Fibronectin-induced proliferation in thyroid cells is mediated by alphavbeta3 integrin through Ras/Raf-1/MEK/ERK and calcium/CaMKII signals.
We recently demonstrated in an immortalized thyroid cell line that integrin stimulation by fibronectin (FN) simultaneously activates two signaling pathways: Ras/Raf/MAPK kinase (Mek)/Erk and calcium Ca2+/calcium calmodulin-dependent kinase II (CaMKII). Both signals are necessary to stimulate Erk phosphorylation because CaMKII modulates Ras-induced Raf-1 activity. In this study we present evidence that extends these findings to normal human thyroid cells in primary culture, demonstrating its biological significance in a more physiological cell model. In normal thyroid cells, immobilized FN-induced activation of p21Ras and Erk phosphorylation. This pathway was responsible for FN-induced cell proliferation. Concurrent increase of intracellular Ca2+ concentration and CaMKII activation was observed. Both induction of p21Ras activity and increase of intracellular Ca2+ concentration were mediated by FN binding to alphavbeta3 integrin. Inhibition of the Ca2+/CaMKII signal pathway by calmodulin or CaMKII inhibitors completely abolished the FN-induced Erk phosphorylation. Binding to FN induced Raf-1 and CaMKII to form a protein complex, indicating that intersection between Ras/Raf/Mek/Erk and Ca2+/CaMKII signaling pathways occurred at Raf-1 level. Interruption of the Ca2+/CaMKII signal pathway arrested cell proliferation induced by FN. We also analyzed thyroid tumor cell lines that displayed concomitant aberrant integrin expression and signal transduction. These data confirm that integrin activation by FN in normal thyroid cells generates Ras/Raf/Mek/Erk and Ca2+/CaMKII signaling pathways and that both are necessary to stimulate cell proliferation, whereas in thyroid tumors integrin signaling is altered.
Illario
Maddalena
M
Department of Biologia, Universitá Federico II, Naples, Italy.
Cavallo
Anna Lina
AL
Monaco
Sara
S
Di Vito
Ennio
E
Mueller
Frank
F
Marzano
Luigi A
LA
Troncone
Giancarlo
G
Fenzi
Gianfranco
G
Rossi
Guido
G
Vitale
Mario
M
D020013:Calcium Signaling; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D019281:Dimerization; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D005353:Fibronectins / Q000502:physiology*; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000502:physiology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000502:physiology*; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D015398:Signal Transduction; D013961:Thyroid Gland / Q000166:cytology*; D013964:Thyroid Neoplasms / Q000473:pathology
D005353:Fibronectins; D039302:Integrin alphaVbeta3; D019908:Proto-Oncogene Proteins c-raf; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)