CUL4-DDB1-CDT2 E3 Ligase Regulates the Molecular Clock Activity by Promoting Ubiquitination-Dependent Degradation of the Mammalian CRY1

The CUL4-DDB1 E3 ligase complex serves as a critical regulator in various cellular processes, including cell proliferation, DNA damage repair, and cell cycle progression. However, whether this E3 ligase complex regulates clock protein turnover and the molecular clock activity in mammalian cells is unknown. Here we show that CUL4-DDB1-CDT2 E3 ligase ubiquitinates CRY1 and promotes its degradation both in vitro and in vivo. Depletion of the major components of this E3 ligase complex, including Ddb1, Cdt2, and Cdt2-cofactor Pcna, leads to CRY1 stabilization in cultured cells or in the mouse liver. CUL4A-DDB1-CDT2 E3 ligase targets lysine 585 within the C-terminal region of CRY1 protein, shown by the CRY1 585KA mutant’s resistance to ubiquitination and degradation mediated by the CUL4A-DDB1 complex. Surprisingly, both depletion of Ddb1 and over-expression of Cry1-585KA mutant enhance the oscillatory amplitude of the Bmal1 promoter activity without altering its period length, suggesting that CUL4A-DDB1-CDT2 E3 targets CRY1 for degradation and reduces the circadian amplitude. All together, we uncovered a novel biological role for CUL4A-DDB1-CDT2 E3 ligase that regulates molecular circadian behaviors via promoting ubiquitination-dependent degradation of CRY1.     

Microvesicles released from microglia stimulate synaptic activity via enhanced sphingolipid metabolism

Microvesicles (MVs) released into the brain microenvironment are emerging as a novel way of cell-to-cell communication. We have recently shown that microglia, the immune cells of the brain, shed MVs upon activation but their possible role in microglia-to-neuron communication has never been explored. To investigate whether MVs affect neurotransmission, we analysed spontaneous release of glutamate in neurons exposed to MVs and found a dose-dependent increase in miniature excitatory postsynaptic current (mEPSC) frequency without changes in mEPSC amplitude. Paired-pulse recording analysis of evoked neurotransmission showed that MVs mainly act at the presynaptic site, by increasing release probability. In line with the enhancement of excitatory transmission in vitro, injection of MVs into the rat visual cortex caused an acute increase in the amplitude of field potentials evoked by visual stimuli. Stimulation of synaptic activity occurred via enhanced sphingolipid metabolism. Indeed, MVs promoted ceramide and sphingosine production in neurons, while the increase of excitatory transmission induced by MVs was prevented by pharmacological or genetic inhibition of sphingosine synthesis. These data identify microglia-derived MVs as a new mechanism by which microglia influence synaptic activity and highlight the involvement of neuronal sphingosine in this microglia-to-neuron signalling pathway.     

Ceramide in nitric oxide inhibition of glioma cell growth. Evidence for the involvement of ceramide traffic

The treatment of C6 glioma cells with the nitric oxide donor, PAPANONOate ((Z)-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate), resulted in a dose-dependent inhibition of cell proliferation. This was associated to a rapid and significant increase of ceramide levels and was mimicked by treatments that augment cellular ceramide. Metabolic experiments with radioactive sphingosine, serine, and choline showed that nitric oxide strongly reduced the utilization of ceramide for the biosynthesis of both sphingomyelin and glucosylceramide. Nevertheless, nitric oxide did not modify the activity of different enzymes of ceramide metabolism. The possibility that nitric oxide impairs the availability of ceramide for sphingolipid biosynthesis was then investigated. The metabolism of N-hexanoyl-[(3)H]sphingosine demonstrated that nitric oxide did not affect the biosynthesis of N-hexanoyl-[(3)H]sphingolipids but inhibited the metabolic utilization of long chain [(3)H]ceramide, synthesized in the endoplasmic reticulum (ER) from the recycled [(3)H]sphingosine. Moreover, results obtained with fluorescent ceramides, brefeldin A, ATP depletion, as well as in a ceramide transport assay indicate that nitric oxide impairs the traffic of ceramide from ER to Golgi apparatus. All this supports that, in glioma cells, the modulation of ceramide traffic can contribute to the regulation of its intracellular levels and participate in the nitric oxide-activated signaling pathway involved in the control of cell proliferation.     

Preparation of spin-labelled sulfatides for EPR studies on model membranes

Using the N-hydroxysuccinimide ester of the fatty acids, galactosylceramide I3-sulfate containing a 5-or 16-doxyl-stearoyl residue was prepared in good yield by acylation of the galactosylsphingosine I3-sulfate (lysosulfatide) obtained from the saponification of the bovine brain sulfatide. The EPR behavior of the two semisynthetic sulfatides was analyzed in natural sulfatide micelles and in multilamellar vesicles of egg phosphatidylcholine. The evaluated parameters demonstrate that these spin-labelled sulfatides can be used for the study of sulfatide behavior in lipid structures.     

Improving Planting Stocks for the Brazilian Atlantic Forest Restoration through Community‐Based Seed Harvesting Strategies

High‐diversity reforestation can help jumpstart tropical forest restoration, but obtaining viable seedlings is a major constraint: if nurseries do not offer them, it is hard to plant all the species one would like. From 2007 to 2009, we investigated five different seed acquisition strategies employed by a well‐established tree nursery in southeastern Brazil, namely (1) in‐house seed harvesters; (2) hiring a professional harvester; (3) amateur seed harvesters; or (4) a seed production cooperative, as well as (5) participating in a seed exchange program. In addition, we evaluated two strategies not dependent on seeds: harvesting seedlings from native tree species found regenerating under Eucalyptus plantations, and in a native forest remnant. A total of 344 native tree and shrub species were collected as seeds or seedlings, including 2,465 seed lots. Among these, a subset of 120 species was obtained through seed harvesting in each year. Overall, combining several strategies for obtaining planting stocks was an effective way to increase species richness, representation of some functional groups (dispersal syndromes, planting group, and shade tolerance), and genetic diversity of seedlings produced in forest tree nurseries. Such outcomes are greatly desirable to support high‐diversity reforestation as part of tropical forest restoration. In addition, community‐based seed harvesting strategies fostered greater socioeconomic integration of traditional communities in restoration projects and programs, which is an important bottleneck for the advance of ecological restoration, especially in developing countries. Finally, we discuss some of the limitations of the various strategies for obtaining planting stocks and the way forward for their improvement.     

