Dominant negative c-Jun inhibits platelet-derived growth factor-directed migration by vascular smooth muscle cells

Antiproliferative Activity of Hinokitiol, a Tropolone Derivative, Is Mediated via the Inductions of p-JNK and p-PLCγ1 Signaling in PDGF-BB-Stimulated Vascular Smooth Muscle Cells

Abnormal proliferation of vascular smooth muscle cells (VSMCs) is important in the pathogenesis of vascular disorders such as atherosclerosis and restenosis. Hinokitiol, a tropolone derivative found in Chamacyparis taiwanensis, has been found to exhibit anticancer activity in a variety of cancers through inhibition of cell proliferation. In the present study, the possible anti-proliferative effect of hinokitiol was investigated on VSMCs. Our results showed that hinokitiol significantly attenuated the PDGF-BB-stimulated proliferation of VSMCs without cytotoxicity. Hinokitiol suppressed the expression of proliferating cell nuclear antigen (PCNA), a maker for cell cycle arrest, and caused G0/G1 phase arrest in cell cycle progression. To investigate the mechanism underlying the anti-proliferative effect of hinokitiol, we examined the effects of hinokitiol on phosphorylations of Akt, ERK1/2, p38 and JNK1/2. Phospholipase C (PLC)-γ1 phosphorylation, its phosphorylated substrates and p27^kip1 expression was also analyzed. Pre-treatment of VSMCs with hinikitiol was found to significantly inhibit the PDGF-BB-induced phosphorylations of JNK1/2 and PLC-γ1, however no effects on Akt, ERK1/2, and p38. The up-regulation of p27^kip1 was also observed in hinokitiol-treated VSMCs. Taken together, our results suggest that hinokitiol inhibits PDGF-BB-induced proliferation of VSMCs by inducing cell cycle arrest, suppressing JNK1/2 phosphorylation and PLC-γ1, and stimulating p27^kip1 expression. These findings suggest that hinokitiol may be beneficial for the treatment of vascular-related disorders and diseases.

Platonin inhibited PDGF-BB-induced proliferation of rat vascular smooth muscle cells via JNK1/2-dependent signaling

AIM

To examine the inhibitory actions of the immunoregulator platonin against proliferation of rat vascular smooth muscle cells (VSMCs).

METHODS

VSMCs were prepared from the thoracic aortas of male Wistar rats. Cell proliferation was examined using MTT assays. Cell cycles were analyzed using flow cytometry. c-Jun N-terminal kinase (JNK)1/2, extracellular signal-regulated kinase (ERK)1/2, AKT, and c-Jun phosphorylation or p27 expression were detected using immunoblotting.

RESULTS

Pretreatment with platonin (1-5 μmol/L) significantly suppressed VSMC proliferation stimulated by PDGF-BB (10 ng/mL) or 10% fetal bovine serum (FBS), and arrested cell cycle progression in the S and G(2)/M phases. The same concentrations of platonin significantly inhibited the phosphorylation of JNK1/2 but not ERK1/2 or AKT in VSMCs stimulated by PDGF-BB. Furthermore, platonin also attenuated c-Jun phosphorylation and markedly reversed the down-regulation of p27 expression after PDGF-BB stimulation.

CONCLUSION

Platonin inhibited VSMC proliferation, possibly via inhibiting phosphorylation of JNK1/2 and c-Jun, and reversal of p27 down-regulation, thereby leading to cell cycle arrest at the S and G(2)/M phases. Thus, platonin may represent a novel approach for lowering the risk of abnormal VSMC proliferation and related vascular diseases.

The effects of myocyte enhancer factor 2A gene on the proliferation, migration and phenotype of vascular smooth muscle cells

The genetic basis for the phenotypic switching of vascular smooth muscle cells (VSMCs) is unclear in atherosclerosis. Recent studies showed that the 21-base pair deletion mutation (Δ21) in myocyte enhancer factor 2A (MEF2A) gene could be an inherited marker for coronary artery disease. MEF2A mutation may affect the phenotypic switching of VSMCs. Human aortic VSMCs were used. Four groups of VSMCs transfected with green fluorescent protein plasmid (control group), MEF2A wild-type (WT) plasmid (WT group), MEF2A Δ21 plasmid (Δ21 group) or MEF2A siRNA (siRNA group) were studied. The proliferation of VSMCs was determined by methylthiazolyldiphenyl-tetrazolium bromide, and the migration of VSMCs was measured by Millicell chamber. The protein expressions of MEF2A, smooth muscle α-actin, SM22α, osteopontin and p38 mitogen-activated protein kinase signaling pathway were detected by Western blotting. MEF2A protein expression was knockdown by siRNA transfection. MEF2A protein was overexpressed in WT and Δ21 groups. Δ21 and siRNA groups obviously showed more proliferation (methylthiazolyldiphenyl-tetrazolium bromide, 0.63 vs 0.66 vs 0.31, P < 0.01) and migration (52.6 vs 58.0 vs 21.2, P < 0.01) of VSMCs as compared with the WT group. In addition, the transfection of Δ21 and siRNA could induce the down-regulation of smooth muscle α-actin and SM22α (P < 0.01) and the up-regulation of osteopontin (P < 0.01) in VSMCs. The phosphorylated p38 signaling pathway expression was significantly enhanced in the Δ21 and siRNA groups as compared with that of the WT group (P < 0.01). These results suggest that MEF2A dominant negative mutation and RNA silence could induce the phenotypic switching of VSMCs, leading to its increased proliferation and migration, and p38 mitogen-activated protein kinase signaling pathway may participate in it.

Protein kinase A-regulated assembly of a MEF2{middle dot}HDAC4 repressor complex controls c-Jun expression in vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs) maintain the ability to modulate their phenotype in response to changing environmental stimuli. This phenotype modulation plays a critical role in the development of most vascular disease states. In these studies, stimulation of cultured vascular smooth muscle cells with platelet-derived growth factor resulted in marked induction of c-jun expression, which was attenuated by protein kinase Cdelta and calcium/calmodulin-dependent protein kinase inhibition. Given that these signaling pathways have been shown to relieve the repressive effects of class II histone deacetylases (HDACs) on myocyte enhancer factor (MEF) 2 proteins, we ectopically expressed HDAC4 and observed repression of c-jun expression. Congruently, suppression of HDAC4 by RNA interference resulted in enhanced c-jun expression. Consistent with these findings, mutation of the MEF2 cis-element in the c-jun promoter resulted in promoter activation during quiescent conditions, suggesting that the MEF2 cis-element functions as a repressor in this context. Furthermore, we demonstrate that protein kinase A attenuates c-Jun expression by promoting the formation of a MEF2.HDAC4 repressor complex by inhibiting salt-inducible kinase 1. Finally, we document a physical interaction between c-Jun and myocardin, and we document that forced expression of c-Jun represses the ability of myocardin to activate smooth muscle gene expression. Thus, MEF2 and HDAC4 act to repress c-Jun expression in quiescent VSMCs, protein kinase A enhances this repression, and platelet-derived growth factor derepresses c-Jun expression through calcium/calmodulin-dependent protein kinases and novel protein kinase Cs. Regulation of this molecular "switch" on the c-jun promoter may thus prove critical for toggling between the activated and quiescent VSMC phenotypes.

Cofilin phosphorylation mediates proliferation in response to platelet-derived growth factor-BB in rat aortic smooth muscle cells

Cofilin, an actin-binding protein, is essential for a variety of cell responses. In this study, we investigated the correlation between proliferation and cofilin phosphorylation in response to platelet-derived growth factor (PDGF) in rat aortic smooth muscle cells (RASMCs). The phosphorylation of cofilin and activity of mitogen-activated protein kinase (MAPK) were measured by Western analyses and proliferation in RASMCs was measured by BrdU incorporation assays. The phosphorylation of cofilin in RASMCs was decreased by PDGF-BB treatment at 10 min, but recovered to the level of the quiescent state at 60 min. PDGF-BB-induced dephosphorylation of cofilin was inhibited by pretreatment with piceatannol (a spleen tyrosine kinase [Syk] inhibitor), PP2 (a Src inhibitor), or SP600125 (a c-Jun N-terminal kinase [JNK] inhibitor), but not by PD98059, an inhibitor of extracellular signal-regulated kinase 1/2. PDGF-BB increased JNK activity and proliferation, and these responses were suppressed by kinase inhibitors and small interference RNA-cofilin. The results suggest that PDGF-BB-induced dephosphorylation of cofilin can be promoted via the JNK pathway, which is regulated by both Syk and Src kinases and that cofilin dephosphorylation may be involved in PDGF-BB-induced RASMC proliferation.

