An activated Ras protein alters cell adhesion by dephosphorylating Dictyostelium DdCAD-1

Microbiology (Reading). 2006 May;152(Pt 5):1497-1505. doi: 10.1099/mic.0.28709-0.

Abstract

RasG-regulated signal transduction has been linked to a variety of growth-specific processes and appears to also play a role in the early development of Dictyostelium discoideum. In an attempt to uncover some of the molecular components involved in Ras-mediated signalling, several proteins have been described previously, including the cell adhesion molecule DdCAD-1, whose phosphorylation state was affected by the expression of the constitutively activated RasG, RasG(G12T). Here it has been shown that a cadA null strain lacks the phosphoproteins that were tentatively identified as DdCAD-1, confirming its previous designation. Further investigation revealed that cells expressing RasG(G12T) exhibited increased cell-cell cohesion, concomitant with reduced levels of DdCAD-1 phosphorylation. This increased cohesion was DdCAD-1-dependent and was correlated with increased localization of DdCAD-1 at the cell surface. DdCAD-1 phosphorylation was also found to decrease during Dictyostelium aggregation. These results revealed a possible role for protein phosphorylation in regulating DdCAD-1-mediated cell adhesion during early development. In addition, the levels of DdCAD-1 protein were substantially reduced in a rasG null cell line. These results indicate that RasG affects both the expression and dephosphorylation of DdCAD-1 during early development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium-Binding Proteins / biosynthesis
  • Calcium-Binding Proteins / metabolism*
  • Cell Adhesion / physiology*
  • Cell Adhesion Molecules / biosynthesis
  • Cell Adhesion Molecules / metabolism*
  • Cell Aggregation
  • Dictyostelium / physiology*
  • Electrophoresis, Gel, Two-Dimensional
  • Electrophoresis, Polyacrylamide Gel
  • Gene Deletion
  • Genes, Protozoan
  • Immunoblotting
  • Membrane Proteins / analysis
  • Microscopy, Fluorescence
  • Mutation
  • Phosphoproteins / analysis
  • Phosphorylation
  • Protozoan Proteins / analysis
  • Protozoan Proteins / isolation & purification
  • Protozoan Proteins / physiology*

Substances

  • Calcium-Binding Proteins
  • Cell Adhesion Molecules
  • DdCAD-1 protein, Dictyostelium discoideum
  • Membrane Proteins
  • Phosphoproteins
  • Protozoan Proteins
  • rasG protein, Dictyostelium