Differential effects of painful and non-painful stimulation on tactile processing in fibromyalgia syndrome and subjects with masochistic behaviour

Background

In healthy subjects repeated tactile stimulation in a conditioning test stimulation paradigm yields attenuation of primary (S1) and secondary (S2) somatosensory cortical activation, whereas a preceding painful stimulus results in facilitation.

Methodology/Principal Findings

Since previous data suggest that cognitive processes might affect somatosensory processing in S1, the present study aims at investigating to what extent cortical reactivity is altered by the subjective estimation of pain. To this end, the effect of painful and tactile stimulation on processing of subsequently applied tactile stimuli was investigated in patients with fibromyalgia syndrome (FMS) and in subjects with masochistic behaviour (MB) by means of a 122-channel whole-head magnetoencephalography (MEG) system. Ten patients fulfilling the criteria for the diagnosis of FMS, 10 subjects with MB and 20 control subjects matched with respect to age, gender and handedness participated in the present study. Tactile or brief painful cutaneous laser stimuli were applied as conditioning stimulus (CS) followed by a tactile test stimulus (TS) 500 ms later. While in FMS patients significant attenuation following conditioning tactile stimulation was evident, no facilitation following painful stimulation was found. By contrast, in subjects with MB no attenuation but significant facilitation occurred. Attenuation as well as facilitation applied to cortical responses occurring at about 70 ms but not to early S1 or S2 responses. Additionally, in FMS patients the amount of attenuation was inversely correlated with catastrophizing tendency.

Conclusion

The present results imply altered cortical reactivity of the primary somatosensory cortex in FMS patients and MB possibly reflecting differences of individual pain experience.     

Ubiquitin-related modifier SUMO1 and nucleocytoplasmic transport

S mall u biquitin related mo difier SUMO-1 and its homologs can be conjugated to a large number of cellular proteins. This involves an enzymatic cascade that resembles ubiquitination, and the modification can be reverted by isopeptidases. SUMOylation does not lead to degradation but instead appears to regulate protein/protein interactions, intracellular localization and protects some modified targets from ubiquitin-dependent degradation. Data collected for more than 30 different target proteins point to two cellular processes, nucleocytoplasmic transport and intranuclear targeting, in which SUMO plays an active role. Here we will focus on links between SUMO and nuclear transport.     

A functional homologue of the RNA1 gene product in Schizosaccharomyces pombe: purification, biochemical characterization, and identification of a leucine-rich repeat motif.

The RNA1 gene from Saccharomyces cerevisiae is defined by the temperature-sensitive rna1-1 mutation that interferes with the maturation and/or nucleocytoplasmic transport of RNA. We describe the purification of a 44-kDa protein from the evolutionary distant fission yeast Schizosaccharomyces pombe and the cloning and sequence analysis of the corresponding gene. Although this protein shares only 42% sequence identity with the RNA1 gene product, it represents a functional homologue because the expression of the S. pombe gene in S. cerevisiae complements the rna1-1 defect. Disruption in S. pombe of the gene encoding the 44-kDa protein, for which we propose the name S. pombe rna1p, reveals that it is essential for growth. Our analysis of purified S. pombe rna1p represents the first biochemical characterization of an RNA1 gene product and reveals that it is a monomeric protein of globular shape. Cell fractionation and immunofluorescence microscopy indicate that rna1p is a cytoplasmic protein possibly enriched in the nuclear periphery. We identify a sequence motif of 29 residues, which is rich in leucine and repeated eight times both in S. pombe and in S. cerevisiae rna1p. Similar leucine-rich repeats present in a series of other proteins, e.g., the mammalian ribonuclease/angiogenin inhibitor, adenylyl cyclase from S. cerevisiae, the toll protein from Drosophila melanogaster, and the sds22 protein phosphatase regulatory subunit from S. pombe, are thought to be involved in protein-protein interactions. Thus rna1p may act as a scaffold protein possibly interacting in the nuclear periphery with a protein ligand that could be associated with exported RNA.     

Cucurbitacin E and I in Iberis amara: Feeding inhibitors for Phyllotreta nemorum

Cucurbitacin E and cucurbitacin I have been isolated from green parts of Iberis amara and identified by TLC, UV and MS. It is shown that cucurbitacins act as feeding inhibitors for the flea beetle Phyllotreta nemorum. The most potent feeding inhibitors in green parts of I. amara towards P. nemorum are cucurbitacin E and I, and the concentrations of these compounds in the plant are found to be high enough to prevent feeding of the flea beetle.     

