Platelet-derived Growth Factor-induced Cell Migration Research Articles

The Matricellular Protein Cyr61 Is a Key Mediator of Platelet-derived Growth Factor-induced Cell Migration

Platelet-derived growth factor (PDGF), a potent chemoattractant, induces cell migration via the MAPK and PI3K/Akt pathways. However, the downstream mediators are still elusive. In particular, the role of extracellular mediators is largely unknown. In this study, we identified the matricellular protein Cyr61, which is de novo synthesized in response to PDGF stimulation, as the key downstream mediator of the ERK and JNK pathways, independent of the p38 MAPK and AKT pathways, and, thereby, it mediates PDGF-induced smooth muscle cell migration but not proliferation. Our results revealed that, when Cyr61 was newly synthesized by PDGF, it was promptly translocated to the extracellular matrix and physically interacted with the plasma membrane integrins α6β1 and αvβ3. We further demonstrate that Cyr61 and integrins are integral components of the PDGF signaling pathway via an "outside-in" signaling route to activate intracellular focal adhesion kinase (FAK), leading to cell migration. Therefore, this study provides the first evidence that the PDGF-induced endogenous extracellular matrix component Cyr61 is a key mediator in modulating cell migration by connecting intracellular PDGF-ERK and JNK signals with integrin/FAK signaling. Therefore, extracellular Cyr61 convergence with growth factor signaling and integrin/FAK signaling is a new concept of growth factor-induced cell migration. The discovered signaling pathway may represent an important therapeutic target in growth factor-mediated cell migration/invasion-related vascular diseases and tumorigenesis.

ROS-mediated downregulation of MYPT1 in smooth muscle cells: a potential mechanism for the aberrant contractility in atherosclerosis

Reactive oxygen species (ROS) mediates the aberrant contractility in hypertension. Abnormal contractility occurs in atherosclerotic vessels but changes in proteins that regulate contractility remain poorly understood. Myosin phosphatase (MP) activity, which regulates smooth muscle relaxation, is regulated by the phosphorylation of its regulatory subunit, MP targeting subunit 1 (MYPT1). In the present study, we examined the roles of ROS in MP subunit expression both in cultured human aortic smooth muscle cells (HASMCs) and during atherosclerosis progression in apolipoprotein E-knockout (apoE-KO) mice. Furthermore, the effect of decreased MYPT1 on actin cytoskeleton and cell migration activity was assessed in HASMCs. Short hairpin RNA-mediated knockdown of MYPT1 increased stress fibers and attenuated platelet-derived growth factor-induced cell migration in HASMCs. Superoxide anion-inducing agent LY83583 downregulated MYPT1 mRNA and protein levels, but did not affect the phosphorylation of MYPT1 and catalytic subunit of MP, PP1δ. The LY83583-induced decrease in MYPT1 was abolished by co-treating with superoxide dismutase or by inhibiting NADPH oxidase with diphenyleneiodonium. Treatment of peroxynitrite, but not hydrogen peroxide (H2O2), downregulated MYPT1 protein expression and induced MYPT1 phosphorylation without affecting mRNA levels. Co-treatment with a proteasome inhibitor, MG-132, eliminated peroxynitrite-induced MYPT1 downregulation. In apoE-KO mice, MYPT1 protein, but not mRNA, levels were markedly decreased in 16-week- and 24-week-old mice. Oral estrogen treatment, which was previously shown to decrease aortic ROS levels, upregulated aortic MYPT1 expression. Moreover, reduction in MYPT1 expression correlated with increased aortic sensitivity toward vasoconstrictors. These results suggested that during atherosclerosis progression oxidative stress mediates the downregulation of MYPT1, which may inhibit smooth muscle cell migration and contribute to the aberrant contractility.

Pharmacology in Health Food: Metabolism of Quercetin In Vivo and Its Protective Effect Against Arteriosclerosis

