Grb2 regulates B-cell maturation, B-cell memory responses and inhibits B-cell Ca²⁺signalling

Abstract

Grb2 is a ubiquitously expressed adaptor protein, which activates Ras and MAP kinases in growth factor receptor signalling, while in B‐cell receptor (BCR) signalling this role is controversial. In B cell lines it was shown that Grb2 can inhibit BCR‐induced Ca2+ signalling. Nonetheless, the physiological role of Grb2 in primary B cells is still unknown. We generated a B‐cell‐specific Grb2‐deficient mouse line, which had a severe reduction of mature follicular B cells in the periphery due to a differentiation block and decreased B‐cell survival. Moreover, we found several changes in important signalling pathways: enhanced BCR‐induced Ca2+ signalling, alterations in mitogen‐activated protein kinase activation patterns and strongly impaired Akt activation, the latter pointing towards a defect in PI3K signalling. Interestingly, B‐cell‐specific Grb2‐deficient mice showed impaired IgG and B‐cell memory responses, and impaired germinal centre formation. Thus, Grb2‐dependent signalling pathways are crucial for lymphocyte differentiation processes, as well as for control of secondary humoral immune responses.

CD22 ligand-binding and signaling domains reciprocally regulate B-cell Ca 2+ signaling

“…Splenic cells were loaded with Indo-1 as described (35). Cells were extracellularly stained with anti-CD5 and anti-CD11b and unstimulated cells were analyzed for 40 s using an LSR II (Becton Dickinson).…”

“…T-cell removal from splenic cell suspensions was achieved as described (35). After 1 h of starvation, cells were stimulated with 10 μg/mL anti-IgM [F(ab′) 2 ] at 37°C.…”

“…Cells were extracellularly stained with anti-CD5 and anti-CD11b and unstimulated cells were analyzed for 40 s using an LSR II (Becton Dickinson). Cells were stimulated with antiIgM [F(ab′) 2 ], (Jackson ImmunoResearch) and cells were further analyzed as described (35).…”

Grb2 Is Important for T Cell Development, Th Cell Differentiation, and Induction of Experimental Autoimmune Encephalomyelitis

“…Surprisingly, Grb2 seems to be dispensable for Ras signaling in CD4 + CD8 + double-positive (DP) thymocytes (2). However, Grb2 was also shown to regulate Ca2 + signaling and PI3K/Akt signaling in lymphocytes via incompletely understood mechanisms (3). Grb2 also plays an important role in lymphocyte development in T and B cells (2)(3)(4).…”

“…However, Grb2 was also shown to regulate Ca2 + signaling and PI3K/Akt signaling in lymphocytes via incompletely understood mechanisms (3). Grb2 also plays an important role in lymphocyte development in T and B cells (2)(3)(4). The analysis of Grb2 fl/fl Lckcre tg T cell-specific Grb2-deficient mice revealed that Grb2 is important for positive and negative selection in the thymus, and it enhances tyrosine phosphorylation downstream of the TCR, including phosphorylation of LAT, PLCg1, and CD3z chain.…”