An isoform of microtubule-associated protein 2 (MAP2) containing four repeats of the tubulin-binding motif.

Microtubule-associated protein 2 (MAP2) exists in both high- and low-molecular mass isoforms, each of which has a tubulin-binding domain consisting of 3 imperfect tandem repeats of 31 amino acids containing a more highly conserved 18 amino acid 'core' sequence. We describe here a novel form of low molecular mass MAP2 (MAP2c) that contains an additional 4th repeat of this tubulin-binding motif. Like the 3 previously known repeat sequences, this 4th copy is highly conserved between MAP2 and the two other known members of the same gene family, tau and MAP4. In each of these three genes the additional 4th repeat is inserted between the 1st and 2nd repeats of the 3-repeat form of the molecule. Experiments with brain cell cultures, in which the relative proportions of neurons and glia had been manipulated by drug treatment, showed that 4-repeat MAP2c is associated with glial cells whereas 3-repeat MAP2c is expressed in neurons. Whereas 3-repeat MAP2c is expressed early in development and then declines, the level of 4-repeat MAP2c increases later in development, corresponding to the relatively late differentiation of glial cells compared to neurons. When transfected into non-neuronal cells, the 4-repeat version of MAP2c behaved indistinguishably from the 3-repeat form in stabilising and rearranging cellular microtubules. The presence of an additional 4th repeat of the tubulin-binding motif in all three members of the MAP2 gene family suggests that this variant arose prior to their differentiation from an ancestral gene.

Regulation of dendritic development by BDNF requires activation of CRTC1 by glutamate.

Dendritic growth is essential for the establishment of a functional nervous system. Among extrinsic signals that control dendritic development, substantial evidence indicates that BDNF regulates dendritic morphology. However, little is known about the underlying mechanisms by which BDNF controls dendritic growth. In this study, we show that the MAPK signaling pathway and the transcription factor cAMP response element-binding protein (CREB) mediate the effects of BDNF on dendritic length and complexity. However, phosphorylation of CREB alone is not sufficient for the stimulation of dendritic growth by BDNF. Thus, using a mutant form of CREB unable to bind CREB-regulated transcription coactivator (CRTC1), we demonstrate that this effect also requires a functional interaction between CREB and CRTC1. Moreover, inhibition of CRTC1 expression by shRNA-mediated knockdown abolished BDNF-induced dendritic growth of cortical neurons. Interestingly, we found that nuclear translocation of CRTC1 results from activation of NMDA receptors by glutamate, a process that is essential for the effects of BDNF on dendritic development. Together, these data identify a previously unrecognized mechanism by which CREB and the coactivator CRTC1 mediate the effects of BDNF on dendritic growth.

Coordinated effects of sequence variation on DNA binding, chromatin structure, and transcription.

DNA sequence variation has been associated with quantitative changes in molecular phenotypes such as gene expression, but its impact on chromatin states is poorly characterized. To understand the interplay between chromatin and genetic control of gene regulation, we quantified allelic variability in transcription factor binding, histone modifications, and gene expression within humans. We found abundant allelic specificity in chromatin and extensive local, short-range, and long-range allelic coordination among the studied molecular phenotypes. We observed genetic influence on most of these phenotypes, with histone modifications exhibiting strong context-dependent behavior. Our results implicate transcription factors as primary mediators of sequence-specific regulation of gene expression programs, with histone modifications frequently reflecting the primary regulatory event.

Remorin, a uronide binding protein with physical properties similar to the tobacco mosaic virus movement protein

The extracellular pectic matrix is a rich source of oligogalacturonic acid (OGA), one of the most abundant polymeric regulatory molecules on the earth's surface. OGAs regulate the expression of a variety of defense genes and have also been implicated in developmental processes. Little is known about how cells perceive OGAs and we have been attempting to characterise proteins capable of interacting with these molecules. We recently succeeded in cloning a cDNA encoding a small OGA-binding protein, remorin. OGA-binding to remorin is not highly specific, the protein binds homogalacturonides, complex pectic polymers and the animal polyuronide heparin. This lack of specificity contrasts with that often observed with classical receptors and the function of remorin remains to be discovered. Remorin copurifies with the plasma membrane but is a very hydrophilic polypeptide. Its behavior during cell fractionation, as well as a number of properties including the OGA-stimulated in vitro phosphorylation and preliminary localization studies, all suggest parallels with some viral movement proteins. Some of these comparisons will be presented. Experiments to directly test for the possible role of this protein in cell-to-cell signalling are in progress. EEF is supported by FNRS grant 31-3672-92.

