NFATc1 targets cyclin A in the regulation of vascular smooth muscle cell multiplication during restenosis

NFAT activation by FKBP52 promotes cancer cell proliferation by suppressing p53

FK506-binding protein 52 (FKBP52) is a member of the FKBP family of proline isomerases. FKBP52 is up-regulated in various cancers and functions as a positive regulator of steroid hormone receptors. Depletion of FKBP52 is known to inhibit cell proliferation; however, the detailed mechanism remains poorly understood. In this study, we found that FKBP52 depletion decreased MDM2 transcription, leading to stabilization of p53, and suppressed cell proliferation. We identified NFATc1 and NFATc3 as transcription factors that regulate MDM2 We also found that FKBP52 associated with NFATc3 and facilitated its nuclear translocation. In addition, calcineurin, a well-known Ca2+ phosphatase essential for activation of NFAT, plays a role in MDM2 transcription. Supporting this notion, MDM2 expression was found to be regulated by intracellular Ca2+ Taken together, these findings reveal a new role of FKBP52 in promoting cell proliferation via the NFAT-MDM2-p53 axis, and indicate that inhibition of FKBP52 could be a new therapeutic tool to activate p53 and inhibit cell proliferation.

Cucurbitacins mitigate vascular neointimal hyperplasia by suppressing cyclin A2 expression and inhibiting VSMC proliferation

BACKGROUND

Restenosis frequently occurs after percutaneous angioplasty in patients with vascular occlusion and seriously threatens their health. Substantial evidence has revealed that preventing vascular smooth muscle cell proliferation using a drug-eluting stent is an effective approach to improve restenosis. Cucurbitacins have been demonstrated to exert an anti-proliferation effect in various tumors and a hypotensive effect. This study aims to investigate the role of cucurbitacins extracted from Cucumis melo L. (CuECs) and cucurbitacin B (CuB) on restenosis.

METHODS

C57BL/6 mice were subjected to left carotid artery ligation and subcutaneously injected with CuECs or CuB for 4 weeks. Hematoxylin-Eosin, immunofluorescence and immunohistochemistry staining were used to evaluate the effect of CuECs and CuB on neointimal hyperplasia. Western blot, real-time PCR, flow cytometry analysis, EdU staining and cellular immunofluorescence assay were employed to measure the effects of CuECs and CuB on cell proliferation and the cell cycle in vitro. The potential interactions of CuECs with cyclin A2 were performed by molecular docking.

RESULTS

The results demonstrated that both CuECs and CuB exhibited significant inhibitory effects on neointimal hyperplasia and proliferation of vascular smooth muscle cells. Furthermore, CuECs and CuB mediated cell cycle arrest at the S phase. Autodocking analysis demonstrated that CuB, CuD, CuE and CuI had high binding energy for cyclin A2. Our study also showed that CuECs and CuB dramatically inhibited FBS-induced cyclin A2 expression. Moreover, the expression of cyclin A2 in CuEC- and CuB-treated neointima was downregulated.

CONCLUSIONS

CuECs, especially CuB, exert an anti-proliferation effect in VSMCs and may be potential drugs to prevent restenosis.

The Exacerbating Effects of the Tumor Necrosis Factor in Cardiovascular Stenosis: Intimal Hyperplasia

TNF-α functions as a master regulator of inflammation, and it plays a prominent role in several immunological diseases. By promoting important cellular mechanisms, such as cell proliferation, migration, and phenotype switch, TNF-α induces its exacerbating effects, which are the underlying cause of many proliferative diseases such as cancer and cardiovascular disease. TNF-α primarily alters the immune component of the disease, which subsequently affects normal functioning of the cells. Monoclonal antibodies and synthetic drugs that can target TNF-α and impair its effects have been developed and are currently used in the treatment of a few select human diseases. Vascular restenosis is a proliferative disorder that is initiated by immunological mechanisms. In this review, the role of TNF-α in exacerbating restenosis resulting from neointimal hyperplasia, as well as molecular mechanisms and cellular processes affected or induced by TNF-α, are discussed. As TNF-α-targeting drugs are currently not approved for the treatment of restenosis, the summation of the topics discussed here is anticipated to provide information that can emphasize on the use of TNF-α-targeting drug candidates to prevent vascular restenosis.

A Senolytic-Eluting Coronary Stent for the Prevention of In-Stent Restenosis

The vast majority of drug-eluting stents (DES) elute either sirolimus or one of its analogues. While limus drugs stymie vascular smooth muscle cell (VSMC) proliferation to prevent in-stent restenosis, their antiproliferative nature is indiscriminate and limits healing of the endothelium in stented vessels, increasing the risk of late-stent thrombosis. Oxidative stress, which is associated with vascular injury from stent implantation, can induce VSMCs to undergo senescence, and senescent VSMCs can produce pro-inflammatory cytokines capable of inducing proliferation of neighboring nonsenescent VSMCs. We explored the potential of senolytic therapy, which involves the selective elimination of senescent cells, in the form of a senolytic-eluting stent (SES) for interventional cardiology. Oxidative stress was modeled in vitro by exposing VSMCs to H₂O₂, and H₂O₂-mediated senescence was evaluated by cytochemical staining of senescence-associated β-galactosidase activity and qRT-PCR. Quiescent VSMCs were then treated with the conditioned medium (CM) of H₂O₂-treated VSMCs. Proliferative effects of CM were analyzed by staining for proliferating cell nuclear antigen. Senolytic effects of the first-generation senolytic ABT263 were observed in vitro, and the effects of ABT263 on endothelial cells were also investigated through an in vitro re-endothelialization assay. SESs were prepared by dip coating. Iliofemoral arteries of hypercholesteremic rabbits were implanted with SES, everolimus-eluting stents (EESs), or bare-metal stents (BMSs), and the area of stenosis was measured 4 weeks post-implantation using optical coherence tomography. We found that a portion of H₂O₂-treated VSMCs underwent senescence, and that CM of H₂O₂-treated senescent VSMCs triggered the proliferation of quiescent VSMCs. ABT263 reverted H₂O₂-mediated senescence and the proliferative capacity of senescent VSMC CM. Unlike everolimus, ABT263 did not affect endothelial cell migration and/or proliferation. SES, but not EES, significantly reduced stenosis area in vivo compared with bare-metal stents (BMSs). This study shows the potential of SES as an alternative to current forms of DES.

