Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tumstatin is a 28-kilodalton fragment of type IV collagen that displays both anti-angiogenic and proapoptotic activity. Here we show that tumstatin functions as an endothelial cell-specific inhibitor of protein synthesis. Through a requisite interaction with alphaVbeta3 integrin, tumstatin inhibits activation of focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3-kinase), protein kinase B (PKB/Akt), and mammalian target of rapamycin (mTOR), and it prevents the dissociation of eukaryotic initiation factor 4E protein (eIF4E) from 4E-binding protein 1. These results establish a role for integrins in mediating cell-specific inhibition of cap-dependent protein synthesis and suggest a potential mechanism for tumstatin's selective effects on endothelial cells.
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PMID:Tumstatin, an endothelial cell-specific inhibitor of protein synthesis. 1177 52

Tumstatin and endostatin are two inhibitors of angiogenesis derived from precursor human collagen molecules known as alpha 3 chain of type IV collagen and alpha1 chain of type XVIII collagen, respectively. Although both these inhibitors are noncollagenous (NC1) domain fragments of collagens, they only share a 14% amino acid homology. In the present study we evaluated the functional receptors, mechanism of action, and intracellular signaling induced by these two collagen-derived inhibitors. Human tumstatin prevents angiogenesis via inhibition of endothelial cell proliferation and promotion of apoptosis with no effect on migration, whereas human endostatin prevents endothelial cell migration with no effect on proliferation. We demonstrate that human tumstatin binds to alpha v beta 3 integrin in a vitronectin/fibronectin/RGD cyclic peptide independent manner, whereas human endostatin competes with fibronectin/RGD cyclic peptide to bind alpha 5 beta 1 integrin. The activity of human tumstatin is mediated by alpha v beta 3 integrin, whereas the activity of human endostatin is mediated by alpha 5 beta 1 integrin. Additionally, although human tumstatin binding to alpha v beta 3 integrin leads to the inhibition of Cap-dependent translation (protein synthesis) mediated by focal adhesion kinase/phosphatidylinositol 3-kinase/Akt/mTOR/4E-BP1 pathway, human endostatin binding to alpha 5 beta 1 integrin leads to the inhibition of focal adhesion kinase/c-Raf/MEK1/2/p38/ERK1 mitogen-activated protein kinase pathway, with no effect on phosphatidylinositol 3-kinase/Akt/mTOR/4E-BP1 and Cap-dependent translation. Collectively, such distinct properties of human tumstatin and human endostatin provide the first insight into their diverse antiangiogenic actions and argue for combining them for targeting tumor angiogenesis.
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PMID:Human tumstatin and human endostatin exhibit distinct antiangiogenic activities mediated by alpha v beta 3 and alpha 5 beta 1 integrins. 3174 8

Canstatin, a 24-kDa peptide derived from the C-terminal globular non-collagenous (NC1) domain of the alpha2 chain of type IV collagen, was previously shown to induce apoptosis in cultured endothelial cells and to inhibit angiogenesis in vitro and in vivo. In this report, we demonstrate that canstatin inhibits the phosphorylation of Akt, focal adhesion kinase, mammalian target of rapamycin, eukaryotic initiation factor-4E-binding protein-1, and ribosomal S6 kinase in cultured human umbilical vein endothelial cells. It also induces Fas ligand expression, activates procaspases 8 and 9 cleavage, reduces mitochondrial membrane potential, and increases cell death (as determined by propidium iodide staining). Canstatin-induced activation of procaspases 8 and 9 as well as the induced reduction in mitochondrial membrane potential and cell viability were attenuated by the forced expression of FLICE-inhibitory protein. Canstatin-induced procaspase 8 activation and cell death were also inhibited by a neutralizing anti-Fas antibody. Collectively, these data indicate that canstatin-induced apoptosis is associated with phosphatidylinositol 3-kinase/Akt inhibition and is dependent upon signaling events transduced through membrane death receptors.
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PMID:Canstatin inhibits Akt activation and induces Fas-dependent apoptosis in endothelial cells. 1287 80

Cell volume changes critically determine hepatic signal transduction and metabolism. Hepatocyte swelling by insulin contributes to p38(MAPK) activation leading to inhibition of autophagic proteolysis. Recently integrins were shown to sense hypoosmotic hepatocyte swelling. Here the role of integrins, Src, and focal adhesion kinase (FAK) in insulin signaling was investigated using the intact organ model of perfused rat liver. Insulin increases [Tyr(P)(418)]Src, [Tyr(P)(397)]FAK, and dual p38(MAPK) phosphorylation by about 2-fold. Infusion of the integrin-antagonizing hexapeptide GRGDSP or the Src inhibitor PP-2 prevented activation of Src and p38(MAPK) and, consequently, proteolysis inhibition by insulin. However, insulin-induced phosphorylation of IRbeta (Tyr(1158)) and protein kinase B (PKB, Ser(473)), as well as K(+)-uptake and cell swelling, was not reduced by the inhibitors. Both hypoosmotic swelling and insulin increase the plasma membrane levels of activated beta(1) integrin. Inhibition of insulin-induced swelling by furosemide largely abolished activation of beta(1) integrin and phosphorylation of Src, but not of PKB. Rapamycin does not affect either insulin-induced K(+)-retention and cell swelling or proteolysis inhibition, indicating that swelling-dependent proteolysis inhibition occurs independently from the mammalian target of rapamycin. The data suggest that sensing of cell swelling by integrins essentially contributes to insulin signaling, thereby defining a novel way of integrin involvement in growth factor signaling.
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PMID:Involvement of integrins and Src in insulin signaling toward autophagic proteolysis in rat liver. 1498 60

We previously reported that the FAS1 domains of betaig-h3 bear motifs that mediate endothelial cell adhesion and migration via interactions with alphavbeta3 integrin and regulate angiogenesis. In the present study, we show that the fourth FAS1 domain, designated fastatin, inhibits endothelial adhesion and migration, not only to betaig-h3, but also fibronectin and vitronectin, in a RGD-dependent manner. Fastatin and other FAS1 domains suppress endothelial cell tube formation and in vivo neovascularization in a Matrigel plug assay. The antiangiogenic activity of fastatin is associated with antitumor activity in mouse tumor models. Fastatin additionally induces apoptosis in several cells expressing alphavbeta3 integrin, including endothelial cells. Binding of fastatin to alphavbeta3 integrin inhibits phosphorylation of focal adhesion kinase, Raf, extracellular signal-regulated kinase, Akt, and mammalian target of rapamycin. Fastatin is thus the first endogenous angiogenesis regulator identified that inhibits both endothelial cell migration and growth by binding to alphavbeta3 integrin. Our data suggest that FAS1 domains from all possible forms of the four human FAS1 family proteins are potential endogenous regulators for pathologic angiogenesis. Moreover, FAS1 domains such as fastatin may be developed into drugs for blocking tumor angiogenesis.
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PMID:Regulation of tumor angiogenesis by fastatin, the fourth FAS1 domain of betaig-h3, via alphavbeta3 integrin. 1589 6

The intracellular mechanisms regulating pancreatic acinar cell function are more complex than previously realized. This is probably due in part to the need to match the biosynthetic and secretory functions of the cells. Much information is available on how secretagogue receptors acutely couple through heterotrimeric G proteins to increase intracellular messengers, particularly cytoplasmic free Ca(2+), although details are still being worked out. Less is known about how Ca(2+) signals to induce fusion of zymogen granules with the apical plasma membrane. Investigation has focused on the proteins of the zymogen granule membrane, and several novel proteins have recently been identified. In addition, understanding of the three MAP kinase cascades, the mTOR-p70S6 kinase pathway, and the focal adhesion kinase pathway in acinar cells is increasing. The functions of these pathways in acini have been linked to mitogenesis, protein synthesis, and regulation of the cytoskeleton.
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PMID:Intracellular regulatory mechanisms in pancreatic acinar cellular function. 1702 78

The collagen type IV cleavage fragment tumstatin and its active subfragments bind to integrin alpha(V)beta(3) and inhibit activation of focal adhesion kinase, phophoinositol-3 kinase, Akt, and mammalian target of rapamycin (mTOR) in what is thought to be an endothelial cell-specific manner. The resultant endothelial cell apoptosis accounts for the ability of tumstatin to function as an endogenous inhibitor of angiogenesis and an indirect suppressor of tumor growth. We hypothesized that the inability of tumstatin to directly suppress tumor cell growth might be the result of the constitutive activation of the Akt/mTOR pathway commonly seen in tumors. Consistent with this idea, several integrin alpha(V)beta(3)-expressing glioma cell lines with PTEN mutations and high levels of phospho-Akt (pAkt) were unaffected by exposure to an active fragment of tumstatin (T3), whereas alpha(V)beta(3)-expressing glioma cell lines with a functional PTEN/low levels of pAkt exhibited T3-induced growth suppression that could be bypassed by small interfering RNA-mediated suppression of PTEN, introduction of a constitutively expressed Akt, or introduction of the Akt and mTOR target eukaryotic translation initiation factor 4E. The direct tumor-suppressive actions of T3 were further shown in an alpha(V)beta(3)-deficient in vivo mouse model in which T3, while unable to alter the tumstatin-insensitive vasculature contributed by the alpha(V)beta(3)-deficient host, nonetheless suppressed the growth and proliferative index of i.c. implanted alpha(V)beta(3)-expressing PTEN-proficient glioma cells. These results show that tumstatin, previously considered to be only an endogenous inhibitor of angiogenesis, also directly inhibits the growth of tumors in a manner dependent on Akt/mTOR activation.
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PMID:The PTEN/Akt pathway dictates the direct alphaVbeta3-dependent growth-inhibitory action of an active fragment of tumstatin in glioma cells in vitro and in vivo. 1714 79