RhoA signaling modulates cyclin D1 expression in human lung fibroblasts; implications for idiopathic pulmonary fibrosis

Background

To elucidate further the pathogenesis of sporadic, idiopathic pulmonary arterial hypertension (IPAH) and identify potential therapeutic avenues, differential gene expression in IPAH was examined by suppression subtractive hybridisation (SSH).

Methods

Peripheral lung samples were obtained immediately after removal from patients undergoing lung transplant for IPAH without familial disease, and control tissues consisted of similarly sampled pieces of donor lungs not utilised during transplantation. Pools of lung mRNA from IPAH cases containing plexiform lesions and normal donor lungs were used to generate the tester and driver cDNA libraries, respectively. A subtracted IPAH cDNA library was made by SSH. Clones isolated from this subtracted library were examined for up regulated expression in IPAH using dot blot arrays of positive colony PCR products using both pooled cDNA libraries as probes. Clones verified as being upregulated were sequenced. For two genes the increase in expression was verified by northern blotting and data analysed using Student's unpaired two-tailed t-test.

Results

We present preliminary findings concerning candidate genes upregulated in IPAH. Twenty-seven upregulated genes were identified out of 192 clones examined. Upregulation in individual cases of IPAH was shown by northern blot for tissue inhibitor of metalloproteinase-3 and decorin (P < 0.01) compared with the housekeeping gene glyceraldehydes-3-phosphate dehydrogenase.

Conclusion

Four of the up regulated genes, magic roundabout, hevin, thrombomodulin and sucrose non-fermenting protein-related kinase-1 are expressed specifically by endothelial cells and one, muscleblind-1, by muscle cells, suggesting that they may be associated with plexiform lesions and hypertrophic arterial wall remodelling, respectively.     

Calcitonin-induced changes in the organization of sulfatide-containing membranes.

The interactions of salmon calcitonin with glycosphingolipid sulfatide are studied by right angle light scattering from the lipid suspension, by the excimer to monomer ratio (E/M) of the fluorescence intensity of pyrene phosphatidylcholine and pyrene sulfatide and by the leakage of carboxyfluorescein. It was found that calcitonin strongly modified the structure of the sulfatide aggregate, as indicated by the light scattering determinations. At a lipid peptide ratio 100:1 (molar ratio) light scattering from the suspension was negligible, indicating the formation of peptide-sulfatide complexes with a structure different from that of the lipid aggregate. The interactions of calcitonin with sulfatide when the latter is a component of a bilayer were also evaluated. A specific calcitonin-membrane sulfatide interaction was demonstrated by determining the temperature-dependent E/M of pyrene phosphatidylcholine and pyrene sulfatide in dipalmitoyl phosphatidylcholine/sulfatide (80:20, molar ratio) liposomes. The E/M curves were modified by calcitonin only when the liposomes were labelled with fluorescent sulfatide which probes the sulfatide behavior in the membrane. Furthermore, the addition of calcitonin to the incubation medium of liposomes containing sulfatide promoted the release of vesicle entrapped carboxyfluorescein without disrupting the bilayer structure, the release being correlated with the amount of sulfatide in the bilayer and the calcitonin concentration in the medium.     

Rapid purification of RNAs using fast performance liquid chromatography (FPLC)

We present here an improved RNA purification method using fast performance liquid chromatography (FPLC) size-exclusion chromatography in place of denaturing polyacrylamide gel electrophoresis (PAGE). The method allows preparation of milligram quantities of pure RNA in a single day. As RNA oligonucleotides behave differently from globular proteins in the size-exclusion column, we present standard curves for RNA oligonucleotides of different lengths on both the Superdex 75 column and the Superdex 200 size-exclusion column. Using this approach, we can separate monomer from multimeric RNA species, purify the desired RNA product from hammerhead ribozyme reactions, and isolate refolded RNA that has aggregated after long-term storage. This methodology allows simple and rapid purification of RNA oligonucleotides for structural and biophysical studies.     

Bilayer-micelle transition in phosphatidylcholine-sulfatide mixtures

Sulfatides are membrane-bound glycosphingolipids which tend to associate in micellar forms in water. In this study, combining the data obtained by several techniques, including 31P-NMR, DTA calorimetry, freeze-fracture electron microscopy, trapped volume and turbidity measurements plus enzymatic determination of outer-side "marker ganglioside", have enabled us to establish that bilayered liposomes of phosphatidylcholine formed in the presence of increasing amounts of sulfatide are stable up to 30 mol % glycolipid. Above thus, bilayered lipids progressively start to break up into micellar forms with bilayer-micelle transition complete at sulfatide concentrations above 80 mol %. The gel-to-liquid-crystalline phase transition of a dipalmitoylphosphatidylcholine-sulfatide dispersion is shown to strongly influence the equilibrium between micellar and bilayered forms, the micelles being present at higher concentrations as the fluidity of the system decreases. The possibility that such structural transitions may occur in vivo and effectively contribute to the modulation of some biological properties of the membranes is discussed.