Silence of Insulin-Like Growth Factor 2 mRNA-Binding Protein 1 Prevents Vascular Smooth Muscle Cells Proliferation via Nuclear Factor of Activated T Cells Isoform-3/Ca2+/Calmodulin Pathway

Increased proliferation of vascular smooth muscle cells (VSMCs) contributes to the pathogenesis of atherosclerosis (AS), and the insulin like growth factor 2 (IGF2) is involved in AS through effects on VSMCs growth and migration. The IGF2 mRNA-binding protein 1(IGF2BP1) is a secreted protein that can bind to IGF2 and regulate its localization, however, whether IGF2BP1 could regulate VSMCs proliferation remains to be elucidated. This study aimed to investigate the role of IGF2BP1 in VSMCs proliferation and uncover the potential mechanism. Primary human aortic VSMCs that transfected with or without shRNA-IGF2BP1 were stimulated by platelet-derived growth factor-BB (PDGF-BB), and then cell proliferation, intracellular Ca2+ level, cell apoptosis and the expression of IGF2BP1, calmodulin (CaM) and cell cycle-related proteins were detected. RNA pull down assay was used to determine the interaction between IGF2BP1 and nuclear factor of activated T cells isoform-3 (NFATc3). We found that PDGF-BB promoted cell proliferation and enhanced IGF2BP1 protein expression in a concentration-dependent manner. The 10 μg/L PDGF-BB significantly increased intracellular Ca2+ level, NFATc3, CaM and calcineurin A protein expression, TUNEL-positive cells, and the expression of cell cycle-related proteins cyclin D1/E1/B1. However, knockdown of IGF2BP1 significantly blunted all these effects induced by PDGF-BB. In addition, IGF2BP1 could bind to NFATc3 RNA. Collectively, knockdown of IGF2BP1 could inhibit PDGFBB- induced VSMCs proliferation via targeting NFATc3/Ca2+/calmodulin pathway and disturbing the effect of NFATc3/ on cell cycle.

Hematopoietic Stem Cell Transcription Factors in Cardiovascular Pathology

Transcription factors as multifaceted modulators of gene expression that play a central role in cell proliferation, differentiation, lineage commitment, and disease progression. They interact among themselves and create complex spatiotemporal gene regulatory networks that modulate hematopoiesis, cardiogenesis, and conditional differentiation of hematopoietic stem cells into cells of cardiovascular lineage. Additionally, bone marrow-derived stem cells potentially contribute to the cardiovascular cell population and have shown potential as a therapeutic approach to treat cardiovascular diseases. However, the underlying regulatory mechanisms are currently debatable. This review focuses on some key transcription factors and associated epigenetic modifications that modulate the maintenance and differentiation of hematopoietic stem cells and cardiac progenitor cells. In addition to this, we aim to summarize different potential clinical therapeutic approaches in cardiac regeneration therapy and recent discoveries in stem cell-based transplantation.

NFATc1-E2F1-LMCD1-Mediated IL-33 Expression by Thrombin Is Required for Injury-Induced Neointima Formation

Objective- IL (interleukin)-33 has been shown to play a role in endothelial dysfunction, but its role in atherosclerosis is controversial. Therefore, the purpose of this study is to examine its role in vascular wall remodeling following injury. Approach and Results- Thrombin induced IL-33 expression in a time-dependent manner in human aortic smooth muscle cells and inhibition of its activity by its neutralizing antibody suppressed thrombin induced human aortic smooth muscle cell migration but not DNA synthesis. In exploring the mechanisms, we found that Par1 (protease-activated receptor 1), Gαq/11 (Gα protein q/11), PLCβ3 (phospholipase Cβ3), NFATc1 (nuclear factor of activated T cells), E2F1 (E2F transcription factor 1), and LMCD1 (LIM and cysteine-rich domains protein 1) are involved in thrombin-induced IL-33 expression and migration. Furthermore, we identified an NFAT-binding site at -100 nt that mediates thrombin-induced IL-33 promoter activity. Interestingly, we observed that NFATc1, E2F1, and LMCD1 bind to NFAT site in response to thrombin and found that LMCD1, while alone has no significant effect, enhanced either NFATc1 or E2F1-dependent IL-33 promoter activity. In addition, we found that guidewire injury induces IL-33 expression in SMC and its neutralizing antibodies substantially reduce SMC migration and neointimal growth in vivo. Increased expression of IL-33 was also observed in human atherosclerotic lesions as compared to arteries without any lesions. Conclusions- The above findings reveal for the first time that thrombin-induced human aortic smooth muscle cell migration and injury-induced neointimal growth require IL-33 expression. In addition, thrombin-induced IL-33 expression requires LMCD1 enhanced combinatorial activation of NFATc1 and E2F1.

LIM and cysteine-rich domains 1 is required for thrombin-induced smooth muscle cell proliferation and promotes atherogenesis

Restenosis arises after vascular injury and is characterized by arterial wall thickening and decreased arterial lumen space. Vascular injury induces the production of thrombin, which in addition to its role in blood clotting acts as a mitogenic and chemotactic factor. In exploring the molecular mechanisms underlying restenosis, here we identified LMCD1 (LIM and cysteine-rich domains 1) as a gene highly responsive to thrombin in human aortic smooth muscle cells (HASMCs). Of note, LMCD1 depletion inhibited proliferation of human but not murine vascular smooth muscle cells. We also found that by physically interacting with E2F transcription factor 1, LMCD1 mediates thrombin-induced expression of the CDC6 (cell division cycle 6) gene in the stimulation of HASMC proliferation. Thrombin-induced LMCD1 and CDC6 expression exhibited a requirement for protease-activated receptor 1-mediated Gα_q/11-dependent activation of phospholipase C β3. Moreover, the expression of LMCD1 was highly induced in smooth muscle cells located at human atherosclerotic lesions and correlated with CDC6 expression and that of the proliferation marker Ki67. Furthermore, the LMCD1- and SMCαactin-positive cells had higher cholesterol levels in the atherosclerotic lesions. In conclusion, these findings indicate that by acting as a co-activator with E2F transcription factor 1 in CDC6 expression, LMCD1 stimulates HASMC proliferation and thereby promotes human atherogenesis, suggesting an involvement of LMCD1 in restenosis.

Wnt signaling in cardiovascular disease: opportunities and challenges

PURPOSE OF REVIEW

Cardiometabolic diseases increasingly afflict our aging, dysmetabolic population. Complex signals regulating low-density lipoprotein receptor-related protein (LRP) and frizzled protein family members - the plasma membrane receptors for the cadre of Wnt polypeptide morphogens - contribute to the control of cardiovascular homeostasis.

RECENT FINDINGS

Both canonical (β-catenin-dependent) and noncanonical (β-catenin-independent) Wnt signaling programs control vascular smooth muscle (VSM) cell phenotypic modulation in cardiometabolic disease. LRP6 limits VSM proliferation, reduces arteriosclerotic transcriptional reprogramming, and preserves insulin sensitivity while LRP5 restrains foam cell formation. Adipose, skeletal muscle, macrophages, and VSM have emerged as important sources of circulating Wnt ligands that are dynamically regulated during the prediabetes-diabetes transition with cardiometabolic consequences. Platelets release Dkk1, a LRP5/LRP6 inhibitor that induces endothelial inflammation and the prosclerotic endothelial-mesenchymal transition. By contrast, inhibitory secreted frizzled-related proteins shape the Wnt signaling milieu to limit myocardial inflammation with ischemia-reperfusion injury. VSM sclerostin, an inhibitor of canonical Wnt signaling in bone, restrains remodeling that predisposes to aneurysm formation, and is downregulated in aneurysmal vessels by epigenetic methylation.

SUMMARY

Components of the Wnt signaling cascade represent novel targets for pharmacological intervention in cardiometabolic disease. Conversely, strategies targeting the Wnt signaling cascade for other therapeutic purposes will have cardiovascular consequences that must be delineated to establish clinically useful pharmacokinetic-pharmacodynamic relationships.

CD137-CD137L interaction modulates neointima formation and the phenotype transformation of vascular smooth muscle cells via NFATc1 signaling

Vascular smooth muscle cell (VSMC) phenotype transformation is an important event in the formation of vessel neointima during lesion progression. CD137 can accelerate plaque formation, but the underlying mechanisms of this process remain unknown. Thus, we investigated the effect of CD137 signaling on VSMC phenotype transformation and potential mechanism underlying this transformation. Mouse recombinant CD137L and anti-CD137 antibody were used to activate or block the CD137 signaling way, respectively. Real-time PCR, immunofluorescence, and western blot analyses were performed to detect the expression of NFATc1 and phenotype markers such as SM-MHC, α-SMA, and vimentin in vivo or in vitro. Inhibition of NFATc1 expression was established by small interfering RNA (siRNA) and lentivirus in vitro and in vivo, respectively. Plenti-virus vector was constructed to overexpress NFATc1. Transwell assay was used to detect the migration ability of cells. The expression of NFATc1 was significantly upregulated by treating VSMCs with CD137L. The contractile phenotype markers decreased, while the synthesis phenotype marker and cell migration increased after CD137 stimulation. This phenomenon can be blocked by combined use of anti-CD137 antibody or siRNA of NFATc1. Overexpression of NFATc1 caused the VSMC phenotype transformation independently. In conclusion, the CD137-CD137L pathway plays an important role in regulating VSMC phenotype transformation via activation of NFATc1 signaling pathway.

Cell cycle and apoptosis regulation by NFAT transcription factors: new roles for an old player

The NFAT (nuclear factor of activated T cells) family of transcription factors consists of four Ca²⁺-regulated members (NFAT1–NFAT4), which were first described in T lymphocytes. In addition to their well-documented role in T lymphocytes, where they control gene expression during cell activation and differentiation, NFAT proteins are also expressed in a wide range of cells and tissue types and regulate genes involved in cell cycle, apoptosis, angiogenesis and metastasis. The NFAT proteins share a highly conserved DNA-binding domain (DBD), which allows all NFAT members to bind to the same DNA sequence in enhancers or promoter regions. The same DNA-binding specificity suggests redundant roles for the NFAT proteins, which is true during the regulation of some genes such as IL-2 and p21. However, it has become increasingly clear that different NFAT proteins and even isoforms can have unique functions. In this review, we address the possible reasons for these distinct roles, particularly regarding N- and C-terminal transactivation regions (TADs) and the partner proteins that interact with these TADs. We also discuss the genes regulated by NFAT during cell cycle regulation and apoptosis and the role of NFAT during tumorigenesis.

Cyclosporin A induces cardiac differentiation but inhibits hemato-endothelial differentiation of P19 cells

Little is known about the mechanisms underlying the effects of Cyclosporin A (CsA) on the fate of stem cells, including cardiomyogenic differentiation. Therefore, we investigated the effects and the molecular mechanisms behind the actions of CsA on cell lineage determination of P19 cells. CsA induced cardiomyocyte-specific differentiation of P19 cells, with the highest efficiency at a concentration of 0.32 μM during embryoid body (EB) formation via activation of the Wnt signaling pathway molecules, Wnt3a, Wnt5a, and Wnt8a, and the cardiac mesoderm markers, Mixl1, Mesp1, and Mesp2. Interestingly, cotreatment of P19 cells with CsA plus dimethyl sulfoxide (DMSO) during EB formation significantly increases cardiac differentiation. In contrast, mRNA expression levels of hematopoietic and endothelial lineage markers, including Flk1 and Er71, were severely reduced in CsA-treated P19 cells. Furthermore, expression of Flk1 protein and the percentage of Flk1+ cells were severely reduced in 0.32 μM CsA-treated P19 cells compared to control cells. CsA significantly modulated mRNA expression levels of the cell cycle molecules, p53 and Cyclins D1, D2, and E2 in P19 cells during EB formation. Moreover, CsA significantly increased cell death and reduced cell number in P19 cells during EB formation. These results demonstrate that CsA induces cardiac differentiation but inhibits hemato-endothelial differentiation via activation of the Wnt signaling pathway, followed by modulation of cell lineage-determining genes in P19 cells during EB formation.

