Pleiotrophin (PTN) also known asheparin-binding brain mitogen (HBBM) orheparin-binding growth factor 8 (HBGF-8) orneurite growth-promoting factor 1 (NEGF1) orheparin affinity regulatory peptide (HARP) orheparin binding growth associated molecule (HB-GAM) is aprotein that in humans is encoded by thePTNgene.[5] Pleiotrophin is an 18-kDagrowth factor that has a high affinity forheparin. It is structurally related tomidkine andretinoic acid induced heparin-binding protein.
Pleiotrophin was initially recognized as a neurite outgrowth-promoting factor present in rat brain around birth[6] and as a mitogen toward fibroblasts isolated from bovine uterus tissue.[7] Together withmidkine these growth-factors constitute a family of (developmentally regulated) secreted heparin-binding proteins[8] now known as the neurite growth-promoting factor (NEGF) family. Duringembryonic and early postnatal development, pleiotrophin is expressed in thecentral andperipheralnervous system and also in several non-neuraltissues, notablylung,kidney,gut andbone.[9] Pleiotrophin is also expressed by severaltumor cells and is thought to be involved in tumorangiogenesis.[10] In the adultcentral nervous system, pleiotrophin is expressed in an activity-dependent manner in thehippocampus[11][12] where it can suppresslong term potentiation induction.[13] Pleiotrophin expression is low in other areas of the adultbrain, but it can be induced byischemic insults.[14][15] or targeted neuronal damaged in theentorhinal cortex or in thesubstantia nigra pars compacta.
Pleiotrophin binds to cell-surfacenucleolin as a low affinity receptor. This binding can inhibit HIV infection.[16]