Binding of ²³⁹Pu and ⁹⁰Sr to organic colloids in soil solutions: evidence from a field experiment.

Colloidal transport has been shown to enhance the migration of plutonium in groundwater downstream from contaminated sites, but little is known about the adsorption of ⁹⁰Sr and plutonium onto colloids in the soil solution of natural soils. We sampled soil solutions using suction cups, and separated colloids using ultrafiltration to determine the distribution of ²³⁹Pu and ⁹⁰Sr between the truly dissolved fraction and the colloidal fraction of the solutions of three Alpine soils contaminated only by global fallout from the nuclear weapon tests. Plutonium was essentially found in the colloidal fraction (>80%) and probably associated with organic matter. A significant amount of colloidal ⁹⁰Sr was detected in organic-rich soil solutions. Our results suggest that binding to organic colloids in the soil solutions plays a key role with respect to the mobility of plutonium in natural alpine soils and, to a lesser extent, to the mobility of ⁹⁰Sr.

Reassessing the role of Staphylococcus aureus clumping factor and fibronectin-binding protein by expression in Lactococcus lactis.

Since Staphylococcus aureus expresses multiple pathogenic factors, studying their individual roles in single-gene-knockout mutants is difficult. To circumvent this problem, S. aureus clumping factor A (clfA) and fibronectin-binding protein A (fnbA) genes were constitutively expressed in poorly pathogenic Lactococcus lactis using the recently described pOri23 vector. The recombinant organisms were tested in vitro for their adherence to immobilized fibrinogen and fibronectin and in vivo for their ability to infect rats with catheter-induced aortic vegetations. In vitro, both clfA and fnbA increased the adherence of lactococci to their specific ligands to a similar extent as the S. aureus gene donor. In vivo, the minimum inoculum size producing endocarditis in > or =80% of the rats (80% infective dose [ID80]) with the parent lactococcus was > or =10(7) CFU. In contrast, clfA-expressing and fnbA-expressing lactococci required only 10(5) CFU to infect the majority of the animals (P < 0.00005). This was comparable to the infectivities of classical endocarditis pathogens such as S. aureus and streptococci (ID80 = 10(4) to 10(5) CFU) in this model. The results confirmed the role of clfA in endovascular infection, but with a much higher degree of confidence than with single-gene-inactivated staphylococci. Moreover, they identified fnbA as a critical virulence factor of equivalent importance. This was in contrast to previous studies that produced controversial results regarding this very determinant. Taken together, the present observations suggest that if antiadhesin therapy were to be developed, at least both of the clfA and fnbA products should be blocked for the therapy to be effective.

Characterization and binding affinities of SmLANP: a new Schistosoma mansoni member of the ANP32 family of regulatory proteins.

Members of the leucine-rich repeat protein family are involved in diverse functions including protein phosphatase 2-inhibition, cell cycle regulation, gene regulation and signalling pathways. A novel Schistosoma mansoni gene, called SmLANP, presenting homology to various genes coding for proteins that belong to the super family of leucine-rich repeat proteins, was characterized here. SmLANP was 1184bp in length as determined from cDNA and genomic sequences and encoded a 296 amino acid open reading frame that spanning from 6 to 894bp. The predicted amino acid sequence had a calculated molecular weight of 32kDa. Analysis of the predicted sequence indicated the presence of 3 leucine-rich domains (LRR) located in the N-terminal region and an aspartic acid rich region in the C-terminal end. SmLANP transcript is expressed in all stages of the S. mansoni life cycle analyzed, exhibiting the highest expression level in males. The SmLANP protein was expressed in a GST expression system and antibodies raised in mice against the recombinant protein. By immunolocalization assay, using adult worms, it was shown that the protein is mainly present in the cell nucleus through the whole body and strongly expressed along the tegument cell body nuclei of adult worms. As members of this family are usually involved in protein-protein interaction, a yeast two hybrid assay was conducted to identify putative binding partners for SmLANP. Thirty-six possible partners were identified, and a protein ATP synthase subunit alpha was confirmed by pull down assays, as a binding partner of the SmLANP protein.

