PDGFRαα Signaling Is Regulated through the Primary Cilium in Fibroblasts

Department of Biochemistry, Institute for Molecular Biology and Physiology, University of Copenhagen, The August Krogh Building, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark.
Current Biology (Impact Factor: 9.57). 11/2005; 15(20):1861-6. DOI: 10.1016/j.cub.2005.09.012
Source: PubMed


Recent findings show that cilia are sensory organelles that display specific receptors and ion channels, which transmit signals from the extracellular environment via the cilium to the cell to control tissue homeostasis and function. Agenesis of primary cilia or mislocation of ciliary signal components affects human pathologies, such as polycystic kidney disease and disorders associated with Bardet-Biedl syndrome. Primary cilia are essential for hedgehog ligand-induced signaling cascade regulating growth and patterning. Here, we show that the primary cilium in fibroblasts plays a critical role in growth control via platelet-derived growth factor receptor alpha (PDGFRalpha), which localizes to the primary cilium during growth arrest in NIH3T3 cells and primary cultures of mouse embryonic fibroblasts. Ligand-dependent activation of PDGFRalphaalpha is followed by activation of Akt and the Mek1/2-Erk1/2 pathways, with Mek1/2 being phosphorylated within the cilium and at the basal body. Fibroblasts derived from Tg737(orpk) mutants fail to form normal cilia and to upregulate the level of PDGFRalpha; PDGF-AA fails to activate PDGFRalphaalpha and the Mek1/2-Erk1/2 pathway. Signaling through PDGFRbeta, which localizes to the plasma membrane, is maintained at comparable levels in wild-type and mutant cells. We propose that ciliary PDGFRalphaalpha signaling is linked to tissue homeostasis and to mitogenic signaling pathways.

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    • "Procedures for immunofluorescence microscopy have been described previously (Schneider et al., 2005; Schrøder et al., 2011). Statistical analysis was performed using GraphPad Prism 6 (GraphPad Software, San Diego, CA). "
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    • "Mouse NIH3T3 fibroblasts and mouse MC3T3-E1 pre-osteoblasts reported previously to exhibit primary cilia in a large number of cells were grown and stained in parallel as a positive control (Figure 1C). We determined that 79.5% þ/À 3.7% and 52.4% þ/À 11.9% of NIH3T3 fibroblasts and MC3T3-E1 pre-osteoblasts, respectively, were ciliated (Figure 1E), similar to published numbers (Alieva et al., 1999; Schneider et al., 2005; Malone et al., 2007). As another control, we used a more traditional stain for primary cilia, acetylated-tubulin and g-tubulin (Figure 1B). "
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    ABSTRACT: For many years now, researchers have known of a sensory appendage on the surface of most differentiated cell types, called primary cilium. Primary cilia are both chemo-and mechano-sensory in function and have an obvious role in cell cycle control. Because of this, it has been thought that primary cilia are not found on rapidly proliferating cells, as e.g. cancer cells. Here we report using immunofluorescent staining for the ciliary protein Arl13b that primary cilia are frequently found on HeLa (human epithelial adenocarcinoma) and other cancer cell lines such as MG63 (human osteosarcoma) commonly used for cell culture studies, and that the ciliated population is significantly higher (ave. 28.6% and 46.5%, respectively in starved and 15.7 to 18.6% in un-starved cells) than previously anticipated. Our finding impacts the current perception of primary cilia formed in highly proliferative cells. This article is protected by copyright. All rights reserved.
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    • "The fact that Grk5l localises to cilia may potentially indicate such integrating function. Moreover, a number of other signalling pathways such as the Sonic Hedgehog (SHH) pathway (Philipp and Caron, 2009) or the PDGF cascade (Schneider et al., 2005) rely on the spatial organisation in cilia. The mTOR pathway would just be another signalling pathway depending on this specialised organelle. "
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