HIV-1 Tat protein directly induces mitochondrial membrane permeabilization and inactivates cytochrome c oxidase

The Trans-activator protein (Tat) of human immunodeficiency virus (HIV)is a pleiotropic protein involved in different aspects of AIDS pathogenesis. Asa number of viral proteins Tat is suspected to disturb mitochondrial function.We prepared pure synthetic full-length Tat by native chemical ligation (NCL),and Tat peptides, to evaluate their direct effects on isolated mitochondria.Submicromolar doses of synthetic Tat cause a rapid dissipation of themitochondrial transmembrane potential (ΔΨ_m) as well ascytochrome c release in mitochondria isolated from mouse liver, heart,and brain. Accordingly, Tat decreases substrate oxidation by mitochondriaisolated from these tissues, with oxygen uptake being initially restored byadding cytochrome c. The anion-channel inhibitor4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) protectsisolated mitochondria against Tat-induced mitochondrial membranepermeabilization (MMP), whereas ruthenium red, a ryanodine receptor blocker,does not. Pharmacologic inhibitors of the permeability transition pore,Bax/Bak inhibitors, and recombinant Bcl-2 and Bcl-XL proteins do not reduceTat-induced MMP. We finally observed that Tat inhibits cytochrome coxidase (COX) activity in disrupted mitochondria isolated from liver, heart, andbrain of both mouse and human samples, making it the first described viralprotein to be a potential COX inhibitor.