ERK activation of p21 activated kinase-1 (Pak1) is critical for medulloblastoma cell migration.
We previously identified that overexpression of the platelet-derived growth factor receptor (PDGFR) is associated with metastatic medulloblastoma (MB) and showed that PDGF treatment increases ERK activity and promotes MB cell migration. In this study, we investigated whether ERK regulates Rac1/Pak1 signaling and is critically linked to MB cell migration. Herein we demonstrate that PDGF-BB treatment of MB cells induces concomitant activation of PDGFRβ, MEK1/ERK, Rac1 and Pak1, but suppresses Rho activity, which together significantly promotes cell migration. Conversely, cells transfected with either PDGFRβ or Pak1 siRNA or treated with an inhibitor of Rac1 (NSC23766) or N-myristoyltransferase-1 (Tris-dipalladium) are unable to activate Rac1 or Pak1 in response to PDGF, and consequently, are unable to undergo PDGF-mediated cell migration. Furthermore, we also demonstrate that either chemical inhibition of MEK/ERK (U0126) or stable downregulation of PDGFRβ by shRNA similarly results in the loss of PDGF-induced ERK phosphorylation and abolishes Rac1/Pak1 activation and cell migration in response to PDGF. However, specific depletion of Pak1 by siRNA has no effect on PDGF-induced ERK phosphorylation, indicating that in MB cells ERK signaling is Pak1-independent, but PDGF-induced migration is dependent on ERK-mediated activation of Pak1. Finally, using tissue microarrays, we detect phosphorylated Pak1 in 53% of medulloblastomas and show that immunopositivity is associated with unfavorable outcome. We conclude that Rac1/Pak1 signaling is critical to MB cell migration and is functionally dependent on PDGFRβ/ERK activity.
Aflac Center for Cancer and Blood Disorders, Emory University School of Medicine, Atlanta, GA 30322, USA.
Liangping
L
Yuan
Mariarita
M
Santi
Elisabeth J
EJ
Rushing
Robert
R
Cornelison
Tobey J
TJ
MacDonald
D015153:Blotting, Western; D001932:Brain Neoplasms / Q000201:enzymology / Q000473:pathology*; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D008527:Medulloblastoma / Q000201:enzymology / Q000473:pathology*; D009362:Neoplasm Metastasis; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D034741:RNA, Small Interfering; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D046888:Tissue Array Analysis; D054462:p21-Activated Kinases / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
D010982:Platelet-Derived Growth Factor; D034741:RNA, Small Interfering; D017479:Receptors, Platelet-Derived Growth Factor; D054462:p21-Activated Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020830:rac1 GTP-Binding Protein