PubMed Health⌕ Search

Biomedical subjects

Nicole R den Elzen

Publications and source records attributed to Nicole R den Elzen.

5 recordsLinked to original sources
PubMed2005

Ena/VASP proteins can regulate distinct modes of actin organization at cadherin-adhesive contacts.

Functional interactions between classical cadherins and the actin cytoskeleton involve diverse actin activities, including filament nucleation, cross-linking, and bundling. In this report, we explored the capacity of Ena/VASP proteins to regulate the actin cytoskeleton at cadherin-adhesive contacts. We extended the observation that Ena/vasodilator-stimulated phosphoprotein (VASP) proteins localize at cell-cell contacts to demonstrate that E-cadherin homophilic ligation is sufficient to recruit Mena to adhesion sites. Ena/VASP activity was necessary both for F-actin accumulation and assembly at cell-cell contacts. Moreover, we identified two distinct pools of Mena within individual homophilic adhesions that cells made when they adhered to cadherin-coated substrata. These Mena pools localized with Arp2/3-driven cellular protrusions as well as at the tips of cadherin-based actin bundles. Importantly, Ena/VASP activity was necessary for both modes of actin activity to be expressed. Moreover, selective depletion of Ena/VASP proteins from the tips of cadherin-based bundles perturbed the bundles without affecting the protrusive F-actin pool. We propose that Ena/VASP proteins may serve as higher order regulators of the cytoskeleton at cadherin contacts through their ability to modulate distinct modes of actin organization at those contacts.

Actin Cytoskeleton↗
PubMed2004

DNA damage checkpoint maintenance through sustained Chk1 activity.

The G2 DNA damage checkpoint prevents mitotic entry in the presence of DNA damage. This requires the activation of the phosphoinositide-3-kinase-related protein kinases ATR and ATM in human cells and the ATR homologue Rad3 in the fission yeast Schizosaccharomyces pombe. Rad3 activates the effector protein kinase Chk1 by phosphorylation. However, in fission yeast, inactivation of Rad3 following checkpoint activation has no impact on checkpoint duration. This demonstrates that Rad3 is not required for checkpoint maintenance and that the processes of checkpoint initiation and maintenance are distinct. Chk1 is required for checkpoint initiation but its role in checkpoint maintenance has not been investigated. We show here that Chk1 kinase activity is rapidly induced following irradiation and is maintained for the duration of a checkpoint arrest. On entry to mitosis, there is a transient decrease in Chk1 activity and phosphorylation, but Chk1 activity remains higher than that observed in unirradiated cells. We have generated temperature-sensitive alleles of chk1, which phenocopy chk1 deletion at the non-permissive temperature. Using these alleles, we have shown that inactivation of Chk1 during a checkpoint arrest leads to premature checkpoint termination, resulting in catastrophic mitoses that are a hallmark of checkpoint failure. Therefore, unlike Rad3, Chk1 is an important determinant of both checkpoint initiation and maintenance.

Amino Acid Sequence↗
PubMed2004

Arp2/3 activity is necessary for efficient formation of E-cadherin adhesive contacts.

Classical cadherin adhesion molecules are fundamental determinants of cell-cell recognition that function in cooperation with the actin cytoskeleton. Productive cadherin-based cell recognition is characterized by a distinct morphological process of contact zone extension, where limited initial points of adhesion are progressively expanded into broad zones of contact. We recently demonstrated that E-cadherin ligation recruits the Arp2/3 actin nucleator complex to the plasma membrane in regions where cell contacts are undergoing protrusion and extension. This suggested that Arp2/3 might generate the protrusive forces necessary for cell surfaces to extend upon one another during contact assembly. We tested this hypothesis in mammalian cells by exogenously expressing the CA region of N-WASP. This fragment, which potently inhibits Arp2/3-mediated actin assembly in vitro, also effectively reduced actin assembly at cadherin adhesive contacts. Blocking Arp2/3 activity by this strategy profoundly reduced the ability of cells to extend cadherin adhesive contacts but did not affect cell adhesiveness. These findings demonstrate that Arp2/3 activity is necessary for cells to efficiently extend and assemble cadherin-based adhesive contacts.

Actin-Related Protein 2↗
PubMed2004

Recovery from DNA damage checkpoint arrest by PP1-mediated inhibition of Chk1.

The G2 DNA damage checkpoint delays mitotic entry via the upregulation of Wee1 kinase and the downregulation of Cdc25 phosphatase by Chk1 kinase, and resultant inhibitory phosphorylation of Cdc2. While checkpoint activation is well understood, little is known about how the checkpoint is switched off to allow cell cycle re-entry. To identify proteins required for checkpoint release, we screened for genes in Schizosaccharomyces pombe that, when overexpressed, result in precocious mitotic entry in the presence of DNA damage. We show that overexpression of the type I protein phosphatase Dis2 sensitises S. pombe cells to DNA damage, causing aberrant mitoses. Dis2 abrogates Chk1 phosphorylation and activation in vivo, and dephosphorylates Chk1 and a phospho-S345 Chk1 peptide in vitro. dis2Delta cells have a prolonged chk1-dependent arrest and a compromised ability to downregulate Chk1 activity for checkpoint release. These effects are specific for the DNA damage checkpoint, because Dis2 has no effect on the chk1-independent response to stalled replication forks. We propose that inactivation of Chk1 by Dis2 allows mitotic entry following repair of DNA damage in the G2-phase.

Cell Cycle Proteins↗