The oncoprotein MDM2 inhibits the tumor suppressor protein p53 by binding to the p53 transactivation domain. The p53 gene is inactivated in many human tumors either by mutations or by binding to oncogenic proteins. In some tumors, such as soft tissue sarcomas, overexpression of MDM2 inactivates an otherwise intact p53, disabling the genome integrity checkpoint and allowing cell cycle progression of defective cells. Disruption of the MDM2/p53 interaction leads to increased p53 levels and restored p53 transcriptional activity, indicating restoration of the genome integrity check and therapeutic potential for MDM2/p53 binding antagonists. Here, we show by multidimensional NMR spectroscopy that chalcones (1,3-diphenyl-2-propen-1-ones) are MDM2 inhibitors that bind to a subsite of the p53 binding cleft of human MDM2. Biochemical experiments showed that these compounds can disrupt the MDM2/p53 protein complex, releasing p53 from both the p53/MDM2 and DNA-bound p53/MDM2 complexes. These results thus offer a starting basis for structure-based drug design of cancer therapeutics.

Angiogenesis is an ordered process requiring the inter-play of numerous cellular and humoral factors. Studies over the past 20 years have identified several growth factors, cytokines, and enzymes that promote blood vessel formation. Most have revealed how individual factors promote an angiogenic phenotype in endothelial cells in vitro or contribute to blood vessel formation in vivo. However, the fundamental question that remains unanswered is how the cellular microenvironment contributes to angiogenesis. Fibrocytes are a recently characterized mesenchymal cell type isolated from peripheral blood that rapidly enter subcutaneously implanted wound chambers and sites of tissue injury. Here we describe the induction of an angiogenic phenotype in microvascular endothelial cells in vitro and promotion of angiogenesis in vivo by cultured fibrocytes. Fibrocytes constitutively secrete extracellular matrix-degrading enzymes, primarily matrix metalloproteinase 9, which promotes endothelial cell invasion. In addition, fibrocytes secrete several proangiogenic factors including VEGF, bFGF, IL-8, PDGF, and hematopoietic growth factors that promote endothelial cell migration, proliferation, and/or tube formation. By contrast, they do not produce representative antiangiogenic factors. Finally, both autologous fibrocytes and fibrocyte-conditioned media were found to induce blood vessel formation in vivo using the Matrigel angiogenesis model.

Histone deacetylases are the catalytic subunits of multiprotein complexes that are targeted to specific promoters through their interaction with sequence-specific DNA-binding factors. We have cloned and characterized a new human cDNA, HDAC-A, with homology to the yeast HDA1 family of histone deacetylases. Analysis of the predicted amino acid sequence of HDAC-A revealed an open reading frame of 967 amino acids containing two domains: a NH 2 -terminal domain with no homology to known proteins and a COOH-terminal domain with homology to known histone deacetylases (42% similarity to RPD3, 60% similarity to HDA1). Three additional human cDNAs with high homology to HDAC-A were identified in sequence data bases, indicating that HDAC-A itself is a member of a new family of human histone deacetylases. The mRNA encoding HDAC-A was differentially expressed in a variety of human tissues. The expressed protein, HDAC-Ap, exhibited histone deacetylase activity and this activity mapped to the COOHterminal region (amino acids 495-967) with homology to HDA1p. In immunoprecipitation experiments, HDAC-A interacted specifically with several cellular proteins, indicating that it might be part of a larger multiprotein complex.Acetylation of core histones, first described by Allfrey and co-workers (1), has been correlated with transcription, chromatin assembly, DNA repair, and recombinational events (2-7). Transfer of an acetyl group from acetyl-CoA onto the ⑀-amino group of different lysines residues in the NH 2 -terminal tail of core histones is a ubiquitous modification found in all eukaryotic species examined. Histone acetylation levels are controlled by the competing activities of histone acetyltransferases and histone deacetylases.Cloning of the first histone acetyltransferase (8) and the first histone deacetylase (9) has led to the identification of a growing number of proteins with similar enzymatic activities (reviewed in Refs. 7 and 10). The characterization of the first histone acetyltransferase and the first histone deacetylase as homologues of Saccharomyces cerevisiae GCN5 and S. cerevisiae RPD3, respectively, two factors previously described genetically as transcriptional regulators, confirmed the long speculated role of histone modification in eukaryotic transcriptional regulation. Together with the demonstration that acetylation levels of nucleosomal histones change in discrete regions associated with certain promoters (11-13), these results established that chromatin is not only a structural scaffold responsible for DNA compaction in the eukaryotic nucleus but is also an active and dynamic participant in transcriptional regulatory mechanisms.This model has been recently validated by the demonstration that the enzymatic activity of the yeast histone acetyltransferase GCN5 is necessary for the transactivational activity of this factor (14,15). Similarly, mutation of amino acids critical for the histone deacetylase activity of RPD3 or HDAC1 reduced partially or totally their repressor activity (16,17). Additional evidence...

