Syk-dependent regulation of Hrs phosphorylation and ubiquitination upon FcεRI engagement: impact on Hrs membrane/cytosol localization.
Several lines of evidence suggest that Syk controls immune receptor endocytic trafficking. However, the Syk substrates that regulate this process are not currently known. Here, we demonstrate that Syk knockdown prevents the trafficking of engaged high affinity IgE receptor (FcεRI) to a degradative compartment in mast cells. We then concentrate our attention on hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) as potential Syk substrate, since it serves as critical regulator for FcεRI entry into lysosomes. We show that Hrs undergoes antigen-dependent tyrosine phosphorylation and ubiquitination, and identify Syk as the kinase responsible for Hrs phosphorylation. Syk was also required for Hrs ubiquitination catalyzed by c-Cbl E3 ligase. Syk-dependent regulation of Hrs covalent modifications, without affecting protein stability, controlled Hrs localization. The majority of phosphorylated Hrs forms were observed only in membrane compartments, whereas ubiquitinated Hrs was predominantly cytosolic, suggesting that both modifications might impact on Hrs function. Together, these findings provide a major step forward in understanding how Syk orchestrates endocytosis of engaged immune receptors.
Department of Molecular Medicine, Sapienza University of Rome, Rome, Italy.
Francesca
F
Gasparrini
Rosa
R
Molfetta
Linda
L
Quatrini
Luigi
L
Frati
Angela
A
Santoni
Rossella
R
Paolini
D000818:Animals; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004705:Endocytosis / Q000276:immunology*; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008407:Mast Cells / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D051381:Rats; D017452:Receptors, IgG / Q000235:genetics / Q000378:metabolism*; D000072377:Syk Kinase; D054875:Ubiquitination
D056827:Endosomal Sorting Complexes Required for Transport; C485701:Fcgr1 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D017452:Receptors, IgG; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate; D050721:Proto-Oncogene Proteins c-cbl; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C000606898:Syk protein, rat