Modulatory effects of taurine on jejunal contractility

Taurine (2-aminoethanesulfonic acid) is widely distributed in animal tissues and has diverse pharmacological effects. However, the role of taurine in modulating smooth muscle contractility is still controversial. We propose that taurine (5-80 mM) can exert bidirectional modulation on the contractility of isolated rat jejunal segments. Different low and high contractile states were induced in isolated jejunal segments of rats to observe the effects of taurine and the associated mechanisms. Taurine induced stimulatory effects on the contractility of isolated rat jejunal segments at 3 different low contractile states, and inhibitory effects at 3 different high contractile states. Bidirectional modulation was not observed in the presence of verapamil or tetrodotoxin, suggesting that taurine-induced bidirectional modulation is Ca2+ dependent and requires the presence of the enteric nervous system. The stimulatory effects of taurine on the contractility of isolated jejunal segments was blocked by atropine but not by diphenhydramine or by cimetidine, suggesting that muscarinic-linked activation was involved in the stimulatory effects when isolated jejunal segments were in a low contractile state. The inhibitory effects of taurine on the contractility of isolated jejunal segments were blocked by propranolol and L-NG-nitroarginine but not by phentolamine, suggesting that adrenergic β receptors and a nitric oxide relaxing mechanism were involved when isolated jejunal segments were in high contractile states. No bidirectional effects of taurine on myosin phosphorylation were observed. The contractile states of jejunal segments determine taurine-induced stimulatory or inhibitory effects, which are associated with muscarinic receptors and adrenergic β receptors, and a nitric oxide associated relaxing mechanism.

Vascular O-GlcNAcylation augments reactivity to constrictor stimuli by prolonging phosphorylated levels of the myosin light chain

O-GlcNAcylation is a modification that alters the function of numerous proteins. We hypothesized that augmented O-GlcNAcylation levels enhance myosin light chain kinase (MLCK) and reduce myosin light chain phosphatase (MLCP) activity, leading to increased vascular contractile responsiveness. The vascular responses were measured by isometric force displacement. Thoracic aorta and vascular smooth muscle cells (VSMCs) from rats were incubated with vehicle or with PugNAc, which increases O-GlcNAcylation. In addition, we determined whether proteins that play an important role in the regulation of MLCK and MLCP activity are directly affected by O-GlcNAcylation. PugNAc enhanced phenylephrine (PE) responses in rat aortas (maximal effect, 14.2±2 vs 7.9±1 mN for vehicle, n=7). Treatment with an MLCP inhibitor (calyculin A) augmented vascular responses to PE (13.4±2 mN) and abolished the differences in PE-response between the groups. The effect of PugNAc was not observed when vessels were preincubated with ML-9, an MLCK inhibitor (7.3±2 vs 7.5±2 mN for vehicle, n=5). Furthermore, our data showed that differences in the PE-induced contractile response between the groups were abolished by the activator of AMP-activated protein kinase (AICAR; 6.1±2 vs 7.4±2 mN for vehicle, n=5). PugNAc increased phosphorylation of myosin phosphatase target subunit 1 (MYPT-1) and protein kinase C-potentiated inhibitor protein of 17 kDa (CPI-17), which are involved in RhoA/Rho-kinase-mediated inhibition of myosin phosphatase activity. PugNAc incubation produced a time-dependent increase in vascular phosphorylation of myosin light chain and decreased phosphorylation levels of AMP-activated protein kinase, which decreased the affinity of MLCK for Ca2+/calmodulin. Our data suggest that proteins that play an important role in the regulation of MLCK and MLCP activity are directly affected by O-GlcNAcylation, favoring vascular contraction.

Transmigração endotelial do fungo patogênico Sporothrix schenckii: modulação da via de p38MAPK/MLCK, Src e de moléculas de adesão celular / Endothelial transmigration of the pathogenic fungus, Sporothrix schenckii: pathway modulation of p38MAPK/MLCK, Src and cell adhesion molecules

Sporothrix schenckii é um fungo dimórfico, agente etiológico da esporotricose, uma micose subaguda ou crônica que pode eventualmente evoluir para complicações sistêmicas, principalmente em pacientes imunocomprometidos. O endotélio exerce um papel crucial durante infecções disseminadas já que, juntamente com as células epiteliais, representa uma barreira a ser ultrapassada por microorganismos invasores. Em estudos anteriores, observamos que S. schenckii transmigra preferencialmente pela rota paracelular (passagem entre células endoteliais adjacentes), interagindo em seguida com componenetes da matriz subendotelial. Também foram identificadas algumas vias de sinalização relacionadas à diferentes fases da interação de leveduras de S. schenckii com o endotélio in vitro (associação/endocitose, transmigração). No entanto, a correlação entre tais vias de sinalização e os mecanismos celulares da invasão do endotélio pelo fungo não foram efetivamente demonstrados. No presente trabalho, a análise do perfil de proteínas endoteliais totais fosforiladas em resíduos de tirosina mostrou que S. schenckii induz fosforilações em tempos curtos (< 15 minutos), em proteínas de massas moleculares 20, 13, 12 e 6KDa, enquanto alunas proteínas de mais alto peso molecular (83, 123, 136, 140 e 193 KDa) persistem fosforiladas em tempos mais longos durante a infecção (6 horas). As vias de transdução de sinais disparadas pela interação do fungo com o endotélio foram investigadas através do uso de inibidores da ativação de MAPKs p38 (SB 203580) e ERK (PD 98059), MLCK (W7) e de um quelante de Ca2+ intracelular (BAPTA). A transmigração de S. schenckii através de monocamadas de HUVECs por 6 horas mostrou ser dependente da ativação de ERK e p38, ions Ca2+ intracelular e MLCK. Estas vias estão também envolvidas nos rearranjos do citoesqueleto de actina que levam à contratilidade celular e aumento da permeabilidade endotelial. A interação do fungo com HUVECs induziu ativação de Src...

