Calcineurin B-like 3 calcium sensor associates with and inhibits 5'-methylthioadenosine nucleosidase 2 in Arabidopsis.

Calcineurin B-like (CBL) proteins constitute a unique family of calcium sensor relays in plants. It is well known that CBLs detect the calcium signals elicited by a variety of abiotic stresses and relay the information to a group of serine/threonine protein kinases called CBL-interacting protein kinases (CIPKs). In this study, we found that a few CBL members can also target another group of enzymes 5'-methylthioadenosine nucleosidases (MTANs), which are encoded by two genes in Arabidopsis, AtMTAN1 and AtMTAN2. In the yeast two-hybrid system, AtMTAN1 interacted with multiple CBL members such as CBL2, CBL3 and CBL6, whereas AtMTAN2 associated exclusively with CBL3. We further demonstrated that the CBL3-AtMTAN2 association occurs in a calcium-dependent manner, which results in a significant decrease in the enzyme activity of the AtMTAN2 protein. Taken together, these results clearly indicate that the CBL family can target at least two distinct groups of enzymes (CIPKs and MTANs), conferring an additional level of complexity on the CBL-mediated signaling networks. In addition, our finding also provides a novel molecular mechanism by which calcium signals are transduced to alter metabolite profiles in plants.

Effect of two lipid emulsions on reversing high-dose levobupivacaine-induced reduced vasoconstriction in the rat aortas.

The goals of this study were to determine which lipid emulsion (Intralipid(®) and Lipofundin MCT/LCT(®)) is more effective in reversing high-dose levobupivacaine-induced reduced vasoconstriction in isolated rat aortas and to examine the associated cellular mechanisms with a particular focus on the endothelium. Two lipid emulsion concentration-response curves were generated using high-dose levobupivacaine-induced reduced vasoconstriction and vasodilation of isolated aortas pretreated with or without 60 mM KCl. Endothelial nitric oxide synthase (eNOS) and caveolin-1 phosphorylation were measured in rat aortic tissue treated with levobupivacaine in the presence or absence of lipid emulsion. Dichlorofluorescein oxidation, a measure of reactive oxygen species production, was measured in lipid emulsion-treated human umbilical vein endothelial cells. In levobupivacaine (0.3 mM)-induced reduced vasoconstriction of isolated aorta, the magnitude of the Intralipid(®)- and Lipofundin MCT/LCT(®)-mediated reversal was not significantly different. Lipid emulsion reversal of levobupivacaine-induced reduced vasoconstriction was greater in endothelium-intact aortas than in endothelium-denuded aortas. The two lipid emulsions similarly inhibited levobupivacaine-induced eNOS phosphorylation in aortic tissue. Pretreatment with both lipid emulsions increased dichlorofluorescein oxidation. Both Intralipid(®) and Lipofundin MCT/LCT(®) are equally effective for vascular tone recovery from high-dose levobupivacaine-induced reduced vasoconstriction. This reversal is mediated partially by decreasing nitric oxide bioavailability.

Protective effects of HV-P411 complex against D-galactosamine-induced hepatotoxicity in rats.

This study examined the hepatoprotective effect of the HV-P411 complex, an herbal extract mixture from the seeds of Vitis vinifera, Schisandra chinensis and Taraxacum officinale, against D-galactosamine (D-GalN)-induced hepatitis. Hepatotoxicity was induced by D-GalN (700 mg/kg, i.p.), and the HV-P411 complex was administered orally 48, 24, and 2 h before and 6 h after D-GalN injection. Increases in serum aminotransferase activity and lipid peroxidation and a decrease in hepatic glutathione content were attenuated by the HV-P411 complex 24 h after D-GalN treatment. The HV-P411 complex attenuated the increases in serum tumor necrosis factor-α, interleukin (IL)-6 level and cyclooxygenase-2 protein production and their mRNA expressions, while increases in serum IL-10 level and heme oxygenase-1 protein production and their mRNA expressions were augmented by the HV-P411 complex. The increased translocation of nuclear factor-κB and c-Jun phosphorylation were attenuated by treatment with the HV-P411 complex. Our results suggest that the HV-P411 complex prevents D-GalN-induced hepatotoxicity via antioxidative and anti-inflammatory activities.

The Arabidopsis calcium sensor calcineurin B-like 3 inhibits the 5'-methylthioadenosine nucleosidase in a calcium-dependent manner.

Calcineurin B-like (CBL) proteins represent a unique family of calcium sensors in plant cells. Sensing the calcium signals elicited by a variety of abiotic stresses, CBLs transmit the information to a group of serine/threonine protein kinases (CBL-interacting protein kinases [CIPKs]), which are currently known as the sole targets of the CBL family. Here, we report that the CBL3 member of this family has a novel interaction partner in addition to the CIPK proteins. Extensive yeast two-hybrid screenings with CBL3 as bait identified an interesting Arabidopsis (Arabidopsis thaliana) cDNA clone (named AtMTAN, for 5'-methylthioadenosine nucleosidase), which encodes a polypeptide similar to EcMTAN from Escherichia coli. Deletion analyses showed that CBL3 utilizes the different structural modules to interact with its distinct target proteins, CIPKs and AtMTAN. In vitro and in vivo analyses verified that CBL3 and AtMTAN physically associate only in the presence of Ca(2+). In addition, we empirically demonstrated that the AtMTAN protein indeed possesses the MTAN activity, which can be inhibited specifically by Ca(2+)-bound CBL3. Overall, these findings suggest that the CBL family members can relay the calcium signals in more diverse ways than previously thought. We also discuss a possible mechanism by which the CBL3-mediated calcium signaling regulates the biosynthesis of ethylene and polyamines, which are involved in plant growth and development as well as various stress responses.