BST2/Tetherin an antagonist of HIV/SIV release: Physiological relevance of its interacting partners in its function and down – regulation by viral proteins. – BST-2-Ints

To evaluate and validate the physiological relevance of the selected partners in the regulation of BST2, we have chosen to specifically shut down their expression in cells by the use of silencing RNA (siRNA), and analyse the consequences of their depletion on BST2 regulation in a non-infectious and infectious context.

Over the last 6 months, we have obtained the tools (antibodies, etc) and developped the assays required to detect the expression as well as the localisation of our candidates proteins in the cells. Moreover we did set-up the condition to specifically shown-down their expressions in the cells.
Therefore we undertook to characterize the consequences of the depletion of the selected proteins on BST2 regulation.
Our preliminary results strongly suggest a physiological relevance of the selected partnerson BST2 regulation. Indeed, for 5 of the selected proteins, we observed a profound alteration of BST2 expression level and/or intracellular localisation upon their cepletion in cells.

Futur work will focus in characterizing the cellular and molecular mechanisms whereby the selected proteins regulates BST2 expression and localisation in the cells. Second we will evaluate their contribution in BST2 antiviral activity and antagonism par the viral proteins Vpu of HIV-1 and Nef of SIV.

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Propagation of HIV and SIV in the host involves a highly orchestrated series of interactions between proteins encoded by the virus and key cellular cofactors. One key challenge for the virus is to evade or overcome several levels of host defense mechanisms to propagate.
The cellular protein “Bone marrow stromal antigen” (BST2 also called Tetherin) was identified as a restriction factor that impedes the release of fully assembled HIV (HIV-1 and HIV-2) and SIV by physically retaining de novo formed matures viral particles at the surface of infected cells thereby reducing virus release and transmission. In HIV–1, the accessory protein Vpu is devoted to counteract BST2 restriction and promotes an efficient release of viral particles. Most strains of SIV and HIV-2 do not express Vpu. Antagonism of BST2-induced restriction of HIV–2 and SIV release is performed respectively, by the Env glycoprotein and the accessory protein Nef. HIV–1 Vpu, HIV–2 Env and SIV Nef antagonize BST2-induced restriction of viral particles release by down-regulating BST2 expression level at the cell surface. To date the exact mechanisms involved in BST2 antiviral activity as well the viral countermeasures to its activity are not fully understood. As viruses use/hijack cellular machinery to favour virus egress, a good understanding of the physiological function and regulation of viruses’ cellular cofactors is a valuable strategy to unravel the interplay between the host and virus. Therefore, we propose to decipher the biological function and regulation of BST2 to gain further insights into the mechanism underlying its antiviral factor activity and antagonism by viral proteins. To this end we performed a proteomic screen to identify BST2 cellular cofactors. We propose to analyse and validate the physiological role of those partners in BST2’s function and regulation in a non-infectious context and then their contribution in BST2 antagonism by the viral proteins Vpu of HIV-1 and Nef of SIV and in viral transmission through virological synapses