Abstract: | The Trans-activator protein (Tat) of human immunodeficiency virus (HIV)
is a pleiotropic protein involved in different aspects of AIDS pathogenesis. As
a 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 the
mitochondrial transmembrane potential (ΔΨm) as well as
cytochrome c release in mitochondria isolated from mouse liver, heart,
and brain. Accordingly, Tat decreases substrate oxidation by mitochondria
isolated from these tissues, with oxygen uptake being initially restored by
adding cytochrome c. The anion-channel inhibitor
4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) protects
isolated mitochondria against Tat-induced mitochondrial membrane
permeabilization (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 reduce
Tat-induced MMP. We finally observed that Tat inhibits cytochrome c
oxidase (COX) activity in disrupted mitochondria isolated from liver, heart, and
brain of both mouse and human samples, making it the first described viral
protein to be a potential COX inhibitor. |