The Adaptor Molecule CIN85 Regulates Syk Tyrosine Kinase Level by Activating the Ubiquitin-Proteasome Degradation Pathway

Sapienza University of Rome, Roma, Latium, Italy
The Journal of Immunology (Impact Factor: 4.92). 09/2007; 179(4):2089-96. DOI: 10.4049/jimmunol.179.4.2089
Source: PubMed


Triggering of mast cells and basophils by IgE and Ag initiates a cascade of biochemical events that lead to cell degranulation and the release of allergic mediators. Receptor aggregation also induces a series of biochemical events capable of limiting FcepsilonRI-triggered signals and functional responses. Relevant to this, we have recently demonstrated that Cbl-interacting 85-kDa protein (CIN85), a multiadaptor protein mainly involved in the process of endocytosis and vesicle trafficking, regulates the Ag-dependent endocytosis of the IgE receptor, with consequent impairment of FcepsilonRI-mediated cell degranulation. The purpose of this study was to further investigate whether CIN85 could alter the FcepsilonRI-mediated signaling by affecting the activity and/or expression of molecules directly implicated in signal propagation. We found that CIN85 overexpression inhibits the FcepsilonRI-induced tyrosine phosphorylation of phospholipase Cgamma, thus altering calcium mobilization. This functional defect is associated with a substantial decrease of Syk protein levels, which are restored by the use of selective proteasome inhibitors, and it is mainly due to the action of the ubiquitin ligase c-Cbl. Furthermore, coimmunoprecipitation experiments demonstrate that CIN85 overexpression limits the ability of Cbl to bind suppressor of TCR signaling 1 (Sts1), a negative regulator of Cbl functions, while CIN85 knockdown favors the formation of Cbl/Sts1 complexes. Altogether, our findings support a new role for CIN85 in regulating Syk protein levels in RBL-2H3 cells through the activation of the ubiquitin-proteasome pathway and provide a mechanism for this regulation involving c-Cbl ligase activity.

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    • "Thus, mutant B cells display a selective partial defect in BCR coupling to IKK signaling pathway. Previous studies with the transformed RBL-2H3 mast cell line showed that overexpression of CIN85 decreases the Syk protein level and enhances FcRI-mediated endocytosis (Peruzzi et al., 2007). Thus, we made a point of carefully checking the Syk protein level in mutant and control B cells but detected no significant difference (Fig. S5 A). "
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