Focal adhesion kinase, a downstream mediator of Raf-1 signaling, suppresses cellular adhesion, migration, and neuroendocrine markers in BON carcinoid cells.
We have recently reported that activation of the Raf-1/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase 1/2 (MEK1/2)/ERK1/2 signaling cascade in gastrointestinal carcinoid cell line (BON) alters cellular morphology and neuroendocrine phenotype. The mechanisms by which Raf-1 mediates these changes in carcinoid cells are unclear. Here, we report that activation of the Raf-1 signaling cascade in BON cells induced the expression of focal adhesion kinase (FAK) protein, suppressed the production of neuroendocrine markers, and resulted in significant decreases in cellular adhesion and migration. Importantly, inactivation of MEK1/2 by 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene or abolition of FAK induction in Raf-1-activated BON cells by targeted siRNA led to reversal of the Raf-1-mediated reduction in neuroendocrine markers and cellular adhesion and migration. Phosphorylation site-specific antibodies detected the phosphorylated FAK(Tyr407), but not FAK(Tyr397), in these Raf-1-activated cells, indicating that FAK(Tyr407) may be associated with changes in the neuroendocrine phenotype. Overexpression of constitutively active FAK plasmids (wild-type FAK or FAK(Tyr397) mutant) into BON cells reduced neuroendocrine markers, whereas the FAK(Tyr407) mutant plasmid did not show any decrease in the levels of neuroendocrine markers, indicating that phosphorylation of FAK at the Tyr(407) residue may be important for these effects. Our results showed for the first time that FAK is an essential downstream effector of the Raf-1/MEK1/2/ERK1/2 signaling cascade and negatively regulated the neuroendocrine and metastatic phenotype in BON cells.
Ning
Li
L
Endocrine Surgery Research Laboratories, Department of Surgery, University of Wisconsin School of Medicine and Public Health and University of Wisconsin Carbone Cancer Center, Madison, Wisconsin, USA.
Chen
Herbert
H
Kunnimalaiyaan
Muthusamy
M
D014408:Biomarkers, Tumor / Q000037:antagonists & inhibitors*; D002276:Carcinoid Tumor / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D002448:Cell Adhesion / Q000502:physiology; D045744:Cell Line, Tumor; D002464:Cell Migration Inhibition / Q000502:physiology*; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000235:genetics / Q000502:physiology*; D005770:Gastrointestinal Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D009362:Neoplasm Metastasis / Q000235:genetics / Q000473:pathology; D055099:Neuroendocrine Cells / Q000378:metabolism / Q000473:pathology; D010190:Pancreatic Neoplasms / Q000201:enzymology / Q000473:pathology; D010641:Phenotype; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics
D014408:Biomarkers, Tumor; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human
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