Dendrite-selective redistribution of the chemokine receptor CXCR4 following agonist stimulation Stéphane J. Baudouin, a,1 Fabien Pujol, b,1 Arnaud Nicot, b Patrick Kitabgi, b and Hélène Boudin a,b, ⁎ a Institut National de la Santé Et de la Recherche Médicale (I.N.S.E.R.M.), Unité 643, I.T.E.R.T, CHU Hotel-Dieu, University of Nantes, 30 Bd Jean Monnet, 44035 Nantes Cedex 01, France b INSERM UMR 732, Hôpital St Antoine, Paris 75012, France; Université Pierre et Marie Curie–Paris 6, Paris 75012, France Received 24 March 2006; revised 20 July 2006; accepted 25 July 2006 The chemokine SDF-1 is a secreted protein that plays a critical role in several aspects of neuron development through interaction with its unique receptor CXCR4. A key mechanism that controls neuron responsiveness to extracellular signals during neuronal growth is receptor endocytosis. Since we previously reported that SDF-1 regulates axon development without affecting the other neurites, we asked whether this could correlate with a compartment-selective trafficking of CXCR4. We thus studied CXCR4 behavior upon SDF-1 exposure in rat hippocampus slices and in transfected neuron cultures. A massive agonist-induced redistribution of CXCR4 in endosomes was observed in dendrites whereas no modification was evidenced in axons. Our data suggest that CXCR4 trafficking may play a role in mediating selective effects of SDF-1 on distinct neuronal membrane subdomains. © 2006 Elsevier Inc. All rights reserved. Keywords: Trafficking; Endocytosis; Hippocampal neuron; Chemokine; Development; G-protein-coupled receptor Introduction Chemokines are small secreted proteins that exert their effects by activating a family of G-protein-coupled receptors (GPCRs) and that play several fundamental roles in many systems, including the immune, hematopoietic, cardiovascular and central nervous systems. Among the chemokines, recent studies highlighted the major role of stromal cell-derived factor-1 (SDF-1) and its unique receptor CXCR4 in brain functions, with a particular emphasis on cellular trafficking and formation of neuronal circuits. Knock-out mice lacking either SDF-1 or its receptor CXCR4 showed marked defects in the architecture of the cerebellum, the hippocampus and the neocortex (Lu et al., 2002; Ma et al., 1998; Stumm et al., 2003; Zou et al., 1998). In support of these observations, further analysis uncovered the role of SDF-1 in the migration of hippocampal, cerebellar and cortical neurons (Bagri et al., 2002; Stumm et al., 2003; Zhu et al., 2002) as well as of sensory neuron progenitors to the dorsal root ganglia (Belmadani et al., 2005). In addition, activation of CXCR4 by SDF-1 influences axon pathfinding (Chalasani et al., 2003; Lieberam et al., 2005; Lu et al., 2001; Xiang et al., 2002) and axonal patterning (Arakawa et al., 2003; Pujol et al., 2005). It thus becomes clear that SDF-1 represents a new extracellular signal regulating cell motility, branching and axon guidance, similarly as the well-documented guidance cues semaphorin, ephrin, Slit and netrin. For some of these latter, recent work has revealed the existence of new mechanisms linked to receptor endocytosis that participate in the spatial and temporal control of cellular adhesion and axon guidance (Fournier et al., 2000; Jurney et al., 2002; Keleman et al., 2002; Williams et al., 2003; Zimmer et al., 2003). Receptor endocytosis triggered by receptor–ligand interaction is a widespread cellular mechanism involved in a large number of biological processes and represents a way to regulate the duration of the intracellular signaling upon receptor activation, the availability of cell surface receptors, and the sorting of receptors in recycling versus degradative pathways (Le Roy and Wrana, 2005). As many other GPCRs, CXCR4 has been shown to undergo agonist-induced receptor endocytosis in various cell systems including dorsal root ganglion neurons, T cells, macrophages and heterologous expression systems (Bodner et al., 2003; Orsini et al., 1999; Signoret et al., 1998; Venkatesan et al., 2003; Wang et al., 2001). The objectives of the present study were to investigate whether CXCR4 expressed in brain neurons undergoes endocytosis following SDF-1 activation, and if so whether receptors expressed on distinct neuronal compartments exhibit different trafficking properties. Since we previously reported in developing neurons that SDF-1 regulates axonal elongation and branching without affecting the other neurites (Pujol et al., 2005), we asked whether these effects could correlate with CXCR4 trafficking in a compartment-selective manner. We thus studied the distribution of CXCR4 following SDF-1 activation in rat hippocampus slices and in a low-density hippocampal neuron www.elsevier.com/locate/ymcne Mol. Cell. Neurosci. 33 (2006) 160 – 169 ⁎ Corresponding author. INSERM U643, ITERT, 30 Bld Jean Monnet, 44093 Nantes cedex 01, France. Fax: +33 2 40 08 74 11. E-mail address: helene.boudin@univ-nantes.fr (H. Boudin). 1 These authors contributed equally to this work. Available online on ScienceDirect (www.sciencedirect.com). 1044-7431/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.mcn.2006.07.007