Inhibition of tyrosine phosphorylation prevents T-cell receptor-mediated signal transduction.
The binding of antigen to the multicomponent T-cell receptor (TCR) activates several signal transduction pathways via coupling mechanisms that are poorly understood. One event that follows antigen receptor engagement is the activation of inositol phospholipid-specific phospholipase C (PLC). TCR activation by antigen, lectins, or anti-TCR monoclonal antibody has also been shown to cause increases in tyrosine phosphorylation of TCR-zeta and other substrates, suggesting stimulation of protein tyrosine kinase (PTK) activity. A critical question is whether these two pathways, PLC and PTK, are independently activated or whether one initiates and/or regulates the other. In the former case, PLC activation could be coupled to the TCR via a GTP-binding protein (G protein). We have reported, however, that tyrosine phosphorylation of intracellular substrates precedes detection of PLC activation and intracellular calcium elevation, suggesting that inositol phospholipid turnover in T cells is initiated by a PTK pathway. In this study, we test this hypothesis by treating T cells with the drug herbimycin A. We demonstrate that this agent inhibits substrate tyrosine phosphorylation, TCR-mediated inositol phospholipid hydrolysis, and calcium elevation. In contrast, under these conditions G-protein-mediated PLC activity, as tested by addition of aluminum fluoride, remains intact. Furthermore, whereas herbimycin treatment prevents TCR-mediated interleukin 2 production and interleukin 2 receptor expression, phorbol ester-induced effects are substantially resistant to herbimycin. The drug thus appears to abrogate TCR-mediated signaling without affecting distal signaling mechanisms.
June
C H
CH
Immune Cell Biology Program, Naval Medical Research Institute, Bethesda, MD 20814.
Fletcher
M C
MC
Ledbetter
J A
JA
Schieven
G L
GL
Siegel
J N
JN
Phillips
A F
AF
Samelson
L E
LE
D000935:Antifungal Agents / Q000494:pharmacology; D000936:Antigen-Antibody Complex; D016227:Benzoquinones; D002460:Cell Line; D015870:Gene Expression / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D047029:Lactams, Macrocyclic; D008213:Lymphocyte Activation; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D017828:Rifabutin / Q000031:analogs & derivatives; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology* / Q000502:physiology; D010738:Type C Phospholipases / Q000378:metabolism*
D000935:Antifungal Agents; D000936:Antigen-Antibody Complex; D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D011809:Quinones; D011948:Receptors, Antigen, T-Cell; D017828:Rifabutin; C020754:herbimycin; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases