Myofibroblast differentiation and activation by transforming growth factor-beta1 (TGF-beta1) is a critical event in the pathogenesis of human fibrotic diseases, but regulatory mechanisms for this effect are unclear. In this report, we demonstrate that stable expression of the myofibroblast phenotype requires both TGF-beta1 and adhesion-dependent signals. TGF-beta1-induced myofibroblast differentiation of lung fibroblasts is blocked in non-adherent cells despite the preservation of TGF-beta receptor(s)-mediated signaling of Smad2 phosphorylation. TGF-beta1 induces tyrosine phosphorylation of focal adhesion kinase (FAK) including that of its autophosphorylation site, Tyr-397, an effect that is dependent on cell adhesion and is delayed relative to early Smad signaling. Pharmacologic inhibition of FAK or expression of kinase-deficient FAK, mutated by substituting Tyr-397 with Phe, inhibit TGF-beta1-induced alpha-smooth muscle actin expression, stress fiber formation, and cellular hypertrophy. Basal expression of alpha-smooth muscle actin is elevated in cells grown on fibronectin-coated dishes but is decreased on laminin and poly-d-lysine, a non-integrin binding polypeptide. TGF-beta1 up-regulates expression of integrins and fibronectin, an effect that is associated with autophosphorylation/activation of FAK. Thus, a safer and more effective therapeutic strategy for fibrotic diseases characterized by persistent myofibroblast activation may be to target this integrin/FAK pathway while not interfering with tumor-suppressive functions of TGF-beta1/Smad signaling.

The stabilization of endothelial cell (EC) barrier function within newly formed capillaries is a critical feature of angiogenesis. We examined human lung EC barrier regulation elicited by hepatocyte growth factor (HGF), a recognized angiogenic factor and EC chemoattractant. HGF rapidly and dose-dependently elevated transendothelial electrical resistance (TER) of EC monolayers (>50% increase at 100 ng/ml), with immunofluorescence microscopic evidence of both cytoplasmic actin stress fiber dissolution and strong augmentation of the cortical actin ring. HGF rapidly stimulated phosphatidylinositol 3'-kinase, ERK, p38 mitogen-activated protein kinase, and protein kinase C activities. Pharmacological inhibitor studies demonstrated each pathway to be intimately involved in HGF-induced increases in TER, cortical actin thickening, and phosphorylation of the Ser/Thr glycogen synthase kinase-3beta (GSK-3beta), a potential target for the HGF barrier-promoting response. GSK-3beta phosphorylation was strongly correlated with reductions in both HGF-induced TER and enhanced beta-catenin immunoreactivity observed at cell-cell junctions. Our data suggest a model in which HGF-mediated EC cytoskeletal rearrangement and barrier enhancement depend critically on the activation of a complex kinase cascade that converges at GSK-3beta to increase the availability of beta-catenin, thereby enhancing endothelial junctional integrity and vascular barrier function.

Abstract-There is now considerable evidence supporting a mitogenic action of serotonin (5-HT) on vascular smooth muscle cells (SMC) that might participate in pulmonary hypertension (PH). Our previous studies have demonstrated that 5-HT-induced proliferation depends on the generation of reactive oxygen species and activation of extracellular signal-regulated kinase (ERK) 1/ERK2. Activation of Rho kinase (ROCK) in SMC also may be important in PH. We undertook the present study to assess the role of Rho A/ROCK and its possible relation to ERK1/ERK2 in 5-HT-induced pulmonary artery SMC proliferation. We found that this stimulation of SMC proliferation requires Rho A/ROCK as inhibition with Y27632, a ROCK inhibitor, or dominant negative (DN) mutant Rho A blocks 5-HT-induced proliferation, cyclin D1 expression, phosphorylation of Elk, and the DNA binding of transcription factors, Egr-1 and GATA-4. 5-HT activated ROCK, and the activation was blocked by GR 55562 and GR127935, 5-HT 1B/1D receptor antagonists, but not by serotonin transport ( Key Words: smooth muscle cells Ⅲ serotonin Ⅲ Rho kinase Ⅲ ERK1/ERK2 Ⅲ pulmonary hypertension I n addition to its actions as a vasoconstrictor and neurotransmitter, serotonin (5-HT) is now recognized to be a cellular mitogen. [1][2][3] There is evidence that this mitogenic action is initiated by active transport via a cell surface transporter (SERT) of bovine, rat, and human pulmonary vascular smooth muscle cells (SMC). 1,4 -6 For other cells, the mitogenic action might be started through 1 or more of the cell surface receptors for 5-HT. A hierarchy of cell signaling responses occurs subsequent to ligation of the cell surface transporter or receptor. It has been well-established that these signaling responses include sequential activations of the small GTPase coupled protein, Rac-1, NADPH oxidase producing superoxide that is dismutated to H 2 O 2 , and extracellular signal-regulated kinase (ERK) 1/ERK2 MAP kinase. 2,[7][8][9] The small GTPase Rho A and its effector, Rho kinase (ROCK), also participate in cellular stress fiber formation and cell cycle progression. 10 -19 There has been limited study of the relationship of Rho A and ROCK to 5-HT. One study showed that Rho A bound to GTP is elevated in the rabbit aortic vascular ring preparation treated with 5-HT. 20 Another study suggested the activation of Rho A and ROCK in 5-HT-induced contraction of the bovine middle cerebral artery. 21 Serotonin participates in pulmonary hypertension, 5,22,23 and a polymorphism of the 5-HT transporter has been proposed to be involved in pulmonary hypertension in humans. 24 Because agents that block ROCK are currently available 25,26 and may be useful in pulmonary hypertension, 27-29 we have undertaken an investigation of the potential participation of ROCK in pulmonary arterial SMC signaling and proliferation produced by 5-HT. The results of our study show that ROCK is activated by 5-HT and that its activation is essential for SMC proliferation produced by 5-HT. Furthermore, with the use of a chemi...

13 C-selective NMR, combined with inhibitor perturbation experiments, shows that the C 1 OH proton of the catalytic histidine in resting ␣-lytic protease and subtilisin BPN resonates, when protonated, at 9.22 ppm and 9.18 ppm, respectively, which is outside the normal range for such protons and Ϸ0.6 to 0. Here, we propose that it enables a reaction-driven imidazole ring flip mechanism, overcoming a major dilemma inherent in all previous mechanisms, namely how these enzymes catalyze both the formation and productive breakdown of tetrahedral intermediates.