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At least 271 records · Page 15Linked to original sources
PubMed2003

Formation of a DNA mismatch repair complex mediated by ATP.

The mismatch repair proteins, MutS and MutL, interact in a DNA mismatch and ATP-dependent manner to activate downstream events in repair. Here, we assess the role of ATP binding and hydrolysis in mismatch recognition by MutS and the formation of a ternary complex involving MutS and MutL bound to a mismatched DNA. We show that ATP reduces the affinity of MutS for mismatched DNA and that the modulation of DNA binding affinity by nucleotide is even more pronounced for MutS E694A, a protein that binds ATP but is defective for ATP hydrolysis. Despite the ATP hydrolysis defect, E694A, like WT MutS, undergoes rapid, ATP-dependent dissociation from a DNA mismatch. Furthermore, MutS E694A retains the ability to interact with MutL on mismatched DNA. The recruitment of MutL to a mismatched DNA by MutS is also observed for two mutant MutL proteins, E29A, defective for ATP hydrolysis, and R266A, defective for DNA binding. These results suggest that ATP binding in the absence of hydrolysis is sufficient to trigger formation of a MutS sliding clamp. However, recruitment of MutL results in the formation of a dynamic ternary complex that we propose is the intermediate that signals subsequent repair steps requiring ATP hydrolysis.

Adenosine Triphosphatases↗
PubMed2003

Kissing complex-mediated dimerisation of HIV-1 RNA: coupling extended duplex formation to ribozyme cleavage.

Initiation of retroviral genomic RNA dimerisation is mediated by the mutual interaction of the dimerisation initiation site (DIS) stem-loops near to the 5' end of the RNA. This process is thought to involve formation of a transient 'kissing' complex over the self-complementary loop bases, which then refolds into a more stable extended interaction. We have developed a novel experimental system that allows us to clearly detect the extended duplex in vitro. Ribozyme sequences were incorporated into or adjacent to the type 1 human immunodeficiency virus DIS stem, leading to the formation of a functional ribozyme only in the extended duplex conformer. Here we show that extended duplex formation results in ribozyme cleavage, thus demonstrating the double-stranded nature of the extended complex and confirming that refolding occurs via melting of the DIS stems. Loop complementarity is essential for extended duplex formation but no sequence requirements for the loops were observed. Efficiency of extended duplex formation is dependent on the strength of the loop-loop interaction, temperature, the magnesium concentration and is strongly accelerated by the viral nucleocapsid protein NCp7. Our ribozyme-coupled approach should be applicable to the analyses of other refolding processes involving RNA loop-loop interactions.

Base Sequence↗
PubMed2001

Activation of Arp2/3 complex-mediated actin polymerization by cortactin.

Cortactin, a filamentous actin (F-actin)-associated protein and prominent substrate of Src, is implicated in progression of breast tumours through gene amplification at chromosome 11q13. However, the function of cortactin remains obscure. Here we show that cortactin co-localizes with the Arp2/3 complex, a de novo actin nucleator, at dynamic particulate structures enriched with actin filaments. Cortactin binds directly to the Arp2/3 complex and activates it to promote nucleation of actin filaments. The interaction of cortactin with the Arp2/3 complex occurs at an amino-terminal domain that is rich in acidic amino acids. Mutations in a conserved amino-acid sequence of DDW abolish both the interaction with the Arp2/3 complex and complex activation. The N-terminal domain is not only essential but also sufficient to target cortactin to actin-enriched patches within cells. Interestingly, the ability of cortactin to activate the Arp2/3 complex depends on an activity for F-actin binding, which is almost 20-fold higher than that of the Arp2/3 complex. Our data indicate a new mechanism for activation of actin polymerization involving an enhanced interaction between the Arp2/3 complex and actin filaments.

3T3 Cells↗
PubMed2003

Exon junction complexes mediate the enhancing effect of splicing on mRNA expression.

Intron-containing genes are generally expressed more effectively in human cells than are intronless versions of the same gene. We have asked whether this effect is due directly to splicing or instead reflects the action of components of the exon junction complex (EJC) that is assembled at splice junctions after splicing is completed. Here, we show that intron removal does not enhance gene expression if EJC formation is blocked. Conversely, RNA tethering of the EJC components SRm160 or RNPS1 boosts the expression of intronless mRNAs but not of spliced mRNAs. Splicing and RNPS1 tethering are shown to enhance the same steps in mRNA biogenesis and function, including mRNA 3' end processing and translation. Together, these data argue that the EJC is primarily responsible for the positive effect of splicing on gene expression.

