Inhibition of the calcium release-activated calcium (CRAC) current in Jurkat T cells by the HIV-1 envelope protein gp160

Abstract

The HIV-1 envelope glycoprotein gp120/160 has pleiotropic effects on T cell function. We investigated whether Ca2+ signaling, a crucial step for T cell activation, was altered by prolonged exposure of Jurkat T cells to gp160. Microfluorometric measurements showed that Jurkat cells incubated with gp160 had smaller (≊40%) increases in [Ca2+]i in response to phytohemagglutinin and had a reduced Ca2+ influx (∼25%). gp160 had similar effects on Jurkat cells challenged with thapsigargin. We used the patch clamp technique to record the Ca2+ current, which is responsible for Ca2+ influx and has properties of the calcium release-activated Ca2+ current (ICRAC). gp160 reduced ICRAC by ≊40%. The inhibitory effects of gp160 were antagonized by staurosporine (0.1 μM), an inhibitor of protein-tyrosine kinases and protein kinase Cs (PKCs), and by Gö 6976 (5 μM), an inhibitor acting especially on PKCα and PKCβ1. 12-O-Tetradecanoyl phorbol 13-acetate (16 nM), a PKC activator, reproduced the effects of gp160 in untreated cells. A Western blotting analysis of PKC isoforms α, βI, δ, and ζ showed that only the cellular distribution of PKCα and -βI were significantly modified by gp160. In addition, gp160 was able to modify the subcellular distribution of PKCα and PKCβI caused by phytohemagglutinin. Therefore the reduction in ICRAC caused by prolonged incubation with gp160 is probably mediated by PKCα or -βI.