236 research outputs found
Evidence for compact cooperatively rearranging regions in a supercooled liquid
We examine structural relaxation in a supercooled glass-forming liquid
simulated by NVE molecular dynamics. Time correlations of the total kinetic
energy fluctuations are used as a comprehensive measure of the system's
approach to the ergodic equilibrium. We find that, under cooling, the total
structural relaxation becomes delayed as compared with the decay of the
component of the intermediate scattering function corresponding to the main
peak of the structure factor. This observation can be explained by collective
movements of particles preserving many-body structural correlations within
compact 3D cooperatively rearranging regions.Comment: 8 pages, 4 figure
Structural characterization of EGFR exon 19 deletion mutation using molecular dynamics simulation
Epidermal growth factor receptor (EGFR) is a tyrosine kinase receptor
important in diverse biological processes including cell proliferation
and survival. Upregulation of EGFR activity due to over-expression or
mutation is widely implicated in cancer. Activating somatic mutations of
the EGFR kinase are postulated to affect the conformation and/or
stability of the protein, shifting the EGFR inactive-active state
equilibrium towards the activated state. Here, we examined a common EGFR
deletion mutation, Δ746ELREA750, which is
frequently observed in non-small cell lung cancer patients. By using
molecular dynamics simulation, we investigated the structural effects of
the mutation that lead to the experimentally reported increases in
kinase activity. Simulations of the active form wild-type and ΔELREA
EGFRs revealed the deletion stabilizes the αC helix of the kinase
domain, which is located adjacent to the deletion site, by rigidifying
the flexible β3-αC loop that accommodates the ELREA sequence.
Consequently, the αC helix is stabilized in the “αC-in” active
conformation that would prolong the time of the activated state.
Moreover, in the mutant kinase, a salt bridge between E762 and K745,
which is key for EGFR activity, was also stabilized during the
simulation. Additionally, the interaction between EGFR and ATP was
favored by ΔELREA EGFR over wild-type EGFR, as reflected by the number
of hydrogen bonds formed and the free energy of binding. Simulation of
inactive EGFR suggested the deletion would promote a shift from the
inactive conformation towards active EGFR, which is supported by the
inward movement of the αC helix. The MDS results also align with the
effects of tyrosine kinase inhibitors on ΔELREA and wild-type EGFR lung
cancer cell lines, where more pronounced inhibition was observed against
ΔELREA than for wild-type EGFR by inhibitors recognizing the active
kinase conformation.</p
Removal of cell surface heparan sulfate increases TACE activity and cleavage of ErbB4 receptor
<p>Abstract</p> <p>Background</p> <p>Nuclear localization of proteolytically formed intracellular fragment of ErbB4 receptor tyrosine kinase has been shown to promote cell survival, and nuclear localization of ErbB4 receptor has been described in human breast cancer. Tumor necrosis factor alpha converting enzyme (TACE) initiates the proteolytic cascade leading to ErbB4 intracellular domain formation. Interactions between matrix metalloproteases and heparan sulfate have been described, but the effect of cell surface heparan sulfate on TACE activity has not been previously described.</p> <p>Results</p> <p>As indicated by immunodetection of increased ErbB4 intracellular domain formation and direct enzyme activity analysis, TACE activity was substantially amplified by enzymatic removal of cell surface heparan sulfate but not chondroitin sulfate.</p> <p>Conclusion</p> <p>In this communication, we suggest a novel role for cell surface heparan sulfate. Removal of cell surface heparan sulfate led to increased formation of ErbB4 intracellular domain. As ErbB4 intracellular domain has previously been shown to promote cell survival this finding may indicate a novel mechanism how HS degradation active in tumor tissue may favor cell survival.</p
SUMOylation regulates nuclear accumulation and signaling activity of the soluble intracellular domain of the ErbB4 receptor tyrosine kinase