Base Sequence↗
PubMed2005

Heteromeric protein complexes mediate zinc transport into the secretory pathway of eukaryotic cells.

The cation diffusion facilitator (CDF) family of metal ion transporters plays important roles in zinc transport at all phylogenetic levels. In this report, we describe a novel interaction between two members of the CDF family in Saccharomyces cerevisiae. One CDF member in yeast, Msc2p, was shown recently to be involved in zinc transport into the endoplasmic reticulum (ER) and required for ER function. We describe here a newly recognized CDF family member in yeast, Zrg17p. ZRG17 was previously identified as a zinc-regulated gene controlled by the zinc-responsive Zap1p transcription factor. A zrg17 mutant exhibits the same zinc-suppressible phenotypes as an msc2 mutant, including an induction of the unfolded protein response in low zinc. Moreover, a significant fraction of the total Zrg17p protein appears to localize to the ER. Their common phenotypes and localization suggested that these two proteins function together to mediate zinc transport into the ER. Consistent with this hypothesis, Msc2p and Zrg17p physically interact with each other, as determined by co-immunoprecipitation. Therefore, we propose that Msc2p and Zrg17p form a heteromeric zinc transport complex in the ER membrane. We also demonstrate that ZnT5 and ZnT6, mammalian homologues of Msc2p and Zrg17p, functionally interact as well. These results suggest that heteromeric complexes formed by different CDF members may be a common phenomenon for this ubiquitous family of metal ion transporters.

Animals↗
PubMed2006

NS1 interaction with CKII alpha: novel protein complex mediating parvovirus-induced cytotoxicity.

During a productive infection, the prototype strain of the parvovirus minute virus of mice (MVMp) induces dramatic morphological alterations in permissive A9 fibroblasts, culminating in cell lysis at the end of infection. These cytopathic effects (CPE) result from rearrangements and destruction of the cytoskeletal micro- and intermediate filaments, while other structures such as the nuclear lamina and particularly the microtubule network remain protected throughout the infection (J. P. F. Nüesch et al., Virology 331:159-174, 2005). In order to unravel the mechanism(s) by which parvoviruses trigger CPE, we searched for NS1 interaction partners by differential affinity chromatography, using distinct NS1 mutants debilitated specifically for this function. Thereby, we isolated an NS1 partner polypeptide, whose interaction with NS1 correlated with the competence of the viral product for CPE induction, and further identified it by tandem mass spectrometry and Western blotting analyses to consist of the catalytic subunit of casein kinase II, CKIIalpha. This interaction of NS1 with CKIIalpha suggested interference by the viral protein with intracellular signaling. Using permanent cell lines expressing dominant-negative CKIIalpha mutants, we were able to show that this kinase activity was indeed specifically involved in parvoviral CPE and progeny particle release. Furthermore, the NS1/CKIIalpha complex proved to be able to specifically phosphorylate viral capsids, indicating a mediator function of NS1 for CKII activity and specificity, at least in vitro. Altogether our data suggest that parvovirus-induced CPE is mediated by NS1 interference with intracellular CKII signaling.

Amino Acid Sequence↗
PubMed2006

Down-regulation of glutaredoxin by estrogen receptor antagonist renders female mice susceptible to excitatory amino acid mediated complex I inhibition in CNS.

beta-N-oxalyl-amino-L-alanine, (L-BOAA), an excitatory amino acid, acts as an agonist of the AMPA subtype of glutamate receptors. It inhibits mitochondrial complex I in motor cortex and lumbosacral cord of male mice through oxidation of critical thiol groups, and glutaredoxin, a thiol disulfide oxido-reductase, helps maintain integrity of complex I. Since incidence of neurolathyrism is less common in women, we examined the mechanisms underlying the gender-related effects. Inhibition of complex I activity by L-BOAA was seen in male but not female mice. Pretreatment of female mice with estrogen receptor antagonist ICI 182,780 or tamoxifen sensitizes them to L-BOAA toxicity, indicating that the neuroprotection is mediated by estrogen receptors. L-BOAA triggers glutathione (GSH) loss in male mice but not in female mice, and only a small but significant increase in oxidized glutathione (GSSG) was seen in females. As a consequence, up-regulation of gamma-glutamyl cysteinyl synthase (the rate-limiting enzyme in glutathione synthesis) was seen only in male mouse CNS but not in females. Both glutathione reductase and glutaredoxin that reduce oxidized glutathione and protein glutathione mixed disulfides, respectively, were constitutively expressed at higher levels in females. Furthermore, glutaredoxin activity in female mice was down-regulated by estrogen antagonist indicating its regulation by estrogen receptor. The higher constitutive expression of glutathione reductase and glutaredoxin could potentially confer neuroprotection to female mice.

