Pleiotrophin (PTN) also known HBBM, HBGF-8, NEGF1, HARP or HB-GAM is a protein that in humans is encoded by the PTN gene. This protein is expressed in the central and peripheral nervous system and also in several non-neural tissues, notably lung, kidney, gut and bone. Pleiotrophin binds anaplastic lymphoma kinase (ALK) which induces MAPK pathway activation, an important step in the anti-apoptotic signaling of PTN and regulation of cell proliferation.