Convergence of integrins and EGF receptor signaling via PI3K/Akt/FoxO pathway in early gene Egr-1 expression.
The early gene early growth response (Egr-1), a broadly expressed member of the zing-finger family of transcription factors, is induced in many cell types by a variety of growth and differentiation stimuli, including epidermal growth factor (EGF). Here we demonstrate that Egr-1 expression is mainly regulated by integrin-mediated adhesion. Integrin-dependent adhesion plays a dual role in Egr-1 regulation, either being sufficient "per se" to induce Egr-1, or required for EGF-dependent expression of Egr-1, which occurs only in adherent cells and not in cells in suspension. To dissect the molecular basis of integrin-dependent Egr-1 regulation, we show by FLIM-based FRET that in living cells beta1-integrin associates with the EGF receptor (EGFR) and that EGF further increases the extent complex formation. Interestingly, Egr-1 induction depends on integrin-dependent PI3K/Akt activation, as indicated by the decrease in Egr-1 levels in presence of the pharmacological inhibitor LY294002, the kinase-defective Akt mutant and Akt1/2 shRNAs. Indeed, upon adhesion activated Akt translocates into the nucleus and phosphorylates FoxO1, a Forkhead transcription factors. Consistently, FoxO1silencing results in Egr-1-increased levels, indicating that FoxO1 behaves as a negative regulator of Egr-1 expression. These data demonstrate that integrin/EGFR cross-talk is required for expression of Egr-1 through a novel regulatory cascade involving the activation of the PI3K/Akt/Forkhead pathway.
Centro di Biotecnologie Molecolari and Dipartimento di Genetica, Biologia e Biochimica, Università di Torino, Torino, Italy.
Sara
S
Cabodi
Virginia
V
Morello
Alessio
A
Masi
Riccardo
R
Cicchi
Chiara
C
Broggio
Paola
P
Distefano
Elisa
E
Brunelli
Lorenzo
L
Silengo
Francesco
F
Pavone
Annarosa
A
Arcangeli
Emilia
E
Turco
Guido
G
Tarone
Laura
L
Moro
Paola
P
Defilippi
D002448:Cell Adhesion / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology; D002470:Cell Survival / Q000187:drug effects; D051766:Early Growth Response Protein 1 / Q000235:genetics*; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D020239:Receptor Cross-Talk / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects
D051766:Early Growth Response Protein 1; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D019012:Integrin beta1; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt