Effect of adiponectin on cardiac β-catenin signaling pathway under angiotensin II infusion

Obesity is associated with heart failure and cardiac hypertrophy. Adiponectin has been shown to play a protective role for cardiovascular diseases. The β-catenin signaling pathway is deeply involved in cardiac hypertrophy. However, the effect of adiponectin on β-catenin signaling has not been investigated in cardiac hypertrophy. Present study aimed to clarify the involvement of adiponectin and β-catenin signaling pathway in the mouse model of angiotensin II (AngII)-induced cardiac hypertrophy. In hearts of Wild type (WT) mice, AngII dose-dependently augmented cytosolic β-catenin protein level. WT and adiponectin knockout (Adipo-KO) mice were administered with AngII at 2.4 mg/kg/day for 14 days and were also injected with adenovirus expressing the adiponectin (Ad-Adipo) or the β-galactosidase (Ad-βgal). Cardiac mRNA levels relating to hypertrophy and β-catenin signaling were increased in Adipo-KO mice and these changes were reversed by Ad-Adipo. Phosphorylation of Akt was increased in Adipo-KO mice and such increases were reversed by Ad-Adipo. Furthermore, the phosphorylation of glycogen synthase kinase 3β (GSK3β) at Ser⁹ and cytosolic β-catenin level were increased in Adipo-KO mice and they were significantly reduced by Ad-Adipo treatment. Phosphorylation of mammalian target of rapamycin (mTOR) was reduced by Ad-Adipo-mediated adiponectin supplementation in WT and Adipo-KO mice. The current study suggests that adiponectin attenuates AngII-induced cardiac hypertrophic signals partly through Akt/GSK3β/β-catenin and Akt/mTOR pathways.     

None of the Rotor Residues of F1-ATPase Are Essential for Torque Generation

F₁-ATPase is a powerful rotary molecular motor that can rotate an object several hundred times as large as the motor itself against the viscous friction of water. Forced reverse rotation has been shown to lead to ATP synthesis, implying that the mechanical work against the motor’s high torque can be converted into the chemical energy of ATP. The minimal composition of the motor protein is α₃β₃γ subunits, where the central rotor subunit γ turns inside a stator cylinder made of alternately arranged α₃β₃ subunits using the energy derived from ATP hydrolysis. The rotor consists of an axle, a coiled coil of the amino- and carboxyl-terminal α-helices of γ, which deeply penetrates the stator cylinder, and a globular protrusion that juts out from the stator. Previous work has shown that, for a thermophilic F₁, significant portions of the axle can be truncated and the motor still rotates a submicron sized bead duplex, indicating generation of up to half the wild-type (WT) torque. Here, we inquire if any specific interactions between the stator and the rest of the rotor are needed for the generation of a sizable torque. We truncated the protruding portion of the rotor and replaced part of the remaining axle residues such that every residue of the rotor has been deleted or replaced in this or previous truncation mutants. This protrusionless construct showed an unloaded rotary speed about a quarter of the WT, and generated one-third to one-half of the WT torque. No residue-specific interactions are needed for this much performance. F₁ is so designed that the basic rotor-stator interactions for torque generation and control of catalysis rely solely upon the shape and size of the rotor at very low resolution. Additional tailored interactions augment the torque to allow ATP synthesis under physiological conditions.     

Prostaglandin EP3 receptor superactivates adenylyl cyclase via the Gq/PLC/Ca pathway in a lipid raft-dependent manner

We previously demonstrated that prostaglandin EP3 receptor augments EP2-elicited cAMP formation in COS-7 cells in a G_i/o-insensitive manner. The purpose of our current study was to identify the signaling pathways involved in EP3-induced augmentation of receptor-stimulated cAMP formation. The enhancing effect of EP3 receptor was irrespective of the C-terminal structure of the EP3 isoform. This EP3 action was abolished by treatment with inhibitors for phospholipase C and intracellular Ca²⁺-related signaling molecules such as U73122, staurosporine, 2-APB and SK&F 96365. Indeed, an EP3 agonist stimulated IP₃ formation and intracellular Ca²⁺ mobilization, which was blocked by U73122, but not by pertussis toxin. The enhancing effect by EP3 on cAMP formation was mimicked by both a Ca²⁺ ionophore and the activation of a typical G_q-coupled receptor. Moreover, EP3 was exclusively localized to the raft fraction in COS-7 cells and EP3-elicited augmentation of cAMP formation was abolished by cholesterol depletion and introduction of a dominant negative caveolin-1 mutant. These results suggest that EP3 elicits adenylyl cyclase superactivation via G_q/phospholipase C activation and intracellular Ca²⁺ mobilization in a lipid raft microdomain-dependent manner.     