Effects of OX40-OX40L interaction on the nuclear factor of activated T cells c1 in ApoE-deficient mice

We previously reported the emerging role of OX40-OX40L interaction in inflammation and atherosclerosis. However, the mechanism by which OX40-OX40L interaction contributes to pathogenesis is poorly understood. This study investigated the effects of OX40-OX40L interaction on the nuclear factor of activated T cells c1 (NFATc1) in ApoE(-/-) mice. Atherosclerotic plaque was induced via rapid perivascular carotid collar placement in ApoE(-/-) mice. The expression levels of OX40, OX40L, and NFATc1 in the lymphocytes were measured via real-time polymerase chain reaction and flow cytometry. The presence of NFATc1 in the atherosclerotic plaque was detected via immunohistochemistry, and the level of IL-4 was measured via enzyme-linked immunosorbent assay. The expression level of NFATc1 significantly increased in atherosclerotic lesion and in the leukocytes from the ApoE(-/-) mice. After stimulating OX40-OX40L interaction, the mRNA and protein expression levels of NFATc1 in the lymphocytes significantly increased. Meanwhile, anti-OX40LmAb significantly suppressed the expression of NFATc1 in the leukocytes and substantially elevated the level of IL-4. NFATc1 inhibitor markedly suppressed IL-4 production. This study suggests that OX40-OX40L interaction regulates the expression of NFATc1, which may play a critical role in atherosclerotic plaque formation, and may therefore have implications with pathophysiology of atherosclerosis.

ERK activation is required for CCK-mediated pancreatic adaptive growth in mice

High levels of cholecystokinin (CCK) can stimulate pancreatic adaptive growth in which mature acinar cells divide, leading to enhanced pancreatic mass with parallel increases in protein, DNA, RNA, and digestive enzyme content. Prolonged release of CCK can be induced by feeding trypsin inhibitor (TI) to disrupt normal feedback control. This leads to exocrine growth in a CCK-dependent manner. The extracellular signal-related kinase (ERK) pathway regulates many proliferative processes in various tissues and disease models. The aim of this study was to evaluate the role of ERK signaling in pancreatic adaptive growth using the MEK inhibitors PD-0325901 and trametinib (GSK-1120212). It was determined that PD-0325901 given two times daily by gavage or mixed into powdered chow was an effective and specific inhibitor of ERK signaling in vivo. TI-containing chow led to a robust increase in pancreatic mass, protein, DNA, and RNA content. This pancreatic adaptive growth was blocked in mice fed chow containing the MEK inhibitors. PD-0325901 blocked TI-induced ERK-regulated early response genes, cell-cycle proteins, and mitogenesis by acinar cells. It was determined that ERK signaling is necessary for the initiation of pancreatic adaptive growth but not necessary to maintain it. PD-0325901 blocked adaptive growth when given before cell-cycle initiation but not after mitogenesis had been established. Furthermore, GSK-1120212, a chemically distinct inhibitor of the ERK pathway that is now approved for clinical use, inhibited growth similar to PD-0325901. These data demonstrate that the ERK pathway is required for CCK-stimulated pancreatic adaptive growth.

Store-operated CRAC channels regulate gene expression and proliferation in neural progenitor cells

Calcium signals regulate many critical processes during vertebrate brain development including neurogenesis, neurotransmitter specification, and axonal outgrowth. However, the identity of the ion channels mediating Ca(2+) signaling in the developing nervous system is not well defined. Here, we report that embryonic and adult mouse neural stem/progenitor cells (NSCs/NPCs) exhibit store-operated Ca(2+) entry (SOCE) mediated by Ca(2+) release-activated Ca(2+) (CRAC) channels. SOCE in NPCs was blocked by the CRAC channel inhibitors La(3+), BTP2, and 2-APB and Western blots revealed the presence of the canonical CRAC channel proteins STIM1 and Orai1. Knock down of STIM1 or Orai1 significantly diminished SOCE in NPCs, and SOCE was lost in NPCs from transgenic mice lacking Orai1 or STIM1 and in knock-in mice expressing the loss-of-function Orai1 mutant, R93W. Therefore, STIM1 and Orai1 make essential contributions to SOCE in NPCs. SOCE in NPCs was activated by epidermal growth factor and acetylcholine, the latter occurring through muscarinic receptors. Activation of SOCE stimulated gene transcription through calcineurin/NFAT (nuclear factor of activated T cells) signaling through a mechanism consistent with local Ca(2+) signaling by Ca(2+) microdomains near CRAC channels. Importantly, suppression or deletion of STIM1 and Orai1 expression significantly attenuated proliferation of embryonic and adult NPCs cultured as neurospheres and, in vivo, in the subventricular zone of adult mice. These findings show that CRAC channels serve as a major route of Ca(2+) entry in NPCs and regulate key effector functions including gene expression and proliferation, indicating that CRAC channels are important regulators of mammalian neurogenesis.

Vein graft failure

After the creation of an autogenous lower extremity bypass graft, the vein must undergo a series of dynamic structural changes to stabilize the arterial hemodynamic forces. These changes, which are commonly referred to as remodeling, include an inflammatory response, the development of a neointima, matrix turnover, and cellular proliferation and apoptosis. The sum total of these processes results in dramatic alterations in the physical and biomechanical attributes of the arterialized vein. The most clinically obvious and easily measured of these is lumen remodeling of the graft. However, although somewhat less precise, wall thickness, matrix composition, and endothelial changes can be measured in vivo within the healing vein graft. Recent translational work has demonstrated the clinical relevance of remodeling as it relates to vein graft patency and the systemic factors influencing it. By correlating histologic and molecular changes in the vein, insights into potential therapeutic strategies to prevent bypass failure and areas for future investigation are explored.

