Objective: Here we investigated the role of spleen tyrosine kinase (Syk) in the migration induced by platelet-derived growth factor (PDGF) in rat aortic smooth muscle cells (RASMC).
Methods: Cell migration was determined using a Boyden chamber, by wound-healing, and by aortic ring assays. Activity of Syk, mitogen-activated protein kinase (MAPK), and heat shock protein 27 (HSP27) were tested using immunoblotting with kinase inhibitors and small interference RNAs.
Results: PDGF-BB induced binding of Syk to the PDGFbeta receptor and increased the phosphorylation of Syk and migration in RASMC. These effects of PDGF-BB were inhibited by piceatannol, an inhibitor of Syk. PDGF-BB increased the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, p38 MAPK, and HSP27, which were significantly inhibited by piceatannol and in Syk-knockdown cells. The p38 MAPK inhibitor SB203580 and ERK1/2 inhibitor PD98059 inhibited the migration, which was further inhibited by the combination of these inhibitors. SB203580, but not PD98059, inhibited the phosphorylation of HSP27 induced by PDGF-BB in RASMC. PDGF-BB-induced migration was attenuated in HSP27-knockdown cells. Kinase inhibitors and Syk-knockdown diminished PDGF-BB-induced sprout outgrowth in the aortic ring assay.
Conclusions: These results imply that Syk is an upstream signal of the p38 MAPK/HSP27 and ERK1/2 pathways that contributes to PDGF-BB-mediated migration in RASMC.