Dissociation between rate of hepatic lipoprotein secretion and hepatocyte microtubule content

The fact that colchicines inhibits hepatic secretion of very low density lipoprotein (VLDL) particles has been interpreted to mean that microtubules are involved in hepatic VLDL secretion. To further define this relationship, we have attempted to see if changes in hepatic VLDL secretion are associated with changes in hepatocyte microtubule or tubulin content. Accordingly, hepatic secretion of VLDL was increased in rats, and the hepatocyte content of both microtubules (using quantitative morphometric methods) and tubulin (using a time-decay colchicine binding assay) was determined. In acute experiments, VLDL secretion was increased by perfusion of isolated rat livers for 2 h with varying concentrations of free fatty acids (FFA). Results indicate that hepatic VLDL triglyceride (TG) secretion at perfusate FFA levels of 0.7 μEq/ml is threefold greater (P < 0.01) than when livers are perfused without added FFA. However, no differences are observed in the content of microtubules in these livers: specifically, microtubules occupy 0.029 percent of hepatocyte cytoplasm in livers perfused without FFA and 0.030 percent of cytoplasm in livers perfused with FFA. In chronic experiments, rats were fed for 1 wk with either standard rat chow or a hyperlipidemic (sucrose/lard) diet. With the experimental diet, plasma triglyceride levels increase threefold over controls, and liver VLDL-TG production, as determined by [(3)H]glycerol turnover studies, is 55 percent greater (P < 0.01) than controls. However, microtubules occupy 0.027 percent of the cytoplasm of hepatocyte cytoplasm whether rats are on standard or hyperlipidemic diets. Furthermore, the tubulin content of isolated hepatocytes does change, and represents 1 percent of hepatocyte soluble protein, irrespective of diet. These results suggest that increases in hepatic VLDL secretion can occur without any demonstrable change in hepatocyte assembled microtubule or tubulin content, and raise questions as to the role played by microtubules in hepatic VLDL secretion.     

Identification of 3-O-[2-O-(β-D-xylopyranosyl)-β-D-galactopyranosyl] flavonoids in horseradish leaves acting as feeding stimulants for a flea beetle

The concentration of flavonol glycosides in leaves of Armoracia rusticana harvested at various times during the growing season has been determined. Quantitatively dominating were 3 - O - [2 - O - (β - D - xylopyranosyl) - β - D - galactopyranosyl] - quercetin and 3 - O - [2 - O - (β - D - xylopyranosyl) - β - D -galactopyranosyl] - kaempferol. The latter was present in highest concentration in leaves throughout the growing season, the highest concentration being found in spring. This compound had the highest feeding stimulatory effect towards the flea beetle Phyllotreta armoraciae. The glycosides are new natural products which have been identified by use of enzymatic and spectroscopic methods, including ¹³C NMR.     

RanGAP1*SUMO1 is phosphorylated at the onset of mitosis and remains associated with RanBP2 upon NPC disassembly

The RanGTPase activating protein RanGAP1 has essential functions in both nucleocytoplasmic transport and mitosis. In interphase, a significant fraction of vertebrate SUMO1-modified RanGAP1 forms a stable complex with the nucleoporin RanBP2/Nup358 at nuclear pore complexes. RanBP2 not only acts in the RanGTPase cycle but also is a SUMO1 E3 ligase. Here, we show that RanGAP1 is phosphorylated on residues T409, S428, and S442. Phosphorylation occurs before nuclear envelope breakdown and is maintained throughout mitosis. Nocodazole arrest leads to quantitative phosphorylation. The M-phase kinase cyclin B/Cdk1 phosphorylates RanGAP1 efficiently in vitro, and T409 phosphorylation correlates with nuclear accumulation of cyclin B1 in vivo. We find that phosphorylated RanGAP1 remains associated with RanBP2/Nup358 and the SUMO E2-conjugating enzyme Ubc9 in mitosis, hence mitotic phosphorylation may have functional consequences for the RanGTPase cycle and/or for RanBP2-dependent sumoylation.     

