File:Janeway-6.14.gif

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Janeway Figure 6.14. Simplified outline of the intracellular signaling pathways initiated by cross-linking of B-cell receptors by antigen. Cross-linking of surface immunoglobulin molecules activates the receptor-associated Src-family protein tyrosine kinases Blk, Fyn, and Lyn. The CD45 phosphatase can remove an inhibitory phosphate from these kinases, thus allowing their activation. The receptor-associated kinases phosphorylate the ITAMs in the receptor complex, which bind and activate the cytosolic protein kinase Syk, whose activation has been described in Fig. 6.13. Syk then phosphorylates other targets, including the adaptor protein BLNK, which help to recruit Tec kinases that in turn phosphorylate and activate the enzyme phospholipase C-γ. PLC-γ cleaves the membrane phospholipid PIP2 into IP3 and DAG, thus initiating two of the three main signaling pathways to the nucleus. IP3 releases Ca2+ from intracellular and extracellular sources, and Ca2+-dependent enzymes are activated, whereas DAG activates protein kinase C with the help of Ca2+. The third main signaling pathway is initiated by guanine-nucleotide exchange factors (GEFs) that become associated with the receptor and activate small GTP-binding proteins such as Ras. These in turn trigger protein kinase cascades (MAP kinase cascades) that lead to the activation of MAP kinases that move into the nucleus and phosphorylate proteins that regulate gene transcription. This scheme is a simplification of the events that actually occur during signaling, showing only the main events and pathways.

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current19:47, 10 March 2004 (35 KB)Tarek (talk | contribs)Janeway Figure 6.14. Simplified outline of the intracellular signaling pathways initiated by cross-linking of B-cell receptors by antigen. Cross-linking of surface immunoglobulin molecules activates the receptor-associated Src-family protein tyrosine kin
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