Sporothrix schenckii, a dimorphic fungus, is the causative agent of sporotrichosis, a cutaneous/subcutaneous mycosis which can eventually evolve to systemic complications, mainly in immunocompromised patients. The primary interaction of pathogenic fungi with endothelial cells (EC) is throught to be essential for the development of systemic infections. We have previously shown that S. schenckii cross endothelial monolayers through a paracellular pathway, in a process also modulated by the subendothelial matrix, and that the fungus is able to alter host signaling pathways. We observed that the interaction of S. schenckii with human umbilical vein endothelial cells (HUVECs) was regulated by tyrosine-phosphorylation of EC proteins. In the present work, we observed that S. schenckii stimulates the early increase (<15 minutes) in tyrosine-phorphorylation of 20, 13, 12 e 6 KDa endothelial proteins, whereas tyrosine-phosphorylation of higher molecular weight proteins (83, 123, 136, 140 e 193 KDa) persists up to 6 hours of endothelial infection. Selective signal transduction inhibitors (SB203580 and W7, for blocking p38 MAPK and MLCK activation, respectively) were able to inhibit transendothelial migration of S. schenckii. The process was also modulated by Ca++ions. These signaling pathways are crucial for the actin rearrangement associated to impairment of endothelial permeability. Long-term (3 hours) interaction of S. schenckii with HUVECs lead to increase of MLC2 phosphorylation and Src activation. Src was shown by others to be involved in the phosphorylation of VE-cadherin, thus provoking adherent junctions (AJs) disassembly. We found that S. schenckii induces tyrosine-phosphorylation of endothelial VE-cadherin up to 3 hours of interaction with endothelial cells. VE-cadherin phosphorylation can be triggered by the activation of E-selectin in endothelial cells. Since the time-course of the major signaling events correlated with the time needed...

Downstream components of RhoA required for signal pathway of superoxide formation during phagocytosis of serum opsonized zymosans in macrophages

Rac1 and Rac2 are essential for the control of oxidative burst catalyzed by NADPH oxidase. It was also documented that Rho is associated with the superoxide burst reaction during phagocytosis of serum- (SOZ) and IgG-opsonized zymosan particles (IOZ). In this study, we attempted to reveal the signal pathway components in the superoxide formation regulated by Rho GTPase. Tat-C3 blocked superoxide production, suggesting that RhoA is essentially involved in superoxide formation during phagocytosis of SOZ. Conversely SOZ activated both RhoA and Rac1/2. Inhibition of RhoA-activated kinase (ROCK), an important downstream effector of RhoA, by Y27632 and myosin light chain kinase (MLCK) by ML-7 abrogated superoxide production by SOZ. Extracellular signaling-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) were activated during phagocytosis of SOZ, and Tat-C3 and SB203580 reduced ERK1/2 and p38 MAPK activation, suggesting that RhoA and p38 MAPK may be upstream regulators of ERK1/2. Inhibition of ERK1/2, p38 MAPK, phosphatidyl inositol 3-kinase did not block translocation of RhoA to membranes, suggesting that RhoA is upstream to these kinases. Inhibition of RhoA by Tat-C3 blocked phosphorylation of p47 PHOX. Taken together, RhoA, ROCK, p38MAPK, ERK1/2, and p47 PHOX may be subsequently activated, leading to activation of NADPH oxidase to produce superoxide.

Ca(2+)-dependent phosphorylation of the tail domain of myosin-V, a calmodulin-binding myosin in vertebrate brain

1. Myosin-V from vertebrate brain is a novel molecular motor with a myosin-like head domain, a calmodulin-binding neck region and a unique tail domain of unknown function. Previous studies showed brain myosin-V to be a phosphoprotein substrate for Ca2+/calmodulin-dependent protein kinase associated with actomyosin. In the present study we describe the preparation of a specific actin-cytoskeletal fraction which is enriched in brain myosin-V. 2. We show that Ca2+/calmodulin-dependent protein kinase activity is also associated with this preparation and phosphorylates brain myosin-V. 3. Calpain, a Ca(2+)-dependent protease, generates a M(r) 80,000 fragment from the COOH terminal region of brain myosin-V containing most or all of the phosphorylation sites. 4. These results suggest that the unique tail domain of this novel myosin is subject to Ca2+ control via phosphorylation by kinase activity associated with the actin cytoskeleton