The role of tyrosine phosphorylation and PTP-1C in CTLA-4 signal transduction.
Recently, there has been increasing interest in the inhibitory regulators of lymphocyte activation, and in particular, the role of CD28 homologue CTLA-4 in the regulation of T cell responses. Interaction of CTLA-4 with B7 ligands inhibits T cell responses, including T cell proliferation and interleukin-2 (IL-2) secretion. The mechanism(s) responsible for CTLA-4 signal transduction are unknown, but it has been suggested that tyrosine phosphorylation is involved. Here we demonstrate that phorbol ester phorbol 12-myrislate 13-acetate (PMA), which increases tyrosine phosphorylation by stimulating protein kinase C and p21ras, can overcome the CTLA-4-mediated inhibition of T cell proliferation. This provides the first functional evidence that tyrosine phosphorylation is involved in CTLA-4 signal transduction. Most interestingly, CTLA-4-mediated inhibition of IL-2 secretion was not influenced by the presence of PMA. Further, we demonstrate that CTLA-4 cross-linking inhibits proliferation and IL-2 secretion of T cells from motheaten mice. These mice lack PTP-1C, a tyrosine phosphatase which mediates in a number of lymphocyte inhibitory responses, indicating that PTP-1C is not essential for CTLA-4 signaling. Collectively, these results demonstrate that regulation of tyrosine phosphorylation plays a pivotal role in CTLA-4 function, and that the inhibition of the transition from G0/G1 to the S phase of the cell cycle and the inhibition of IL-2 secretion require distinct signaling pathways. These experiments provide a useful model system which can be used to elucidate the signaling pathways involved in CTLA-4 function and to understand how CTLA-4, CD28 and Tcell receptor-mediated signals are integrated in T cell responses to antigen.
Chambers
C A
CA
Department of Molecular and Cellular Biology, Cancer Research Laboratory, University of California, Berkeley 94720, USA.
Allison
J P
JP
D000069594:Abatacept; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000494:pharmacology*; D060908:CTLA-4 Antigen; D018796:Immunoconjugates; D007376:Interleukin-2 / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation / Q000187:drug effects; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000032:analysis* / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000032:analysis* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*
D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D007376:Interleukin-2; D047908:Intracellular Signaling Peptides and Proteins; D000069594:Abatacept; D011505:Protein-Tyrosine Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516725:Ptpn11 protein, mouse; C509248:Ptpn6 protein, mouse