A dominant negative form of the transcription factor c-Jun affects genes that have opposing effects on lipid homeostasis in mice

c-Jun is a transcription factor activated by phosphorylation by the stress-activated protein kinase/c-Jun N-terminal kinase pathway in response to extracellular signals and cytokines. We show that adenovirus-mediated gene transfer of the dominant negative form of c-Jun (dn-c-Jun) in C57BL/6 mice increased greatly apoE hepatic mRNA and plasma levels, increased plasma cholesterol, triglyceride, and very low density lipoprotein levels, and resulted in the accumulation of discoidal high density lipoprotein particles. A similar but more severe phenotype was generated by overexpression of the mouse apoE in C57BL/6 mice, suggesting that dyslipidemia induced by dn-c-Jun was the result of apoE overexpression. Unexpectedly, infection of apoE(-/-) mice with adenovirus expressing dn-c-Jun reduced plasma cholesterol by 70%, suggesting that dn-c-Jun affected other genes that control plasma cholesterol levels. To identify these genes, we performed whole genome expression analysis (34,000 genes) of isolated livers from two groups of five apoE(-/-) mice, infected with adenoviruses expressing either the dn-c-Jun or the green fluorescence protein. Bioinformatic analysis and Northern blotting validation revealed that dn-c-Jun increased 40-fold the apoE mRNA and reduced by 70% the Scd-1 (stearoyl-CoA-desaturase 1) mRNA. The involvement of Scd-1 in lowering plasma cholesterol was confirmed by restoration of high cholesterol levels of apoE(-/-) mice following coinfection with adenoviruses expressing dn-c-Jun and Scd-1. In conclusion, dn-c-Jun appears to trigger two opposing events in mice that affect plasma cholesterol and triglyceride levels as follows: one results in apoE overexpression and triggers dyslipidemia and the other results in inhibition of Scd-1 and offsets dyslipidemia.

Mechanisms of vascular smooth muscle cell migration

Smooth muscle cell migration occurs during vascular development, in response to vascular injury, and during atherogenesis. Many proximal signals and signal transduction pathways activated during migration have been identified, as well as components of the cellular machinery that affect cell movement. In this review, a summary of promigratory and antimigratory molecules belonging to diverse chemical and functional families is presented, along with a summary of key signaling events mediating migration. Extracellular molecules that modulate migration include small biogenic amines, peptide growth factors, cytokines, extracellular matrix components, and drugs used in cardiovascular medicine. Promigratory stimuli activate signal transduction cascades that trigger remodeling of the cytoskeleton, change the adhesiveness of the cell to the matrix, and activate motor proteins. This review focuses on the signaling pathways and effector proteins regulated by promigratory and antimigratory molecules. Prominent pathways include phosphatidylinositol 3-kinases, calcium-dependent protein kinases, Rho-activated protein kinase, p21-activated protein kinases, LIM kinase, and mitogen-activated protein kinases. Important downstream targets include myosin II motors, actin capping and severing proteins, formins, profilin, cofilin, and the actin-related protein-2/3 complex. Actin filament remodeling, focal contact remodeling, and molecular motors are coordinated to cause cells to migrate along gradients of chemical cues, matrix adhesiveness, or matrix stiffness. The result is recruitment of cells to areas where the vessel wall is being remodeled. Vessel wall remodeling can be antagonized by common cardiovascular drugs that act in part by inhibiting vascular smooth muscle cell migration. Several therapeutically important drugs act by inhibiting cell cycle progression, which may reduce the population of migrating cells.

