Activity of Rap1 is regulated by bombesin, cell adhesion, and cell density in NIH3T3 fibroblasts.
Rap1 and Ras are homologous GTPases that are implicated in cell proliferation and differentiation. At present, little is known about the regulation of Rap1 activity. Using a recently developed assay with activation-specific probes, we found increased activity of endogenous Rap1 in NIH3T3 cells after stimulation with the neuropeptide growth factor bombesin in a concentration- and time-dependent manner. The activity of endogenous Ras was unaffected. Analysis of putative effectors showed no activation of c-Raf-1 or B-Raf after bombesin stimulation. However, MAPK/Erk-phosphorylation and the proliferation rate was increased. In addition, Rap1 was activated during cell adhesion to coated and uncoated tissue culture plates, as well as in response to various mitogens. Surprisingly, the basal Rap1 activity was observed to be cell density-dependent, with low levels when cells were reaching confluency. The results suggest that Rap1 acts as an important mediator of mitogenic signals distinct to Ras activation.
Posern
G
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Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), Julius-Maximilians-University, D-97078 Würzburg, Germany.
Weber
C K
CK
Rapp
U R
UR
Feller
S M
SM
D016475:3T3 Cells; D000818:Animals; D000077214:Becaplermin; D001839:Bombesin / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002448:Cell Adhesion / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D015638:Cytochalasin D / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D020668:rap GTP-Binding Proteins; D018631:ras Proteins / Q000378:metabolism
D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D014157:Transcription Factors; D000077214:Becaplermin; D015638:Cytochalasin D; D006160:Guanosine Triphosphate; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate; D001839:Bombesin