HUMAN-IMMUNODEFICIENCY-VIRUS TAT PROTEIN INDUCES INTERLEUKIN-6 MESSENGER-RNA EXPRESSION IN HUMAN BRAIN ENDOTHELIAL-CELLS VIA PROTEIN-KINASE-C-DEPENDENT AND CAMP-DEPENDENT PROTEIN-KINASE PATHWAYS

The intracellular signal transduction pathways utilized by the HIV-1-d erived protein, Tat, in the activation of human central nervous system -derived endothelial cells (CNS-ECs) were examined using specific enzy matic assays. Tat induced an increase in interleukin 6 (IL-6) mRNA wit hin 1 hr of treatment. This biological effect of Tat involved activati on of both protein kinase C (PK-C) and cAMP-dependent protein kinase ( PK-A) in CNS-ECs, Tat at 10 ng/ml induced a sharp, transient increase in membrane PK-C activity within 30 sec of incubation, and reached max imum levels at 2 min, declining to control values within 10 min, Tat a lso induced a sharp increase in intracellular cAMP levels and PK-A act ivity in these cells, with the PK-A activity reaching a maximum at 10 min and slowly declining to control values in 4 hr of incubation, Acti vation of PK-A was dependent on a Tat-induced increase in membrane PK- C activity as demonstrated by calphostin C (a PK-C inhibitor) abolishi ng this effect, Incubation of cells with the cyclooxygenase inhibitor indomethacin did not affect Tat-induced activation of PK-A, indicating that prostacyclins are not involved in this process, Tat-induced incr ease in IL-6 mRNA was abolished in the presence on PK-A inhibitor H-89 , demonstrating that activation of PK-A is necessary and sufficient fo r the increase in IL-6 production by these cells, Both the Tat-induced increase in intracellular cAMP and IL-6 mRNA levels in CNS-ECs may pl ay a role in altering the blood-brain barrier and thereby inducing pat hology often observed in AIDS dementia.