Epidermal growth factor induces vasoconstriction through the phosphatidylinositol 3-kinase-mediated mitogen-activated protein kinase pathway in hypertensive rats

We investigated whether increased contractile responsiveness to epidermal growth factor (EGF) is associated with altered activation of mitogen-activated protein kinase (MAPK) in the aortic smooth muscle of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. EGF induced contraction and MAPK activity in aortic smooth muscle strips, which were significantly increased in tissues from the DOCA-salt hypertensive rats compared with those from sham-operated rats. AG1478, PD98059, and LY294002, inhibitors of EGF receptor (EGFR) tyrosine kinase, MAPK/extracellular signal-regulated kinase (ERK) kinase, and phosphatidylinositol 3-kinase (PI3K), respectively, inhibited the contraction and the activity of ERK1/2 that were elevated by EGF. Y27632 and GF109203X, inhibitors of Rho kinase and protein kinase C, respectively, attenuated EGF-induced contraction, with no diminution of ERK1/2 activity. Although EGF also elevated the activity of EGFR tyrosine kinase in both sham-operated and DOCA-salt hypertensive rats, the expression and the magnitude of activation did not differ between strips. These results strongly suggest that EGF induces contraction by the activation of ERK1/2, which is regulated by the PI3K pathway in the aortic smooth muscle of DOCA-salt hypertensive rats.

c-Jun N-terminal kinase is necessary for platelet-derived growth factor-mediated chemotaxis in primary fibroblasts

c-Jun N-terminal kinase (JNK) is a member of the mitogen-activated protein kinase family. It has become clear that JNK does not only have a role in induction of stress responses but also in processes such as cell movement. In this report we demonstrate that JNK activity is necessary for platelet-derived growth factor (PDGF)-BB-induced chemotaxis of primary foreskin fibroblasts and in other cell types. PDGF-BB stimulation was found to lead to activation of JNK with a maximum after 30 min. Inhibition of JNK reduced Ser178 phosphorylation of the focal adhesion component paxillin. Paxillin phosphorylation at this site has been shown to be involved in the dynamics of focal adhesions and consequently cell migration. Moreover, we observed localization of JNK to the actin-dense membrane ruffles induced by PDGF-BB stimulation both using immunofluorescence staining and green fluorescent protein-tagged JNK. This suggests a role for JNK at the leading edge of the cell compatible with a function in cell migration. Furthermore, we show that phosphatidylinositol 3-kinase (PI 3-kinase), which has an established role in PDGF-stimulated cell migration, is necessary for PDGF-induced activation of JNK. In conclusion, JNK is a critical component downstream of PI 3-kinase that may be involved in PDGF-stimulated chemotaxis presumably by modulating the integrity of focal adhesions by phosphorylating its components.

c-Jun N-terminal kinase contributes to norepinephrine-induced contraction through phosphorylation of caldesmon in rat aortic smooth muscle

Vascular smooth muscle contraction is mediated by activation of extracellular signal-regulated kinase (ERK) 1/2, an isoform of mitogen-activated protein kinase (MAPK). However, the role of stress-activated protein kinase/c-Jun N-terminal kinase (JNK) in vascular smooth muscle contraction has not been defined. We investigated the role of JNK in the contractile response to norepinephrine (NE) in rat aortic smooth muscle. NE evoked contraction in a dose-dependent manner, and this effect was inhibited by the JNK inhibitor SP600125. NE increased the phosphorylation of JNK, which was greater in aortic smooth muscle from hypertensive rats than from normotensive rats. NE-induced JNK phosphorylation was significantly inhibited by SP600125 and the conventional-type PKC (cPKC) inhibitor Gö6976, but not by the Rho kinase inhibitor Y27632 or the phosphatidylinositol 3-kinase inhibitor LY294002. Thymeleatoxin, a selective activator of cPKC, increased JNK phosphorylation, which was inhibited by Gö6976. SP600125 attenuated the phosphorylation of caldesmon, an actin-binding protein whose phosphorylation is increased by NE. These results show that JNK contributes to NE-mediated contraction through phosphorylation of caldesmon in rat aortic smooth muscle, and that this effect is regulated by the PKC pathway, especially cPKC.