Gene transfer of interleukin-18-binding protein attenuates cardiac allograft rejection.

Interleukin (IL) 18 is a potent pro-inflammatory Th1 cytokine that exerts pleiotropic effector functions in both innate and acquired immune responses. Increased IL-18 production during acute rejection has been reported in experimental heart transplantation models and in kidney transplant recipients. IL-18-binding protein (IL-18BP) binds IL-18 with high affinity and neutralizes its biologic activity. We have analyzed the efficacy of an adenoviral vector expressing an IL-18BP-Ig fusion protein in a rat model of heart transplantation. IL-18BP-Ig gene transfer into Fisher (F344) rat donor hearts resulted in prolonged graft survival in Lewis recipients (15.8 +/- 1.4 days vs. 10.3 +/- 2.5 and 10.1 +/- 2.1 days with control virus and buffer solution alone, respectively; P < 0.001). Immunohistochemical analysis revealed decreased intra-graft infiltrates of monocytes/macrophages, CD4(+), CD8alpha(+) and T-cell receptor alphabeta(+) cells after IL-18BP-Ig versus mock gene transfer (P < 0.05). Real-time reverse transcriptase polymerase chain reaction analysis showed decreased cytokine transcripts for the RANTES chemokine and transforming growth factor-beta after IL-18BP-Ig gene transfer (P < 0.05). IL-18BP-Ig gene transfer attenuates inflammatory cell infiltrates and prolongs cardiac allograft survival in rats. These results suggest a contributory role for IL-18 in acute rejection. Further studies aiming at defining the therapeutic potential of IL-18BP are warranted.

Mutational analysis of BTAF1-TBP interaction: BTAF1 can rescue DNA-binding defective TBP mutants.

The BTAF1 transcription factor interacts with TATA-binding protein (TBP) to form the B-TFIID complex, which is involved in RNA polymerase II transcription. Here, we present an extensive mapping study of TBP residues involved in BTAF1 interaction. This shows that residues in the concave, DNA-binding surface of TBP are important for BTAF1 binding. In addition, BTAF1 interacts with residues in helix 2 on the convex side of TBP as assayed in protein-protein and in DNA-binding assays. BTAF1 drastically changes the TATA-box binding specificity of TBP, as it is able to recruit DNA-binding defective TBP mutants to both TATA-containing and TATA-less DNA. Interestingly, other helix 2 interacting factors, such as TFIIA and NC2, can also stabilize mutant TBP binding to DNA. In contrast, TFIIB which interacts with a distinct surface of TBP does not display this activity. Since many proteins contact helix 2 of TBP, this provides a molecular basis for mutually exclusive TBP interactions and stresses the importance of this structural element for eukaryotic transcription.

Characterization of a cAMP-regulated enhancer-binding protein.

The transcription regulation of many hormone genes is modulated by intracellular second messengers such as cAMP. The cAMP response element binding protein, CREB, binds to the 8 base pair CRE enhancer, TGACGTCA, that is found in the 5'-flank of certain genes including those for somatostatin and the alpha-subunit of human chorionic gonadotropin. The recent characterization of CREB and CREB-related cDNA clones, combined with Southwesterns and Northern blot analyses, reveals a family of transcription factors that dimerize via a leucine zipper motif and bind to the CRE through positively charged basic regions. The CREB cDNA encoding a 327 residue protein is transcriptionally activated via phosphorylation by protein kinases, including the cAMP-dependent protein kinase-A.

