Engagement of the Human Pre-B Cell Receptor Generates a Lipid Raft–Dependent Calcium Signaling Complex

Abstract

Pre-B cell receptor (pre-BCR) expression is critical for B lineage development. The signaling events initiated by the pre-BCR, however, remain poorly defined. We demonstrate that lipid rafts are the major functional compartment for human pre-B cell activation. A fraction of pre-BCR was constitutively raft associated, and receptor engagement enhanced this association. These events promoted Lyn activation and Igbeta phosphorylation and led to the generation of a raft-associated signaling module composed of tyrosine phosphorylated Lyn, Syk, BLNK, PI3K, Btk, VAV, and PLCgamma2. Formation of this module was essential for pre-BCR calcium signaling. Together, these observations directly link the previously identified genetic requirement for the components of this module in B lineage development with theirfunctional role(s) in human preBCR signaling.

Translocation of the B Cell Antigen Receptor into Lipid Rafts Reveals a Novel Step in Signaling

“…The lipid rafts are thought to be platforms for signaling, as Lyn kinase is concentrated within raft regions, while the phosphatase CD45 is excluded. Consistent with a role for lipid rafts in signal transduction, our recent results (16) and that of others (17,18,32) showed that both the BCR and Lyn within lipid rafts are phosphorylated in cells in which the BCR has been cross-linked. Translocation of the BCR into lipid rafts has also been shown to result in the recruitment of several components of the BCR signal cascade, including BLNK, phosphatidylinositol 3 kinase, VAV, and Btk (17,18,32).…”

“…Consistent with a role for lipid rafts in signal transduction, our recent results (16) and that of others (17,18,32) showed that both the BCR and Lyn within lipid rafts are phosphorylated in cells in which the BCR has been cross-linked. Translocation of the BCR into lipid rafts has also been shown to result in the recruitment of several components of the BCR signal cascade, including BLNK, phosphatidylinositol 3 kinase, VAV, and Btk (17,18,32). Evidence that the rafts play important physiological roles in B cell activation has been provided by the recent observations that BCR access to rafts is controlled during B cell development (19), by viral infection (20), and by the essential B cell coreceptor CD19 (Cherukuri, Sohn, and Pierce, unpublished observations).…”

Syk-mediated Tyrosine Phosphorylation Is Required for the Association of Hematopoietic Lineage Cell-specific Protein 1 with Lipid Rafts and B Cell Antigen Receptor Signalosome Complex

“…The role of Syk in HS1 association with rafts is further strengthened by the fact that HS1 was neither translocated into rafts nor tyrosine phosphorylated in the cells lacking Syk. Moreover association of Syk itself in the rafts of B cells upon BCR cross-linking has also been recently reported (39). Despite these facts, a strong direct association between Syk and HS1 in response to antigen stimulation remains to be established.…”

Genetic regulation of host responses to Salmonella infection in mice

“…108 btk, as a major component of the BCR signalosome, plays a critical role in the regulation of pre-B and mature BCR signaling. [109][110][111] Recruitment of btk to the cellular membrane and its subsequent activation triggers the mobilization of intracellular calcium and the activation of PKC, resulting in the degradation of the NFkB inhibitory protein I-kBa and the translocation of NF-kB to the nucleus. [112][113][114] In humans, more than 175 different mutations involving all domains of the btk gene have been identified in XLA patients.…”