Release of calcium from inositol 1,4,5-trisphosphate receptor-regulated stores by HIV-1 Tat regulates TNF-alpha production in human macrophages

HIV-1 protein Tat is neurotoxic and increases macrophage and microglia prod uction of TNF-alpha, a cytopathic cytokine linked to the neuropathogenesis of HIV dementia, Others have shown that intracellular calcium regulates TNF -alpha production in macrophages, and we have shown that Tat releases calci um from inositol 1,4,5-trisphosphate (IP3) receptor-regulated stores in neu rons and astrocytes, Accordingly, we tested the hypothesis that Tat-induced TNF-alpha production was dependent on the release of intracellular calcium from IP3-regulated calcium stores in primary macrophages, We found that Ta t transiently and dose-dependently increased levels of intracellular calciu m and that this increase was blocked by xestospongin C, pertussis toxin, an d hy phospholipase C and type 1 protein kinase C inhibitors but not by prot ein kinase A or phospholipase A(2) inhibitors. Xestospongin C, BAPTA-AM, U7 3122, and bisindolylmalemide significantly inhibited Tat-induced TNF-cu pro duction. These results demonstrate that in macrophages, Tat-induced release of calcium from IP3-sensitive intracellular stores and activation of nonco nventional PKC isoforms play an important role in Tat-induced TNF-alpha pro duction.