Abstract
Astroglia are key cellular sites where opiate drug signals converge with the proinflammatory effects of HIV-1 Tat signals to exacerbate HIV encephalitis. Despite this understanding, the molecular sites of convergence driving opiate-accelerated neuropathogenesis have not been deciphered. We therefore explored potential points of interaction between the signaling pathways initiated by HIV-1 Tat and opioids in striatal astrocytes. Profiling studies screening 152 transcription factors indicated that the nuclear factor-kappa B (NF-kappaB) subunit, c-Rel, was a likely candidate for Tat or Tat plus opiate-induced increases in cytokine and chemokine production by astrocytes. Pretreatment with the NF-kappaB inhibitor parthenolide provided evidence that Tat+/-morphine-induced release of MCP-1, IL-6 and TNF-alpha by astrocytes is NF-kappaB dependent. The nuclear export inhibitor, leptomycin B, blocked the nucleocytoplasmic shuttling of NF-kappaB; causing p65 (RelA) accumulation in the nucleus, and significantly attenuated cytokine production in Tat+/-morphine exposed astrocytes. Similarly, chelating intracellular calcium ([Ca(2+)](i)) blocked Tat+/-morphine-evoked MCP-1 and IL-6 release, while artificially increasing the concentration of extracellular Ca(2+) reversed this effect. Taken together, these results demonstrate that: 1) exposure to Tat+/-morphine is sufficient to activate NF-kappaB and cytokine production, 2) the release of MCP-1 and IL-6 by Tat+/-morphine are highly Ca(2+)-dependent, while TNF-alpha appears to be less affected by the changes in [Ca(2+)](i), and 3) in the presence of Tat, exposure to opiates augments Tat-induced NF-kappaB activation and cytokine release through a Ca(2+)-dependent pathway.