Volume 2, Issue 1-2 pp. 29-39
Research Paper

An essential role of ubiquitination in Cbl-mediated negative regulation of the Src-family kinase Fyn

Navin Rao

Navin Rao

Brigham and Women's Hospital, Harvard Medical School, Lymphocyte Biology Section, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Boston, MA, USA

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Amiya K. Ghosh

Amiya K. Ghosh

Brigham and Women's Hospital, Harvard Medical School, Lymphocyte Biology Section, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Boston, MA, USA

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Pengcheng Zhou

Pengcheng Zhou

Brigham and Women's Hospital, Harvard Medical School, Lymphocyte Biology Section, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Boston, MA, USA

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Patrice Douillard

Patrice Douillard

Brigham and Women's Hospital, Harvard Medical School, Lymphocyte Biology Section, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Boston, MA, USA

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Christopher E. Andoniou

Christopher E. Andoniou

Brigham and Women's Hospital, Harvard Medical School, Lymphocyte Biology Section, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Boston, MA, USA

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Hamid Band

Corresponding Author

Hamid Band

Brigham and Women's Hospital, Harvard Medical School, Lymphocyte Biology Section, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Boston, MA, USA

Brigham & Women's Hospital, Division of Rheumatology, Immunology and Allergy, Department of Medicine, Harvard Medical School,Smith Building, Room 538C, One Jimmy Fund Way, Boston, MA 02115, USA. Phone: +1-617-525-1101, Fax: +1-617-525-1010Search for more papers by this author

Abstract

The Cbl family of ubiquitin ligases function as negative regulators of activated receptor tyrosine kinases by facilitating their ubiquitination and subsequent lysosomal targeting. Here, we have investigated the role of Cbl ubiquitin ligase activity in the negative regulation of a non-receptor tyrosine kinase, the Src-family kinase Fyn. Using mouse embryonic fibroblasts from Cbl+/+ and Cbl−/− mice, we demonstrate that endogenous Cbl mediates the ubiquitination of Fyn and dictates the rate of Fyn turnover. By analyzing CHO-TS20 cells with a temperature-sensitive ubiquitin activating enzyme, we demonstrate that intact cellular ubiquitin machinery is required for Cbl-induced degradation of Fyn. Analyses of Cbl mutants, with mutations in or near the RING finger domain, in 293T cells revealed that the ubiquitin ligase activity of Cbl is essential for Cbl-induced degradation of Fyn by the proteasome pathway. Finally, use of a SRE-luciferase reporter demonstrated that Cbl-dependent negative regulation of Fyn function requires the region of Cbl that mediates the ubiquitin ligase activity. Given the conservation of structure between various Src-family kinases and the ability of Cbl to interact with multiple members of this family, Cbl-dependent ubiquitination could serve a general role to negatively regulate activated Src-family kinases.

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