The Scaffolding Protein EBP50 Promotes Vascular Smooth Muscle Cell Proliferation and Neointima Formation by Regulating Skp2 and p21

Objective—The Ezrin-radixin–moesin– binding phosphoprotein 50 (EBP50) is a scaffolding protein known to regulate ion homeostasis in the kidney and intestine. Previous work showed that EBP50 expression increases after balloon injury in rat carotids. This study was designed to determine the role of EBP50 on vascular smooth muscle cells (VSMC) proliferation and the development of neointimal hyperplasia. Methods and Results—Wire injury was performed in wild type (WT) and EBP50 knockout (KO) mice. Two weeks after injury, neointima formation was 80% lower in KO than in WT mice. Proliferation of KO VSMC was significantly lower than WT cells and overexpression of EBP50 increased VSMC proliferation. Akt activity and expression of S-phase kinase protein2 decreased in KO cells resulting in the stabilization of the cyclin-dependent kinase inhibitor, p21 cip1. Consequently, KO cells were arrested in G 0 /G 1 phase. Consistent with these observations, p21 cip1 was detected in injured femoral arteries of KO but not WT mice. No differences in apoptosis between WT and KO were observed. Conclusion—EBP50 is critical for neointima formation and induces VSMC proliferation by decreasing S-phase kinase protein2 stability, thereby accelerating the degradation of the cell cycle inhibitor p21 cip1. N eointimal hyperplasia is a common complication of atherosclerosis and surgical vascular interventions, particularly angioplasty. Although it is clear that neointima formation following arterial injury originates from several cellular processes, including the initial inflammatory response , increased matrix production and migration of vascu-lar smooth muscle cells (VSMC), the proliferation of VSMC is a major contributing factor. 1 Consequently, several studies examined how manipulation of the expression of molecules involved in cell cycle progression affects neointimal hyper-plasia. Of particular interest in this respect are the cyclin-dependent kinase inhibitors p21 cip1 and p27 kip1. Studies in animal models clearly demonstrated that increased expression of p21 cip1 in vessels decreases the progression and severity of neointima formation following injury. p21 cip1 is undetectable in uninjured human and porcine arteries but its expression increases following injury and inversely correlates with VSMC proliferation. 2 Adenoviral delivery of p21 cip1 inhibits neointimal thickening in rats and pigs. 2,3 Moreover, p21 cip1 mediates the antiproliferative effect of nitric oxide on VSMC. 4 However, 2 studies show that reduction of p21 cip1 does not increase neointimal hyperplasia in animal models. 5,6 Similar to p21 cip1 , p27 kip1 exerts important effects on disease progression. Overexpression of p27 kip1 in pig arteries reduced intima formation by 50%. …