Sonic Hedgehog promotes the survival of neural crest cells by limiting apoptosis induced by the dependence receptor CDON during branchial arch development Céline Delloye-Bourgeois a,1 , Nicolas Rama a,1 , José Brito b,2 , Nicole Le Douarin b , Patrick Mehlen a,⇑ a Apoptosis, Cancer and Development Laboratory-Equipe labellisée ‘La Ligue’, Centre de Cancérologie de Lyon, INSERM U1052-CNRS UMR5286, Université de Lyon, Centre Léon Bérard, 69008 Lyon, France b Laboratoire Développement, Evolution et Plasticité du Système Nerveux, Institut de Neurobiologie Alfred Fessard, Gif-sur-Yvette, France article info Article history: Received 19 August 2014 Available online 1 September 2014 Keywords: Dependence receptors Apoptosis CDO Embryonic development Neural crest cells abstract Cell-adhesion molecule-related/Downregulated by Oncogenes (CDO or CDON) was identified as a receptor for the classic morphogen Sonic Hedgehog (SHH). It has been shown that, in cell culture, CDO also behaves as a SHH dependence receptor: CDO actively triggers apoptosis in absence of SHH via a proteolytic cleav- age in CDO intracellular domain. We present evidence that CDO is also pro-apoptotic in the developing neural tube where SHH is known to act as a survival factor. SHH, produced by the ventral foregut endo- derm, was shown to promote survival of facial neural crest cells (NCCs) that colonize the first branchial arch (BA1). We show here that the survival activity of SHH on neural crest cells is due to SHH-mediated inhibition of CDO pro-apoptotic activity. Silencing of CDO rescued NCCs from apoptosis observed upon SHH inhibition in the ventral foregut endoderm. Thus, the pair SHH/dependence receptor CDO may play an important role in neural crest cell survival during the formation of the first branchial arch. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Sonic Hedgehog (SHH) is a multifunctional cue with multiple known functions during both embryonic development and through adulthood. SHH is a classic morphogen known to regulate many developmental processes including ventrodorsal patterning of the neural tube, establishment of limb polarity and development of the foregut and axio-cranial skeleton [1,2]. However, SHH is not only implicated in the promotion of differentiation but was also more recently described as a survival factor. Indeed, inhibition of SHH in the developing neural tube induces massive neuroepithelial cell death [3,4]. Similarly, SHH produced by the ventral foregut endoderm promotes survival of facial neural crest cells (NCCs) that colonize the first branchial arch (BA1), induces the patterning of BA1 [5] and is therefore an early signal for jaw development during facial skeleton formation. SHH canonical signaling includes its interaction with the twelve-transmembrane receptor Patched 1 (Ptc). Binding of SHH to Ptc prevents Ptc suppressive effect on Smoothened (Smo), an orphan seven-transmembrane receptor that initiates a signaling pathway leading to the activation of the glioma-associated (Gli) family of transcription factors. However, SHH also appears to inter- act with other single-transmembrane proteins such as Cell-adhe- sion molecule-related/Downregulated by Oncogenes (CDO) and Brother of CDO (BOC), two homologous members of the Neural Cell Adhesion Molecule (N-CAM) family [6–9]. CDO extracellular domain was indeed shown to directly bind SHH in a calcium- dependent and heparin-independent manner in mammals. This interaction enhances SHH–Ptc–Smo signaling in specific subre- gions of SHH expression [10]. CDO resembles in many aspects to DCC (Deleted in Colorectal Carcinoma), the prototypical netrin-1 dependence receptor [11]. Dependence receptors share the property of creating cellular state of dependence upon their ligand by inducing apoptosis when unbound by their ligand [12]. We have shown that CDO is a depen- dence receptor: upon forced expression, CDO triggers apoptosis in various cancer cell lines, a pro-apoptotic activity blocked by the addition of SHH in the milieu [13]. CDO pro-apoptotic activity requires the caspase cleavage of CDO in its intracellular domain leading to the exposure of a pro-apoptotic domain able to recruit and activate the apical caspase-9. We proposed that this pro- apoptotic activity is a safeguard mechanism to limit cancer http://dx.doi.org/10.1016/j.bbrc.2014.08.134 0006-291X/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. E-mail address: patrick.mehlen@lyon.unicancer.fr (P. Mehlen). 1 Contributed equally to this work. 2 Present address: Instituto de Ciências Biomédicas.Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. Biochemical and Biophysical Research Communications 452 (2014) 655–660 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc