Essential, Nonredundant Role for the Phosphoinositide 3-Kinase p110δ in Signaling by the B-Cell Receptor Complex

Abstract

Many receptor and nonreceptor tyrosine kinases activate phosphoinositide 3-kinases (PI3Ks). To assess the role of the ␦ isoform of the p110 catalytic subunit of PI3Ks, we derived enzyme-deficient mice. The mice are viable but have decreased numbers of mature B cells, a block in pro-B-cell differentiation, and a B1 B-cell deficiency. Both immunoglobulin M receptor-induced Ca 2؉ flux and proliferation in response to B-cell mitogens are attenuated. Immunoglobulin levels are decreased substantially. The ability to respond to T-cellindependent antigens is markedly reduced, and the ability to respond to T-cell-dependent antigens is completely eliminated. Germinal center formation in the spleen in response to antigen stimulation is disrupted. These results define a nonredundant signaling pathway(s) utilizing the ␦ isoform of p110 PI3K for the development and function of B cells.Lymphocyte development and function are regulated through the coordinated action of receptors of the cytokine receptor superfamily and the B-cell antigen-specific receptor (BCR) or T-cell antigen-specific receptors (TCR). Engagement of either receptor complex initiates tyrosine phosphorylation of a variety of intracellular substrates, including receptor chains, resulting in the initiation of cellular responses. Members of the cytokine receptor superfamily utilize JAK family cytoplasmic kinases (14), while the BCR and TCR complexes utilize members of the Src, Tec, and Zap70/Syk families of tyrosine kinases. In BCR signal transduction, the Tec family kinase Btk plays a critical role as evidenced by the loss of a proliferative response to BCR engagement in Btk-deficient B cells (15,16). Among the substrates typically phosphorylated and recruited to hematopoietic receptor complexes are the regulatory subunits for phosphoinositide 3-kinases (PI3Ks) (9,10,30). In mammals there are three genes that encode adapter proteins for PI3K catalytic subunits, including p85␣, p85␤, and p55␥. The adapter proteins facilitate association of the catalytic subunits with the receptor complex and are proposed to regulate enzyme activity. The disruption of the p85␣ gene, in a manner that deletes the p85 isoform as well as two splice variants of p55 and p50, results in defective BCR signaling comparable to that seen with Btk deficiency (11,26). This strongly suggests that PI3K activity is critical in BCR signal transduction.Three of the known PI3Ks, i.e., PI3K␣, PI3K␤, and PI3K␦, are regulated through their interaction with regulatory subunits (30). The fourth PI3K, PI3K␥, functions in the context of heterotrimeric G-protein-coupled receptors and is essential for leukocyte function (12). The critical, nonredundant role that PI3K␣ plays in cellular responses has been demonstrated through the derivation of mice lacking the gene. This deficiency results in an embryonic lethality at E9.5 to E10.5 due to a severe proliferative defect in many tissues (2). Similarly, deletion of the PI3K␤ gene alone results in a very early embryonic lethality (1, 2). In contrast to PI3K␣ and PI...

Cell biology of embryonic migration

“…In addition, knockouts of some of the regulatory molecules directly involved in the regulation of the mechanistic components of cell migration have been described and are listed separately in the table. Knockouts of other regulatory molecules, such as PI3K and PTEN, have also been characterized (Di Cristofano et al, 1998;Jou et al, 2002;Katso et al, 2001;Stambolic et al, 2000;Suzuki et al, 2003), but are too general to be implicated directly in migration and have therefore been removed from our list.…”

Requirement for Phosphoinositide 3-Kinase p110δ Signaling in B Cell Antigen Receptor-Mediated Antigen Presentation

“…Similar results were observed using LY294002 inhibitor (data not shown). Because the PI3K catalytic subunit p110␦ contributes a significant proportion of PI3K signaling in B cells (31)(32)(33), we examined the role of this isoform, using the p110␦-selective inhibitor IC (37,38) and B cells from mice carrying an inactivating mutation of p110␦ (33). Pretreatment of normal B cells with IC partially inhibited their ability to induce IL-2 production in a dose-dependent fashion (Fig.…”

“…30). The expression of the p110␦ isoform is restricted to immune cells and has been shown to play critical roles in B cell activation (31)(32)(33). In this study, we have investigated whether p110␦ plays a role in Ag presentation function of primary B cells using both genetic inactivation of p110␦ and a p110␦-specific inhibitor IC87114 (IC).…”

Role of the phosphoinositide 3‐kinase p110δ in generation of type 2 cytokine responses and allergic airway inflammation

“…Our previous study found that T cells from p110d-D910A mice had reduced antigen-induced proliferation in vitro, but this appears in some cases to be overcome by strong signaling through costimulatory receptors [11]. In contrast, p110d-deficient B cells have major defects in activation by multiple stimuli in vitro, and blunted antibody responses in vivo [11][12][13]. Thus, while PI3K isoforms likely play distinct roles in B cells, T cells and neutrophils, their respective roles in regulating systemic cytokine production patterns, cell-mediated immunity and host defense functions remain unexplored.…”