The colony-stimulating factor-1 receptor (CSF-1 receptor) is a member of the PDGF receptor sub-family of protein-tyrosine kinases. These receptors are defined by an insert of about 70-100 amino acids within the intracellular kinase domain and 5 Ig repeats within the extracellular domain. Binding of CSF-1 regulates the proliferation and differentiation of macrophage precursor cells. Regulatory abnormalities in CSF-1 expression or CSF-1 receptor kinase activity have been implicated in a variety of cancers. The gene encoding the CSF-1 receptor was first identified based on it's homology with a transforming gene in the v-fms feline sarcoma virus.

Upon ligand binding, the CSF-1 receptor dimerizes and autophosphorylates several tyrosine residues within the intracellular domain. These phosphotyrosines serve as docking sites for various signaling molecules or regulate kinase activity of the receptor. In addition to the tyrosine phosphorylation sites, the carboxy-terminus negatively regulates the receptor. When it is deleted in conjunction with two extracellular point mutations, such as in the transforming protein of v-fms, the receptor is constitutively activated and able to transform cells in vitro and in vivo.

Recently, the ubiquitin-protein ligase c-Cbl was shown to bind the PDGF and EGF receptors in a phosphotyrosine dependent manner. Binding of c-Cbl to these activated receptors results in their ubiquitination, marking them for degradation. The role of c-Cbl in the negative regulation of the CSF-1 receptor is currently being investigated. Upon stimulation with ligand, the c-Cbl protein is tyrosine phosphorylated and ubiquitinates the CSF-1 receptor, leading to it's degradation. However, direct binding of c-Cbl to the CSF-1 receptor has not been established.

We have demonstrated the ability of the c-Cbl TKB domain to bind to activated CSF-1 receptors in vivo and in vitro. Binding is dependent on the receptor kinase activity and can be blocked by deletion of the carboxy-terminal 50 amino acids. This led to the identification of Tyr 973 as the binding site for c-Cbl. Phosphopeptide mapping of in vitro phosphorylated receptors confirmed that the CSF-1 receptor is capable of autophosphorylation at Tyr 973. These data explain the observation that deletion of the carboxy-terminus contributes to the transforming potential of v-fms.

PUBLICATIONS (resulting from this training, and some recent ones)

Wilhelmsen K, Burkhalter S, van der Geer P. (2002) C-Cbl binds the CSF-1 receptor at tyrosine 973, a novel phosphorylation site in the receptor's carboxy-terminus. Oncogene 21:1079-89.

Wilhelmsen K, van der Geer P. (2004) Phorbol 12-myristate 13-acetate-induced release of the colony-stimulating factor 1 receptor cytoplasmic domain into the cytosol involves two separate cleavage events. Mol Cell Biol. 24:454-64.

Wilhelmsen K, Copp J, Glenn G, Hoffman RC, Tucker P, van der Geer P. (2004) Purification and identification of protein-tyrosine kinase-binding proteins using synthetic phosphopeptides as affinity reagents. Mol Cell Proteomics. 3:887-95.

Litjens SH, Wilhelmsen K, de Pereda JM, Perrakis A, Sonnenberg A. (2005) Modeling and experimental validation of the binary complex of the plectin actin-binding domain and the first pair of fibronectin type III (FNIII) domains of the beta4 integrin. J Biol Chem. 280:22270-7.

Wilhelmsen K, Litjens SH, Kuikman I, Tshimbalanga N, Janssen H, van den Bout I, Raymond K, Sonnenberg A. (2005) Nesprin-3, a novel outer nuclear membrane protein, associates with the cytoskeletal linker protein plectin. J Cell Biol. 171:799-810.

Wilhelmsen K, Litjens SH, Sonnenberg A. (2006) Multiple functions of the integrin alpha6beta4 in epidermal homeostasis and tumorigenesis. Mol Cell Biol. 26:2877-86.

Wilhelmsen K, Ketema M, Truong H, Sonnenberg A. (2006) KASH-domain proteins in nuclear migration, anchorage and other processes. J Cell Sci. 119:5021-9.