Impaired carotenogenesis can affect organization and functionality of etioplast membranes

The effects of impaired carotenogenesis on plastid membrane organization, functionality and stability were studied in etiolated barley plants grown at 20 and 30°C. The plants were treated with norflurazon or amitrole, two herbicides affecting phytoene desaturation and lycopene cyclization, respectively. At 20°C, the amitrole-treated etioplasts, which accumulated lycopene in their inner membranes, exhibited disorganized prolamellar bodies, containing a prevalent form of non-phototransformable protochlorophyllide (Pchlide). They also showed a certain difficulty in reducing the phototransformable pigment to chlorophyllide when exposed to light, and were unable to reform the active ternary complex [protochlorophyllide–oxidoreductase (POR)–Pchlide–NADPH] when placed back in darkness. No ultrastructural alterations were found in norflurazon-treated etioplasts, with carotenogenesis inhibited at the phytoene desaturation step. In these latter organelles, Pchlide, whose forms were comparable with those of the control etioplasts, was photoreduced quickly after illumination and the ternary complex was reformed during a subsequent dark period. Thus, the impaired carotenogenesis leading to the accumulation of lycopene showed greater interference with the etioplast membrane arrangement and functionality than did the earlier interruption of the biosynthetic pathway at the phytoene level. This might be due to the different interactions of the distinct carotenoid precursors with other membrane components. However, in etioplasts of norflurazon-treated plants, a rise in growth temperature caused a partial demolition of prolamellar bodies, showing a lowered thermostability of the carotenoid-deficient membranes. This latter effect strengthens the concept that a correct and complete carotenogenesis pathway, leading to the synthesis of polar carotenoids (i.e. xanthophylls), is required for the maintenance of stable plastid membranes.     

Heterologous expression in Escherichia coli of Neurospora crassa neutral trehalase as an active enzyme

Neutral trehalase from Neurospora crassa was expressed in Escherichia coli as a polypeptide of 84 kDa in agreement with the theoretical size calculated from the corresponding cDNA. The recombinant neutral trehalase, purified by affinity chromatography exhibited a specific activity of 80–150 mU/mg protein. Optima of pH and temperature were 7.0 and 30 °C, respectively. The enzyme was absolutely specific for trehalose, and was quite sensitive to incubation at 40 °C. The recombinant enzyme was totally dependent on calcium, and was inhibited by ATP, copper, silver, aluminium and cobalt. K_M was 42 mM, and V_max was 30.6 nmol of glucose/min. The recombinant protein was phosphorylated by cAMP-dependent protein kinase, but not significantly activated. Immunoblotting with polyclonal antiserum prepared against the recombinant protein showed that neutral trehalase protein levels increased during exponential phase of N. crassa growth and dropped at the stationary phase. This is the first report of a neutral trehalase produced in E. coli with similar biochemical properties described for fungi native neutral trehalases, including calcium-dependence.     

Regulation of Nedd4-2 self-ubiquitination and stability by a PY motif located within its HECT-domain

Ubiquitin ligases play a pivotal role in substrate recognition and ubiquitin transfer, yet little is known about the regulation of their catalytic activity. Nedd4 (neural-precursor-cell-expressed, developmentally down-regulated 4)-2 is an E3 ubiquitin ligase composed of a C2 domain, four WW domains (protein-protein interaction domains containing two conserved tryptophan residues) that bind PY motifs (L/PPXY) and a ubiquitin ligase HECT (homologous with E6-associated protein C-terminus) domain. In the present paper we show that the WW domains of Nedd4-2 bind (weakly) to a PY motif (LPXY) located within its own HECT domain and inhibit auto-ubiquitination. Pulse-chase experiments demonstrated that mutation of the HECT PY-motif decreases the stability of Nedd4-2, suggesting that it is involved in stabilization of this E3 ligase. Interestingly, the HECT PY-motif mutation does not affect ubiquitination or down-regulation of a known Nedd4-2 substrate, ENaC (epithelial sodium channel). ENaC ubiquitination, in turn, appears to promote Nedd4-2 self-ubiquitination. These results support a model in which the inter- or intra-molecular WW-domain-HECT PY-motif interaction stabilizes Nedd4-2 by preventing self-ubiquitination. Substrate binding disrupts this interaction, allowing self-ubiquitination of Nedd4-2 and subsequent degradation, resulting in down-regulation of Nedd4-2 once it has ubiquitinated its target. These findings also point to a novel mechanism employed by a ubiquitin ligase to regulate itself differentially compared with substrate ubiquitination and stability.     