Cross-inhibition by quorum-sensing pheromones between Staphylococcus aureus and Staphylococcus epidermidis was investigated using all known S. aureus agr pheromone subgroups. All S. aureus subgroups were sensitive towards the S. epidermidis pheromone, with the exception of the recently identified subgroup 4. The subgroup 4 pheromone was also the only S. aureus pheromone able to inhibit the S. epidermidis agr response. The close relation of subgroup 4 to subgroup 1 suggests that subgroup 4 might have evolved from subgroup 1 by mutation under the selective pressure of competition with S. epidermidis. The competition between S. aureus and S. epidermidis by means of quorum-sensing cross talk seems to be generally in favor of S. epidermidis, which might explain the predominance of S. epidermidis on the skin and in infections on indwelling medical devices.

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The conformation of the polypeptide thymosin beta 4 in solutions of 60% (v/v) trifluoroethanol-d3 and 50% (v/v) hexafluoroisopropyl-d2 alcohol in water is investigated by nuclear magnetic resonance (NMR) spectroscopy. Under these conditions thymosin beta 4 adopts an ordered structure. By use of a combination of two-dimensional NMR techniques, the 1H NMR spectrum of thymosin beta 4 is assigned. A set of 180 approximate interproton distance constraints is derived from nuclear Overhauser enhancement (NOE) measurements. These, together with 33 phi constraints obtained for JNH alpha coupling data and the 23 psi dihedral angles identified on the basis of the pattern of short-range NOEs, form the basis of a three-dimensional structure determination by dynamical simulated annealing. The calculations are carried out starting from three initial structures, an alpha-helix, an extended beta-strand, and a mixed alpha/beta structure. Ten independent structures are computed from each starting structure by using different random number seeds for the assignments of the initial velocities. All 30 calculated structures satisfy the experimental constraints, display very small deviations from idealized covalent geometry, and possess good nonbonded contacts. Analysis of the 30 converged structures indicates that there are two helical regions extending from residues 4-16 and from residues 30-40, which are well defined both in terms of atomic root mean square differences and backbone torsion angles. For the two helical regions individually the average backbone rms difference between all pairs of structures is approximately 2 A. The two helices exhibit typical amino acid preferences for specific locations at the ends of helices.(ABSTRACT TRUNCATED AT 250 WORDS)

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The conformational preferences of a 43-amino-acid G-actin-binding peptide, thymosin P4, in water at 1, 4 and 14°C and at pH 3.0 and 6.5 were studied by NMR. NMR showed that thymosin p4 lacks a uniquely folded conformation in water. However, some preferential a-helical conformations of thymosin /I4 can be observed in aqueous solutions. The segment at residues 5-16 showed characteristic interactions for conformations in both the P-strand and a-helical regions of the 4-y space, based on strong CH(i)-NH(i+ 1) interactions and NH-NH, C"H(i)-NH(i+3), and C"H(i)-CpH(i+3) interactions, respectively. At 1 -4"C, another segment at residues 31 -37 also shows both p and a conformations, forming however a less well-defined helix than the segment at residues 5 -16. At 14"C, the conformational population of the helix at positions 5-16 is shifted more towards the random and turn-like structures, whereas the segment at positions 31 -37 becomes exclusively a random coil.The cytoplasmic salt conditions in a non-muscle cell strongly favor the polymerization of actin and only recently has it been determined how cells manage to keep more than 50% of the actin pool in an unpolymerized state. It is now thought that thymosin P4 is the main actin-sequestering peptide, which forms a 1 : 1 complex with actin and thus shifts the polymerization equilibrium from filamentous (F-actin) to globular actin (G-actin;Weeds and Way, 1991;Safer, 1992). Furthermore, the interaction of thymosin and actin inhibits of ADP/ATP exchange in actin, consequently leading to a high concentration of ADP-actin, which has a drastically decreased tendency to form actin filaments. Profilins, another class of G-actin-binding proteins, increase the nucleotide exchange and are thought to compete with thymosin in this reaction (Goldschmidt-Clermont et al., 1992).Since the elucidation of the crystal structure of actin (Kabsch et al., 1990), it is of prime importance to determine the structures of actin-binding proteins and to characterize the nature of the protein/protein interactions. Recently, we determined the NMR structure of hisactophilin, a histidinerich actin-binding protein (Scheel et al., 1989;Habazettl et al., 1992), and of thymosin p4 (Zarbock et al., 1990). The latter, however, was obtained in solutions containing fluorinated alcohols, i.e. conditions which might not reflect the true conformation of the protein in the aqueous environment. We present in this study the determination of the solution conformation of thymosin / I 4 in water by 'H-NMR spectroscopy. Using a variety of two-dimensional (2D) NMR techniques (Emst et al., 1987), the 'H-NMR spectra were assigned in a sequential manner (Wuthrich, 1986 spectra formed the basis for the determination of the conformational preferences of thymosin p4 at different temperatures and pH. MATERIALS AND METHODS Sample preparation of thymosin p4Thymosin P4 was isolated as described by Zarbock et al. (1990). The NMR samples of thymosin P4 were dissolved in 90% H,0/10% D,O at an approximate concentration of 2 mM peptide...