Role of c-Jun N-terminal kinase in the PDGF-induced proliferation and migration of human adipose tissue-derived mesenchymal stem cells

Platelet-derived growth factor (PDGF) is a critical regulator of proliferation and migration for mesenchymal type cells. In this study, we examined the role of mitogen-activated protein (MAP) kinases in the PDGF-BB-induced proliferation and migration of human adipose tissue-derived mesenchymal stem cells (hATSCs). The PDGF-induced proliferation was prevented by a pretreatment with the c-Jun N-terminal kinase (JNK) inhibitor, SP600125. However, it was not prevented by a pretreatment with a p38 MAP kinase inhibitor, SB202190, and a specific inhibitor of the upstream kinase of extracellular signal-regulated kinase (ERK1/2), U0126. Treatment with PDGF induced the activation of JNK and ERK in hATSCs, and pretreatment with SP600125 specifically inhibited the PDGF-induced activation of JNK. Treatment with PDGF induced the cell cycle transition from the G0/G1 phase to the S phase, the elevated expression of cyclin D1, and the phosphorylation of Rb, which were prevented by a pretreatment with SP600125. In addition, the PDGF-induced migration of hATSCs was completely blocked by a pretreatment with SP600125, but not with U0126 and SB202190. These results suggest that JNK protein kinase plays a key role in the PDGF-induced proliferation and migration of mesenchymal stem cells.

Stimulation of vascular smooth muscle cell migration by macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a well known proinflammatory factor that influences the migration and proliferation of various cell types, predominantly monocytes and macrophages. Recent evidence suggests an important role for MIF in the progression of atherosclerosis and restenosis. For this reason, we studied the effect of MIF on platelet-derived growth factor-BB (PDGF-BB)-induced migration and PDGF receptor protein expression in vascular smooth muscle cells (VSMCs). Furthermore, the possibility of MIF influencing the migration of VSMCs was investigated. Our results show that short-term incubation of MIF is able to enhance PDGF-BB-induced migration. Long-term incubation decreases PDGF-BB-induced migration, but preserves a short-term stimulatory effect. These effects are not regulated at the level of PDGF receptor protein expression. MIF also acts as a chemoattractant for VSMCs, with a maximum response at 15 ng/ml. In contrast, the proliferation of VSMCs was unaffected by MIF. We conclude that MIF has a biphasic effect on VSMC migration. It remains unclear whether this effect is direct or involves the secretion of unidentified promigratory factors. Exogenous MIF does not stimulate VSMC proliferation; however, a role for MIF in proliferation cannot be fully ruled out. In view of the known key contributions of macrophage-derived MIF and VSMCs, the observed effects may well play a role in the progression of atherosclerosis and restenosis.

Signal-Crosstalk Between Rho/ROCK and c-Jun NH2-Terminal Kinase Mediates Migration of Vascular Smooth Muscle Cells Stimulated by Angiotensin II

BACKGROUND

Rho and its effector Rho-kinase/ROCK mediate cytoskeletal reorganization as well as smooth muscle contraction. Recent studies indicate that Rho and ROCK are critically involved in vascular remodeling. Here, we tested the hypothesis that Rho/ROCK are critically involved in angiotensin II (Ang II)-induced migration of vascular smooth muscle cells (VSMCs) by mediating a specific signal cross-talk.

METHODS AND RESULTS

Immunoblotting demonstrated that Ang II stimulated phosphorylation of a ROCK substrate, regulatory myosin phosphatase targeting subunit (MYPT)-1. Phosphorylation of MYPT-1 as well as migration of VSMCs induced by Ang II was inhibited by dominant-negative Rho (dnRho) or ROCK inhibitor, Y27632. Ang II-induced c-Jun NH2-terminal kinase (JNK) activation, but extracellular signal-regulated kinase (ERK) activation was not mediated through Rho/ROCK. Thus, infection of adenovirus encoding dnJNK inhibited VSMC migration by Ang II. We have further demonstrated that the Rho/ROCK activation by Ang II requires protein kinase C-delta (PKCdelta) and proline-rich tyrosine kinase 2 (PYK2) activation, but not epidermal growth factor receptor transactivation. Also, VSMCs express PDZ-Rho guanine nucleotide exchange factor (GEF) and Ang II stimulated PYK2 association with tyrosine phosphorylated PDZ-RhoGEF.

CONCLUSIONS

PKCdelta/PYK2-dependent Rho/ROCK activation through PDZ-RhoGEF mediates Ang II-induced VSMC migration via JNK activation in VSMCs, providing a novel mechanistic role of the Rho/ROCK cascade that is involved in vascular remodeling.

