Crystal Structure of the Tyrosine Kinase Domain of Colony-stimulating Factor-1 Receptor (cFMS) in Complex with Two Inhibitors

Carsten Schubert,Benjamin Brandt,Hong-Chang Ma,Barry A. Springer,Ioanna P. Petrounia,John C. Spurlino,Raymond J. Patch,Ingrid C. Deckman,Geoffrey T. Struble,Mark R. Player,Céline Schalk-Hihi

doi:10.1074/jbc.m608183200

Carsten Schubert, Benjamin Brandt

Open Access

https://doi.org/10.1074/jbc.m608183200

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Abstract

The cFMS proto-oncogene encodes for the colony-stimulating factor-1 receptor, a receptor-tyrosine kinase responsible for the differentiation and maturation of certain macrophages. Upon binding its ligand colony-stimulating factor-1 cFMS autophosphorylates, dimerizes, and induces phosphorylation of downstream targets. We report the novel crystal structure of unphosphorylated cFMS in complex with two members of different classes of drug-like protein kinase inhibitors. cFMS exhibits a typical bi-lobal kinase fold, and its activation loop and DFG motif are found to be in the canonical inactive conformation. Both ATP competitive inhibitors are bound in the active site and demonstrate a binding mode similar to that of STI-571 bound to cABL. The DFG motif is prevented from switching into the catalytically competent conformation through interactions with the inhibitors. Activation of cFMS is also inhibited by the juxtamembrane domain, which interacts with residues of the active site and prevents formation of the activated kinase. Together the structures of cFMS provide further insight into the autoinhibition of receptor-tyrosine kinases via their respective juxtamembrane domains; additionally the binding mode of two novel classes of kinase inhibitors will guide the design of novel molecules targeting macrophage-related diseases.

Highlights

Protein kinases can be divided into two classes: those which preferentially phosphorylate tyrosine residues, and those which preferentially phosphorylate ser
They can be classified as either receptor protein-tyrosine kinases (RTKs)2 or intracellular protein-tyrosine kinases
The FMS or CSF-1-R proto-oncogene encodes the receptor-tyrosine kinase cFMS (CSF-1-R), which is the cell surface receptor for the colony-stimulating factor-1 (CSF-1 or M-CSF) [1]. cFMS is part of the plateletderived growth factor (PDGF) receptor family, which includes PDGFR-␣ and -␤, the stem cell factor receptor, and the FMS-like tyrosine kinase 3 (FLT3) [2]. This family shares a common architecture consisting of an extracellular ligandbinding domain comprised of five immunoglobulin-like domains, a single transmembrane segment, a juxtamembrane (JM) domain and a kinase domain divided by a kinase insert domain (KID)

Summary

Crystal Structure of cFMS Kinase

Csf1op mice are resistant to collagen-induced arthritis and show a reduced rate of mammary tumor progression into metastasis [6]. CSF-1 and cFMS are expressed in some types of breast carcinomas and other epithelia of the female reproductive tract, where activation of the receptor by ligand, produced either by the tumor cells or by stromal elements, stimulates tumor cell invasion through a urokinase-dependent mechanism [11]. These results support other preclinical findings that the CSF1-signaling pathway may be involved in local invasion and metastasis, rendering cFMS a putative anti-cancer target. We investigated the structural basis for the partial autoinhibition of cFMS via its juxtamembrane (JM) domain and compared it to the autoinhibitory mechanisms employed by the homologous kinases cKIT [12] and FLT3 [13]

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

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