The Journal of Immunology, Vol 152, Issue 9 4433-4443, Copyright © 1994 by American Association of Immunologists

ARTICLES

Phosphatidylinositol synthesis is a proximal event in intracellular signaling coupled to T cell receptor ligation. Differential induction by conventional antigen and retroviral superantigen

GF Weber and H Cantor
Laboratory of Immunopathology, Dana-Farber Cancer Institute, Boston, MA.

There is increasing evidence that at least two functionally distinct signal transduction pathways may be coupled to the TCR complex. A conventional signal transduction pathway coupled to TCR ligation by peptide/MHC complexes includes increased [Ca2+]i, phosphatidylinositol (PI) hydrolysis, and cytokine expression. TCR ligation by MIs-1a/MTV superantigens may be coupled to an alternative signal transduction pathway without increased [Ca2+]i or detectable PI hydrolysis. We asked whether early events in the PI hydrolytic pathway might account for differential levels of PI breakdown after TCR ligation by conventional Ag and superantigen. We show that TCR ligation by conventional peptide Ag is coupled to a burst of PI synthesis in nontransformed T cells, which may represent a rate-limiting step for downstream PI hydrolysis. Incorporation of radiolabeled glucose by newly synthesized PI as well as inositol-1,4,5-trisphosphate provided direct evidence that this intracellular pool of PI represents an important substrate for this signaling pathway. By contrast, TCR ligation of the same T cell clone by retroviral superantigen leads to similar levels of T cell proliferation without detectable PI synthesis. Increased levels of radiolabeled intracellular PI reflected de novo synthesis of PI from glucose-6-phosphate rather than recycling of inositol phosphates because labeled phosphate and glucose were incorporated into PI but extracellular [3H]inositol was not. These findings suggest that differential PI synthesis represents an early biochemical event that distinguishes two functionally distinct signaling pathways coupled to TCR ligation by peptide Ag and retroviral superantigen.