Related Experiment Videos
A novel regulator of p21-activated kinases
S Bagrodia1, S J Taylor, K A Jordon
1Department of Molecular Medicine, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853-6401, USA.
Abstract:
Proteins of the p21-activated kinase (Pak) family have been implicated in the regulation of gene expression, cytoskeletal architecture, and apoptosis. Although the ability of Cdc42 and Rac GTPases to activate Pak is well established, relatively little else is known about Pak regulation or the identity of Pak cellular targets. Here we report the identification of two closely related Pak3-binding proteins, possibly arising from alternative splicing, designated p50 and p85(Cool-1) (cloned out of library). Both isoforms of Cool contain a Src homology 3 domain that directly mediates interaction with Pak3 and tandem Dbl homology and pleckstrin homology domains. Despite the presence of the Dbl homology-pleckstrin homology motif, a characteristic of Rho family activators, activation of Cdc42 or Rac by Cool is not detectable. Instead binding of p50(Cool-1), but not p85(Cool-1), to Pak3 represses its activation by upstream activators such as the Dbl oncoprotein, indicating a novel mechanism of regulation of Pak signaling.
Insights
Researchers identified two new proteins, p50 and p85(Cool-1), that bind to p21-activated kinase 3 (Pak3). Binding of p50(Cool-1) to Pak3 inhibits its activation, revealing a new regulatory pathway for Pak signaling.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Protein interactions
Background:
- The p21-activated kinase (Pak) family plays roles in gene expression, cytoskeleton, and apoptosis.
- Cdc42 and Rac GTPases are known activators of Pak, but Pak regulation and targets are not fully understood.
Purpose of the Study:
- To identify novel proteins that interact with Pak3.
- To elucidate the functional consequences of these interactions on Pak3 signaling.
Main Methods:
- Cloning and characterization of Pak3-binding proteins.
- Analysis of protein-protein interactions using Src homology 3 (SH3) domains.
- Investigation of the effect of binding proteins on Pak3 activation by upstream activators.
Main Results:
- Two related Pak3-binding proteins, p50(Cool-1) and p85(Cool-1), were identified.
- Both isoforms contain SH3 domains mediating Pak3 interaction.
- p50(Cool-1), but not p85(Cool-1), binding to Pak3 inhibits Pak3 activation by oncoproteins like Dbl.
- Cool-1 isoforms do not activate Cdc42 or Rac GTPases.
Conclusions:
- p50(Cool-1) acts as a novel negative regulator of Pak3 signaling by inhibiting its activation.
- This discovery uncovers a new mechanism in the regulation of the Pak signaling pathway.