Peroxisome proliferator-activated receptor-gamma ligands inhibit nuclear but not cytosolic extracellular signal-regulated kinase/mitogen-activated protein kinase-regulated steps in vascular smooth muscle cell migration

Vascular smooth muscle cell (VSMC) migration involves adhesion, locomotion, and invasion regulated by various signaling molecules, among which the ext racellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK) play a critical role. We have shown that the peroxisome proliferator -activated receptor-gamma (PPAR-gamma) ligands troglitazone and rosiglitazo ne inhibit VSMC migration downstream of ERK MAPK. The purpose of the curren t study was to more specifically determine which step(s) in VSMC migration are targeted by inhibition of the ERK MAPK pathway or activation of PPAR-ga mma. VSMC adhesion was not affected by the ERK MAPK pathway inhibitor PD980 59 or PPAR-gamma ligands. Phosphorylation and activation of myosin light ch ain kinase (MLCK) play important roles in cell locomotion. Platelet-derived growth factor (PDGF)-induced MLCK phosphorylation (1.7-fold) was completel y blocked by PD98059 at 30 muM (p < 0.05), but not by troglitazone or rosig litazone. PDGF-directed migration (5.8-fold) was inhibited by PD98059 -88% at 30 <mu>M and the MLCK inhibitor ML9 (0.1-1 muM, -84% at 1 muM) (all p < 0.05). The transcription factor Ets-1 mediates matrix metalloproteinase ind uction required for tissue invasion by VSMC. PDGF (20 ng/ml) stimulated an Ets-1 protein expression (14-fold at 60 min) in VSMC, which was inhibited b y PD98059 (-72% at 30 <mu>M), troglitazone (-69% at 20 muM), and rosiglitaz one (-54% at 10 muM) (all p < 0.05). Immunohistochemistry of rat aortae 2 h after balloon injury showed a dramatic upregulation of Ets-1, which was ma rkedly inhibited in animals that had received troglitazone treatment. In co ntrast, phosphorylated ERK MAPK was not affected by troglitazone. These dat a are consistent with PPAR-<gamma> ligands exerting their anti-migratory ef fects downstream of ERK MAPK activation by blocking nuclear events, such as Ets-1 expression. required for cell invasion in response to arterial injur y.