Amino Acids, Diamino↗
PubMed1981

Immune complex-mediated renal involvement in relapsing polychondritis.

A patient with relapsing polychondritis who presented with rapidly progressive glomerulonephritis is described. This is the fourth case in which this association is reported. Crescentic glomerulonephritis was found on renal biopsy. Evidence for immunologic participation in the pathogenesis of this condition is suggested by the demonstration of circulating immune complexes, immunoglobulin and complement deposition by immunofluorescence, and electron dense deposits by electron microscopy of the kidney. Favorable response followed therapy with prednisone and dapsone.

Aged↗
PubMed1983

Immune complex mediated destruction of cartilage in antigen-induced arthritis of rabbits.

Antigen-induced arthritis of rabbits is used as a model to study pannus-free destruction of cartilage in rheumatoid arthritis (RA) by transmission and scanning electron microscopy, incorporating plain and immune labeling techniques. During the acute "arthus" phase of the RA, immune complexes form and persist in these tissues. We observed the progressive formation of electron dense material rich in immune complexes within a millimicron of the hyaline cartilage surfaces that preceded erosion and loss of surface tissue. Polymorphonuclear neutrophils congregated at the cartilage margins to engulf immune complexes at and within the cartilage surfaces. The changes occurred in regions of hyaline and fibrocartilage free of pannus. Immune complex formation appeared to be a central feature of the cartilage destructive changes, and may be central to mechanisms of tissue loss and similar to those observed in RA.

Animals↗
PubMed1998

The mammalian AP-3 adaptor-like complex mediates the intracellular transport of lysosomal membrane glycoproteins.

In mammalian cells, the mannose 6-phosphate receptors (MPRs) and the lysosomal glycoproteins, lysosomal-associated membrane protein (LAMP) I, lysosomal integral membrane protein (LIMP) II, are directly transported from the trans-Golgi network to endosomes and lysosomes. While MPR traffic relies on the AP-1 adaptor complex, we report that proper targeting of LAMP I and LIMP II to lysosomes requires the AP-3 adaptor-like complex. Overexpression of these proteins, which contain either a tyrosine- or a di-leucine-based-sorting motif, promotes AP-3 recruitment on membranes. Inhibition of AP-3 function using antisense oligonucleotides leads to a selective misrouting of both LAMP I and LIMP II to the cell surface without affecting MPR trafficking. These results provide evidence that AP-3 functions in the intracellular targeting of transmembrane glycoproteins to lysosomes.

Adaptor Protein Complex 3↗
PubMed1990

Immune complex-mediated inhibition of lymphocyte Fc-gamma receptors in the plasma of patients with type 1 (insulin-dependent) diabetes mellitus: association with anti-ssDNA antibodies.

Sera of 43 patients with type 1 (insulin-dependent) diabetes and from 42 normal subjects were examined for the presence of Fc-gamma receptor-blocking IgG immune complexes, detected by EA rosette inhibition, and for the presence of anti-ssDNA antibodies by ELISA. Forty-four percent of diabetic patients had levels of inhibition above the upper limit of normality in comparison to 7% of normal controls. Anti-ssDNA antibodies were found in the sera of 14 out of 43 diabetic patients. Ten out of 14 anti-ssDNA positive patients (71.5%) had inhibition levels above the upper limit of normality in comparison to 9 out of 29 (31%) of the anti-ssDNA negative population. The difference was statistically significant (P less than 0.005). Levels of EA rosette inhibition were found to be high in patients with duration of diabetes of less than 2 years and correlated with high prevalence of anti-ssDNA antibodies. The percentage of EA rosette inhibition was found not to correlate with the levels of C1q-binding immune complexes, suggesting that immune complexes detected by EA rosette inhibition may belong to a pool of noncomplement-fixing immune complexes. The possible role of immune complexes with autoantibodies anti-ssDNA in the mechanism triggering and perpetuating autoimmune phenomena in diabetes is discussed.

Age Factors↗
PubMed2004

Effect of Fgd1 on cortactin in Arp2/3 complex-mediated actin assembly.

Mutations in faciogenital dysplasia protein (Fgd1) result in the human disease faciogenital dysplasia (FGDY). Fgd1 contains a RhoGEF domain specific for Cdc42. Fgd1 also contains a Src homology (SH3) binding domain (SH3-BD) that binds directly to the SH3 domain of cortactin, which promotes actin assembly by actin-related protein (Arp)2/3 complex. Here, we report the effect of ligation of cortactin's SH3 domain by the Fgd1 SH3-BD on actin polymerization in vitro. Glutathione S-transferase (GST)-fused Fgd1 SH3-BD enhanced the ability of cortactin to stimulate Arp2/3-mediated actin polymerization. However, a synthetic peptide containing only the SH3-BD sequence had no effect. The SH3-BD peptide bound to cortactin and inhibited the effect of GST-Fgd1 SH3-BD, suggesting that GST dimerization was responsible for the stimulating effect of GST-Fgd1 SH3-BD. When GST-Fgd1 SH3-BD was prepared as a heterodimer with a control GST fusion protein (GST-Pac1), no stimulatory effect on actin polymerization was observed. In addition, when cortactin was dimerized via its N-terminus, away from the C-terminal SH3 domain, actin polymerization with Arp2/3 complex increased markedly, compared to free cortactin. Thus, cortactin ligated by Fgd1 is fully active, indicating that the cell can use Fgd1 to target actin assembly. Moreover, if Fgd1 is multimerized, then cortactin's activity should be enhanced. Fgd1 and cortactin may participate as scaffolds and signal transducers in a positive feedback cycle to promote actin assembly at the cell cortex.

Actin-Related Protein 2↗
PubMed2003

Interaction of Smad3 and SRF-associated complex mediates TGF-beta1 signals to regulate SM22 transcription during myofibroblast differentiation.

Myofibroblasts play important roles in a variety of developmental and pathological processes, such as vascular remodeling, atherosclerosis and wound healing. In this study, we used the TGF-beta1-treated 10T1/2 cells as an in vitro model to understand how Smad-mediated TGF-beta1 signals regulate SM22 promoter transcription during myofibroblast differentiation. We found that TGF-beta1 transiently induces SRF and SM22 transcription, and that this process is accompanied by transient increases of SRF and Smad3 binding to the SM22 promoter. Interestingly, Smad3, not Smad2, is the primary mediator for TGF-beta1-induced transactivation of the SM22 promoter, while Smad6 and Smad7 repress such a transactivation. Smad3 can bind to a Smad-binding element (SBE) in the first exon of SM22, and directly associate with the SRF complex in response to TGF-beta1 treatment. Moreover, Smad3 and I-Smads regulate the SM22 promoter through CArG box-dependent transcription using dominant-negative SRF mutants and SRF-VP16. Although SBE as well as CArG boxes and TGF-beta control element are all important for the SM22 promoter activities, the promoters with mutations at either one or all of them still respond to TGF-beta1 treatment. Consistently, TGF-beta1 stimulates SM22 transcription in Smad3 null mouse embryonic fibroblasts. These findings provide the first evidence that Smad3 directly links TGF-beta1 signaling to an SRF-associated regulatory network in controlling SM22 transcription; it also implies that TGF-beta1 regulates the SM22 promoter via Smad3-dependent and Smad3-independent pathways.

Animals↗
PubMed1991

Menière's disease: an immune complex-mediated illness?

The cause of Menière's disease is unknown. Recent clinical research suggests that one etiology is immune-mediated damage to the inner ear. The diagnosis of autoimmune Menière's syndrome is largely based on history, response to steroids, or results of nonspecific laboratory tests such as serological studies. Polyethylene glycol (PEG) assay was used to determine levels of circulating immune complexes (CIC) in 30 patients with Menière's disease and 20 control subjects. Patients with Menière's disease had a statistically significant elevation of serum circulating immune complexes when compared to the control group. This suggests that CICs may be involved in the pathogenesis of Menière's disease, either as a direct cause of damage, or as a by-product of an underlying autoimmune abnormality. Therapeutic implications include use of plasmapheresis to remove the complexes or CIC monitoring to serve as a marker for treatment efficacy.

Adult↗
PubMed1999

Atypical nucleoprotein complexes mediate CRE-dependent regulation of the early promoter of minute virus of mice.

The P4 promoter of the parvovirus minute virus of mice (MVMp) directs transcription of the genes encoding non-structural proteins. We have previously shown that functional upstream CRE elements contribute to both the ras oncogene-dependent activation of promoter P4 and its down-modulation by known activators of cyclic AMP-dependent protein kinase A (PKA). In the present work, the nucleoprotein complexes formed with the P4 CRE elements were characterized with regard to their polypeptide constituents and the nucleotides taking part in the interaction. Atypical interactions, both at the protein-protein and protein-DNA level, were observed, which may be a reflection of the divergence of the parvoviral CREs from the usual consensus. The CRE-mediated regulation of promoter P4 by PKA and Ras is discussed in light of these findings.

Animals↗