A new class of GTP-binding protein transglutaminase II (G h ) couples to a 69-kDa phospholipase C (PLC). An 8-amino acid region (Leu 665 -Lys 672 ) of the ␣-subunit of G h (G␣ h ) is involved in interaction and activation of PLC, an observation that has now been used to characterize the 69-kDa PLC further. A 20-amino acid peptide corresponding to Leu 654 -Leu 673 of G␣ h was used to prepare an affinity resin. On incubation with a partially purified PLC preparation from rat liver membranes, the affinity resin-bound ϳ69-and 85-kDa proteins were recognized by an antibody to the 69-kDa PLC. Both purified 69-kDa PLC and PLC-␦1 bound to the affinity resin; moreover, antibodies to PLC-␦1 recognized the 69-kDa PLC, and antibodies to the 69-kDa PLC recognized PLC-␦1.

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Oxidative stress plays an important role in the pathogenesis of bronchial asthma. An excess production of reactive oxygen species (ROS) and defective endogenous antioxidant defense mechanisms may be present in asthma. Reduced glutathione (GSH) is one of the most important reducing agents against oxidant free radicals. A reducing agent, L-2-oxothiazolidine-4-carboxylic acid (OTC), a prodrug of cysteine, increases intracellular GSH. We have used a mouse model for asthma to determine effects of OTC on allergen-induced bronchial inflammation and airway hyper-responsiveness. The administration of OTC reduced bronchial inflammation and airway hyper-responsiveness. ROS generation in bronchoalveolar lavage fluids was increased by ovalbumin (OVA) inhalation, but this increase was diminished by administration of OTC. The increased IL-4, IL-5, IL-13, and eosinophil cationic protein levels in lungs after OVA inhalation were significantly reduced by the administration of OTC. In addition, the increased expression of ICAM-1, VCAM-1, RANTES, and eotaxin in lungs after OVA inhalation was significantly reduced by the administration of OTC. We also showed that the increased NF-kappaB levels in nuclear protein extracts of lung tissues at 72 h after OVA inhalation were decreased by the administration of OTC. These findings suggest that OTC may reduce airway inflammation and hyper-responsiveness through regulation of NF-kappaB activity.

Tissue type transglutaminase (TGII, also known as G h ) has been considered a multifunctional protein, with both transglutaminase and GTPase activity. The role of the latter function, which is proposed as a coupling mechanism between ␣ 1 -adrenergic receptors and phospholipase C (PLC), is not well defined. TGII was overexpressed in transgenic mice in a cardiac specific manner to delineated relevant signaling pathways and their consequences in the heart. Cardiac transglutaminase activity in the highest expressing line was ϳ37-fold greater than in nontransgenic lines. However, in vivo signaling to PLC, as assessed by inositol phosphate turnover in [ 3 H]myoinositol organ bath atrial preparations, was not increased in the TGII mice at base line or in response to ␣ 1 -adrenergic receptor stimulation; nor was protein kinase C␣ (PKC␣) or PKC⑀ activity enhanced in the TGII transgenic mice. This is in contrast to mice moderately (ϳ5-fold) overexpressing G ␣q , where inositol phosphate turnover and PKC activity were found to be clearly enhanced. TGII overexpression resulted in a remodeling of the heart with mild hypertrophy, elevated expression of ␤-myosin heavy chain and ␣-skeletal actin genes, and diffuse interstitial fibrosis. Resting ventricular function was depressed, but responsiveness to ␤-agonist was not impaired. This set of pathophysiologic findings is distinct from that evoked by overexpression of G ␣q . We conclude that TGII acts in the heart primarily as a transglutaminase, and modulation of this function results in unique pathologic sequelae. Evidence for TGII acting as a G-protein-like transducer of receptor signaling to PLC in the heart is not supported by these studies.Tissue type transglutaminase (TGII, 1 also known as G h ) is a multifunctional GTP-binding protein that has been proposed to mediate both transglutamination and receptor-stimulated PLC activation (1, 2). As a transglutaminase, TGII catalyzes Ca 2ϩ -dependent post-translational modification of proteins through formation of isopeptide bonds between glutamine and lysine residues (3). However, unlike other transglutaminases, TGII binds guanine nucleotides in a 1:1 ratio and hydrolyzes GTP (4,5). This GTPase activity is independent of transglutaminase activity (6) and has been shown to mediate ␣ 1 -adrenergic receptor (␣ 1 AR) stimulation of phospholipase C ␦1, increasing inositol phosphate turnover in TGII-transfected cells (7-13).Numerous in vitro studies implicate TGII in a wide variety of biological processes, including regulation of cell growth and differentiation (14 -16), apoptosis (17), and tissue repair (18,19), as well as signal transduction via ␣ 1 AR. The role of TGII, however, in regulation of these events in relevant target tissues remains unclear. Activation of ␣ 1 AR expressed on myocytes by catecholamines stimulates PLC activity, increasing inositol phosphate turnover in the heart (20). Traditionally, this signal has been considered to be transduced by the ␣ subunit of the heterotrimeric G protein G q (21). Indeed, a number of ...

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