Core Binding Factor Beta Plays a Critical Role by Facilitating the Assembly of the Vif-Cullin 5 E3 Ubiquitin Ligase

Abstract

The HIV-1 virion infectivity factor (Vif) targets the cellular cytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F) for degradation via the host ubiquitin-proteasome pathway. Vif recruits a cellular E3 ubiquitin ligase to polyubiquitinate A3G/F. The activity of Vif critically depends on the cellular core binding factor beta (CBF␤). In this study, we investigated the Vif-CBF␤ interaction and the role of CBF␤ in the E3 ligase assembly. Vif-CBF␤ interaction requires an extensive region of Vif spanning most of its amino terminus and zinc finger region, and cullin 5 (Cul5) binding enhances the stability of the Vif-CBF␤ interaction. Our results further demonstrate that CBF␤ plays a critical role in facilitating Cul5 binding to the Vif/elongin B/elongin C complex. Vif, with or without bound substrate, is unable to bind Cul5 in the absence of CBF␤. These studies support the notion that CBF␤ serves as a molecular chaperone to facilitate Vif-E3 ligase assembly. IMPORTANCEThe host antiviral restriction factors A3G/F inhibit viral replication. The HIV-1 protein Vif targets A3G/F for degradation. This immune evasion activity of Vif is dependent on the cellular factor CBF␤. Multiple regions of Vif are known to be important for Vif function, but the mechanisms are unclear. The studies described here provide important information about the Vif-CBF␤ interaction interface and the function of CBF␤ in E3 ligase assembly. In particular, our comprehensive Vif-CBF␤ interface mapping results help to delineate the role of various Vif regions, determining if they are important for binding CBF␤ or A3G/F. Furthermore, our studies reveal an important potential mechanism of CBF␤ that has not been shown before. Our results suggest that CBF␤ may serve as a molecular chaperone to enable Vif to adopt an appropriate conformation for interaction with the Cul5-based E3 ligase. This study advances our understanding of how CBF␤ facilitates the Vif-mediated degradation of APOBEC3 proteins.

Core-Binding Factor Subunit Beta Is Not Required for Non-Primate Lentiviral Vif-Mediated APOBEC3 Degradation

“…Recent studies have shown that the transcription cofactor core-binding factor subunit beta (CBF-␤) is a key factor in Vif function (29,30). CBF-␤ interacts with HIV-1 Vif to enhance Vif's biosynthesis and facilitate Vif folding and stability, thereby enhancing the nucleation of the E3 ubiquitin ligase complex, promoting A3G degradation, and supporting viral infectivity (31)(32)(33)(34)(35)(36)(37)(38).…”

The Road Less Traveled: HIV's Use of Alternative Routes through Cellular Pathways

“…While intrinsically disordered proteins can generally fold independently of chaperon assistance (44,45), recruitment of these molecular chaperoning factors can facilitate particular interactions. In support of this notion, recent biochemical and structural studies indicated that the disordered viral accessory Vif protein recruits cellular core-binding-factor-␤ (CBF-␤; a transcription cofactor known to form functional complexes with the RUNX family of transcription factors [46]), mainly as a molecular chaperon that increases Vif stability and solubility and induces a specific Vif-conformation mandatory for its interaction with cullin-5 and consequent Vif-E3 ligase assembly (47)(48)(49)(50)(51).…”

“…To tag the APOBEC3 restriction factors for proteasomal degradation, HIV-1 Vif (ϳ50% of Vif-host interactions are within the ubiquitylation and proteosome degradation pathway [9]) provides a particularly well-investigated example in which it exploits the E3-ligase complex to evade the APOBEC3 innate im-munity restriction (9,(66)(67)(68)(69). The E3-ligase complex (CRL5) is assembled by Vif and comprises cullin-5 and Elongin B/C and in humans and rhesus macaque crucially requires CBF-␤ for APOBEC3 degradation (50,66,(70)(71)(72) (Fig. 2).…”

Conserved Interaction of Lentiviral Vif Molecules with HIV-1 Gag and Differential Effects of Species-Specific Vif on Virus Production

“…These lentiviral Vif proteins have evolved to use different strategies for overcoming their host's APOBEC3 (7,38,39,75). HIV-1 Vif assembles the CRL5 E3 ubiquitin ligase to induce the polyubiquitination and proteasome-mediated degradation of APOBEC3 (17,30,(76)(77)(78)(79)(80); this assembly is regulated by CBF␤ (14,(23)(24)(25)(26)(27)(28)39). In contrast, BIV Vif assembles with the CRL2 E3 ubiquitin ligase to induce the polyubiquitination and proteasome-mediated degradation of bovine APOBEC3, and BIV Vif activity is not regulated by CBF␤ (7,38,39).…”

“…The HIV-1 vif gene encodes a 23-kDa protein of 192 amino acids that counteracts host antiviral factors, the apolipoprotein B mRNA-editing catalytic polypeptide-like 3 (APOBEC3) family cytidine deaminases, by recruiting host cullin-5 (Cul5)-elonginB/elonginC (CRL5) E3 ubiquitin ligase to induce APOBEC3 polyubiquitination, followed by proteasome-mediated degradation in virus-producing cells (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). HIV-1 Vif function is regulated by the transcriptional factor CBF␤ (14,18,(23)(24)(25)(26)(27)(28)(29)(30). When Vif is absent from HIV-1, the host's antiviral APOBEC3 proteins can be packaged into viral progeny and induce lethal mutation in the viruses (13,(31)(32)(33)(34)(35)(36).…”