Erb-B2 receptor tyrosine kinase 4 (ErbB4) is a kinase that can signal via a proteolytically released intracellular domain (ICD) in addition to classical receptor tyrosine kinase-activated signaling cascades. Previously, we have demonstrated that ErbB4 ICD is posttranslationally modified by the small ubiquitin-like modifier (SUMO) and functionally interacts with the PIAS3 SUMO E3 ligase. However, direct evidence of SUMO modification in ErbB4 signaling has remained elusive. Here, we report that the conserved lysine residue 714 in the ErbB4 ICD undergoes SUMO modification, which was reversed by sentrin-specific proteases (SENPs) 1, 2, and 5. Although ErbB4 kinase activity was not necessary for the SUMOylation, the SUMOylated ErbB4 ICD was tyrosine phosphorylated to a higher extent than unmodified ErbB4 ICD. Mutation of the SUMOylation site compromised neither ErbB4-induced phosphorylation of the canonical signaling pathway effectors Erk1/2, Akt, or STAT5 nor ErbB4 stability. In contrast, SUMOylation was required for nuclear accumulation of the ErbB4 ICD. We also found that Lys-714 was located within a leucine-rich stretch, which resembles a nuclear export signal, and could be inactivated by site-directed mutagenesis. Furthermore, SUMOylation modulated the interaction of ErbB4 with chromosomal region maintenance 1 (CRM1), the major nuclear export receptor for proteins. Finally, the SUMO acceptor lysine was functionally required for ErbB4 ICD-mediated inhibition of mammary epithelial cell differentiation in a three-dimensional cell culture model. Our findings indicate that a SUMOylation-mediated mechanism regulates nuclear localization and function of the ICD of ErbB4 receptor tyrosine kinase
Pim-1 Kinase Expression Predicts Radiation Response in Squamocellular Carcinoma of Head and Neck and Is under the Control of Epidermal Growth Factor Receptor
Pim-1 is an oncogenic serine/threonine kinase with poorly defined function in epithelial cancers. In this study, we determined 1) associations of Pim-1 expression with clinicopathological parameters including responsiveness to irradiation in squamocellular cancers of head and neck and 2) how Pim-1 expression is controlled subsequent to irradiation. Moderate to high expression of Pim-1 correlated to poor response to radiation therapy (P = .003). It is also associated to the expression of epidermal growth factor receptor (EGFR, P < .0001), which has been shown to be activated by irradiation. In radioresistant tumors, irradiation promoted nuclear translocation of Pim-1 (P < .005). When directly testing EGFR dependence of Pim-1 expression, up-regulation and nuclear translocation of Pim-1 could be induced through stimulation of EGFR with its ligands EGF or transforming growth factor a. Both ligand- and irradiation-induced changes in Pim-1 expression and localization could be inhibited by the monoclonal anti-EGFR antibody cetuximab and by the tyrosine kinase inhibitor gefitinib also targeting EGFR. These results suggest that irradiation-induced activation of EGFR upregulates Pim-1, and Pim-1 may be used as a novel predictive marker of radiation response in patients with squamocellular cancers of head and neck.</p
Nature of vibrational eigenmodes in topologically disordered solids
We use a local projectional analysis method to investigate the effect of
topological disorder on the vibrational dynamics in a model glass simulated by
molecular dynamics. Evidence is presented that the vibrational eigenmodes in
the glass are generically related to the corresponding eigenmodes of its
crystalline counterpart via disorder-induced level-repelling and hybridization
effects. It is argued that the effect of topological disorder in the glass on
the dynamical matrix can be simulated by introducing positional disorder in a
crystalline counterpart.Comment: 7 pages, 6 figures, PRB, to be publishe
Syndecan-1 expression has prognostic significance in head and neck carcinoma
The syndecans are a family of cell-surface heparan sulphate proteoglycans that regulate cell behaviour by binding extracellular matrix molecules such as growth factors. The syndecan family has four members, of which syndecan-1 is the most studied and best characterized. We have studied the prognostic significance of syndecan-1 expression in squamous cell carcinoma (SCC) of the head and neck treated with surgery and post-operative radiotherapy. Paraffin-embedded tissue samples taken from 175 patients with primary SCC, followed up from 2 to 15 years after surgery, were studied for expression of syndecan-1 by immunohistochemistry. A low number (≤50%, the median value) of syndecan-1-positive tumour cells was associated with low histological grade of differentiation (P < 0.0001), a large primary tumour size (T1–2 vs T3–4, P = 0.02), positive nodal status (N0 vs N1–3, P = 0.0006), and high clinical stage (stage I or II vs III or IV, P < 0.0001). Low syndecan-1 expression was also associated with unfavourable overall survival in a univariate analysis (P = 0.001). In a multivariate survival analysis, the clinical stage and syndecan-1 expression were the only independent prognostic factors. We conclude that syndecan-1 is a novel prognostic factor in SCC of the head and neck treated with surgery and post-operative radiotherapy. © 1999 Cancer Research Campaig
