SummaryCaveolin-1-dependent β1 integrin endocytosis is a critical regulator of fibronectin turnover
munication between cells and the extracellular matrix (ECM) is critical for regulation of cell growth, survival, migration, and differentiation. Remodeling of the ECM can occur under normal physiological conditions, as a result of tissue injury, and in certain pathological conditions. ECM remodeling leads to alterations in ECM composition and organization that can alter many aspects of cell behavior, including cell migration. The cell migratory response varies depending on the type, amount, and organization of ECM molecules present, as well as the integrin and proteoglycan repertoire of the cells. We and others have shown that the deposition of several ECM molecules, including collagen types I and III, depends on the presence and stability of ECM fibronectin. Hence, the effect of fibronectin and fibronectin matrix on cell function may partially depend on its ability to direct the deposition of collagen in the ECM. In this study, we used collagen-binding fibronectin mutants and recombinant peptides that interfere with fibronectin-collagen binding to show that fibronectindependent collagen I deposition regulates the cell migratory response to fibronectin. These data show that the ability of fibronectin to organize other proteins in the ECM is an important aspect of fibronectin function and highlight the importance of understanding how interactions between ECM proteins influence cell behavior. extracellular matrix; contractility CELL FATE DECISIONS involving cell growth, differentiation, and survival rely on the ability of cells to coordinate diverse input from cytokines, growth factors, and extracellular matrix (ECM) molecules (3,89,94). The effects of ECM molecules on cell behavior are particularly complicated, since they depend on the mixture of ECM molecules that are present, the way the ECM proteins are organized and presented to cells, and the presence of proteases, protease inhibitors, and endocytic mechanisms that can alter the levels of ECM proteins and ECM degradation products. Understanding how ECM proteins act in concert to elicit biological effects is key to understanding how cell-ECM interactions maintain normal tissue function and influence the cell response to tissue injury.There is much data showing that mixtures of different ECM molecules can have effects distinct from that of a single ECM molecule. For example, coating dishes with a combination of tenascin C and fibronectin results in altered expression of matrix metalloproteinases (MMPs) (86), whereas addition of tenascin C to dishes coated with fibrin and fibronectin results in altered cytoskeletal organization (90) compared with cells seeded in the absence of tenascin C. The ability of fibronectin null cells to produce a fibronectin matrix is also dependent on the combination of matrix proteins present on the substrate (4). Furthermore, mixed collagen and fibronectin substrates have been shown to alter the response of endothelial cells to shear stress compared with their response to fibronectin alone (59). Similarly, addition of soluble matric...
Objective Fibronectin is an important regulator of cell migration, differentiation, growth, and survival. Our data show that fibronectin also plays an important role in regulating extracellular matrix (ECM) remodeling. Fibronectin circulates in the plasma, and is also deposited into the ECM by a cell dependent process. To determine whether fibronectin affects vascular remodeling in vivo, we asked whether the fibronectin polymerization inhibitor, pUR4, inhibits intima-media thickening, and prevents excess ECM deposition in arteries using a mouse model of vascular remodeling. Methods and Results To induce vascular remodeling, partial ligation of the left external and internal carotid arteries was performed in mice. pUR4 and the control peptide were applied periadventitially in pluronic gel immediately after surgery. Animals were sacrificed 7 or 14 days post surgery. Morphometric analysis demonstrated that the pUR4 fibronectin inhibitor reduced carotid intima (63%), media (27%), and adventitial thickening (40%) compared to the control peptide (III-11C). Treatment with pUR4 also resulted in a dramatic decrease in leukocyte infiltration into the vessel wall (80%), decreased ICAM-1 and VCAM-1 levels, inhibited cell proliferation (60-70%), and reduced fibronectin and collagen I accumulation in the vessel wall. In addition, the fibronectin inhibitor prevented SMC phenotypic modulation, as evidence by the maintenance of smooth muscle (SM) α-actin and SM myosin heavy chain levels in medial cells. Conclusions These data are the first to demonstrate that fibronectin plays an important role in regulating the vascular remodeling response. Collectively, these data suggest a therapeutic benefit of periadventitial pUR4 in reducing pathologic vascular remodeling.
The genomic DNA sequence of the widely studied yeast Saccharomyces cerevisiae, which is a model organism for eukaryotic cells, contains three NAD kinase homologues, namely, Utr1p, Pos5p and Yel041wp [1][2][3]. NAD kinase (EC 2.7.1.23) catalyses NAD phosphorylation by using phosphoryl donors (ATP or inorganic polyphosphate [poly(P)]), constituting the last step of the NADP biosynthetic pathway [4,5] ATP-NAD kinase phosphorylates NAD to produce NADP by using ATP, whereas ATP-NADH kinase phosphorylates both NAD and NADH. Three NAD kinase homologues, namely, ATP-NAD kinase (Utr1p), ATP-NADH kinase (Pos5p) and function-unknown Yel041wp (Yef1p), are found in the yeast Saccharomyces cerevisiae. In this study, Yef1p was identified as an ATP-NADH kinase. The ATP-NADH kinase activity of Utr1p was also confirmed. Thus, the three NAD kinase homologues were biochemically identified as ATP-NADH kinases. The phenotypic analysis of the single, double and triple mutants, which was unexpectedly found to be viable, for UTR1, YEF1 and POS5 demonstrated the critical contribution of Pos5p to mitochondrial function and survival at 37°C and the critical contribution of Utr1p to growth in low iron medium. The contributions of the other two enzymes were also demonstrated; however, these were observed only in the absence of the critical contributor, which was supported by complementation for some pos5 phenotypes by the overexpression of UTR1 and YEF1. The viability of the triple mutant suggested that a 'novel' enzyme, whose primary structure is different from those of all known NAD and NADH kinases, probably catalyses the formation of cytosolic NADP in S. cerevisiae. Finally, we found that LEU2 of Candida glabrata, encoding b-isopropylmalate dehydrogenase and being used to construct the triple mutant, complemented some pos5 phenotypes; however, overexpression of LEU2 of S. cerevisiae did not. The complementation was putatively attributed to an ability of Leu2p of C. glabrata to use NADP as a coenzyme and to supply NADPH.Abbreviations CgLEU2, LEU2 of yeast Candida glabrata; FOA, 5-fluoroorotic acid; GFP, green fluorescent protein; KNDE, 10 mM potassium phosphate, pH 7.0, containing 0.1 mM NAD, 0.5 mM dithiothreitol and 1.0 mM EDTA; poly(P), inorganic polyphosphate; ScLEU2, LEU2 of yeast Saccharomyces cerevisiae; SD, synthetic dextrose; SG, synthetic glycerol; SD+FOA+Ura, synthetic dextrose ⁄ 5-fluoroorotic acid ⁄ uracil; WT, wild type; YPD, yeast extract ⁄ peptone ⁄ dextrose; YPG, yeast extract ⁄ peptone ⁄ glycerol.
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