Submitted April 10, 2008
Accepted September 16, 2008
Extracellular ligation-dependent CD45RB enzymatic activity negatively regulates lipid raft signal transduction
Kaushal Parikh*, Sibrand Poppema, Maikel P Peppelenbosch, and Lydia Visser
Department of Cell Biology, University Medical Center Groningen, Groningen, Netherlands
Department of Pathology, University Medical Center Groningen, Groningen, Netherlands
* Corresponding author; email: k.parikh{at}med.umcg.nl.
CD45 is the most prominent membrane protein on lymphocytes. The function and regulation of this protein tyrosine phosphatase (PTP) remains largely obscure, mainly because of the lack of a known ligand and it still remains unknown whether such tyrosine phosphatases are subject to extracellular control at all. We report that an anti-CD45RB antibody that prevents rejection and induces tolerance, activates CD45RB tyrosine phosphatase enzymatic activity in T lymphocytes allowing us to directly monitor the effects of increased CD45RB activity on signal transduction. By employing both kinase substrate peptide arrays as well as conventional biochemistry, we also provide evidence of the various kinases involved in bringing about the inhibitory effect of this antibody on CD3 induced TCR signaling. Furthermore, we report that activated CD45RB translocates to lipid rafts and interferes with lipid raft localisation and activation state of CD45 substrate Lck. Thus, these findings indeed prove that CD45 is subject to extracellular control and also define a novel mechanism by which receptor tyrosine phosphatases control lymphocyte biology and provide further insight into the intracellular signaling pathways effected by anti-CD45RB mAb treatment.
