Pertussis toxin B-oligomer suppresses human immunodeficiency virus-1 Tat-induced neuronal apoptosis through feedback inhibition of phospholipase C-beta by protein kinase C.
Human immunodeficiency virus (HIV)-1 Tat is a multifunctional protein involved in viral replication, inflammation and apoptosis. Tat activates phospholipase C-beta (PLC-beta), presumably via a pertussis toxin (PTX) sensitive G(i) protein, which is critical for neuronal apoptosis. In this study, we show that Tat-mediated intracellular Ca(2+) release in rat pheochromocytoma (PC-12) cells and rat primary cortical neuronal cultures was abrogated by pretreatment with either pertussis toxin and/or its B-oligomer subunit (PTX-B), devoid of ADP ribosyltransferase activity. PTX-B pretreatment also inhibited intracellular Ca(2+) release by bradykinin and 2,4,6-trimethyl-N-(m-3-trifluoromethylphenyl) benzenesulfonamide (m-3M3FBS), a director activator of phospholipase C. Activation of protein kinase C (PKC) by phorbol 12,13-dibutyrate (PdBu) mimicked the PTX-B-mediated inhibition of m-3M3FBS-stimulated intracellular Ca(2+) increase, while inhibition of PKC by bisindolylmaleimide I hydrochloride (BIM) reversed the inhibitory action of PTX-B. Functionally, PTX-B reduced Tat-induced Bax and caspase-3 proteins and reduced cell apoptosis. We conclude that PTX inhibition of Tat-mediated intracellular Ca(2+) release is independent of ADP ribosylation of the G(i) protein via the A protomer, but mediated by the B-oligomer. Furthermore, PTX-B suppresses HIV-1 Tat-mediated apoptosis by reducing its activation of PLC-beta through a PKC activation pathway.
Jajoo
S
S
Department of Pharmacology, Southern Illinois University School of Medicine, PO Box 19629, Springfield, IL 62794-9629, USA.
Mukherjea
D
D
Brewer
G J
GJ
Ramkumar
V
V
D000246:Adenosine Diphosphate Ribose / Q000502:physiology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D025461:Feedback, Physiological; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D007150:Immunohistochemistry; D009474:Neurons / Q000187:drug effects* / Q000473:pathology; D016716:PC12 Cells; D037342:Pertussis Toxin / Q000494:pharmacology*; D054799:Phospholipase C beta / Q000037:antagonists & inhibitors*; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000037:antagonists & inhibitors* / Q000633:toxicity*
D004791:Enzyme Inhibitors; D054322:tat Gene Products, Human Immunodeficiency Virus; D000246:Adenosine Diphosphate Ribose; D037342:Pertussis Toxin; D011493:Protein Kinase C; D054799:Phospholipase C beta; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D002118:Calcium