Quercetin, a member of the bioflavonoids family, has been proposed to have antiatherogenic, anti-inflammatory, and anti-hypertensive properties leading to the beneficial effects against cardiovascular diseases. It was recently demonstrated that quercetin 3-O-β-D-glucuronide (Q3GA) is one of the major quercetin conjugates in human plasma, in which the aglycone could not be detected. Although most of the in vitro pharmacological studies have been carried out using only the quercetin aglycone form, experiments using Q3GA would be important to discover the preventive mechanisms of cardiovascular diseases by quercetin in vivo. Therefore we examined the effects of the chemically synthesized Q3GA, as an in vivo form, on vascular smooth muscle cell (VSMC) disorders related to the progression of arteriosclerosis. Platelet-derived growth factor–induced cell migration and proliferation were inhibited by Q3GA in VSMCs. Q3GA attenuated angiotensin II–induced VSMC hypertrophy via its inhibitory effect on JNK and the AP-1 signaling pathway. Q3GA scavenged 1,1-diphenyl-2-picrylhydrazyl radical measured by the electron paramagnetic resonance method. In addition, immunohistochemical studies with monoclonal antibody 14A2 targeting the Q3GA demonstrated that the positive staining specifically accumulates in human atherosclerotic lesions, but not in the normal aorta. These findings suggest Q3GA would be an active metabolite of quercetin in plasma and may have preventative effects on arteriosclerosis relevant to VSMC disorders.

Nectin-like Molecule-5/Tage4 Enhances Cell Migration in an Integrin-dependent, Nectin-3-independent Manner

Cell migration plays roles in invasion of transformed cells and scattering of embryonic mesenchymal cells into surrounding tissues. We have found that Ig-like Necl-5/Tage4 is up-regulated in NIH3T3 cells transformed by an oncogenic Ras (V12Ras-NIH3T3 cells) and heterophilically trans-interacts with a Ca(2+)-independent Ig-like cell adhesion molecule nectin-3, eventually enhancing their intercellular motility. We show here that Necl-5 furthermore enhances cell migration in a nectin-3-independent manner. Studies using L fibroblasts expressing various mutants of Necl-5, NIH3T3 cells, and V12Ras-NIH3T3 cells have revealed that Necl-5 enhances serum- and platelet-derived growth factor-induced cell migration. The extracellular region of Necl-5 is necessary for directional cell migration, but not for random cell motility. The cytoplasmic region of Necl-5 is necessary for both directional and random cell movement. Necl-5 colocalizes with integrin alpha(V)beta(3) at leading edges of migrating cells. Analyses using an inhibitor or an activator of integrin alpha(V)beta(3) or a dominant negative mutant of Necl-5 have shown the functional association of Necl-5 with integrin alpha(V)beta(3) in cell motility. Cdc42 and Rac small G proteins are activated by the action of Necl-5 and required for the serum-induced, Necl-5-enhanced cell motility. These results indicate that Necl-5 regulates serum- and platelet-derived growth factor-induced cell migration in an integrin-dependent, nectin-3-independent manner, when cells do not contact other cells. We furthermore show here that enhanced motility and metastasis of V12Ras-NIH3T3 cells are at least partly the result of up-regulated Necl-5.

Bradykinin B(1) receptor mediates inhibition of neointima formation in rat artery after balloon angioplasty.

We evaluated the effects of the kallikrein-kinin system on the proliferation and migration of primary cultured vascular smooth muscle cells (VSMCs) in vitro and neointima formation in balloon-injured rat carotid arteries in vivo. In cultured rat VSMCs, tissue kallikrein inhibited cell proliferation, and this inhibitory effect was blocked by Sar-Tyr-Aca(epsilon)-Lys [D-betaNal(7), Ile(8)]-des-Arg(9)-bradykinin, a bradykinin B(1) receptor antagonist, and by icatibant, a bradykinin B(2) receptor antagonist. Platelet-derived growth factor significantly increased the expression of the B(1) receptor but not the B(2) receptor in VSMCs. Platelet-derived growth factor-induced cell migration was significantly attenuated by des-Arg(9)-bradykinin and to a lesser degree by bradykinin. Endogenous B(1) receptor mRNA increased in rat carotid arteries after balloon angioplasty. After local delivery of adenovirus carrying the human tissue kallikrein gene into the rat carotid artery, we observed a 54% reduction in the intima/media ratio at the injured site compared with the control ratio (n=7, P:<0.01). Administration of the B(1) receptor antagonist via minipumps blocked the protective effect of kallikrein and partially reversed the intima/media ratio toward the control ratio. Kallikrein gene delivery results in the regeneration of endothelium compared with the control groups, and the B(1) receptor antagonist abolished this effect. Nitrite/nitrate, cGMP, and cAMP levels in balloon-injured arteries significantly increased after kallikrein gene delivery, whereas the B(1) receptor antagonist abolished these increases (n=4 or 5, P:<0.05). These results indicate that the B(1) receptor contributes to the reduction of neointima formation via the promotion of reendothelialization and inhibition of VSMC proliferation and migration through NO-cGMP and cAMP signaling pathways. This study provides significant implications in treating restenosis after revascularization.