EXTRACELLULAR HIV-1 TAT PROTEIN INDUCES A RAPID AND SELECTIVE ACTIVATION OF PROTEIN-KINASE-C (PKC)-ALPHA, (PKC)-EPSILON, AND (PKC)-ZETA ISOFORMS IN PC12 CELLS

The addition in culture of extracellular HIV-1 Tat protein (0.1-1 mM) to PC12 cells induced a rapid increase of the bulk protein kinase C (P KC) catalytic activity. Among various PKC isoforms (alpha, beta I, bet a II, delta, epsilon, eta, theta, and zeta) expressed in PC12 cells, T at selectively stimulated alpha, epsilon, and zeta, as judged by activ ities in immunoprecipitates. Activation of these isoforms was suppress ed by the tyrosine kinase inhibitor genistein. Moreover, PKC-zeta show ed the fastest kinetics of activation in response to Tat, but PKC-alph a and PKC-epsilon showed the highest levels of activation. PKC-alpha a ctivation was accompanied by a rise of intracellular IP3, while the PI 3-kinase inhibitors wortmannin and LY294002 suppressed PKC-epsilon ac tivation. Taken together, these findings demonstrate that extracellula r Tat shows a cytokine-like activity in PC12 cells, being able to trig ger an intracellular signalling cascade which involves PKC-alpha, -eps ilon, and -zeta. (C) 1998 Academic Press.