CCR2 and CD62L levels and underwent efficient transendothelial migration in response to fractalkine (FKN; FKN/CX3CL1) and stromal-derived factor 1 alpha (CXCL12) but not monocyte chemoattractant protein 1 (CCL2). CD16+ monocytes arrested on cell surface-expressed FKN under flow with higher frequency compared with CD16- monocytes. These results demonstrate that FKN preferentially mediates arrest and migration of CD16+ monocytes and suggest that recruitment of this proinflammatory monocyte subset to vessel walls via the CX3CR1-FKN pathway may contribute to vascular and tissue injury during pathological conditions.

Antibodies, Monoclonal↗

PubMed2002

Increased CCR5 affinity and reduced CCR5/CD4 dependence of a neurovirulent primary human immunodeficiency virus type 1 isolate.

Most human immunodeficiency virus type 1 (HIV-1) viruses in the brain use CCR5 as the principal coreceptor for entry into a cell. However, additional phenotypic characteristics are necessary for HIV-1 neurotropism. Furthermore, neurotropic strains are not necessarily neurovirulent. To better understand the determinants of HIV-1 neurovirulence, we isolated viruses from brain tissue samples from three AIDS patients with dementia and HIV-1 encephalitis and analyzed their ability to induce syncytia in monocyte-derived macrophages (MDM) and neuronal apoptosis in primary brain cultures. Two R5X4 viruses (MACS1-br and MACS1-spln) were highly fusogenic in MDM and induced neuronal apoptosis. The R5 viruses UK1-br and MACS2-br are both neurotropic. However, only UK1-br induced high levels of fusion in MDM and neuronal apoptosis. Full-length Env clones from UK1-br required lower CCR5 and CD4 levels than Env clones from MACS2-br to function efficiently in cell-to-cell fusion and single-round infection assays. UK1-br Envs also had a greater affinity for CCR5 than MACS2-br Envs in binding assays. Relatively high levels of UK1-br and MACS2-br Envs bound to CCR5 in the absence of soluble CD4. However, these Envs could not mediate CD4-independent infection, and MACS2-br Envs were unable to mediate fusion or infection in cells expressing low levels of CD4. The UK1-br virus was more resistant than MACS2-br to inhibition by the CCR5-targeted inhibitors TAK-779 and Sch-C. UK1-br was more sensitive than MACS2-br to neutralization by monoclonal antibodies (2F5 and immunoglobulin G1b12 [IgG1b12]) and CD4-IgG2. These results predict the presence of HIV-1 variants with increased CCR5 affinity and reduced dependence on CCR5 and CD4 in the brains of some AIDS patients with central nervous system disease and suggest that R5 variants with increased CCR5 affinity may represent a pathogenic viral phenotype contributing to the neurodegenerative manifestations of AIDS.

AIDS Dementia Complex↗