Frizzled gene expression and negative regulation of canonical WNT-β-catenin signaling in mouse F9 teratocarcinoma cells.
Mouse F9 cells differentiate into primitive endoderm (PrE) following the activation of the canonical WNT-β-catenin pathway. The upregulation of Wnt6 and activation of β-catenin-TCF-LEF-dependent transcription is known to accompany differentiation, but the Frizzled (FZD) receptor responsible for transducing the WNT6 signal is not known. Eight of the 10 Fzd genes were found to be expressed in F9 cells, with Fzd7 being the most highly expressed, and chosen for further analysis. To alter steady-state Fzd7 levels and test the effect this has on differentiation, siRNA and overexpression approaches were used to knock-down and ectopically express the Fzd7 message, respectively. siRNA knock-down of Fzd7 resulted in reduced DAB2 levels, and the overexpression activated a TCF-LEF reporter, but neither approach affected differentiation. Our focus turned to how canonical WNT6 signaling was attenuated to allow PrE cells to form parietal endoderm (PE). Dkk1, encoding a WNT antagonist, was examined and results showed that its expression increased in F9 cells treated with retinoic acid (RA) or overexpressing Wnt6. F9 cells overexpressing human DKK1 or treated with DKK1-conditioned medium and then treated with RA failed to differentiate, indicating that a negative feedback loop involving WNT6 and DKK1 attenuates canonical WNT-β-catenin signaling, thereby allowing PE cells to differentiate.
a Department of Biology, Molecular Genetics Unit, Western University, London, ON N6A 5B7, Canada.
Gregory
G
Golenia
a Department of Biology, Molecular Genetics Unit, Western University, London, ON N6A 5B7, Canada.
Mohamed I
MI
Gatie
a Department of Biology, Molecular Genetics Unit, Western University, London, ON N6A 5B7, Canada.|b Child Health Research Institute, London, ON N6C 2V5, Canada.|c Ontario Institute for Regenerative Medicine, Toronto, ON M5G 0A4, Canada.
Gregory M
GM
Kelly
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004707:Endoderm / Q000378:metabolism / Q000473:pathology; D025461:Feedback, Physiological; D051157:Frizzled Receptors; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D051538:Hepatocyte Nuclear Factor 1-alpha / Q000235:genetics / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D018243:Teratocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014212:Tretinoin / Q000494:pharmacology; D051153:Wnt Proteins / Q000235:genetics* / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics* / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051017:Apoptosis Regulatory Proteins; C495267:CTNNB1 protein, mouse; D017077:Culture Media, Conditioned; C478773:Dab2 protein, mouse; C501127:Dkk1 protein, mouse; D051157:Frizzled Receptors; C492041:Fzd7 protein, mouse; D051538:Hepatocyte Nuclear Factor 1-alpha; C496488:Hnf1a protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; C497574:Lef1 protein, mouse; D051821:Lymphoid Enhancer-Binding Factor 1; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled; D051153:Wnt Proteins; C095936:Wnt6 protein, mouse; D051176:beta Catenin; D014212:Tretinoin
Dickkopf; WNT; embryon de souris; endoderme extra-embryonnaire; extraembryonic endoderm; mouse embryo; β-catenin; β-caténine