Nuclear factor of activated T cells c1 mediates p21-activated kinase 1 activation in the modulation of chemokine-induced human aortic smooth muscle cell F-actin stress fiber formation, migration, and proliferation and injury-induced vascular wall remodeling

Recent literature suggests that cyclin-dependent kinases (CDKs) mediate cell migration. However, the mechanisms were not known. Therefore, the objective of this study is to test whether cyclin/CDKs activate Pak1, an effector of Rac1, whose involvement in the modulation of cell migration and proliferation is well established. Monocyte chemotactic protein 1 (MCP1) induced Pak1 phosphorylation/activation in human aortic smooth muscle cells (HASMCs) in a delayed time-dependent manner. MCP1 also stimulated F-actin stress fiber formation in a delayed manner in HASMCs, as well as the migration and proliferation of these cells. Inhibition of Pak1 suppressed MCP1-induced HASMC F-actin stress fiber formation, migration, and proliferation. MCP1 induced cyclin D1 expression as well as CDK6 and CDK4 activities, and these effects were dependent on activation of NFATc1. Depletion of NFATc1, cyclin D1, CDK6, or CDK4 levels attenuated MCP1-induced Pak1 phosphorylation/activation and resulted in decreased HASMC F-actin stress fiber formation, migration, and proliferation. CDK4, which appeared to be activated downstream of CDK6, formed a complex with Pak1 in response to MCP1. MCP1 also activated Rac1 in a time-dependent manner, and depletion/inhibition of its levels/activation abrogated MCP1-induced NFATc1-cyclin D1-CDK6-CDK4-Pak1 signaling and, thereby, decreased HASMC F-actin stress fiber formation, migration, and proliferation. In addition, smooth muscle-specific deletion of NFATc1 led to decreased cyclin D1 expression and CDK6, CDK4, and Pak1 activities, resulting in reduced neointima formation in response to injury. Thus, these observations reveal that Pak1 is a downstream effector of CDK4 and Rac1-dependent, NFATc1-mediated cyclin D1 expression and CDK6 activity mediate this effect. In addition, smooth muscle-specific deletion of NFATc1 prevented the capacity of vascular smooth muscle cells for MCP-1-induced activation of the cyclin D1-CDK6-CDK4-Pak1 signaling axis, affecting their migration and proliferation in vitro and injury-induced neointima formation in vivo.

OX40-OX40L interaction promotes proliferation and activation of lymphocytes via NFATc1 in ApoE-deficient mice

Background

Our previous studies have shown that OX40-OX40L interaction regulates the expression of nuclear factor of activated T cells c1(NFATc1) in ApoE^−/− mice during atherogenesis. The aim of this study was to investigate whether OX40-OX40L interaction promotes Th cell activation via NFATc1 in ApoE^−/− mice.

Methods and Results

The lymphocytes isolated from spleen of ApoE^−/− mice were cultured with anti-CD3 mAb in the presence or absence of anti-OX40 or anti-OX40L antibodies. The expression of NFATc1 mRNA and protein in isolated lymphocytes were measured by real time PCR (RT-PCR) and flow cytometry (FCM), respectively. The proliferation of lymphocytes was analyzed by MTT method,and the expression of IL-2, IL-4 and IFN-γ in the cultured cells and supernatant were measured by RT-PCR and enzyme-linked immunosorbent assary (ELISA), respectively. After stimulating OX40-OX40L signal pathway, the expression of NFATc1 and the proliferation of leukocytes were significantly increased. Anti-OX40L suppressed the expression of NFATc1 in lymphocytes of ApoE−/− mice. Anti-OX40L or the NFATc1 inhibitor (CsA) markedly suppressed the cell proliferation induced by anti-OX40. Moreover, the expression of IL-2 and IFN-γ was increased in lymphocytes induced by OX40-OX40L interaction. Blocking OX40-OX40L interaction or NFATc1 down-regulated the expression of IL-2 and IFN-γ, but didn’t alter the expression of IL-4 in supernatants.

Conclusion

These results suggest that OX40-OX40L interaction promotes the proliferation and activation of lymphocytes through NFATc1.

Neonatal β cell development in mice and humans is regulated by calcineurin/NFAT

Little is known about the mechanisms governing neonatal growth and maturation of organs. Here we demonstrate that calcineurin/Nuclear Factor of Activated T cells (Cn/NFAT) signaling regulates neonatal pancreatic development in mouse and human islets. Inactivation of calcineurin b1 (Cnb1) in mouse islets impaired dense core granule biogenesis, decreased insulin secretion, and reduced cell proliferation and mass, culminating in lethal diabetes. Pancreatic β cells lacking Cnb1 failed to express genes revealed to be direct NFAT targets required for replication, insulin storage, and secretion. In contrast, glucokinase activation stimulated Cn-dependent expression of these genes. Calcineurin inhibitors, such as tacrolimus, used for human immunosuppression, induce diabetes. Tacrolimus exposure reduced Cn/NFAT-dependent expression of factors essential for insulin dense core granule formation and secretion and neonatal β cell proliferation, consistent with our genetic studies. Discovery of conserved pathways regulating β cell maturation and proliferation suggests new strategies for controlling β cell growth or replacement in human islet diseases.

Protein kinase N1 is a novel substrate of NFATc1-mediated cyclin D1-CDK6 activity and modulates vascular smooth muscle cell division and migration leading to inward blood vessel wall remodeling

Toward understanding the mechanisms of vascular wall remodeling, here we have studied the role of NFATc1 in MCP-1-induced human aortic smooth muscle cell (HASMC) growth and migration and injury-induced rat aortic wall remodeling. We have identified PKN1 as a novel downstream target of NFATc1-cyclin D1/CDK6 activity in mediating vascular wall remodeling following injury. MCP-1, a potent chemoattractant protein, besides enhancing HASMC motility, also induced its growth, and these effects require NFATc1-dependent cyclin D1 expression and CDK4/6 activity. In addition, MCP-1 induced PKN1 activation in a sustained and NFATc1-cyclin D1/CDK6-dependent manner. Furthermore, PKN1 activation is required for MCP-1-induced HASMC growth and migration. Balloon injury induced PKN1 activation in NFAT-dependent manner and pharmacological or dominant negative mutant-mediated blockade of PKN1 function or siRNA-mediated down-regulation of its levels substantially suppressed balloon injury-induced smooth muscle cell migration and proliferation resulting in reduced neointima formation. These novel findings suggest that PKN1 plays a critical role in vascular wall remodeling, and therefore, it could be a promising new target for the next generation of drugs for vascular diseases, particularly restenosis following angioplasty, stent implantation, or vein grafting.

Novel interactions between NFATc1 (Nuclear Factor of Activated T cells c1) and STAT-3 (Signal Transducer and Activator of Transcription-3) mediate G protein-coupled receptor agonist, thrombin-induced biphasic expression of cyclin D1, with first phase influencing cell migration and second phase directing cell proliferation

Thrombin, a G protein-coupled receptor agonist, induced a biphasic expression of cyclin D1 in primary vascular smooth muscle cells. Although both phases of cyclin D1 expression require binding of the newly identified cooperative complex, NFATc1·STAT-3, to its promoter, the second phase, which is more robust, depends on NFATc1-mediated recruitment of p300 onto the complex and the subsequent acetylation of STAT-3. In addition, STAT-3 is tyrosine-phosphorylated in a biphasic manner, and the late phase requires NFATc1-mediated p300-dependent acetylation. Furthermore, interference with acetylation of STAT-3 by overexpression of acetylation null STAT-3 mutant led to the loss of the late phase of cyclin D1 expression. EMSA analysis and reporter gene assays revealed that NFATc1·STAT-3 complex binding to the cyclin D1 promoter led to an enhanceosome formation and facilitated cyclin D1 expression. In the early phase of its expression, cyclin D1 is localized mostly in the cytoplasm and influenced cell migration. However, during the late and robust phase of its expression, cyclin D1 is translocated to the nucleus and directed cell proliferation. Together, these results demonstrate for the first time that the dual function of cyclin D1 in cell migration and proliferation is temperospatially separated by its biphasic expression, which is mediated by cooperative interactions between NFATc1 and STAT-3.

Estrogen controls embryonic stem cell proliferation via store-operated calcium entry and the nuclear factor of activated T-cells (NFAT)

Embryonic stem cells (ESCs) can self-renew indefinitely and differentiate into all cell lineages. Calcium is a universal second messenger which regulates a number of cellular pathways. Previous studies showed that store-operated calcium channels (SOCCs) but not voltage-operated calcium channels are present in mouse ESCs (mESCs). In this study, store-operated calcium entry (SOCE) was found to exist in mESCs using confocal microscopy. SOCC blockers lanthanum, 2-aminoethoxydiphenyl borate (2-APB) and SKF-96365 reduced mESC proliferation in a concentration-dependent manner, suggesting that SOCE is important for ESC proliferation. Pluripotent markers, Sox-2, Klf-4, and Nanog, were down-regulated by 2-APB, suggesting that self-renewal property of mESCs relies on SOCE. 17β-estradiol (E2) enhanced mESC proliferation. This enhanced proliferation was associated with an increment of SOCE. Both stimulated proliferation and increased SOCE could be reversed by SOCC blockers suggesting that E2 mediates its stimulatory effect on proliferation via enhancing SOCE. Also, cyclosporin A and INCA-6, inhibitors of calcineurin [phosphatase that de-phosphorylates and activates nuclear factor of activated T-cells (NFAT)], reversed the proliferative effect of E2, indicating that NFAT is involved in E2-stimulated proliferation. Interestingly, E2 caused the nuclear translocation of NFATc4, and this could be reversed by 2-APB. These results suggested that NFATc4 is the downstream target of E2-induced SOCE. The present investigation provides the first line of evidence that SOCE and NFAT are crucial for ESCs to maintain their unique characteristics. In addition, the present investigation also provides novel information on the mechanisms of how E2, an important female sex hormone, affects ESC proliferation.

Genome-wide microarray analyses identify the protein C receptor as a novel calcineurin/nuclear factor of activated T cells-dependent gene in vascular smooth muscle cell phenotypic modulation

OBJECTIVE

Calcineurin (Cn) and the nuclear factor of activated T cells (NFAT) family of transcription factors are critical in vascular smooth muscle cell (SMC) development and pathology. Here, we used a genomics approach to identify and validate NFAT gene targets activated during platelet-derived growth factor-BB (PDGF-BB)-induced SMC phenotypic modulation.

METHODS AND RESULTS

Genome-wide expression arrays were used to identify genes both (1) differentially activated in response to PDGF-BB and (2) whose differential expression was reduced by both the Cn inhibitor cyclosporin A and the NFAT inhibitor A-285222. The 20 most pharmacologically sensitive genes were validated by quantitative reverse transcription-polymerase chain reaction analysis of PDGF-BB-stimulated SMCs in the presence of Cn/NFAT inhibitors, including the VIVIT peptide. In all experiments, protein C receptor (PROCR) gene activation was reduced. We showed that PROCR expression was virtually absent in untreated, quiescent SMCs. PDGF-BB stimulation, however, induced significant PROCR promoter activation and downstream protein expression in a Cn/NFAT-dependent manner. Mutation of a species-conserved, NFAT binding motif significantly attenuated PDGF-BB-induced PROCR promoter activity, thereby distinguishing NFAT as the first PROCR transcriptional activator to date. Moreover, SMC PROCR expression was upregulated in the neointima as early as 7 days following acute vascular injury in rat carotid arteries.

CONCLUSION

We hereby report PROCR as a novel, NFAT-dependent gene that may be implicated in vascular restenosis and consequent inward remodeling.

Nuclear factor of activated T cells 5 regulates vascular smooth muscle cell phenotypic modulation

OBJECTIVE

The tonicity-responsive transcription factor, nuclear factor of activated T cells 5 (NFAT5/tonicity enhancer binding protein [TonEBP]), has been well characterized in numerous cell types; however, NFAT5 function in vascular smooth muscle cells (SMCs) is unknown. Our main objective was to determine the role of NFAT5 regulation in SMCs.

