NO serves as a signaling intermediate downstream of H2O2 to modulate dynamic microtubule cytoskeleton during responses to VD-toxins in Arabidopsis

Although hydrogen peroxide (H₂O₂) and nitric oxide (NO) can act as an upstream signaling molecule to modulate the dynamic microtubule cytoskeleton during the defense responses to Verticillium dahliae (VD) toxins in Arabidopsis, it is not known the relationship between these two signaling molecules. Here, we show that VD-toxin-induced NO accumulation was dependent on prior H₂O₂ production, NO is downstream of H₂O₂ in the signaling process, and that H₂O₂ acted synergistically with NO to modulate the dynamic microtubule cytoskeleton responses to VD-toxins in Arabidopsis.     

The CCAAT binding factor can mediate interactions between CONSTANS-like proteins and DNA

CONSTANS-Like (COL) proteins are plant-specific nuclear regulators of gene expression but do not contain a known DNA-binding motif. We tested whether a common DNA-binding protein can deliver these proteins to specific cis-acting elements. We screened for proteins that interact with two members of a subgroup of COL proteins. These COL proteins were Tomato COL1 (TCOL1), which does not seem to be involved in the control of flowering time, and the Arabidopsis thaliana CONSTANS (AtCO) protein which mediates photoperiodic induction of flowering. We show that the C-terminal plant-specific CCT (CO, CO-like, TIMING OF CAB EXPRESSION 1) domain of both proteins binds the trimeric CCAAT binding factor (CBF) via its HAP5/NF-YC component. Chromatin immunoprecipitation demonstrated that TCOL is recruited to the CCAAT motifs of the yeast CYC1 and HEM1 promoters by HAP5. In Arabidopsis, each of the three CBF components is encoded by several different genes that are highly transcribed. Under warm long days, high levels of expression of a tomato HAP5 (THAP5a) gene can reduce the flowering time of Arabidopsis. A mutation in the CCT domain of TCOL1 disrupts the interaction with THAP5 and the analogous mutation in AtCO impairs its function and delays flowering. CBFs are therefore likely to recruit COL proteins to their DNA target motifs in planta.     

The complexities of G-protein-coupled receptor kinase function in Hedgehog signaling

Hedgehog (Hh) signaling is essential for proper tissue patterning and maintenance and has a substantial impact on human disease. While many of the main components and mechanisms involved in transduction of the Hh signal have been identified, the details of how the pathway functions are continually being refined. One aspect that has attracted much attention recently is the involvement of G-protein-coupled receptor kinases (GRKs) in the pathway. These regulators of G-protein-coupled receptor (GPCR) signaling have an evolutionarily-conserved function in promoting high-threshold Hh target gene expression through regulation of Smoothened (Smo), a GPCR family member that activates intracellular Hh signaling. Several models of how GRKs impact on Smo to increase downstream signaling have been proposed. Recently, we demonstrated that these kinases have surprisingly complex and conflicting roles, acting to limit signaling through the pathway while also promoting Smo activity. In addition to the previously described direct effects of Gprk2 on Smo activation, Gprk2 also indirectly affects Hh signaling by controlling production of the second messenger cyclic AMP to influence Protein kinase A activity.     

Entamoeba histolytica: lipid rafts are involved in adhesion of trophozoites to host extracellular matrix components

Adhesion is an important virulence function for Entamoeba histolytica, the causative agent of amoebic dysentery. Lipid rafts, cholesterol-rich domains, function in compartmentalization of cellular processes. In E. histolytica, rafts participate in parasite-host cell interactions; however, their role in parasite-host extracellular matrix (ECM) interactions has not been explored. Disruption of rafts with a cholesterol extracting agent, methyl-β-cyclodextrin (MβCD), resulted in inhibition of adhesion to collagen, and to a lesser extent, to fibronectin. Replenishment of cholesterol in MβCD-treated cells, using a lipoprotein-cholesterol concentrate, restored adhesion to collagen. Confocal microscopy revealed enrichment of rafts at parasite-ECM interfaces. A raft-resident adhesin, the galactose/N-acetylgalactosamine-inhibitable lectin, mediates interaction to host cells by binding to galactose or N-acetylgalactosamine moieties on host glycoproteins. In this study, galactose inhibited adhesion to collagen, but not to fibronectin. Together these data suggest that rafts participate in E. histolytica-ECM interactions and that raft-associated Gal/GalNAc lectin may serve as a collagen receptor.     

