IQGAP1 is a conserved modular protein overexpressed in cancer and involved in organizing actin and microtubules in motile processes such as adhesion, migration, and cytokinesis. A variety of proteins ...have been shown to interact with IQGAP1, including the small G proteins Rac1 and Cdc42, actin, calmodulin, β-catenin, the microtubule plus end-binding proteins CLIP170 (cytoplasmic linker protein) and adenomatous polyposis coli. However, the molecular mechanism by which IQGAP1 controls actin dynamics in cell motility is not understood. Quantitative co-localization analysis and down-regulation of IQGAP1 revealed that IQGAP1 controls the co-localization of N-WASP with the Arp2/3 complex in lamellipodia. Co-immunoprecipitation supports an in vivo link between IQGAP1 and N-WASP. Pull-down experiments and kinetic assays of branched actin polymerization with N-WASP and Arp2/3 complex demonstrated that the C-terminal half of IQGAP1 activates N-WASP by interacting with its BR-CRIB domain in a Cdc42-like manner, whereas the N-terminal half of IQGAP1 antagonizes this activation by association with a C-terminal region of IQGAP1. We propose that signal-induced relief of the autoinhibited fold of IQGAP1 allows activation of N-WASP to stimulate Arp2/3-dependent actin assembly.
The Rho-GTPase Cdc42 is important for the establishment and maintenance of epithelial polarity. Signaling from Cdc42 is propagated
via its effector molecules that specifically bind to Cdc42 in the ...GTP-bound form. The cell-cell contact regulator and actin-binding
protein IQGAP1 is described as effector of Cdc42 and Rac. Unexpectedly, we show in this study that IQGAP1 bound also directly
nucleotide-depleted Cdc42 (Cdc42-ND). This interaction was enhanced in the presence of phosphatase inhibitors and in epithelial
cells without cell-cell contacts. Tandem mass spectrometry analysis and immunoprecipitation experiments revealed that IQGAP1
was Ser 1443 -phosphorylated in vivo , potentially by protein kinase Cϵ and upon loss of cell-cell contacts. In addition, we identified two independent domains
of the IQGAP1 C terminus that bound exclusively Cdc42-ND. These domains interacted with each other, favoring the binding to
Cdc42-GTP. Moreover, phosphorylation on Ser 1443 strongly inhibited this intramolecular interaction. Thus, we unraveled a molecular mechanism that reveals a novel type of
Rho-GTPase regulator. We propose that, depending on its phosphorylation state, IQGAP1 might serve as an effector or sequester
nucleotide-free Cdc42 to prevent signaling.
Septins are conserved GTPases that form heteromultimeric complexes and assemble into filaments that play a critical role in cell division and polarity. Results from budding and fission yeast indicate ...that septin complexes form around a tetrameric core. However, the molecular structure of the core and its influence on the polarity of septin complexes and filaments is poorly defined. The septin complex of the nematode Caenorhabditis elegans is formed entirely by the core septins UNC‐59 and UNC‐61. We show that UNC‐59 and UNC‐61 form a dimer of coiled‐coil‐mediated heterodimers. By electron microscopy, this heterotetramer appears as a linear arrangement of four densities representing the four septin subunits. Fusion of GFP to the N termini of UNC‐59 and UNC‐61 and subsequent electron microscopic visualization suggests that the sequence of septin subunits is UNC‐59/UNC‐61/UNC‐61/UNC‐59. Visualization of GFP extensions fused to the extremity of the C‐terminal coiled coils indicates that these extend laterally from the heterotetrameric core. Together, our study establishes that the septin core complex is symmetric, and suggests that septins form nonpolar filaments.
Uncertainties concerning anatomy and function of cortico-subcortical projections have arisen during the recent years. A clear distinction between cortico-subthalamic (hyperdirect) and ...cortico-tegmental projections (superolateral medial forebrain bundle, slMFB) so far is elusive. Deep Brain Stimulation (DBS) of the slMFB (for major depression, MD and obsessive compulsive disorders, OCD) has on the one hand been interpreted as actually involving limbic (prefrontal) hyperdirect pathways. On the other hand slMFB’s stimulation region in the mesencephalic ventral tegmentum is said to impact on other structures too, going beyond the antidepressant (or anti OCD) efficacy of sole modulation of the cortico-tegmental reward-associated pathways. We have here used a normative diffusion MRT template (HCP,
n
= 80) for long-range tractography and augmented this dataset with ex-vivo high resolution data (
n
= 1) in a stochastic brain space. We compared this data with histological information and used the high resolution ex-vivo data set to scrutinize the mesencephalic tegmentum for small fiber pathways present. Our work resolves an existing ambiguity between slMFB and prefrontal hyperdirect pathways which—for the first time—are described as co-existent. DBS of the slMFB does not appear to modulate prefrontal hyperdirect cortico-subthalamic but rather cortico-tegmental projections. Smaller fiber structures in the target region—as far as they can be discerned—appear not to be involved in slMFB DBS. Our work enfeebles previous anatomical criticism and strengthens the position of the slMFB DBS target for its use in MD and OCD.
In the industrialized world a large part of the emission of the primary air pollutants (NOx, volatile organic compounds (VOC) and CO) originates from road traffic. Here we present the concept and ...first results of a tunnel study which took place from September 20th to September 26th, 1993 at the Gubrist tunnel (close to Zürich, Switzerland) in which the emission factors of a large number of individual VOCs, total hydrocarbons (t-HC), CO, NOx and SO2 are determined. The first tentative results of the emission factors of NOx, CO, t-HC and 26 individual hydrocarbons (alkanes and aromatics in the volatility range from n-heptane to n-decane) for the average of all vehicles and the light duty vehicles at an average speed of 90 km/h are given.
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