Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway; Department of Computer Science, Norwegian University of Science and Technology, Trondheim, Norway
Department of Surgery and Cancer, Hammersmith Hospital, Imperial College London, London, United Kingdom
Justin M Drake
Department of Pharmacology, University of Minnesota, Minneapolis, United States; Masonic Cancer Center, University of Minnesota, Minneapolis, United States; Department of Urology, University of Minnesota, Minneapolis, United States
Kathryn L Schwertfeger
Department of Pharmacology, University of Minnesota, Minneapolis, United States; Masonic Cancer Center, University of Minnesota, Minneapolis, United States; Center for Immunology, University of Minnesota, Minneapolis, United States; Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, United States
Department of Pharmacology, University of Minnesota, Minneapolis, United States; Masonic Cancer Center, University of Minnesota, Minneapolis, United States; Center for Immunology, University of Minnesota, Minneapolis, United States; Center for Autoimmune Diseases Research, University of Minnesota, Minneapolis, United States
The activity of Src-family kinases (SFKs), which phosphorylate immunoreceptor tyrosine-based activation motifs (ITAMs), is a critical factor regulating myeloid-cell activation. We reported previously that the SFK LynA is uniquely susceptible to rapid ubiquitin-mediated degradation in macrophages, functioning as a rheostat regulating signaling (Freedman et al., 2015). We now report the mechanism by which LynA is preferentially targeted for degradation and how cell specificity is built into the LynA rheostat. Using genetic, biochemical, and quantitative phosphopeptide analyses, we found that the E3 ubiquitin ligase c-Cbl preferentially targets LynA via a phosphorylated tyrosine (Y32) in its unique region. This distinct mode of c-Cbl recognition depresses steady-state expression of LynA in macrophages derived from mice. Mast cells, however, express little c-Cbl and have correspondingly high LynA. Upon activation, mast-cell LynA is not rapidly degraded, and SFK-mediated signaling is amplified relative to macrophages. Cell-specific c-Cbl expression thus builds cell specificity into the LynA checkpoint.
