Neurotoxicity of the human immunodeficiency virus type 1 Tat transactivator to PC12 cells requires the Tat amino acid 49‐58 basic domain

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Abstract
The acquired immunodeficiency syndrome (AIDS) frequently involves the central nervous system (CNS) and manifests as dementia due to encephalitis or diffuse neurodegeneration. Human immunodeficiency virus type 1 (HIV‐1) proteins, potentially transported into the CNS by mononuclear inflammatory cells, have been implicated in the etiology of this HIV‐1 associated neurological dysfunction. Here we investigate the neurotoxicity of the essential HIV‐1 regulator protein Tat in vivo after microinfusion into the rat brain and in vitro using PC12, NG108‐15, and GT17 neuronal cell lines. Infusion of either chemically synthesized Tat (Tat86) or recombinant Tat (rTat) into the striatal gray matter in Sprague‐Dawley rats resulted in postural deviation ipsilateral to the infusion, a clinical presentation in rats associated with complete striatal dysfunction. Histologic examination 3 days after infusion revealed massive necrosis in the area of the distribution of the infusion. Infusion of heat denatured rTat, peptide Tat49‐58, or peptide Tat57‐86 did not result in clinically or histologically detectable brain damage. After 3 days incubation in vitro, the lethal dose for half (LD50) of PC 12 cells due to rTat was 5 μg/ml. The LD50 for Tat86 under the same conditions was 10 μg/ml. Tat49‐58 and Tat57‐86 peptides were not toxic in vitro even at 10‐fold higher doses. At 5 μg/ml, rTat was toxic to 100% of GT17 cells after 24 hr. At 5 μg/ml, Tat86 was toxic to 90% of the NG108‐15 cells after 7 days of treatment. Prior experiments have shown Tat49‐58 is specifically recognized by a cell surface protein that mediates Tat uptake. Here we show that Tat toxicity is inhibited by cotreatment with excess Tat49‐58, suggesting Tat neurotoxicity requires binding to its surface ligand. Chloroquine, which increases nuclear accumulation of Tat, enhances Tat toxicity to PC 12 cells, suggesting that Tat internalization is a required step in the mechanism of its toxicity. © 1995 Wiley‐Liss, Inc. 1 This article is a US Government work and, as such, is in the public domain in the United States of America.