Desulfovibrio vulgaris bacterioferritin uses H(2)O(2) as a co-substrate for iron oxidation and reveals DPS-like DNA protection and binding activities

β?-GPI (β?-glycoprotein I) is a plasma glycoprotein ascribed with an anti-angiogenic function; however, the biological role and molecular basis of its action in cell migration remain unknown. The aim of the present study was to assess the contribution of β?-GPI to HAEC (human aortic endothelial cell) migration and the details of its underlying mechanism. Using wound healing and Boyden chamber assays, we found that β?-GPI inhibited endothelial cell migration, which was restored by its neutralizing antibody. NF-κB (nuclear factor κB) inhibitors and lentiviral siRNA (small interfering RNA) silencing of NF-κB significantly attenuated the inhibitory effect of β?-GPI on cell migration. Moreover, β?-GPI was found to induce IκBα (inhibitor of NF-κB) phosphorylation and translocation of p65 and p50. We further demonstrated that mRNA and protein levels of eNOS [endothelial NO (nitric oxide) synthase] and NO production were all increased by β?-GPI and these effects were remarkably inhibited by NF-κB inhibitors and siRNAs of p65 and p50. Furthermore, β?-GPI-mediated inhibition of cell migration was reversed by eNOS inhibitors and eNOS siRNAs. The findings of the present study provide novel insight into the ability of β?-GPI to inhibit endothelial cell migration predominantly through the NF-κB/eNOS/NO signalling pathway, which indicates a potential direction for clinical therapy in vascular diseases.     

Protein kinase CK2 promotes cancer cell viability via up-regulation of cyclooxygenase-2 expression and enhanced prostaglandin E2 production

Augmented expression of protein kinase CK2 is associated with hyperproliferation and resistance to apoptosis in cancer cells. Effects of CK2 are at least partially linked to signaling via the Wnt/β-catenin pathway, which is dramatically enhanced in colon cancer. Cyclooxygenase-2 (COX-2), a Wnt/β-catenin target gene, has been associated with enhanced cancer progression and metastasis. However, the possibility that a connection may exist between CK2 and COX-2 has not been explored previously. Here we investigated changes in COX-2 expression and activity upon CK2 modulation and evaluated how these changes affected cell viability. COX-2 expression and cell viability decreased upon selective inhibition of COX-2 with SC-791 or CK2 with 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole (DMAT), both in human colon (HT29-ATCC, HT29-US, DLD-1) and breast (ZR-75) cancer cells, as well as in human embryonic kidney (HEK-293T) cells. On the other hand, ectopic CK2α expression promoted up-regulation of COX-2 by activating the Wnt/β-catenin pathway in HEK-293T cells. Noteworthy, over-expression of either CK2α, β-catenin or COX-2, as well as supplementation of the medium with prostaglandin E2 (PGE2), all were individually sufficient to overcome limitations in cell viability triggered by CK2 inhibition either upon addition of DMAT or over-expression of a dominant negative CK2α variant. Altogether, these findings provide new insight to the role of CK2 in cancer by up-regulating COX-2 expression and thereby PGE2 production.     

Selection of multipotent cells and enhanced muscle reconstruction by myogenic macrophage-secreted factors

Skeletal muscle regeneration relies on satellite cells, a population of myogenic precursors. Inflammation also plays a determinant role in the process, as upon injury, macrophages are attracted by the damaged myofibers and the activated satellite cells and act as key elements of dynamic muscle supportive stroma. Yet, it is not known how macrophages interact with the more profound stem cells of the satellite cell niche. Here we show that in the presence of a murine macrophage conditioned medium (mMCM) a subpopulation of multipotent cells could be selected and expanded from adult rat muscle. These cells were small, round, poorly adhesive, slow-growing and showed mesenchymal differentiation plasticity. At the same time, mMCM showed clear myogenic capabilities, as experiments with satellite cells mechanically isolated from suspensions of single myofibers showed that the macrophagic factors inhibited their tendency to shift towards adipogenesis. In vivo, intramuscular administrations of concentrated mMCM in a rat model of extensive surgical ablation dramatically improved muscle regeneration. Altogether, these findings suggest that macrophagic factors could be of great help in developing therapeutic protocols with myogenic stem cells.     

E3-independent monoubiquitination of ubiquitin-binding proteins

Ubiquitin (Ub)-binding domains (UBDs) are key elements in conveying Ub-based cellular signals. UBD-containing proteins interact with ubiquitinated targets and control numerous biological processes. They themselves undergo UBD-dependent monoubiquitination, which promotes intramolecular binding of the UBD to the attached Ub and leads to their inactivation. Here, we report that, in contrast to the established ubiquitination pathway, the presence of UBDs allows the ubiquitination of host proteins independently of E3 ligases. UBDs of different types, including UBA, UIM, UBM, NFZ, and UBZ, can directly cooperate with Ub-charged E2 enzymes to promote monoubiquitination. Using FRET and siRNA technologies, we verify that Ub-loaded E2 and substrates interact in cells and that E2 enzymes are essential for their monoubiquitination in vivo. This modification is mechanistically and functionally distinct from E3-mediated and growth factor-dependent monoubiquitination.     

Asymmetric synthesis of the four diastereoisomers of a novel non-steroidal farnesoid X receptor (FXR) agonist: Role of the chirality on the biological activity

An asymmetric synthetic strategy was designed for the preparation of the four possible diastereoisomers of 3,6-dimethyl-1-(2-methylphenyl)-4-(4-phenoxyphenyl)-4,8-dihydro-1H-pyrazolo[3,4-e][1,4]thiazepin-7-one, a non-steroidal FXR agonist, we recently discovered following a virtual screening approach. The results obtained from an AlphaScreen assay clearly demonstrated that only the isomer endowed with 4R,6S absolute configuration is responsible for the biological activity. A deep investigation of the different putative binding modes adopted by these enantiomerically pure ligands using computational modeling studies confirmed the enantioselectivity of FXR towards this class of molecules.