Involvement of inositol 1,4,5-trisphosphate-regulated stores of intracellular calcium in calcium dysregulation and neuron cell death caused by HIV-1 protein tat.
HIV-1 infection commonly leads to neuronal cell death and a debilitating syndrome known as AIDS-related dementia complex. The HIV-1 protein Tat is neurotoxic, and because cell survival is affected by the intracellular calcium concentration ([Ca2+]i), we determined mechanisms by which Tat increased [Ca2+]i and the involvement of these mechanisms in Tat-induced neurotoxicity. Tat increased [Ca2+]i dose-dependently in cultured human fetal neurons and astrocytes. In neurons, but not astrocytes, we observed biphasic increases of [Ca2+]i. Initial transient increases were larger in astrocytes than in neurons and in both cell types were significantly attenuated by antagonists of inositol 1,4,5-trisphosphate (IP3)-mediated intracellular calcium release [8-(diethylamino)octyl-3,4,5-trimethoxybenzoate HCI (TMB-8) and xestospongin], an inhibitor of receptor-Gi protein coupling (pertussis toxin), and a phospholipase C inhibitor (neomycin). Tat significantly increased levels of IP3 threefold. Secondary increases of neuronal [Ca2+]i in neurons were delayed and progressive as a result of excessive calcium influx and were inhibited by the glutamate receptor antagonists ketamine, MK-801, (+/-)-2-amino-5-phosphonopentanoic acid, and 6,7-dinitroquinoxaline-2,3-dione. Secondary increases of [Ca2+]i did not occur when initial increases of [Ca2+]i were prevented with TMB-8, xestospongin, pertussis toxin, or neomycin, and these inhibitors as well as thapsigargin inhibited Tat-induced neurotoxicity. These results suggest that Tat, via pertussis toxin-sensitive phospholipase C activity, induces calcium release from IP3-sensitive intracellular stores, which leads to glutamate receptor-mediated calcium influx, dysregulation of [Ca2+]i, and Tat-induced neurotoxicity.
Haughey
N J
NJ
Department of Pharmacology and Therapeutics, University of Manitoba Faculty of Medicine, Winnipeg, Canada.
Holden
C P
CP
Nath
A
A
Geiger
J D
JD
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000166:cytology / Q000196:embryology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005333:Fetus; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D015696:Gene Products, tat / Q000633:toxicity*; D015497:HIV-1; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D007649:Ketamine / Q000494:pharmacology; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D009498:Neurotoxins; D037342:Pertussis Toxin; D011810:Quinoxalines / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014741:Video Recording; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D054322:tat Gene Products, Human Immunodeficiency Virus
D002121:Calcium Channel Blockers; D018691:Excitatory Amino Acid Antagonists; D015696:Gene Products, tat; D009498:Neurotoxins; D011810:Quinoxalines; D010566:Virulence Factors, Bordetella; D054322:tat Gene Products, Human Immunodeficiency Virus; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; C056723:FG 9041; D005707:Gallic Acid; D019284:Thapsigargin; D007649:Ketamine; D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D002118:Calcium