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Blood, 1 October 2007, Vol. 110, No. 7, pp. 2511-2519.
Prepublished online as a Blood First Edition Paper on May 18, 2007; DOI 10.1182/blood-2007-01-066092.
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Submitted January 8, 2007
Accepted May 8, 2007
The Src family kinase Hck regulates mast cell activation
by suppressing an inhibitory Src family kinase Lyn
Hong Hong, Jiro Kitaura, Wenbin Xiao, Vaclav Horejsi, Chisei Ra, Clifford A. Lowell, Yuko Kawakami, and Toshiaki Kawakami*
Division of Cell Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA, United States
Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
Division of Molecular Cell Immunobiology and Allergology, Advanced Medical Research Center, Nihon University Graduate School of Medical Science, Tokyo, Japan
Department of Laboratory Medicine, University of California, San Francisco, San Francisco, CA, United States
* Corresponding author; email: toshi{at}liai.org.
IgE/antigen-dependent mast cell activation plays a central role in immediate hypersensitivity and other allergic reactions. The Src family tyrosine kinase (SFK) Lyn is activated by crosslinking of high-affinity IgE receptors (Fc RI), phosphorylates the Fc RI subunits, and , and triggers subsequent activation of various signaling pathways. Lyn also plays a negative regulatory function by activating negative regulatory molecules. Another SFK Fyn also contributes to mast cell degranulation by inducing Gab2-dependent microtubule formation. Here we show that a third SFK Hck plays a critical role in mast cell activation. Degranulation and cytokine production are reduced in Fc RI-stimulated hck-/- mast cells. The reduced degranulation can be accounted for by defects in Gab2 phosphorylation and microtubule formation. Importantly, Lyn activity is increased in hck-/- cells, leading to increased phosphorylation of several negative regulators. On the other hand, positive regulatory events, such as activation of Syk, Btk, JNK, p38, Akt, and NF- B, are substantially reduced in hck-/- mast cells. Analysis of lyn-/-hck-/-, lyn-/-Fc RI -/-, and hck-/-Fc RI -/- cells shows that Hck exerts these functions via both Lyn-dependent and Lyn-independent mechanisms. Thus, this study has revealed a hierarchical regulation among SFK members to fine-tune mast cell activation.

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