Cell-cell adhesion through N-cadherin enhances VCAM-1 expression via PDGFRβ in a ligand-independent manner in mesenchymal stem cells

Cell-cell adhesions induce various intracellular signals through hierarchical and synergistic molecular interac- tions. Recently, we demonstrated that a high cell density induces the expression of vascular cell adhesion molecule-1 (VCAM-1) through the nuclear factor-κB (NF-κB) pathway in human bone marrow-derived mesenchymal stem cells (MSCs). However, the specific molecules that activated the NF- κB pathway were not determined. In the present study, in experiments with receptor tyrosine kinase inhibitors, VCAM-1 expression was completely suppressed by platelet-derived growth factor (PDGF) receptor (PDGFR) inhibitors. In addition, VCAM-1 expression was significantly suppressed by knockdown with PDGFR β siRNA, but not with PDGFRα siRNA. However, VCAM-1 expression did not increase following treatment with PDGF. The over- expression of N-cadherin, a structural molecule in adherence junctions in MSCs, promoted VCAM-1 expression and induced the marked phosphorylation of the intracellular signaling factor, Src. In addition, VCAM-1 expression and Src phosphorylation were reduced by the overexpression of a dominant negative mutant of N-cadherin. These results suggest that cell-cell adhe- sion, through N-cadherin, enhances the expression of VCAM-1 via PDGFRβ and the activation of Src in a ligand-independent manner in MSCs.