No abstract

Neuronal loss in HIV encephalopathy remains a mystery since HIV-1 productively infects macrophage and microglia and only rarely infects neurons in the central nervous system. Apoptosis is a mechanism which may account for the loss of neurons in HIV-1 infected brain. Putative toxic factors that result in neuronal cell death in HIV-1 infection include the regulatory protein Tat, since this protein is known to be released from HIV-1 infected cells. Here we show that Tat induces cell death by apoptosis in cultured human fetal neuronsproducing characteristic morphological and biochemical features associated with apoptosis. These findings suggest that Tat may play an important role as a secreted, soluble neurotoxin in HIV-1 associated dementia.

We measured the cellular uptake of 125 I-labeled full-length Tat (amino acids 1 to 86) (125 I-Tat 1-86) and 125 I-Tat 1-72 (first exon) in human fetal astrocytes, neuroblastoma cells, and human fetal neurons and demonstrated that the uptake of 125 I-Tat 1-72 without the second exon was much lower than that of 125 I-Tat 1-86 (P < 0.01). This suggests an important role for the C-terminal region of Tat for its cellular uptake. 125 I-Tat uptake could be inhibited by dextran sulfate and competitively inhibited by unlabeled Tat but not by overlapping 15-mer peptides, suggesting that Tat internalization is charge and conformationally dependent. Interestingly, one of 15-mer peptides, Tat 28-42 , greatly enhanced 125 I-Tat uptake. These findings are important for understanding the neuropathogenesis of human immunodeficiency virus type 1 infection and in the potential application of Tat for drug delivery to cells.

No abstract

1251_labeled recombinant gpl20 bound to primary cultures of human fetal astrocytes with a single class of 260-kDa binding sites, with a Kd of 26 nM and maximal number of binding sites of 29.9 fmol/4 x 104 cells. Neither CD4 nor galactocerebroside was detectable on astrocytes, and 2-51-labeled recombinant gpl20 binding to astrocytes was not blocked by antibodies against galactocerebroside or the gpl20 binding domain of CD4.