Discoidin Domain Receptors Promote α1β1- and α2β1-Integrin Mediated Cell Adhesion to Collagen by Enhancing Integrin Activation

Huifang Xu,Birgit Leitinger,Dominique Bihan,Paul H Huang,Francis Chang,Richard W Farndale,Donald Gullberg

doi:10.1371/journal.pone.0052209

Huifang Xu, Birgit Leitinger + Show 5 more

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https://doi.org/10.1371/journal.pone.0052209

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Abstract

The discoidin domain receptors, DDR1 and DDR2, are receptor tyrosine kinases that bind to and are activated by collagens. Similar to collagen-binding β1 integrins, the DDRs bind to specific motifs within the collagen triple helix. However, these two types of collagen receptors recognize distinct collagen sequences. While GVMGFO (O is hydroxyproline) functions as a major DDR binding motif in fibrillar collagens, integrins bind to sequences containing Gxx’GEx”. The DDRs are thought to regulate cell adhesion, but their roles have hitherto only been studied indirectly. In this study we used synthetic triple-helical collagen-derived peptides that incorporate either the DDR-selective GVMGFO motif or integrin-selective motifs, such as GxOGER and GLOGEN, in order to selectively target either type of receptor and resolve their contributions to cell adhesion. Our data using HEK293 cells show that while cell adhesion to collagen I was completely inhibited by anti-integrin blocking antibodies, the DDRs could mediate cell attachment to the GVMGFO motif in an integrin-independent manner. Cell binding to GVMGFO was independent of DDR receptor signalling and occurred with limited cell spreading, indicating that the DDRs do not mediate firm adhesion. However, blocking the interaction of DDR-expressing cells with collagen I via the GVMGFO site diminished cell adhesion, suggesting that the DDRs positively modulate integrin-mediated cell adhesion. Indeed, overexpression of the DDRs or activation of the DDRs by the GVMGFO ligand promoted α1β1 and α2β1 integrin-mediated cell adhesion to medium- and low-affinity integrin ligands without regulating the cell surface expression levels of α1β1 or α2β1. Our data thus demonstrate an adhesion-promoting role of the DDRs, whereby overexpression and/or activation of the DDRs leads to enhanced integrin-mediated cell adhesion as a result of higher integrin activation state.

Highlights

The extracellular matrix (ECM) physically supports cells in multicellular organisms and signals to these cells through cell surface receptors
Cell adhesion to collagen I was completely inhibited by the use of an anti-b1 integrin blocking Ab, indicating that adhesion to collagen I is mediated by b1 integrin family members in all tested cell lines (Fig. 1B)
Our results further showed that discoidin domain receptors (DDRs)-expressing cells, but not empty-vector control cells, exhibited moderate levels of adhesion to the DDR ligand GPRGQOGVNleGFO, and this adhesion was not affected by the anti-b1 Ab (Fig. 1B)

Summary

Introduction

The extracellular matrix (ECM) physically supports cells in multicellular organisms and signals to these cells through cell surface receptors. The interactions between ECM proteins and cell surface receptors activate a variety of signalling pathways that regulate cell behaviour and determine physiological functions. Fibrillar collagens such as collagens I, II or III further assemble into fibrils and fibres, providing mechanical support. In addition to this main architectural role, collagens play a regulatory role in many cellular processes, such as cell adhesion, migration, growth and wound healing, which is achieved by interacting with collagen receptors that recognize specific motifs within the collagen triple helix [2]. Two major types of collagenbinding receptors are widely distributed in mammalian tissues: collagen-binding b1 integrin family members and the discoidin domain receptors (DDRs)

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