Spreading of differentiating human monocytes is associated with a major increase in membrane-bound CDC42.
In a search for a model cell system that might allow studies of the function of the Rho-related GTPase CDC42Hs in human cells, we measured the content and distribution of CDC42Hs in monocytes that were differentiating into macrophages. The total content of this protein increased 5- to 6-fold in phorbol ester-treated human monocytic THP-1 and U-937 cells and increased 13-fold in normal human blood monocytes. Moreover, membrane-associated CDC42Hs in these cells increased 13-fold and 30-fold, respectively, while cytosolic CDC42Hs increased only 3- and 6-fold. Measurements made specifically in U-937 cells showed that the increase in membrane CDC42Hs correlated closely with an increase in cell spreading. The changes in CDC42Hs in U-937 cells probably depended on increased mRNA translation and/or decreased protein degradation, since no change in CDC42Hs mRNA could be detected. Finally, the changes in CDC42Hs were relatively specific, since contents of the CDC42Hs-binding protein Rho-GDI and the Rho-related protein Rac2 were unaffected and no change in CDC42Hs occurred when the cells were stimulated by agonists that induce monocytes to differentiate into nonadherent cells. These findings show that marked changes in content and distribution of CDC42Hs occur when monocytes differentiate into macrophages, suggesting that membrane CDC42Hs may play a role in cell spreading.
Aepfelbacher
M
M
Howard Hughes Medical Institute, University of Washington, Seattle 98195.
Vauti
F
F
Weber
P C
PC
Glomset
J A
JA
D015153:Blotting, Western; D002448:Cell Adhesion / Q000187:drug effects; D002454:Cell Differentiation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D005434:Flow Cytometry; D019204:GTP-Binding Proteins / Q000096:biosynthesis* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009000:Monocytes / Q000166:cytology* / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic; D020764:cdc42 GTP-Binding Protein
D012333:RNA, Messenger; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D013755:Tetradecanoylphorbol Acetate