Immunoreceptor tyrosine-based inhibitory motif (ITIM)-mediated inhibitory signaling is regulated by sequential phosphorylation mediated by distinct nonreceptor tyrosine kinases: a case study involving PECAM-1. Biochemistry 2013 Apr 16;52(15):2597-608
Date
02/20/2013Pubmed ID
23418871Pubmed Central ID
PMC3666314DOI
10.1021/bi301461tScopus ID
2-s2.0-84876268989 (requires institutional sign-in at Scopus site) 36 CitationsAbstract
The activation state of many blood and vascular cells is tightly controlled by a delicate balance between receptors that contain immunoreceptor tyrosine-based activation motifs (ITAMs) and those that contain immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Precisely how the timing of cellular activation by ITAM-coupled receptors is regulated by ITIM-containing receptors is, however, poorly understood. Using platelet endothelial cell adhesion molecule 1 (PECAM-1) as a prototypical ITIM-bearing receptor, we demonstrate that initiation of inhibitory signaling occurs via a novel, sequential process in which Src family kinases phosphorylate the C-terminal ITIM, thereby enabling phosphorylation of the N-terminal ITIM of PECAM-1 by other Src homology 2 domain-containing nonreceptor tyrosine kinases (NRTKs). NRTKs capable of mediating the second phosphorylation event include C-terminal Src kinase (Csk) and Bruton's tyrosine kinase (Btk). Btk and Csk function downstream of phosphatidylinositol 3-kinase (PI3K) activation during ITAM-dependent platelet activation. In ITAM-activated platelets that were treated with a PI3K inhibitor, PECAM-1 was phosphorylated but did not bind the tandem SH2 domain-containing tyrosine phosphatase SHP-2, indicating that it was not phosphorylated on its N-terminal ITIM. Csk bound to and phosphorylated PECAM-1 more efficiently than did Btk and required its SH2 domain to perform these functions. Additionally, the phosphorylation of the N-terminal ITIM of Siglec-9 by Csk is enhanced by the prior phosphorylation of its C-terminal ITIM, providing evidence that the ITIMs of other dual ITIM-containing receptors are also sequentially phosphorylated. On the basis of these findings, we propose that sequential ITIM phosphorylation provides a general mechanism for precise temporal control over the recruitment and activation of tandem SH2 domain-containing tyrosine phosphatases that dampen ITAM-dependent signals.
Author List
Tourdot BE, Brenner MK, Keough KC, Holyst T, Newman PJ, Newman DKAuthors
Michelle Brenner in the CTSI department at Medical College of Wisconsin - CTSIDebra K. Newman PhD Investigator in the Blood Research Institute department at BloodCenter of Wisconsin
Peter J. Newman PhD Professor in the Pharmacology and Toxicology department at Medical College of Wisconsin
Debra K. Newman PhD Professor in the Pharmacology and Toxicology department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
Amino Acid MotifsBlood Platelets
Cytoplasm
Humans
Phosphopeptides
Phosphorylation
Platelet Endothelial Cell Adhesion Molecule-1
Platelet Membrane Glycoproteins
Protein Structure, Tertiary
Protein-Tyrosine Kinases
Signal Transduction
src Homology Domains
src-Family Kinases