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

HIV-1 protein Tat is neurotoxic and increases macrophage and microglia production of TNF-α, a cytopathic cytokine linked to the neuropathogenesis of HIV dementia. Others have shown that intracellular calcium regulates TNF- α production in macrophages, and we have shown that Tat releases calcium from inositol 1,4,5-trisphosphate (IP₃) receptor-regulated stores in neurons and astrocytes. Accordingly, we tested the hypothesis that Tat-induced TNF-α production was dependent on the release of intracellular calcium from IP₃- regulated calcium stores in primary macrophages. We found that Tat transiently and dose-dependently increased levels of intracellular calcium and that this increase was blocked by xestospongin C, pertussis toxin and by phospholipase C and type 1 protein kinase C inhibitors but not by protein kinase A or phospholipase A₂ inhibitors. Xestospongin C, BAPTA-AM, U73122, and bisindolylmalemide significantly inhibited Tat-induced TNF-α production. These results demonstrate that in macrophages, Tat-induced release of calcium from IP₃-sensitive intracellular stores and activation of nonconventional PKC isoforms play an important role in Tat-induced TNF-α production.