Mitogen-activated protein kinase feedback phosphorylation regulates MEK1 complex formation and activation during cellular adhesion.
Cell adhesion and spreading depend on activation of mitogen-activated kinase, which in turn is regulated both by growth factor and integrin signaling. Growth factors, such as epidermal growth factor, are capable of activating Ras and Raf, but integrin signaling is required to couple Raf to MEK and MEK to extracellular signal-regulated protein kinase (ERK). It was previously shown that Rac-p21-activated kinase (PAK) signaling regulated the physical association of MEK1 with ERK2 through phosphorylation sites in the proline-rich sequence (PRS) of MEK1. It was also shown that activation of MEK1 and ERK by integrins depends on PAK phosphorylation of S298 in the PRS. Here we report a novel MEK1-specific regulatory feedback mechanism that provides a means by which activated ERK can terminate continued PAK phosphorylation of MEK1. Activated ERK can phosphorylate T292 in the PRS, and this blocks the ability of PAK to phosphorylate S298 and of Rac-PAK signaling to enhance MEK1-ERK complex formation. Preventing ERK feedback phosphorylation on T292 during cellular adhesion prolonged phosphorylation of S298 by PAK and phosphorylation of S218 and S222, the MEK1 activating sites. We propose that activation of ERK during adhesion creates a feedback system in which ERK phosphorylates MEK1 on T292, and this in turn blocks additional S298 phosphorylation in response to integrin signaling.
Department of Microbiology, School of Medicine, University of Virginia, Charlottesville, Virginia 22908, USA. ste4n@virginia.edu
Scott T
ST
Eblen
Jill K
JK
Slack-Davis
Adel
A
Tarcsafalvi
J Thomas
JT
Parsons
Michael J
MJ
Weber
Andrew D
AD
Catling
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D002448:Cell Adhesion / Q000502:physiology*; D004789:Enzyme Activation; D005246:Feedback; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054462:p21-Activated Kinases
D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases