Pleiotrophin (PTN) is a secreted growth factor that induces neurite outgrowth. The receptor tyrosine kinase anaplastic lymphoma kinase (ALK) binds PTN and transduces PTN-mediated signals through RAS, PI3K, PLCG1 and IRS1 (Stoica et al. 2001, Bowden et al. 2002), as well as through GSK3B/CTTNB1 (Yanagisawa et al. 2010).