The role of docking proteins and adapter proteins in signalling by the B cell receptor

The production of antibodies (Abs) by B cells is an important part of the immune response. In order for B cells to differentiate into Ab-producing plasma cells, they require signals that are generated by the B cell receptor (BCR) when it binds antigen (Ag). The BCR activates multiple signalling pathways and a common theme of these pathways utilized by the BCR is that they consist of components that are physically separated in resting cells. Therefore, in order for efficient signal transmission, these components must be brought together during BCR signalling. My hypothesis was that two groups of proteins, docking proteins and adapter proteins, play an important role in this process. Docking and adapter proteins contain protein/protein and protein/lipid interaction domains that allow them to mediate the formation of signalling complexes and recruit signalling proteins to different areas of the cell. In this thesis, I will show that the BCR utilizes a number of docking and adapter proteins to perform these functions. I will present data showing that the BCR uses the Cas, c-Cbl, and Gabl docking proteins to recruit SH2 domain-containing signalling proteins including Crk, Ptdlns 3-kinase, SHP-2, She, and Grb2 to cellular membranes. This may be important for bringing these signalling proteins in close proximity to membrane-associated substrates. Furthermore, I will show that the BCR uses the Crk adapter proteins to recruit the C3G guanine nucleotide exchange factor to membrane-associated docking proteins. This may be important for bringing C3G close to its targets, Rapl and R-Ras, both of which associate with cellular membranes. Finally, I will show that in order for the She adapter protein to become tyrosine phosphorylated and function as a docking site for Grb2 complexes, both the She SH2 and PTB domains are required. Interestingly, the She-binding protein, SHIP, is also required for phosphorylation of She by the BCR. Thus, it appears that the BCR uses a number of docking and adapter proteins to mediate the formation of signalling complexes and to recruit signaling molecules to different areas of the cell. This likely improves the efficiency of signalling by the BCR.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat