Mesenchymal stem cell migration is regulated by fibronectin through α5β1-integrin-mediated activation of PDGFR-β and potentiation of growth factor signals

Jennifer Veevers-Lowe,Cay M Kielty,Stephen G Ball,Adrian Shuttleworth

doi:10.1242/jcs.076935

Abstract

Cell migration during vascular remodelling is regulated by crosstalk between growth factor receptors and integrin receptors, which together coordinate cytoskeletal and motogenic changes. Here, we report extracellular matrix (ECM)-directed crosstalk between platelet-derived growth factor receptor (PDGFR)-β and α5β1-integrin, which controls the migration of mesenchymal stem (stromal) cells (MSCs). Cell adhesion to fibronectin induced α5β1-integrin-dependent phosphorylation of PDGFR-β in the absence of growth factor stimulation. Phosphorylated PDGFR-β co-immunoprecipitated with α5-integrin and colocalised with α5β1-integrin in the transient tidemarks of focal adhesions. Adhesion to fibronectin also strongly potentiated PDGF-BB-induced PDGFR-β phosphorylation and focal adhesion kinase (FAK) activity, in an α5β1-integrin-dependent manner. PDGFR-β-induced phosphoinositide 3-kinase (PI3K) and Akt activity, actin reorganisation and cell migration were all regulated by fibronectin and α5β1-integrin. This synergistic relationship between α5β1-integrin and PDGFR-β is a fundamental determinant of cell migration. Thus, fibronectin-rich matrices can prime PDGFR-β to recruit mesenchymal cells at sites of vascular remodelling.

Highlights

Adhesion to extracellular matrix (ECM) induces plateletderived growth factor receptor (PDGFR) tyrosine phosphorylation To evaluate how adhesion to ECM regulates PDGFR activation in mesenchymal stem cells (MSCs), tyrosine phosphorylation of PDGFR-a and PDGFR-b was examined in serum-free conditions, after plating onto fibronectin, laminin, fibrillin-1 PF8 [an Arg-Gly-Asp (RGD)-containing fragment that engages the a5b1-integrin] (Bax et al, 2007; Cain et al, 2005), collagen type I or collagen type IV for 90 minutes
When MSCs were plated onto fibrillin-1 PF8, collagen type I or collagen type IV for 90 minutes, PDGFR-b phosphorylation was induced at lower levels compared with that on fibronectin, but no PDGFR-a phosphorylation was detected
The percentage of MSCs adhering to the different ECM substrates after 90 minutes was similar, indicating that the MSC lysates, taken at 90 minutes, from BSA-coated wells or wells coated with 10 g/ml fibronectin, laminin, fibrillin-1 (PF8), collagen type I or collagen type IV

Summary

Introduction

Signalling through the receptor tyrosine kinase (RTK) plateletderived growth factor receptor (PDGFR)-b is essential for the migration and differentiation of cells during vascular development (Yancopoulos et al, 2000; Betsholtz et al, 2001; Kinner et al, 2002; Lindblom et al, 2003; Ball et al, 2007; Andrae et al, 2008). PDGF-BB, the main growth factor ligand of PDGFR-b, is a potent stimulant of smooth muscle cell (SMC) recruitment during neointimal hyperplasia following vascular injury (Andrae et al, 2008). Dimerisation of PDGFR-b, induced by ligating growth factor dimers, stimulates autophosphorylation of specific tyrosine residues within its cytoplasmic domain (Kelly et al, 1991). Integrins are ab heterodimeric cell-surface receptors that act as a transmembrane link between extracellular matrix (ECM) ligands and the actin cytoskeleton

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