DDR receptor effector mechanisms are not well understood Mos

DDR receptor effector mechanisms are not well understood. Most descriptions of DDR function have focused on downstream signaling pathways activated by collagen that regulate cell proliferation and transcriptional activation [7]. Natural occurring or induced DDR2−/− genotypes in mice induce dwarfism, reduce fibroblasts have proliferation [8], [9], delayed cutaneous wound repair, as well as decreased expression of syndecan 1 and the collagen crosslinking enzymes lysyl oxidase and lysyl hydroxylase [10]. Conversely, functional mutations in DDR2 contribute to development of squamous cell lung cancer [11]. However, DDR functions involving collagen interactions, e.g., DDR1−/− smooth muscle cell adhesion to collagen [12] and DDR control of collagen are independent of tyrosine kinase activation [13], [14]. In addition, DDR1 is required for cell chemotaxis towards soluble collagen [15], [16], [17]: yet not all aspects of DDR-dependent cell motile activity depend on DDR-collagen interactions. DDR1 is required for collective cancer cell migration in organotypic collagen culture models. Fibroblast migration through matrigel, which is inhibited in DDR2−/− cells, occurs with serum rather than collagen as the chemotactic stimulus [18].
Materials and methods
Results
Discussion DDR2 played a role in cell motile behavior, but the relationship between motility and collagen activation of DDR2 tyrosine kinase was unclear. Studies with smooth muscle 5416 from DDR1−/− mice demonstrated a defect in cell attachment to collagen and a loss of cell chemotaxis towards soluble collagen, but only the latter required a functional DDR-kinase domain [15]. Investigators reported that DDR1 was a negative regulator of cell spreading [16], which could be attributed to DDR1 activation of myosin [29] or inhibition of α2β1 function [28]. Yet others reported that DDR2 was required for fibroblast migration through matrigel, but the chemotactic stimulus for migration was serum not soluble collagen [18]. Finally, rather than interacting with collagen, the role of DDR1 in cell–cell interaction [30] and collective cell migration in organotypic collagen culture models [17] was found to depend on DDR1 interaction with E-cadherin. We found that silencing DDR2 inhibited BR5 cells spreading and migration regardless whether cells were interacting with fibronectin or collagen-coated 2D surfaces. However, cells attached to either surface did not show DDR2 tyrosine kinase activation unless soluble collagen was added to the medium. The requirement for DDR2 in spreading and migration appeared to be independent of adhesion ligand and collagen-stimulated DDR2 activation but dependent of activation of pFak. Inhibition of cell migration by silencing DDR2 also was observed for human fibroblasts migrating in nested collagen matrices, but collagen matrix contraction by these cells was not inhibited indicating the specificity of the DDR2 silencing effect. Our new observations support previous work comparing cell migration and collagen matrix contraction, which showed that different growth factors and regulatory mechanisms control migration and contraction in 3D collagen matrices [23].