Morphine Exacerbates HIV-1 Tat-Induced Cytokine Production in Astrocytes through Convergent Effects on [Ca2+]i, NF-κB Trafficking and Transcription

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-kappa B) 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-kappa B inhibitor parthenolide provided evidence that Tat +/- morphine-induced release of MCP-1, IL-6 and TNF-alpha by astrocytes is NF-kappa B dependent. The nuclear export inhibitor, leptomycin B, blocked the nucleocytoplasmic shuttling of NF-kappa B; causing p65 (RelA) accumulation in the nucleus, and significantly attenuated cytokine production in Tat +/- morphine exposed astrocytes. Similarly, chelating intracellular calcium ([Ca2+](i)) blocked Tat +/- morphine-evoked MCP-1 and IL-6 release, while artificially increasing the concentration of extracellular Ca2+ reversed this effect. Taken together, these results demonstrate that: 1) exposure to Tat +/- morphine is sufficient to activate NF-kappa B and cytokine production, 2) the release of MCP-1 and IL-6 by Tat +/- morphine are highly Ca2+ -dependent, while TNF-alpha appears to be less affected by the changes in [Ca2+](i), and 3) in the presence of Tat, exposure to opiates augments Tat-induced NF-kappa B activation and cytokine release through a Ca2+ -dependent pathway.