Combined simulation and mutagenesis analyses reveal the involvement of key residues for peroxisome proliferator-activated receptor alpha helix 12 dynamic behavior.

The dynamic properties of helix 12 in the ligand binding domain of nuclear receptors are a major determinant of AF-2 domain activity. We investigated the molecular and structural basis of helix 12 mobility, as well as the involvement of individual residues with regard to peroxisome proliferator-activated receptor alpha (PPARalpha) constitutive and ligand-dependent transcriptional activity. Functional assays of the activity of PPARalpha helix 12 mutants were combined with free energy molecular dynamics simulations. The agreement between the results from these approaches allows us to make robust claims concerning the mechanisms that govern helix 12 functions. Our data support a model in which PPARalpha helix 12 transiently adopts a relatively stable active conformation even in the absence of a ligand. This conformation provides the interface for the recruitment of a coactivator and results in constitutive activity. The receptor agonists stabilize this conformation and increase PPARalpha transcription activation potential. Finally, we disclose important functions of residues in PPARalpha AF-2, which determine the positioning of helix 12 in the active conformation in the absence of a ligand. Substitution of these residues suppresses PPARalpha constitutive activity, without changing PPARalpha ligand-dependent activation potential.

The N-terminal DNA-binding 'zinc finger' of the oestrogen and glucocorticoid receptors determines target gene specificity.

Steroid hormone receptors activate specific gene transcription by binding as hormone-receptor complexes to short DNA enhancer-like elements termed hormone response elements (HREs). We have shown previously that a highly conserved 66 amino acid region of the oestrogen (ER) and glucocorticoid (GR) receptors, which corresponds to part of the receptor DNA binding domain (region C) is responsible for determining the specificity of target gene activation. This region contains two sub-regions (CI and CII) analogous to the 'zinc-fingers' of the transcription factor TFIIIA. We show here that CI and CII appear to be separate domains both involved in DNA binding. Furthermore, using chimaeric ERs in which either the first (N-terminal) (CI) or second (CII) 'zinc finger' region has been exchanged with that of the GR, indicates that it is the first 'zinc finger' which largely determines target gene specificity. We suggest that receptor recognition of the HRE is analogous to that of the helix-turn-helix DNA binding motif in that the receptor binds to DNA as a dimer with the first 'zinc finger' lying in the major groove recognizing one half of the palindromic HRE, and that protein-DNA interaction is stabilized through non-specific DNA binding and dimer interactions contributed by the second 'zinc finger'.

Fab antibodies capable of blocking T cells by competitive binding have the identical specificity but a higher affinity to the MHC-peptide-complex than the T cell receptor.

In transplant rejection, graft versus host or autoimmune diseases T cells are mediating the pathophysiological processes. Compared to unspecific pharmacological immune suppression specific inhibition of those T cells, that are involved in the disease, would be an alternative and attractive approach. T cells are activated after their T cell receptor (TCR) recognizes an antigenic peptide displayed by the Major Histocompatibility Complex (MHC). Molecules that interact with MHC-peptide-complexes in a specific fashion should block T cells with identical specificity. Using the model of the SSX2 (103-111)/HLA-A*0201 complex we investigated a panel of MHC-peptide-specific Fab antibodies for their capacity blocking specific T cell clones. Like TCRs all Fab antibodies reacted with the MHC complex only when the SSX2 (103-111) peptide was displayed. By introducing single amino acid mutations in the HLA-A*0201 heavy chain we identified the K66 residue as the most critical binding similar to that of TCRs. However, some Fab antibodies did not inhibit the reactivity of a specific T cell clone against peptide pulsed, artificial targets, nor cells displaying the peptide after endogenous processing. Measurements of binding kinetics revealed that only those Fab antibodies were capable of blocking T cells that interacted with an affinity in the nanomolar range. Fab antibodies binding like TCRs with affinities on the lower micromolar range did not inhibit T cell reactivity. These results indicate that molecules that block T cells by competitive binding with the TCR must have the same specificity but higher affinity for the MHC-peptide-complex than the TCR.