Overexpression of Arabidopsis ATX1 retards plant growth under severe copper deficiency

In a previous study, we demonstrated that Arabidopsis Antioxidant Protein1 (ATX1) plays an essential role in copper (Cu) homeostasis, conferring tolerance to both excess and subclinically deficient Cu. The Cu-binding motif MXCXXC was required for the physiological function of ATX1. In this study, we found that overexpression of ATX1 resulted in hypersensitivity to severe Cu deficiency despite enhancing tolerance to subclinical Cu deficiency. However, overexpression of mutated ATX1, replacing the Cu-binding motif MXCXXC with MXGXXG, abolished the hypersensitivity, for no differences from the wild type under the same conditions. Thus, the expression of ATX1 must be cautiously regulated to avoid homeostatic imbalance with the over-chelation of Cu.     

Transformed 3T3 cells have reduced levels and altered subcellular distribution of the major PKC substrate protein marcks

The MARCKS (myristylated alanine-rich C-kinase substrate) protein is an abundant calmodulin-binding protein that is a major and specific endogenous substrate of protein kinase C (PKC). Stimulation of cells with phorbol esters or other activators of PKC has been shown previously to result in rapid phosphorylation of MARCKS proteins and redistribution of these myristylated C-kinase substrates from membrane to cytosol. Here we show that NIH3T3 murine fibroblasts transformed by p21-HA-C-RAS or pp60-V-SRC oncoproteins have markedly reduced levels of p68-MARCKS and that most of the remaining MARCKS protein is found in the cytosol. 3T3 cells containing a nontransforming oncoprotein p26-BCL2, in contrast, exhibited normal levels and distribution of p68-MARCKS. When taken together with recent evidence that MARCKS proteins are involved in regulating organization of the membrane cytoskeleton, our findings suggest that oncoprotein-mediated alterations in MARCKS protein levels and subcellular distribution may contribute to the development or maintenance of the transformed phenotpe.     

Association Between the Rat Homologue of CO-029, a Metastasis-associated Tetraspanin Molecule and Consumption Coagulopathy

Recently, we have described a panel of metastasis-associated antigens in the rat, i.e., of molecules expressed on metastasizing, but not on nonmetastasizing tumor lines. One of these molecules, recognized by the monoclonal antibody D6.1 and named accordingly D6.1A, was found to be abundantly expressed predominantly on mesenchyme-derived cells. The DNA of the antigen has been isolated and cloned. Surprisingly, the gene product proved to interfere strongly with coagulation.

The 1.182-kb cDNA codes for a 235–amino acid long molecule with a 74.2% homology in the nucleotide and a 70% homology in the amino acid sequence to CO-029, a human tumor-associated molecule. According to the distribution of hydrophobic and hydrophilic amino acids, D6.1A belongs to the tetraspanin superfamily. Western blotting of D6.1A-positive metastasizing tumor lines revealed that the D6.1A, like many tetraspanin molecules, is linked to further membrane molecules, one of which could be identified as α6β1 integrin. Transfection of a low-metastasizing tumor cell line with D6.1A cDNA resulted in increased metastatic potential and provided a clue as to the functional role of D6.1A. We noted massive bleeding around the metastases and, possibly as a consequence, local infarctions predominantly in the mesenteric region and all signs of a consumption coagulopathy. By application of the D6.1 antibody the coagulopathy was counterregulated, though not prevented.

It has been known for many years that tumor growth and progression is frequently accompanied by thrombotic disorders. Our data suggest that the phenomenon could well be associated with the expression of tetraspanin molecules.

     

Genistein Inhibits the Activity of Kv1.3 Potassium Channels in Human T Lymphocytes

In the present study, the whole-cell patch-clamp technique was applied to follow the inhibitory effect of genistein — a tyrosine kinase inhibitor and a natural anticancer agent—on the activity of voltage-gated potassium channels Kv1.3 expressed in human T lymphocytes (TL). Obtained data provide evidence that genistein application in the concentration range of 1–80 μM reversibly decreased the whole-cell potassium currents in TL in a concentration-dependent manner to about 0.23 of the control value. The half-blocking concentration range of genistein was from 10 to 40 μM. The current inhibition was correlated in time with a significant decrease of the current activation rate. The steady-state activation of the currents was unchanged upon application of genistein, as was the inactivation rate. The inhibitory effect of genistein on the current amplitude and activation kinetics was voltage-independent. The current inhibition was not changed significantly in the presence of 1 mM of sodium orthovanadate, a tyrosine phosphatase inhibitor. Application of daidzein, an inactive genistein analogue, did not affect significantly either the current amplitudes or the activation kinetics. Possible mechanisms of the observed phenomena and their significance for genistein-induced inhibition of cancer cell proliferation are discussed.