cAMP attenuates angiotensin-II-induced Egr-1 expression via PKA-dependent signaling pathway in vascular smooth muscle cells.

cAMP has been shown to inhibit vascular smooth muscle cell proliferation and exerts a vasculoprotective effect. An upregulation of the early growth response protein-1 (Egr-1) expression has been linked with the development of atherosclerosis and intimal hyperplasia. We have recently demonstrated that angiotensin-II (Ang-II) stimulates Egr-1 expression via Ca2+/ERK-mediated cAMP-response element binding protein (CREB) activation. However, whether Ang-II-induced signaling leading to Egr-1 expression is modulated by cAMP remains unexplored. Therefore, in the present studies, we have examined the effect of cAMP on Ang-II-induced expression of Egr-1 and associated signaling pathways. Isoproterenol (ISO) and forskolin (FSK) attenuated Ang-II-induced Egr-1 expression in a dose-dependent fashion. In addition, dibutyryl-cAMP and benzoyl-cAMP, as well as isobutylmethylxanthine, attenuated Ang-II-induced Egr-1 expression. Moreover, inhibition of Ang-II-induced Egr-1 expression was accompanied by an increase in the phosphorylation of the vasodilator-activated phosphoprotein (VASP), and this was associated with a concomitant decrease in ERK phosphorylation. Blockade of PKA using H89 decreased VASP phosphorylation, restored Ang-II-induced ERK phosphorylation, and abolished ISO- and FSK-mediated inhibition of Ang-II-induced Egr-1 expression. In summary, these results suggest that PKA-mediated suppression of Ang-II-induced Egr-1 expression and phosphorylation of ERK may be among the mechanisms by which cAMP exerts its vasculoprotective effects.

Early Growth Response Protein-1 Expression by Insulin-Like Growth Factor-1 Requires ROS-Dependent Activation of ERK1/2 and PKB Pathways in Vascular Smooth Muscle Cells.

Early growth response protein-1 (Egr-1) is a transcription factor that plays an important role in the regulation of several genes implicated in the pathogenesis of cardiovascular disease (CVD) such as atherosclerosis. Insulin-like growth factor-1 (IGF-1), a potent mitogen, is believed to contribute to the development of CVD through the hyperactivation of mitogenic and growth promoting pathways, including the MAPK and PKB pathways, as well as regulation of multiple transcription factors. Reactive oxygen species (ROS) have been shown to mediate the effects of IGF-1 and are believed to contribute to the pathogenesis of vascular abnormalities. We have previously shown that IGF-1 induces the expression of Egr-1 in vascular smooth muscle cells (VSMC); however, the signaling pathways involved in this process remain unexplored. Therefore, we have investigated the involvement of MAPK, PKB, and ROS in IGF-1-induced Egr-1 expression in VSMC. Treatment of VSMC with IGF-1 enhanced Egr-1 protein levels in a time and dose-dependent fashion and PD98059 and SP600125, two selective inhibitors of ERK1/2 and JNK, respectively, significantly decreased IGF-1-induced increase in Egr-1 expression in these cells. In addition, blockade of PI3-K/PKB pathways by Wortmannin/SC-66 respectively, also attenuated IGF-1-induced Egr-1 protein as well as mRNA expression. Diphenyleneiodonium (DPI), an NAD(P)H oxidase inhibitor, blocked the Egr-1 expression in response to IGF-1. In summary, these data demonstrate that ROS-dependent activation of ERK1/2/JNK, PI3-K/PKB signaling events play a critical role in IGF-1 induced expression of Egr-1 in VSMC.

Involvement of the early growth response protein 1 in vascular pathophysiology: an overview.

Hyperactivation of proliferative and growth promoting pathways underlies the progression of vessel remodeling, leading to vascular dysfunction. An upregulation of early growth response protein 1 (Egr-1), a zinc finger transcription factor has been observed in several models of vascular diseases. In the vasculature, Egr-1 expression can be induced by multiple hormonal, metabolic and external stimuli, such as growth factors, cytokines, reactive oxygen species, hyperglycaemia and stretch-induced stress. The structure of the Egr-1 promoter allows both its auto-regulation and its binding with several regulatory transcription cofactors like the serum response factor and the cAMP response element binding protein. Pharmacological and genetic studies have revealed the involvement of several signaling pathways that contribute to the expression of Egr-1. Among them, the mitogen-activated protein kinase pathway has emerged as a predominant signaling cascade that regulates Egr-1 transcription in response to various stimuli. Moreover, targeted deletion of Egr-1 by DNAzymes, antisense oligonucleotides or RNA interference has also helped in defining the importance of Egr-1 in the pathophysiology of vascular diseases. Neointimal formation and expression of genes directly linked with proinflammatory processes have been demonstrated to be enhanced by Egr-1 expression and activity. This review provides an overview on the signaling components implicated in Egr-1 expression and discusses its potential involvement in vascular pathophysiology.

Insulin-like growth-factor-1-induced PKB signaling and Egr-1 expression is inhibited by curcumin in A-10 vascular smooth muscle cells.

Insulin-like growth factor 1 (IGF-1) is a mitogenic factor that stimulates the signaling pathways responsible for inducing hypertrophic and proliferative responses in vascular smooth muscle cells (VSMC). We have previously demonstrated that IGF-1 receptor (IGF-1R) plays a key role in transducing the hypertrophic and proliferative responses of angiotensin II (Ang-II) and endothelin-1 (ET-1). Curcumin, a polyphenolic compound derived from the spice turmeric is known to possess antiproliferative properties and exerts vasculoprotective effects. However, the ability of curcumin to modulate IGF-1-induced signaling responses in VSMC remains to be investigated. In this study, we determined the effect of curcumin on IGF-1-induced phosphorylation of protein kinase B (PKB), glycogen synthase kinase-3ß (GSK-3ß), and IGF-1R in VSMC. Curcumin inhibited IGF-1-induced phosphorylation of PKB and GSK-3ß as well as the IGF-1R ß subunit in a dose-dependent fashion. In addition, IGF-1-induced expression of early growth response protein 1 (Egr-1) which plays a pathogenic role in vascular dysfunctions, was also attenuated by curcumin. In conclusion, these results indicate that curcumin is a potent inhibitor of key components of the IGF-1-induced mitogenic and proliferative signaling system in VSMC, and suggest that curcumin-induced attenuation of these signaling components may constitute a potential mechanism for its vasculoprotective effects.

Cardiovascular protection by curcumin: molecular aspects.

Curcumin is the active component in turmeric--a spice that has been extensively used as a culinary agent and a home remedy to prevent and treat many diseases in India and other countries for hundreds of years. However, systematic studies to understand the molecular basis of disease preventing or therapeutic properties of curcumin began to appear in the scientific literature only during the last 40 years. As a result of these studies, substantial evidence has accumulated to suggest that curcumin can affect signaling pathways linked to cellular growth, proliferation, survival, inflammation and transcription. In addition, curcumin has also been shown to exert anti-atherosclerotic, anti-cancer, anti-diabetic, anti-inflammatory and anti-oxidative properties in animal models of various diseases and in human subjects. In this article, we highlight the cardiovascular protective role of curcumin with an emphasis on the molecular basis of this effect.

Attenuation of endothelin-1-induced PKB and ERK1/2 signaling, as well as Egr-1 expression, by curcumin in A-10 vascular smooth muscle cells.

Endothelin-1 (ET-1) is implicated in the pathogenesis of vascular abnormalities through the hyperactivation of growth promoting pathways, including protein kinase B (PKB) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. ET-1 has been shown to elicit its responses through the generation of reactive oxygen species (ROS). Curcumin, the main constituent of the spice turmeric, exhibits cardio-protective, anti-proliferative, and antioxidant properties; however, the precise molecular mechanism of its action is unclear. Therefore, in the present study, we investigated the effects of curcumin on ET-1-induced PKB and ERK1/2 signaling, as well as insulin-like growth factor type receptor (IGF-1R) phosphorylation. Curcumin dose-dependently inhibited ET-1-induced phosphorylation of PKB, ERK1/2, c-Raf, and insulin-like growth factor type 1 receptor (IGF-1R), in vascular smooth muscle cells (VSMC). Furthermore, curcumin also attenuated ET-1-induced expression of early growth response (Egr)-1, a transcription factor downstream of ERK1/2 that plays a regulatory role in several cardiovascular pathological processes. In conclusion, these data demonstrate that curcumin is a potent inhibitor of ET-1-induced mitogenic and proliferative signaling events in VSMC and suggest that the ability of curcumin to attenuate these events may contribute as a potential mechanism for its cardiovascular protective response.