An extracellular receptor tyrosine kinase motif orchestrating intracellular STAT activation
Specificity in signaling activated by receptor tyrosine kinases is typically attributed to characteristics of their intracellular domains. Here, the authors demonstrate that an extracellular receptor sequence motif controls intracellular signaling as a result of extracellular glycan interactions.The ErbB4 receptor isoforms JM-a and JM-b differ within their extracellular juxtamembrane (eJM) domains. Here, ErbB4 isoforms are used as a model to address the effect of structural variation in the eJM domain of receptor tyrosine kinases (RTK) on downstream signaling. A specific JM-a-like sequence motif is discovered, and its presence or absence (in JM-b-like RTKs) in the eJM domains of several RTKs is demonstrated to dictate selective STAT activation. STAT5a activation by RTKs including the JM-a like motif is shown to involve interaction with oligosaccharides of N-glycosylated cell surface proteins such as beta 1 integrin, whereas STAT5b activation by JM-b is dependent on TYK2. ErbB4 JM-a- and JM-b-like RTKs are shown to associate with specific signaling complexes at different cell surface compartments using analyses of RTK interactomes and super-resolution imaging. These findings provide evidence for a conserved mechanism linking a ubiquitous extracellular motif in RTKs with selective intracellular STAT signaling.Peer reviewe
A Structural Model for Octagonal Quasicrystals Derived from Octagonal Symmetry Elements Arising in -Mn Crystallization of a Simple Monatomic Liquid
While performing molecular dynamics simulations of a simple monatomic liquid,
we observed the crystallization of a material displaying octagonal symmetry in
its simulated diffraction pattern. Inspection of the atomic arrangements in the
crystallization product reveals large grains of the beta-Mn structure aligned
along a common 4-fold axis, with 45 degree rotations between neighboring
grains. These 45 degree rotations can be traced to the intercession of a second
crystalline structure fused epitaxially to the beta-Mn domain surfaces, whose
primitive cell has lattice parameters a = b = c = a_{beta-Mn}, alpha = beta =
90 degrees, and gamma = 45 degrees. This secondary phase adopts a structure
which appears to have no known counterpart in the experimental literature, but
can be simply derived from the Cr_3Si and Al_3Zr_4 structure types. We used
these observations as the basis for an atomistic structural model for octagonal
quasicrystals, in which the beta-Mn and the secondary phase structure unit
cells serve as square and rhombic tiles (in projection), respectively. Its
diffraction pattern down the octagonal axis resembles those experimentally
measured. The model is unique in being consistent with high-resolution electron
microscopy images showing square and rhombic units with edge-lengths equal to
that of the beta-Mn unit cell. Energy minimization of this configuration, using
the same pair potential as above, results in an alternative octagonal
quasiperiodic structure with the same tiling but a different atomic decoration
and diffraction pattern.Comment: 25 pages, 10 figure
O-sulfated bacterial polysaccharides with low anticoagulant activity inhibit metastasis
Heparin-like polysaccharides possess the capacity to inhibit cancer cell
proliferation, angiogenesis, heparanase-mediated cancer cell invasion,
and cancer cell adhesion to vascular endothelia via adhesion receptors,
such as selectins. The clinical applicability of the antitumor effect of
such polysaccharides, however, is compromised by their anticoagulant
activity. We have compared the potential of chemically O-sulfated and
N,O-sulfated bacterial polysaccharide (capsular polysaccharide from E. coli
K5 [K5PS]) species to inhibit metastasis of mouse B16-BL6 melanoma
cells and human MDA-MB-231 breast cancer cells in two in vivo models. We
demonstrate that in both settings, O-sulfated K5PS was a potent
inhibitor of metastasis. Reducing the molecular weight of the
polysaccharide, however, resulted in lower antimetastatic capacity.
Furthermore, we show that O-sulfated K5PS efficiently inhibited the
invasion of B16-BL6 cells through Matrigel and also inhibited the in
vitro activity of heparanase. Moreover, treatment with O-sulfated K5PS
lowered the ability of B16-BL6 cells to adhere to endothelial cells,
intercellular adhesion molecule-1, and P-selectin, but not to
E-selectin. Importantly, O-sulfated K5PSs were largely devoid of
anticoagulant activity. These findings indicate that O-sulfated K5PS
polysaccharide should be considered as a potential antimetastatic agent.</p
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