title: Disassociation of MAPK activation and c-Fos expression in F9 embryonic carcinoma cells following retinoic acid-induced endoderm differentiation.
abstract: Retinoic acid induces cell differentiation and suppresses cell growth in a wide spectrum of cell lines, and down-regulation of activator protein-1 activity by retinoic acid contributes to these effects. In embryonic stem cell-like F9 teratocarcinoma cells, which are widely used to study retinoic acid actions on gene regulation and early embryonic differentiation, retinoic acid treatment for 4 days resulted in suppression of cell growth and differentiation into primitive and then visceral endoderm-like cells, accompanied by a suppression of serum-induced c-Fos expression. The MAPK (ERK) pathway was involved in mitogenic signaling in F9 cells stimulated with serum. Surprisingly, although c-Fos expression was reduced, the MAPK activity was not decreased by retinoic acid treatment. We found that retinoic acid treatment inhibited the phosphorylation of Elk-1, a target of activated MAPK required for c-Fos transcription. In F9 cells, the MAPK/MEK inhibitor PD98059 suppressed Elk-1 phosphorylation and c-Fos expression, indicating that MAPK activity is required for Elk-1 phosphorylation/activation. Phosphoprotein phosphatase 2B (calcineurin), the major phosphatase for activated Elk-1, is not the target in the disassociation of MAPK activation and c-Fos expression since its inhibition by cyclosporin A or activation by ionomycin had no significant effects on serum-stimulated c-Fos expression and Elk-1 phosphorylation. Thus, we conclude that retinoic acid treatment to induce F9 cell differentiation uncouples Ras/MAPK activation from c-Fos expression by reduction of Elk-1 phosphorylation through a mechanism not involving the activation of phosphoprotein phosphatase 2B.
authors.affiliation: Ovarian Cancer Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
authors.forename: E R
authors.initials: ER
authors.lastname: Smith
authors.forename: J L
authors.initials: JL
authors.lastname: Smedberg
authors.forename: M E
authors.initials: ME
authors.lastname: Rula
authors.forename: T C
authors.initials: TC
authors.lastname: Hamilton
authors.forename: X X
authors.initials: XX
authors.lastname: Xu
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D018236:Carcinoma, Embryonal / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation / Q000187:drug effects*; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D014157:Transcription Factors; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D050807:ets-Domain Protein Elk-1
chemical_list: D004268:DNA-Binding Proteins; C494113:Elk1 protein, mouse; D004791:Enzyme Inhibitors; D005419:Flavonoids; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D014212:Tretinoin; D020928:Mitogen-Activated Protein Kinases; D019703:Calcineurin; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one