Regulation of Vascular Smooth Muscle Proliferation by Heparin

Abstract

Uncontrolled proliferation of vascular smooth muscle cells (VSMCs) contribute to intimal hyperplasia during atherosclerosis and restenosis. Heparin is an antiproliferative agent for VSMCs and has been shown to block VSMC proliferation both in tissue culture systems and in animals. Despite the well documented antiproliferative actions of heparin, its cellular targets largely remain unknown. In an effort to characterize the mechanism of the antiproliferative property of heparin, we have analyzed the effect of heparin on cell cycle in VSMC. Our results indicate that the heparin-induced block in G 1 to S phase transition is imposed by p27 kip1 -mediated inhibition of cyclin-dependent kinase 2 activity. Further analysis of p27 kip1 mRNA levels showed that the increase in p27 kip1 protein levels in heparin-treated VSMC occurs at posttranscriptional levels. We present evidence that heparin causes stabilization of p27 kip1 protein during G 1 phase and thereby prevents activation of cyclin-dependent kinase 2.The proliferation of vascular smooth muscle cells (VSMCs) 1 is a key event in the development of atherosclerotic lesions and postangioplasty restenosis (1). In a normal artery, the VSMCs are in a non-proliferative quiescent state and show a well differentiated contractile phenotype. After the vascular injury, there is a loss of differentiated phenotype and a shift to a synthetic phenotype, which is also accompanied by entry into the cell cycle and proliferation (2). Several cytokines, growth factors, vasoregulatory molecules, and extracellular matrix components exert their effects on the proliferation of VSMC. The development of an atherosclerotic lesion can be blocked significantly by effective inhibition of VSMC proliferation (3). Natural glycosaminoglycans such as heparin are also known inhibit VSMC proliferation in vitro in tissue culture (4 -6) and in vivo in animal models (7,8). Despite the well documented antiproliferative effect of heparin on VSMC, the molecular mechanisms responsible for inhibition of cell cycle remain uncharacterized.Cellular proliferation is regulated primarily by regulation of the cell cycle (9), which consists of four distinct sequential phases (G 0 /G 1 , S, G 2 , and M). This tightly regulated temporal order is controlled by the sequential activation of certain serine/threonine protein kinases known as cyclin-dependent kinases (Cdks) that phosphorylate the Rb protein (10). In quiescent cells, Rb exists in its hypophosphorylated state and is thus able to bind and sequester the members of E2F family of transcription factors (11). Phosphorylation of Rb at multiple sites by Cdks causes the release of E2F because hyperphosphorylated Rb cannot bind and sequester E2F factors, thus enabling them to activate transcription of genes whose products are absolutely essential for further cell cycle progression (12). The activity of Cdks is further regulated negatively by a number of Cdk inhibitors, which are grouped into two classes (13) (14), and the members of Cip family (p21 cip1 , p27 kip1 , and ...

Interaction of human tRNA-dihydrouridine synthase-2 with interferon-induced protein kinase PKR

“…Heparin binds to PKR at a site that is nonoverlapping with PKR's dsRBD and leads to PKR activation ( 41 , 42 ). Activation of PKR by heparin in vascular smooth muscle cells leads to an arrest in cell cycle progression by causing elevation in p27 kip1 protein levels, inhibition of Cdk2 activity and Rb phosphorylation ( 43 ). PACT interacts with PKR by binding to its dsRBD in a dsRNA-independent manner and activates PKR in response to cellular stress ( 14 ).…”

Histochemical Study of Heparin‐positive Mast Cells in the Terminal Part of Porcine Ductus Choledochus and Papilla Duodeni Major

“…In this case, it is obvious that the role of heparin in the function of smooth muscle cells of both circular and longitudinal layers of the choledochus sphincter muscle is quite different. Having in mind the well‐known role of heparin in the inhibition of motility and proliferation of the vascular and myometrial smooth muscle cells (Lake and Castellot, ; Masson et al., ; Fasciano et al., ), it could be presumed a similar role predominates also in the circular smooth layer of the musculus sphincter ductus choledochus . That opinion could also be supported by recently reported data regarding the role of canine and porcine heparin‐positive MCs in the motility of smooth and skeletal muscle cells (Stefanov et al., ; Vodenicharov, ).…”

Targeted Inhibitory Effect of Lenti-SM22alpha-p27-EGFP Recombinant Lentiviral Vectors on Proliferation of Vascular Smooth Muscle Cells without Compromising Re-Endothelialization in a Rat Carotid Artery Balloon Injury Model

“…The cell cycle mechanisms underlying the inhibition of proliferation of VSMCs and VECs after DES implantation remain unclear. However, the G1/S transition point has been shown to play an important role in VSMCs under conditions of mechanical or inflammatory injury [ 23 ]. P27 kip1 regulates the G1/S transition by inhibiting the activity of cyclin E/CDK2, which is considered to be an endogenous regulator in VSMCs.…”