Transforming growth factor beta signaling via Ras in mesenchymal cells requires p21-activated kinase 2 for extracellular signal-regulated kinase-dependent transcriptional responses.
Transforming growth factor beta (TGF-beta) signaling via Smad proteins occurs in various cell types. However, whereas the biological response to TGF-beta can be as distinct as growth promoting (i.e., mesenchymal cells) versus growth inhibiting (i.e., epithelial cells), few discernible differences in TGF-beta signaling have been reported. In the current study, we examined the role of Ras in the proliferative response to TGF-beta and how it might interface with Smad-dependent and Smad-independent TGF-beta signaling targets. TGF-beta stimulated Ras activity in a subset of mesenchymal, but not epithelial, cultures and was required for extracellular signal-regulated kinase (ERK)-dependent transcriptional responses. Although dominant negative Ras had no effect on TGF-beta internalization or Smad-dependent signaling (i.e., phosphorylation, nuclear translocation, or SBE-luciferase activity), it did prevent the hyperphosphorylation of the Smad transcriptional corepressor TG-interacting factor (TGIF). This was not sufficient, however, to overcome the mitogenic response stimulated by TGF-beta, which was dependent on signals downstream of p21-activated kinase 2 (PAK2). Moreover, although the initial activation of Ras and PAK2 are distinctly regulated, TGF-beta-stimulated PAK2 activity is required for Ras-dependent ERK phosphorylation and Elk-1 transcription. These findings show the requirement for crosstalk between two Smad-independent pathways in regulating TGF-beta proliferation and indicate that the mechanism(s) by which TGF-beta stimulates growth is not simply the opposite of its growth inhibitory actions.
Suzuki
Kaori
K
Department of Biochemistry and Molecular Biology, Thoracic Diseases Research Unit, and Mayo Clinic Cancer Center, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
Wilkes
Mark C
MC
Garamszegi
Nandor
N
Edens
Maryanne
M
Leof
Edward B
EB
D000818:Animals; D048708:Cell Growth Processes / Q000502:physiology; D004285:Dogs; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D054462:p21-Activated Kinases; D018631:ras Proteins / Q000378:metabolism*
D048049:Extracellular Signal-Regulated MAP Kinases; D018398:Homeodomain Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D012097:Repressor Proteins; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D054462:p21-Activated Kinases; D018631:ras Proteins; C515907:PAK2 protein, human; C515909:Pak2 protein, mouse