Autophosphorylation-dependent degradation of Pak1, triggered by the Rho-family GTPase, Chp

Biochem J. 2007 Jun 15;404(3):487-97. doi: 10.1042/BJ20061696.

Abstract

The Paks (p21-activated kinases) Pak1, Pak2 and Pak3 are among the most studied effectors of the Rho-family GTPases, Rac, Cdc42 (cell division cycle 42) and Chp (Cdc42 homologous protein). Pak kinases influence a variety of cellular functions, but the process of Pak down-regulation, following activation, is poorly understood. In the present study, we describe for the first time a negative-inhibitory loop generated by the small Rho-GTPases Cdc42 and Chp, resulting in Pak1 inhibition. Upon overexpression of Chp, we unexpectedly observed a T-cell migration phenotype consistent with Paks inhibition. In line with this observation, overexpression of either Chp or Cdc42 caused a marked reduction in the level of Pak1 protein in a number of different cell lines. Chp-induced degradation was accompanied by ubiquitination of Pak1, and was dependent on the proteasome. The susceptibility of Pak1 to Chp-induced degradation depended on its p21-binding domain, kinase activity and a number of Pak1 autophosphorylation sites, whereas the PIX- (Pak-interacting exchange factor) and Nck-binding sites were not required. Together, these results implicate Chp-induced kinase autophosphorylation in the degradation of Pak1. The N-terminal domain of Chp was found to be required for Chp-induced degradation, although not for Pak1 activation, suggesting that Chp provides a second function, distinct from kinase activation, to trigger Pak degradation. Collectively, our results demonstrate a novel mechanism of signal termination mediated by the Rho-family GTPases Chp and Cdc42, which results in ubiquitin-mediated degradation of one of their direct effectors, Pak1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cell Movement / physiology
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism*
  • Gene Expression Regulation
  • Humans
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism*
  • Phosphorylation
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Binding
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Signal Transduction / physiology*
  • T-Lymphocytes / cytology
  • T-Lymphocytes / physiology
  • Ubiquitin / metabolism
  • p21-Activated Kinases
  • rho GTP-Binding Proteins / genetics
  • rho GTP-Binding Proteins / metabolism*

Substances

  • Neoplasm Proteins
  • RHOV protein, human
  • Ubiquitin
  • PAK4 protein, human
  • PAK1 protein, human
  • PAK2 protein, human
  • Protein Serine-Threonine Kinases
  • p21-Activated Kinases
  • Proteasome Endopeptidase Complex
  • GTP-Binding Proteins
  • rho GTP-Binding Proteins