Human alpha3 chain, a noncollagenous domain of type IV collagen [alpha3(IV)NC1], inhibits angiogenesis and tumor growth. These biologic functions are partly attributed to the binding of alpha3(IV)NC1 to alphaVbeta3 and alpha3beta1 integrins. alpha3(IV)NC1 binds alphaVbeta3 integrin, leading to translation inhibition by inhibiting focal adhesion kinase/phosphatidylinositol 3-kinase/Akt/mTOR/4E-BP1 pathways. In the present study, we evaluated the role of alpha3beta1 and alphaVbeta3 integrins in tube formation and regulation of cyclooxygenase-2 (COX-2) on alpha3(IV)NC1 stimulation. We found that although both integrins were required for the inhibition of tube formation by alpha3(IV)NC1 in endothelial cells, only alpha3beta1 integrin was sufficient to regulate COX-2 in hypoxic endothelial cells. We show that binding of alpha3(IV)NC1 to alpha3beta1 integrin leads to inhibition of COX-2-mediated pro-angiogenic factors, vascular endothelial growth factor, and basic fibroblast growth factor by regulating IkappaBalpha/NFkappaB axis, and is independent of alphaVbeta3 integrin. Furthermore, beta3 integrin-null endothelial cells, when treated with alpha3(IV)NC1, inhibited hypoxia-mediated COX-2 expression, whereas COX-2 inhibition was not observed in alpha3 integrin-null endothelial cells, indicating that regulation of COX-2 by alpha3(IV)NC1 is mediated by integrin alpha3beta1. Our in vitro and in vivo findings demonstrate that alpha3beta1 integrin is critical for alpha3(IV)NC1-mediated inhibition of COX-2-dependent angiogenic signaling and inhibition of tumor progression.
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PMID:Regulation of COX-2 mediated signaling by alpha3 type IV noncollagenous domain in tumor angiogenesis. 1742 56

The vascular smooth muscle phenotype is regulated by environmental factors, such as mechanical forces, that exert effects on signaling to differentiation and growth. We used the mouse portal vein in organ culture to investigate stretch-dependent activation of Akt, ERK, and focal adhesion kinase (FAK), which have been suggested to be involved in the regulation of stretch-dependent protein synthesis. The role of actin polymerization in these signaling events was examined using the actin-stabilizing agent jasplakinolide. Stretch caused a biphasic activation of FAK at 5-15 min and 24-72 h, which may reflect first a direct phosphorylation of preexisting focal adhesions followed by a rearrangement of focal adhesions to accommodate for the increased mechanical load. Phosphorylation of ERK was increased by acute stretch but then decreased, and Akt did not have a distinct peak in stretch-induced phosphorylation. Inhibition of ERK, phosphatidylinositol 3-kinase, or mammalian target of rapamycin reduced global but not contractile protein synthesis with maintained stretch sensitivity. Stabilization of actin filaments with jasplakinolide, in unstretched portal veins, resulted in increased ERK phosphorylation and global protein synthesis as well as the synthesis of contractile proteins. In contrast, stretch during culture with jasplakinolide did not affect FAK phosphorylation or contractility. Therefore, remodeling of smooth muscle cells to adapt to stretch requires a dynamic cytoskeleton.
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PMID:Integration of signal pathways for stretch-dependent growth and differentiation in vascular smooth muscle. 1750 30

Secondary resistance to hormonal therapy for breast cancer commonly develops after an initial response to tamoxifen or aromatase inhibitors. Agents to abrogate these adaptive changes would substantially enhance the long-term benefits of hormonal therapy. Our studies with a stilbene derivative called TMS (2,3',4,5'-tetramethoxystilbene) identified unexpected effects with potential utility for treatment of breast tumors secondarily resistant to hormonal therapy. TMS was originally developed as an inhibitor of cytochrome P450 1B1 to block the conversion of estradiol to 4-OH-estradiol. While studying this agent in three models of hormone resistance, we detected direct antitumor effects not related to its role as an inhibitor of catecholestrogens. During examination of the mechanisms involved, we showed that treatment with 3 micromol/L TMS for 24 h inhibited tubulin polymerization and microtubule formation, caused a cell cycle block at the G2-M phase, and induced apoptosis. TMS also inhibited activated focal adhesion kinase (FAK), Akt, and mammalian target of rapamycin (mTOR) and stimulated c-jun-NH2-kinase and p38 mitogen-activated protein kinase activity. With respect to antitumor effects, TMS at a concentrations of 0.2 to 0.3 micromol/L inhibited the growth of long-term tamoxifen-treated MCF-7 cells by 80% and fulvestrant-treated MCF-7 cells by 70%. In vivo studies, involving 8 weeks of treatment with TMS via a 30-mg s.c. implant, reduced tumor volume of tamoxifen-resistant MCF-7 breast cancer xenografts by 53%. Our data suggest that TMS is a promising therapeutic agent because of its unique ability to block several pathways involved in the development of hormone resistance.
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PMID:Effects of tetramethoxystilbene on hormone-resistant breast cancer cells: biological and biochemical mechanisms of action. 1757 38


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