ABSTRACT
Cyclophilin A (CypA) promotes HIV-1 infection by facilitating reverse transcription, nuclear entry and by countering the antiviral activity of TRIM5α. These multifunctional roles of CypA are driven by its binding to the viral capsid. Interestingly, recent studies suggest that the HIV-1 capsid lattice enters the nucleus of an infected cell and uncoats just before integration. Therefore, we tested whether CypA-capsid interaction regulates post-nuclear entry steps of infection, particularly integration. First, we challenged CypA-expressing (CypA +/+ ) and CypA-depleted (CypA -/- ) cells with HIV-1 particles and quantified the resulting levels of provirus. Surprisingly, CypA-depletion significantly reduced integration, an effect that was independent of CypA's effect on reverse transcription, nuclear entry, and the presence or absence of TRIM5α. Additionally, cyclosporin A, an inhibitor that disrupts CypA-capsid binding, inhibited HIV-1 integration in CypA +/+ cells but not in CypA -/- cells. Accordingly, HIV-1 capsid mutants (G89V and P90A) deficient in CypA binding were also blocked at integration in CypA +/+ cells but not in CypA -/- cells. Then, to understand the mechanism, we assessed the integration activity of HIV-1 preintegration complexes (PICs) extracted from infected cells. The PICs from CypA -/- cells had lower activity in vitro compared to those from CypA +/+ cells. PICs from cells depleted for CypA and TRIM5α also had lower activity, suggesting that CypA's effect on PIC activity is independent of TRIM5α. Finally, addition of CypA protein significantly stimulated the integration activity of PICs extracted from both CypA +/+ and CypA -/- cells. Collectively, these results suggest that CypA promotes HIV-1 integration, a previously unknown role of this host factor. Importance: HIV-1 capsid interaction with host cellular factors is essential for establishing a productive infection. However, the molecular details of such virus-host interactions are not fully understood. Cyclophilin A (CypA) is the first host protein identified to specifically bind to the HIV-1 capsid. Now it is established that CypA promotes reverse transcription and nuclear entry steps of HIV-1 infection. In this report, we show that CypA promotes HIV-1 integration by binding to the viral capsid. Specifically, our results demonstrate that CypA promotes HIV-1 integration by stimulating the activity of the viral preintegration complex and identifies a novel role of CypA during HIV-1 infection. This new knowledge is important because recent reports suggest that an operationally intact HIV-1 capsid enters the nucleus of an infected cell.
ABSTRACT
RESUMEN El material de elección para el reemplazo del hueso perdido por traumatismos, procesos patológicos congénitos o adquiridos y atrofia, son los injertos óseos autógenos o autólogos (hueso del propio paciente). A partir de la introducción del concepto de osteointegración por Branemark, los implantes dentales son parte de la terapéutica diaria para rehabilitar áreas edéntulas. La atrofia alveolar es quizás una de las condiciones bucales más incapacitantes; la razón reside en que es crónica, progresiva, acumulativa e irreversible, altera las relaciones maxilomandibulares, reduce la cantidad de hueso del área dentosoportada y la profundidad del surco. El material de injerto óseo ideal no debería ser sólo un sustituto óseo, sino un material de regeneración que se reabsorba completamente de modo simultáneo a la formación de hueso nuevo. Evaluar el éxito y fracaso de una terapia permite tomar decisiones para un mejoramiento continuo de la práctica clínica. El objetivo de la investigación fue demostrar la importancia de la utilización de biomateriales e injertos óseos autólogos en pacientes con atrofia alveolar (AU).
SUMMARY The elective material for replacing the bone lost by trauma, congenital or acquired pathological processes and atrophy are the autogenic or autologous bone grafts (the patient´s own bones). From the introduction of the concept of osseointegration by Branemark on, dental implants are part of the daily therapeutic for rehabilitating edentulous areas. Alveolar atrophy is perhaps one of the most disabling oral conditions, because it is chronic, progressive, cumulative and irreversible. It alters maxilla-mandibular relations, reduces the bone quality of the dentosupported area and the depth of the sulcus. The ideal bone graft material should not be only a bone substitute, by a regenerative material that could be completely reabsorbed simultaneously with the new bone formation. To assess the success and failure of a therapy allows taking decisions for the continuous improvement of the clinical practice. The aim of the research was to prove the importance of using biomaterials or autologous bone grafts in patients with alveolar atrophy (AU).