Integrin-mediated adhesion regulates ERK nuclear translocation and phosphorylation of Elk-1.
Integrin-mediated adhesion to the extracellular matrix permits efficient growth factor-mediated activation of extracellular signal-regulated kinases (ERKs). Points of regulation have been localized to the level of receptor phosphorylation or to activation of the downstream components, Raf and MEK (mitogen-activated protein kinase/ERK kinase). However, it is also well established that ERK translocation from the cytoplasm to the nucleus is required for G1 phase cell cycle progression. Here we show that phosphorylation of the nuclear ERK substrate, Elk-1 at serine 383, is anchorage dependent in response to growth factor treatment of NIH 3T3 fibroblasts. Furthermore, when we activated ERK in nonadherent cells by expression of active components of the ERK cascade, subsequent phosphorylation of Elk-1 at serine 383 and Elk-1-mediated transactivation were still impaired compared with adherent cells. Elk-1 phosphorylation was dependent on an intact actin cytoskeleton, as discerned by treatment with cytochalasin D (CCD). Finally, expression of active MEK failed to predominantly localize ERK to the nucleus in suspended cells or adherent cells treated with CCD. These data show that integrin-mediated organization of the actin cytoskeleton regulates localization of activated ERK, and in turn the ability of ERK to efficiently phosphorylate nuclear substrates.
Aplin
A E
AE
Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. aaplin@med.unc.edu
Stewart
S A
SA
Assoian
R K
RK
Juliano
R L
RL
D016475:3T3 Cells; D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism*; D016895:Culture Media, Serum-Free; D019938:Cyclin D1 / Q000378:metabolism; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins; D017930:Genes, Reporter / Q000235:genetics; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D016023:Integrins / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D050807:ets-Domain Protein Elk-1
D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; C494113:Elk1 protein, mouse; D006133:Growth Substances; D016023:Integrins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D019938:Cyclin D1; D015638:Cytochalasin D; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases