Nitric oxide regulates angiogenesis through a functional switch involving thrombospondin-1

Abstract

Nitric oxide (NO) donors have been shown to stimulate and inhibit the proliferation, migration, and differentiation of endothelial cells in vitro and angiogenesis in vivo. Recently, we have shown distinct thresholds for NO to regulate p53-Ser-15P, phosphorylated extracellular signal-regulated kinase (pERK), and hypoxia inducible factor 1␣ in tumor cells. Because these signaling pathways also promote the growth and survival of endothelial cells, we examined their roles in angiogenic responses of venous endothelial cells and vascular outgrowth of muscle explants elicited by NO. An additional protein involved in the regulation of angiogenesis is thrombospondin-1 (TSP1), a matricellular glycoprotein known to influence adhesion, migration, and proliferation of endothelial cells. Here we demonstrate a triphasic regulation of TSP1 mediated by a slow and prolonged release of NO that depends on ERK phosphorylation. Under conditions of 5% serum, a 24-h exposure of NO donor (0.1-1,000 M) mediated a triphasic response in the expression of TSP1 protein: decreasing at 0.1 M, rebounding at 100 M, and decreasing again at 1,000 M. Under the same conditions, we observed a dose-dependent increase in P53 phosphorylation and inverse biphasic responses of pERK and mitogen-activated protein kinase phosphatase-1. Both the growth-stimulating activity of low-dose NO for endothelial cells and suppression of TSP1 expression were ERK-dependent. Conversely, exogenous TSP1 suppressed NO-mediated pERK. These results suggest that dosedependent positive-and negative-feedback loops exist between NO and TSP1. Limiting TSP1 expression by positive feedback through the ERK mitogen-activated protein kinase pathway may facilitate switching to a proangiogenic state at low doses of NO.guanyl cyclase ͉ endothelial S ince its discovery, nitric oxide (NO) has acquired a reputation as both friend and foe (1). To assimilate this discordant information, it is important to consider cell͞tissue specificity, redox conditions, NO concentration, as well as the duration of exposure associated with a specific response. An important question in NO research involves its role during specific stages of cancer progression (2-6). A key aspect of cancer progression as well as treatment involves the regulation of angiogenesis, which entails the induction of endothelial cell proliferation, migration, and differentiation, culminating in the sprouting of new capillaries from existing vasculature (7,8). In addition to providing blood flow and nutrients to the tumor, angiogenesis is also involved in tumor progression and metastasis because the vasculature provides the tumor with access to distant organs, and enhanced vascularization is a marker of advanced tumors (8).One of the many physiological functions of NO is as an important modulator of endothelial function pertaining to angiogenesis (9). Although low concentrations of NO induce an angiogenic response, high concentrations are inhibitory (10). NO mediates the proangiogenic response of several key factors including VEGF, ang...

Thrombospondin-1 inhibits endothelial cell responses to nitric oxide in a cGMP-dependent manner

“…By analogy to NO signaling in breast carcinoma cells (41), high-dose NO may inhibit these endothelial cell responses through activation of p53 and MKP1 expression (47). Further work is required to define these inhibitory signaling pathways.…”

Netrin-1 induces angiogenesis via a DCC-dependent ERK1/2-eNOS feed-forward mechanism

“…Whereas U0126 inhibited eNOS s1179 phosphorylation, scavenging NO ⅐ with PTIO reduced ERK1͞2 phosphorylation. Indeed, physiological concentrations of NO ⅐ are capable of activating ERK1͞2 in endothelial cells (27) and other cell types (28). Fig.…”

Donepezil, an acetylcholinesterase inhibitor against Alzheimer's dementia, promotes angiogenesis in an ischemic hindlimb model

“…Furthermore, ACh transduces signals through nitric oxide (NO) production, and NO plays a key role in angiogenesis [4][5][6][7][8]. Specifically, according to our previous study, the NO donor S-nitroso-N-acetylpenicillamine activates the PI3K/Akt/HIF-1 pathway to increase VEGF expression in cardiomyocytes, and VEGF derived from cardiomyocytes accelerates tube formation in human umbilical endothelial cells (HUVECs), i.e., in vitro angiogenesis [4].…”