A role for guanine-nucleotide-binding proteins in mediating T-cell-receptor coupling to inositol phospholipid hydrolysis in a murine T-helper (type II) lymphocyte clone

Abstract

Perturbation of the T-cell receptor (TCR) complex is followed by the rapid hydrolysis of inositol phospholipids (InsPL) by phospholipase C (PLC), producing diacylglycerol and inositol phosphates, which act as second messengers in signal transduction. The mechanism coupling the TCR to InsPL hydrolysis is not clearly defined, and no information is available on this mechanism in the CD4+ helper subset of T-lymphocytes (Th). We have tested the hypothesis that guanine-nucleotide-binding proteins (G-proteins) may couple the TCR to PLC in a murine Th type II (Th2) cell clone. Cell permeabilization with streptolysin O (SLO) or tetanolysin (TL) was used to allow membrane-impermeable nucleotides access to intracellular sites of action. Exposure of permeabilized Th2 cells to guanosine 5'-[gamma-thio]triphosphate (GTP gamma S), a non-hydrolysable GTP analogue, resulted in a 2.1-2.5-fold increase in inositol phosphate generation. Similarly, perturbation of the TCR with the monoclonal antibody 145.2C11 (directed against the epsilon-chain of the CD3 component of the TCR) resulted in a 3.1-4.2-fold increase in InsPL hydrolysis by permeabilized cells. Both lysins were similarly effective in allowing GTP gamma S induction of InsPL hydrolysis, but TL-permeabilized cells responded better to TCR perturbation than SLO-treated cells. A role for G-proteins in TCR coupling to PLC was further supported by the inhibition of TCR-induced InsPL hydrolysis by guanosine 5'-[beta-thio]diphosphate (GDP beta S), a guanine nucleotide analogue that inhibits G-protein function. ATP was required for TCR-mediated InsPL hydrolysis, and potentiated GTP gamma S-induced hydrolysis. Other nucleotides (i.e. CTP, GDP, GTP, ITP) did not affect the response. These data indicate that G-proteins may contribute to the regulation of PLC activation in Th2 cells, coupling it to the TCR.