Release of Calcium from Inositol 1,4,5-Trisphosphate Receptor-Regulated Stores by HIV-1 Tat Regulates TNF-α Production in Human Macrophages

Abstract

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.

Functional Synergy between CD40 Ligand and HIV-1 Tat Contributes to Inflammation: Implications in HIV Type 1 Dementia

“…The ability of Tat to up-regulate CD40 may explain the previously described increase in CD40 expression in microglial cells within brain tissue from HIV-1-infected subjects (55) and is probably mediated by a calciumdependent signaling pathway. However, it remains controversial as to whether Tat triggers release of calcium from intracellular stores (56) or whether it enhances uptake of extracellular calcium (57,58).…”

Regulating Factors for Microglial Activation.

“…51) Tat triggers intracellular Ca 2ϩ elevation 51) and TNFa production. 52) 3.5. Cytokines LPS-induced microglia produce various kinds of proinflammatory cytokines, as mentioned above.…”

Expression and function of Na+/Ca2+ exchangers 1 and 3 in human macrophages and monocytes

“…Rapid activation of NCX activity seems sufficient to induce this response since brief exposure of macrophages to Na 1 -free medium (10 min) was just as effective as prolonged incubation (4 h) in inducing TNF-a release. Ca 21 is involved in the production of TNF-a and other cytokines in macrophages [42,45] and many stimuli that activate cytokine production also generate Ca 21 signals [44,[55][56][57]. However, these stimuli raise cytoplasmic Ca 21 concentrations by energy-dependent mechanisms related to intracellular intermediates.…”

“…These include the release of preformed granule proteins (exocytosis) [26,42] and the production of proinflammatory cytokines and chemokines [42][43][44][45]. Therefore, we evaluated the effects of Na 1 -free medium on the release of b-glucuronidase -a lysosomal enzyme used as a marker of exocytosis [42,46] -from HLM.…”

“…To evaluate whether NCX can operate in the forward mode contributing to restore Ca 21 gradients after a receptor-mediated Ca 21 -spike event, we preincubated HLM Effects of Na 1 -free medium on exocytosis and cytokine/chemokine production in HLM Macrophages and monocytes rely on Ca 21 signaling to activate cell functions relevant to inflammation and immune regulation. These include the release of preformed granule proteins (exocytosis) [26,42] and the production of proinflammatory cytokines and chemokines [42][43][44][45]. Therefore, we evaluated the effects of Na 1 -free medium on the release of b-glucuronidase -a lysosomal enzyme used as a marker of exocytosis [42,46] -from HLM.…”