B lymphocytes are an important type of immune cell that contributes to pathogen clearance. When dysregulated, these cells contribute significantly to diseases such as autoimmunity, allergy and B cell cancers. Here we examine an important regulatory circuit that involves the lipid phosphatase SHIP, a key regulator of the PI3K signaling pathway. SHIP was first described as the major effector of inhibitory IgG receptor FcγRIIB, which downregulates B cell antigen receptor (BCR) signaling pathways when co-engaged. However, it is also known to inhibit signaling downstream of several other receptors, both activating and inhibitory. Here we examine the regulation and function of SHIP in B cells, focusing on the inter-related influences of binding partners, tyrosine phosphorylation and subcellular localization dynamics.
First, we assess interaction of SHIP to selected candidate binding partners using an in vitro screening approach. The two most robust interactions were further characterized with respect to dissociation constant. These were: a novel interaction between SHIP phospho-Tyr944 and the SH2 domain of Nck, and a known interaction between the SH2 domain of SHIP and FcγRIIB phospho-Y292. Next, we perform the first examination of SHIP Tyr944. We provide evidence that it contributes to interaction with Nck after BCR engagement and is required for inhibition of actin turnover by SHIP. Finally, we perform the first detailed examination of the mechanisms controlling SHIP localization in human B cells stimulated through the BCR with and without co-engagement of FcγRIIB. We discover that SHIP is recruited to the plasma membrane equally in both stimulation contexts, however FcγRIIB co-ligation results in reduced mobility of SHIP molecules at the cell periphery. We identify a novel and essential role for Syk kinase in promoting SHIP membrane localization, tyrosine phosphorylation, and interaction with known binding partner Shc1.
Together, these results provide significant and exploitable insight into the molecular control of a clinically important regulator of B cell responses. / February 2017
| Identifer | oai:union.ndltd.org:MANITOBA/oai:mspace.lib.umanitoba.ca:1993/31875 |
| Date | 25 July 2016 |
| Creators | Pauls, Samantha |
| Contributors | Marshall, Aaron (Immunology, Biochemistry and Medical Genetics), Rastegar, Mojgan (Biochemistry and Medical Genetics); Wilkins, John (Biochemistry and Medical Genetics); Soussi Gounni, Abdel (Immunology); Johnson, Pauline (Microbiology and Immunology, University of British Columbia) |
| Publisher | The American Association of Immunologists, Inc. |
| Source Sets | University of Manitoba Canada |
| Detected Language | English |
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