An activated Ras protein alters cell adhesion by dephosphorylating Dictyostelium DdCAD-1.
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.
Secko
David M
DM
Department of Microbiology and Immunology, University of British Columbia, Life Sciences Centre, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z4, Canada.
Siu
Chi-Hung
CH
Banting and Best Department of Medical Research, and Department of Biochemistry, University of Toronto, Toronto, Ontario M5G 1L6, Canada.
Spiegelman
George B
GB
Department of Microbiology and Immunology, University of British Columbia, Life Sciences Centre, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z4, Canada.
Weeks
Gerald
G
Department of Microbiology and Immunology, University of British Columbia, Life Sciences Centre, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z4, Canada.
D000818:Animals; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000378:metabolism*; D002449:Cell Aggregation; D004023:Dictyostelium / Q000502:physiology*; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D017125:Genes, Protozoan; D015151:Immunoblotting; D008565:Membrane Proteins / Q000032:analysis; D008856:Microscopy, Fluorescence; D009154:Mutation; D010750:Phosphoproteins / Q000032:analysis; D010766:Phosphorylation; D015800:Protozoan Proteins / Q000032:analysis / Q000302:isolation & purification / Q000502:physiology*
D002135:Calcium-Binding Proteins; D015815:Cell Adhesion Molecules; C100604:DdCAD-1 protein, Dictyostelium discoideum; D008565:Membrane Proteins; D010750:Phosphoproteins; D015800:Protozoan Proteins; C424065:rasG protein, Dictyostelium