METHODS AND RESULTS

We showed that NFAT5 is regulated by hypertonicity in SMCs and is upregulated in atherosclerosis and neointimal hyperplasia. RNAi knockdown of NFAT5 inhibited basal expression of several SMC differentiation marker genes, including smooth muscle α actin (SMαA). Bioinformatic analysis of SMαA revealed 7 putative NFAT5 binding sites in the first intron, and chromatin immunoprecipitation analysis showed NFAT5 enrichment of intronic DNA. Overexpression of NFAT5 increased SMαA promoter-intron activity, which requires an NFAT5 cis element at +1012, whereas dominant-negative NFAT5 decreased SMαA promoter-intron activity. Because it is unlikely that SMCs experience extreme changes in tonicity, we investigated other stimuli and uncovered 2 novel NFAT5-inducing factors: angiotensin II, a contractile agonist, and platelet-derived growth factor-BB (PDGF-BB), a potent mitogen in vascular injury. Angiotensin II stimulated NFAT5 translocation and activity, and NFAT5 knockdown inhibited an angiotensin II-mediated upregulation of SMαA mRNA. PDGF-BB increased NFAT5 protein, and loss of NFAT5 inhibited PDGF-BB-induced SMC migration.

CONCLUSIONS

We have identified NFAT5 as a novel regulator of SMC phenotypic modulation and have uncovered the role of NFAT5 in angiotensin II-induced SMαA expression and PDGF-BB-stimulated SMC migration.

Activation of cytosolic phospholipase A2 downstream of the Src-phospholipase D1 (PLD1)-protein kinase C γ (PKCγ) signaling axis is required for hypoxia-induced pathological retinal angiogenesis

In view of understanding the mechanisms of retinal neovascularization, we had reported previously that vascular endothelial growth factor (VEGF)-induced pathological retinal angiogenesis requires the activation of Src-PLD1-PKCγ signaling. In the present work, we have identified cytosolic phospholipase A(2) (cPLA(2)) as an effector molecule of Src-PLD1-PKCγ signaling in the mediation of VEGF-induced pathological retinal angiogenesis based on the following observations. VEGF induced cPLA(2) phosphorylation in a time-dependent manner in human retinal microvascular endothelial cells (HRMVECs). VEGF also induced arachidonic acid (AA) release in a dose-, time-, and cPLA(2)-dependent manner. Depletion of cPLA(2) levels inhibited VEGF-induced HRMVEC DNA synthesis, migration, and tube formation. In addition, the exogenous addition of AA rescued VEGF-induced HRMVEC DNA synthesis, migration, and tube formation from inhibition by down-regulation of cPLA(2). Inhibition of Src, PLD1, or PKCγ attenuated VEGF-induced cPLA(2) phosphorylation and AA release. Consistent with these findings, hypoxia induced cPLA(2) phosphorylation and activity in VEGF-Src-PLD1-PKCγ-dependent manner in a mouse model of oxygen-induced retinopathy. In addition, siRNA-mediated down-regulation of cPLA(2) levels in the retina abrogated hypoxia-induced retinal endothelial cell proliferation and neovascularization. These observations suggest that cPLA(2)-dependent AA release is required for VEGF-induced Src-PLD1-PKCγ-mediated pathological retinal angiogenesis.

The neuropeptide catestatin promotes vascular smooth muscle cell proliferation through the Ca2+-calcineurin-NFAT signaling pathway

The Chromogranin A-derived neuropeptide catestatin is an endogenous nicotinic cholinergic antagonist that acts as a pleiotropic hormone. Since catestatin shares several functions with other members derived from the chromogranin/secretogranin protein family and other neuropeptides which exert proliferative effects on vascular smooth muscle cells (VSMCs), we therefore hypothesized that catestatin would regulate VSMC proliferation. The present study demonstrates that catestatin caused a dose-dependent induction of proliferation in rat aortic smooth muscle cells and furthermore evoked a sustained increase in intracellular calcium. This subsequently leaded to enhanced activation of the Ca(2+)/calmodulin-dependent phosphatase, calcineurin and resulted in an activation of the Ca(2+)-dependent transcription factor, nuclear factor of activated T cells (NFAT), initiating transcription of proliferative genes. In addition, cyclosporin A (CsA), a potent inhibitor of calcineurin, abrogated catestatin-mediated effect on VSMCs, indicating that the calcineurin-NFAT signaling is strongly required for catestatin-induced growth of VSMCs. The present study establishes catestatin as a novel proliferative cytokine on vascular smooth muscle cells and this effect is mediated by the Ca(2+)-calcineurin-NFAT signaling pathway.

PLD1-dependent PKCgamma activation downstream to Src is essential for the development of pathologic retinal neovascularization

Vascular endothelial growth factor (VEGF) appears to be an important mediator of pathologic retinal angiogenesis. In understanding the mechanisms of pathologic retinal neovascularization, we found that VEGF activates PLD1 in human retinal microvascular endothelial cells, and this event is dependent on Src. In addition, VEGF activates protein kinase C-gamma (PKCgamma) via Src-dependent PLD1 stimulation. Inhibition of Src, PLD1, or PKCgamma via pharmacologic, dominant negative mutant, or siRNA approaches significantly attenuated VEGF-induced human retinal microvascular endothelial cell migration, proliferation, and tube formation. Hypoxia also induced Src-PLD1-PKCgamma signaling in retina, leading to retinal neovascularization. Furthermore, siRNA-mediated down-regulation of VEGF inhibited hypoxia-induced Src-PLD1-PKCgamma activation and neovascularization. Blockade of Src-PLD1-PKCgamma signaling via the siRNA approach also suppressed hypoxia-induced retinal neovascularization. Thus, these observations demonstrate, for the first time, that Src-dependent PLD1-PKCgamma activation plays an important role in pathologic retinal angiogenesis.