The intermediate filament protein vimentin binds specifically to a recombinant integrin alpha2/beta1 cytoplasmic tail complex and co-localizes with native alpha2/beta1 in endothelial cell focal adhesions

Integrin receptors are crucial players in cell adhesion and migration. Identification and characterization of cellular proteins that interact with their short alpha and beta cytoplasmic tails will help to elucidate the molecular mechanisms by which integrins mediate bi-directional signaling across the plasma membrane. Integrin alpha2beta1 is a major collagen receptor but to date, only few proteins have been shown to interact with the alpha2 cytoplasmic tail or with the alpha2beta1 complex. In order to identify novel binding partners of a alpha2beta1cytoplasmic domain complex, we have generated recombinant GST-fusion proteins, incorporating the leucine zipper heterodimerization cassettes of Jun and Fos. To ascertain proper functionality of the recombinant proteins, interaction with natural binding partners was tested. GST-alpha2 and GST-Jun alpha2 bound His-tagged calreticulin while GST-beta1 and GST-Fos beta1 proteins bound talin. In screening assays for novel binding partners, the immobilized GST-Jun alpha2/GST-Fos beta1 heterodimeric complex, but not the single subunits, interacted specifically with endothelial cell-derived vimentin. Vimentin, an abundant intermediate filament protein, has previously been shown to co-localize with alphavbeta3-positive focal contacts. Here, we provide evidence that this interaction also occurs with alpha2beta1-enriched focal adhesions and we further show that this association is lost after prolonged adhesion of endothelial cells to collagen.     

The RanBP2 SUMO E3 ligase is neither HECT- nor RING-type

Post-translational modification with the ubiquitin-related protein SUMO1 requires the E1 enzyme Aos1-Uba2 and the E2 enzyme Ubc9. Distinct E3 ligases strongly enhance modification of specific targets. The SUMO E3 ligase RanBP2 (also known as Nup358) has no obvious similarity to RING- or HECT-type enzymes. Here we show that RanBP2's 30-kDa catalytic fragment is a largely unstructured protein. Despite two distinct but partially overlapping 79-residue catalytic domains, one of which is sufficient for maximal activity, RanBP2 binds to Ubc9 in a 1:1 stoichiometry. The identification of nine RanBP2 and three Ubc9 side chains that are important for RanBP2-dependent SUMOylation indicates largely hydrophobic interactions. These properties distinguish RanBP2 from all other known E3 ligases, and we speculate that RanBP2 exerts its catalytic effect by altering Ubc9's properties rather than by mediating target interactions.     

Probing conformational changes in the I-like domain and the cysteine-rich repeat of human beta 3 integrins following disulfide bond disruption by cysteine mutations: identification of cysteine 598 involved in alphaIIbbeta3 activation

We have investigated receptor function and epitope expression of recombinant alpha(IIb)beta(3) mutated at Cys(177) or Cys(273) in the I-like domain as well as Cys(598), located in the fourth repeat of the membrane-proximal cysteine-rich region and mutated in a Glanzmann's thrombasthenia type II patient. The beta(3) mutants beta(3)C177A, beta(3)C273A, and beta(3)C598Y exhibited a decreased electrophoretic mobility in SDS-polyacrylamide gel electrophoresis under nonreducing conditions, confirming the disruption of the respective disulfide loops. Despite reduced surface expression, the alpha(IIb)beta(3)C177A, alpha(IIb)beta(3)C273A, and alpha(IIb)beta(3)C598Y receptors mediated cell adhesion to immobilized fibrinogen and translocated into focal adhesion plaques. The beta(3)C598Y mutation, but not the beta(3)C177A or beta(3)C273A mutations, induced spontaneous binding of the ligand mimetic monoclonal antibody PAC-1, while the beta(3)C177A and beta(3)C273A mutants exhibited reduced complex stability in the absence of Ca(2+). Epitope mapping of function-blocking monoclonal antibodies (mAbs) allowed the identification of two distinct subgroups; mAbs A2A9, pl2-46, 10E5, and P256 did not interact with alpha(IIb)beta(3)C273A and bound only weakly to alpha(IIb)beta(3)C177A, while mAbs AP2, LM609 and 7E3 bound normally to mutant alpha(IIb)beta(3)C273A, but interacted only weakly with mutant alpha(IIb)beta(3)C177A. Furthermore, a cryptic epitope recognized by mAb 4D10G3 and not exposed on wild type alpha(IIb)beta(3) became accessible only on mutant alpha(IIb)beta(3)C177A and was mapped to the 60-kDa chymotrypsin fragment of beta(3). Finally, the ligand-induced binding site (LIBS) epitopes AP5, D3, LIBS1, and LIBS2 were spontaneously expressed on all three mutants independent of RGDS or dithiothreitol treatment. Our results provide evidence that disruption of a single cysteine disulfide bond in the cysteine-rich repeat domain, but not in the I-like domain, activates integrin alpha(IIb)beta(3). In contrast, disruption of each of the disulfide bonds in the two long insertions of the I-like domain predicted to be in close contact with the alpha subunit beta-propeller domain affect the stability of the alpha(IIb)beta(3) heterodimer and inhibit complex-specific mAb binding without affecting the RGD binding capacity of the metal ion-dependent adhesion site-like domain.