The pattern of enhancement of Src kinase activity on platelet-derived growth factor stimulation of glioblastoma cells is affected by the integrin engaged.

Enhanced expression of both integrin alpha v beta 3 and platelet-derived growth factor receptor (PDGFr) has been described in glioblastoma tumors. We therefore explored the possibility that integrin alpha v beta 3 cooperates with PDGFr to promote cell migration in glioblastoma cells, and extended the study to identify the Src family members that are activated on PDGF stimulation. Glioblastoma cells utilize integrins alpha v beta 3 and alpha v beta 5 to mediate vitronectin attachment. We found that physiologic PDGF stimulation (83 pm, 10 min) of vitronectin-adherent cells promoted the specific recruitment of integrin alpha v beta 3-containing focal adhesions to the cell cortex and alpha v beta 3-mediated cell motility. Analysis of PDGFr immunoprecipitates indicated an association of the PDGFr beta with integrin alpha v beta 3, but not integrin alpha v beta 5. Cells plated onto collagen or laminin, which engage different integrins, exhibited significantly less migration on PDGF stimulation, indicating a cooperation of alpha v beta 3 and the PDGFr beta in glioblastoma cells that promotes migration. Further analysis of the cells plated onto vitronectin indicated that PDGF stimulation caused an increase in Src kinase activity, which was associated with integrin alpha v beta 3. In the vitronectin-adherent cells, Lyn was associated preferentially with alpha v beta 3 both in the presence and absence of PDGF stimulation. In contrast, Fyn was associated with both alpha v beta 3 and alpha v beta 5. Moreover, PDGF stimulation increased the activity of Lyn, but not Fyn, in vitronectin-adherent cells, and the activity of Fyn, but not Lyn, in laminin-adherent cells. Using cells attached to mAb anti-alpha v beta 3 or mAb anti-integrin alpha 6, we confirmed the activation of specific members of the Src kinase family with PDGF stimulation. Down-regulation of Lyn expression by siRNA significantly inhibited the cell migration mediated by integrin alpha v beta 3 in PDGF-stimulated cells, demonstrating the PDGFr beta cooperates with integrin alpha v beta 3 in promoting the motility of vitronectin-adherent glioblastoma cells through a Lyn kinase-mediated pathway. Notably, the data indicate that engagement of different integrins alters the identity of the Src family members that are activated on stimulation with PDGF.