Decorin Binds to a Narrow Region of the Epidermal Growth Factor (EGF) Receptor, Partially Overlapping but Distinct from the EGF-binding Epitope

Abstract

Decorin, a small leucine-rich proteoglycan, is a key regulator of tumor growth by acting as an antagonist of the epidermal growth factor receptor (EGFR) tyrosine kinase. To search for cell surface receptors interacting with decorin, we generated a decorin/alkaline phosphatase chimeric protein and used it to screen a cDNA library by expression cloning. We identified two strongly reactive clones that encoded either the full-length EGFR or its ectodomain. A physiologically relevant interaction between decorin and EGFR was confirmed in the yeast two-hybrid system and further validated by experiments using EGF/EGFR interaction and transient cell transfection assays. Using a panel of deletion mutants, decorin binding was mapped to a narrow region of the EGFR within its ligand-binding L2 domain. Moreover, the central leucine-rich repeat 6 of decorin was required for interaction with the EGFR. Site-directed mutagenesis of the EGFR L2 domain showed that a cluster of residues, His 394 -Ile 402 , was essential for both decorin and EGF binding. In contrast, K465, previously shown to be cross-linked to epidermal growth factor (EGF), was required for EGF but not for decorin binding. Thus, decorin binds to a discrete region of the EGFR, partially overlapping with but distinct from the EGF-binding domain. These findings could lead to the generation of protein mimetics capable of suppressing EGFR function.Decorin, a prototype member of an expanding family of small leucine-rich proteoglycans (1), plays pivotal roles in modulating matrix assembly (2-5) and cell proliferation (6 -8). Most of the biological functions of decorin are mediated by the protein core's unique organization of 10 tandem leucine-rich repeats (LRR) 1 which fold into an arch-shaped structure (9) whose concave surface is well suited to bind both globular and nonglobular proteins (2, 10, 11) as well as metal ions (12). Decorin expression is markedly suppressed in most transformed cells derived from primary malignant tumors (13-15) or in cells transformed by oncogenes such as vSrc (16), vJun (17), and ATF3 (18). On the contrary, decorin expression is markedly up-regulated during quiescence (19,20), and its levels can reach ϳ40-fold in post-confluent fibroblasts (21). We have previously shown that decorin expression is enhanced around invasive carcinomas (22) and have proposed that decorin might represent a natural antagonist to the growing cancer cells (1). This working hypothesis is corroborated by the established effects of decorin on growth factor-mediated tumor progression (23, 4) and by its profound cytostatic effects on a wide variety of tumor cell lines (13,14,24,25). Lack of decorin is permissive for tumor development insofar as bitransgenic mice, lacking both decorin and the tumor suppressor p53, develop an accelerated lymphoma tumorigenesis (26). These earlier reports have been supported by the recent observation that decorin gene expression is differentially down-regulated in hepatocellular (27) and ovarian (28) carcinomas vis á vis their normal counter...

Ectopic Doublecortin Gene Expression Suppresses the Malignant Phenotype in Glioblastoma Cells

“…Another collagen and fibronectin binding leucine-rich protein, decorin, a chondroitin sulfate proteoglycan, shows similar properties to SPARC. Decorin is an antioncogenic and antitumorigenic gene (17,22,33,34). Decorin promotes glioma survival in vitro via the phosphatidylinositol 3-kinase/AKT pathway, as previously reported (18), and glioma survival in vivo in rats as reported by others (35).…”

Decorin, a Novel Player in the Insulin-like Growth Factor System

“…For these experiments the following mutants were used: DCN-Q153, a mutant that contains the N terminus and the first 5 leucine-rich repeats of decorin, and DCN-E180K, a mutant with a point mutation reducing its affinity to collagen type I (21). These two mutants were chosen because previous studies (15) had shown that the N-terminal part of decorin is not involved in binding the EGF receptor but leucine-rich repeat 7, which contains the point mutation (DCN-E180K). Our investigation demonstrated that DCN-Q153 alone was still able to induce Akt phosphorylation ( Fig.…”

“…How decorin affects differentiation and apoptosis is not completely understood. In tumor cells, decorin binds to the epithelial growth factor (EGF) receptor or ErbB4 and leads to activation of the mitogen-activated kinase (MAPK) pathway, Ca 2ϩ influx, induction of the cyclin-dependent kinase inhibitor, p21, and subsequently to down-regulation of the receptor (13)(14)(15). In endothelial cells decorin affects different pathways.…”

Development of Stepwise Osteogenesis-mimicking Matrices for the Regulation of Mesenchymal Stem Cell Functions

“…It has been shown that the ECM modulates the activity of growth factors by controlling the proteolytic activation of latent factors, as occurs in the case of transforming growth factor-␤ (37). In addition, ECM molecules, such as decorin, can interact with cell surface receptors so as to prevent binding of the cognate ligand, as occurs in the case of the epidermal growth factor receptor (38). The ECM may also bind growth-promoting factors from the serum for optimal presentation to MSCs.…”