Heme oxygenase-1/p21WAF1 mediates peroxisome proliferator-activated receptor-gamma signaling inhibition of proliferation of rat pulmonary artery smooth muscle cells

Activation of peroxisome proliferator-activated receptor (PPAR)-gamma suppresses proliferation of rat pulmonary artery smooth muscle cells (PASMCs), and therefore ameliorates the development of pulmonary hypertension in animal models. However, the molecular mechanisms underlying this effect remain largely unknown. This study addressed this issue. The PPARgamma agonist rosiglitazone dose-dependently stimulated heme oxygenase (HO)-1 expression in PASMCs, 5 microm rosiglitazone inducing a 12.1-fold increase in the HO-1 protein level. Cells pre-exposed to rosiglitazone showed a dose-dependent reduction in proliferation in response to serotonin; this was abolished by pretransfection of cells with sequence-specific small interfering RNA against HO-1. In addition, rosiglitazone stimulated p21(WAF1) expression in PASMCs, a 2.34-fold increase in the p21(WAF1) protein level being achieved with 5 microm rosiglitazone; again, this effect was blocked by knockdown of HO-1. Like loss of HO-1, loss of p21(WAF1) through siRNA transfection also reversed the inhibitory effect of rosiglitazone on PASMC proliferation triggered by serotonin. Taken together, our findings suggest that activation of PPARgamma induces HO-1 expression, and that this in turn stimulates p21(WAF1) expression to suppress PASMC proliferation. Our study also indicates that rosiglitazone, a medicine widely used in the treatment of type 2 diabetes mellitus, has potential benefits for patients with pulmonary hypertension.

Deregulated NFATc1 activity transforms murine fibroblasts via an autocrine growth factor-mediated Stat3-dependent pathway

The nuclear factor of activated T cells (NFAT) family of transcription factors has recently been implicated with a role in tumorigenesis. Forced expression of a constitutively active NFATc1 mutant (caNFATc1) has been shown to transform immortalized murine fibroblasts in vitro, while constitutive activation of the NFAT-signaling pathway has been found in a number of human cancers, where it has been shown to contribute towards various aspects of the tumor phenotype. Here we have investigated the molecular mechanisms underlying the oncogenic potential of deregulated NFAT activity. We now show that ectopic expression of caNFATc1 in murine 3T3-L1 fibroblasts induces the secretion of an autocrine factor(s) that is sufficient to promote the transformed phenotype. We further demonstrate that this NFATc1-induced autocrine factor(s) specifically induces the tyrosine phosphorylation of the Stat3 transcription factor via a JAK kinase-dependent pathway. Interestingly, this effect of sustained NFAT signaling on the autocrine growth factor-mediated activation of Stat3 is not restricted to murine fibroblasts, but is also observed in the PANC-1 and MCF10A human cell lines. Most importantly, we find that the shRNA-mediated depletion of endogenous Stat3 significantly attenuates the ability of caNFATc1 to transform 3T3-L1 fibroblasts. Taken together, our results afford significant new insights into the molecular mechanisms underlying the oncogenic potential of deregulated NFATc1 activity by demonstrating that constitutive NFATc1 activity transforms cells via an autocrine factor-mediated pathway that is critically dependent upon the activity of the Stat3 transcription factor.

Cyclin D1 is a bona fide target gene of NFATc1 and is sufficient in the mediation of injury-induced vascular wall remodeling

Platelet-derived growth factor BB induced cyclin D1 expression in a time- and nuclear factor of activated T cells (NFAT)-dependent manner in human aortic smooth muscle cells (HASMCs), and blockade of NFATs prevented HASMC DNA synthesis and their cell cycle progression from G(1) to S phase. Selective inhibition of NFATc1 by its small interfering RNA also blocked HASMC proliferation and migration. Characterization of the cyclin D1 promoter revealed the presence of several NFAT binding sites, and the site at nucleotide -1333 was found to be sufficient in mediating platelet-derived growth factor BB-induced cyclin D1 promoter-luciferase reporter gene activity. In addition to its role in cell cycle progression, cyclin D1 mediated HASMC migration in an NFATc1-dependent manner. Balloon injury-induced cyclin D1-CDK4 activity requires NFAT activation, and adenovirus-mediated transduction of cyclin D1 was found to be sufficient to overcome the blockade effect of NFATs by VIVIT on balloon injury-induced vascular wall remodeling events, including smooth muscle cell migration from the medial to luminal region, their proliferation in the intimal region, and neointima formation. Together, these results provide more mechanistic evidence for the role of NFATs, particularly NFATc1, in the regulation of HASMC proliferation and migration as well as vascular wall remodeling. NFATc1 could be a potential therapeutic target against the renarrowing of artery after angioplasty.

Integrative genomics identifies DSCR1 (RCAN1) as a novel NFAT-dependent mediator of phenotypic modulation in vascular smooth muscle cells

Vascular smooth muscle cells (SMCs) display remarkable phenotypic plasticity in response to environmental cues. The nuclear factor of activated T-cells (NFAT) family of transcription factors plays a critical role in vascular pathology. However, known functional NFAT gene targets in vascular SMCs are currently limited. Publicly available whole-genome expression array data sets were analyzed to identify differentially expressed genes in human, mouse and rat SMCs. Comparison between vehicle and phenotypic modulatory stimuli identified 63 species-conserved, upregulated genes. Integration of the 63 upregulated genes with an in silico NFAT-ome (a species-conserved list of gene promoters containing at least one NFAT binding site) identified 18 putative NFAT-dependent genes. Further intersection of these 18 potential NFAT target genes with a mouse in vivo vascular injury microarray identified four putative NFAT-dependent, injury-responsive genes. In vitro validations substantiated the NFAT-dependent role of Cyclooxygenase 2 (COX2/PTGS2) in SMC phenotypic modulation and uncovered Down Syndrome Candidate Region 1 (DSCR1/RCAN1) as a novel NFAT target gene in SMCs. We show that induction of DSCR1 inhibits calcineurin/NFAT signaling through a negative feedback mechanism; DSCR1 overexpression attenuates NFAT transcriptional activity and COX2 protein expression, whereas knockdown of endogenous DSCR1 enhances NFAT transcriptional activity. Our integrative genomics approach illustrates how the combination of publicly available gene expression arrays, computational databases and empirical research methods can answer specific questions in any cell type for a transcriptional network of interest. Herein, we report DSCR1 as a novel NFAT-dependent, injury-inducible, early gene that may serve to negatively regulate SMC phenotypic switching.