Modulation of GR transcriptional signalling by HIV-1 Vpr insights into regulation by progestins

Abstract

It has been 30 years since HIV was first discovered, yet the molecular mechanisms whereby the virus mediates its pathogenic effects have not yet been completely elucidated. The glucocorticoid receptor (GR) is a ligand-activated host transcription factor, which mediates anti-inflammatory effects in response to stimulation with glucocorticoids (GC). One of the HIV-1 accessory proteins, Vpr, is highly immunosuppressive and contributes to suppression of the immune system thereby creating an environment favourable for viral proliferation. Vpr has been previously reported to act as a GR co-activator on glucocorticoid response element (GRE) containing promoters. Thus, the GR appears likely to play a role in HIV-1 pathogenesis. Contraceptive usage is also likely to affect HIV-1 pathogenesis as some hormonal contraceptives can bind to and activate the GR. Progesterone (P4) regulates the female reproductive system and the synthetic progestins medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-A) are extensively used as injectable contraceptives. MPA has been shown to act as a partial or full GR agonist and recent evidence indicates that injectable MPA increases HIV-1 acquisition and transmission. The molecular mechanisms of this remain unclear, but may involve decreasing the thickness of the vaginal epithelium as well as actions via the GR that affect gene expression in the cervo-vaginal environment and/or elsewhere. This study aims to investigate the actions of GC's, P4, MPA and NET-A via the GR in the absence and presence of Vpr protein towards gaining some insight into the potential interplay between the host GR, contraceptive use, HIV-1 pathogenesis, and the mechanisms thereof.