Depletion of serum response factor by RNA interference mimics the mitogenic effects of platelet derived growth factor-BB in vascular smooth muscle cells

Promoters of many smooth muscle-specific genes (SM-genes) contain multiple CArG boxes, which represent a binding site for serum response factor (SRF). Transcriptional control through these regions involves interactions with SRF and specific coactivators such as myocardin. We have previously reported that suppression of SM-gene expression by platelet derived growth factor (PDGF) is associated with redistribution of SRF, leading to lower intra-nuclear levels, and a reduction in SRF transactivation. To further assess the role of SRF depletion on VSMC phenotype, the current study used RNA interference (RNAi). Two SRF-specific sequences constructed as hairpins were stably expressed in rat VSMC. Clones expressing SRF RNAi had no detectable SRF expression by immunoblotting, and showed diminished levels of SM alpha-actin protein and promoter activity. Unexpectedly, depletion of VSMC resulted in increased rates of proliferation and migration. Several genes whose expression is increased by PDGF stimulation, including c-Jun, were similarly induced in cells lacking SRF. Effects of SRF depletion were not attributable to altered PDGF receptor activity or alterations in activation of Akt. These data indicate that loss of SRF transactivation in VSMC, in this case through suppression via RNAi, induces biological responses similar to that seen with PDGF.

Stress-activated protein kinases mediate cell migration in human airway epithelial cells

Airway epithelial cell (AEC) repair immediately after injury requires coordinated cell spreading and migration at the site of injury. Stress-activated protein kinases such as p38 MAPK and c-Jun N-terminal Protein Kinase (JNK) modulate several responses to cell stress and injury, but their role in AEC migration is not clear. We examined migration in confluent 16HBE14o(-) human AEC lines and in primary AEC grown on collagen-IV. Wounds were created by mechanical abrasion and followed to closure using digital microscopy. Inhibitors of either p38 extracellular signal-regulated kinase (ERK)1/2 (PD98059), mitogen-activated protein kinase (MAPK) (SB203580), or JNK (SP600125) could block cell migration substantially. Inhibiting JNK but not p38 MAPK or ERK1/2 blocked extension of cells into the wound region from the original line of injury. Initial migration was associated with phosphorylation of ERK, p38 MAPK, and JNK within 5-15 min. The downstream effector of p38, heat shock protein 27, also was phosphorylated rapidly after injury; phosphorylation could be blocked by prior treatment with SB203580 but not SP600125. The downstream effector of JNK, c-Jun, likewise was phosphorylated rapidly after injury and could be blocked by inhibiting JNK. Our data demonstrate that p38 MAPK, JNK, and ERK1/2 participate in the early stages of AEC migration.

c-Jun N-terminal kinase regulates lamellipodial protrusion and cell sheet migration during epithelial wound closure by a gene expression-independent mechanism

c-Jun N-terminal kinase (JNK) is emerging as an important regulator of cell migration. Perturbing the JNK signaling pathway with three structurally and mechanistically distinct inhibitors that selectively target either JNKs themselves or the upstream mixed-lineage kinases, we found dramatic inhibition of membrane protrusion and cell sheet migration during wound closure in Madin-Darby canine kidney (MDCK) epithelial cell monolayers. Extension of lamellipodia is blocked from the earliest times after wounding in the presence of JNK pathway inhibitors, whereas assembly of non-protrusive actin bundles at the wound margin is unaffected. Inhibitors of the other mitogen-activated protein kinase (MAPK) pathways, the extracellular signal-regulated kinase and p38 MAPK pathways, only have comparatively weak or marginal inhibitory effects on wound closure. Multiple splice variants of both JNK1 and JNK2 are expressed in MDCK cells, and JNK1 and JNK2 are rapidly and transiently activated upon wounding. Phosphorylation of c-Jun does not appear relevant to MDCK wound closure, and membrane protrusion directly after wounding is not affected by inhibitors of RNA or protein synthesis. While most known substrates of JNK are transcription factors or proteins regulating apoptosis, our data indicate that JNK regulates protrusion and migration in a gene expression-independent manner and suggest an important cytoplasmic role for JNK in the control of cell motility.