Role for protein geranylgeranylation in adult T-cell leukemia cell survival

Adult T-cell leukemia (ATL) is a fatal lymphoproliferative disease that develops in human T-cell leukemia virus type I (HTLV-I)-infected individuals. Despite the accumulating knowledge of the molecular biology of HTLV-I-infected cells, effective therapeutic strategies remain to be established. Recent reports showed that the hydroxyl-3-methylglutaryl (HMG)-CoA reductase inhibitor statins have anti-proliferative and apoptotic effects on certain tumor cells through inhibition of protein prenylation. Here, we report that statins hinder the survival of ATL cells and induce apoptotic cell death. Inhibition of protein geranylgeranylation is responsible for these effects, since simultaneous treatment with isoprenoid precursors, geranylgeranyl pyrophosphate or farnesyl pyrophosphate, but not a cholesterol precursor squalene, restored the viability of ATL cells. Simvastatin inhibited geranylgeranylation of small GTPases Rab5B and Rac1 in ATL cells, and a geranylgeranyl transferase inhibitor GGTI-298 reduced ATL cell viability more efficiently than a farnesyl transferase inhibitor FTI-277. These results not only unveil an important role for protein geranylgeranylation in ATL cell survival, but also implicate therapeutic potentials of statins in the treatment of ATL.     

House dust mite allergen Der f 1 can induce the activation of latent TGF-β via its protease activity

A major house dust mite allergen Der f 1 belongs to the papain-like cysteine protease family. This study investigated whether Der f 1 can cleave the latency-associated peptide (LAP) of transforming growth factor (TGF)-β via its proteolytic activity and activate latent TGF-β. We found that Der f 1 can cleave LAP and induce the activation of latent TGF-β, leading to functional Smad signaling. Importantly, these actions of Der f 1 were inhibited by cysteine protease inhibitor E64 or inactivation of the protease activity by heat. Thus, latent TGF-β may be a direct target of Der f 1 protease activity.     

Molecular Cloning and Crystal Structural Analysis of a Novel β-N-Acetylhexosaminidase from Paenibacillus sp. TS12 Capable of Degrading Glycosphingolipids

We report the molecular cloning and characterization of two novel β-N-acetylhexosaminidases (β-HEX, EC 3.2.1.52) from Paenibacillus sp. strain TS12. The two β-HEXs (Hex1 and Hex2) were 70% identical in primary structure, and the N-terminal region of both enzymes showed significant similarity with β-HEXs belonging to glycoside hydrolase family 20 (GH20). Interestingly, however, the C-terminal region of Hex1 and Hex2 shared no sequence similarity with the GH20 β-HEXs or other known proteins. Both recombinant enzymes, expressed in Escherichia coli BL21(DE3), hydrolyzed the β-N-acetylhexosamine linkage of chitooligosaccharides and glycosphingolipids such as asialo GM2 and Gb4Cer in the absence of detergent. However, the enzyme was not able to hydrolyze GM2 ganglioside in the presence or in the absence of detergent. We determined three crystal structures of Hex1; the Hex1 deletion mutant Hex1-ΔC at a resolution of 1.8 Å; Hex1-ΔC in complex with β-N-acetylglucosamine at 1.6 Å; and Hex1-ΔC in complex with β-N-acetylgalactosamine at 1.9 Å. We made a docking model of Hex1-ΔC with GM2 oligosaccharide, revealing that the sialic acid residue of GM2 could hinder access of the substrate to the active site cavity. This is the first report describing the molecular cloning, characterization and X-ray structure of a procaryotic β-HEX capable of hydrolyzing glycosphingolipids.     

Immunohistochemical study of NG2 chondroitin sulfate proteoglycan expression in the small and large intestines

The intestinal subepithelial myofibroblasts (ISEMFs) are located in the lamina propria under the epithelial cells. ISEMFs are thought to have an important role in protecting and maintaining the integrity of the epithelial cell layer and also in the process of wound healing. In this study, we report that the membrane-bound proteoglycan NG2 is abundantly distributed in the ISEMF layer of the mouse and human intestines. NG2 immunostaining in this layer is distributed with similar intensity from the crypt to villi. NG2 is also immunolocalized along the membranes of smooth muscle cells in the intestinal muscle layer. However, skeletal and cardiac muscles are not immunostained for NG2, demonstrating selective expression of the proteoglycan by smooth muscle cells. Using electron microscopy, NG2 immunoreactivity was strongly observed along the cell membranes of ISEMF, with weak diffusion into the neighboring matrix, indicative of the presence of some “shed” NG2. This first report of NG2 proteoglycan expression by ISEMF provides insights into the nature of the interaction of these cells with extracellular matrix and/or intestinal epithelial cells.