Pleiotrophin

Pleiotrophin (PTN) also known as heparin-binding brain mitogen (HBBM) or heparin-binding growth factor 8 (HBGF-8) or neurite growth-promoting factor 1 (NEGF1) or heparin affinity regulatory peptide (HARP) or heparin binding growth associated molecule (HB-GAM) is a is_associated_with::protein that in humans is encoded by the PTN is_associated_with::gene. Pleiotrophin is an 18-kDa is_associated_with::growth factor that has a high affinity for is_associated_with::heparin. It is structurally related to is_associated_with::midkine and is_associated_with::retinoic acid induced heparin-binding protein.

Function
Pleiotrophin was initially recognized as a neurite outgrowth-promoting factor present in rat brain around birth and as a mitogen toward fibroblasts isolated from bovine uterus tissue. Together with is_associated_with::midkine these growth-factors constitute a family of (developmentally regulated) secreted heparin-binding proteins now known as the neurite growth-promoting factor (NEGF) family. During embryonic and early postnatal development, pleiotrophin is expressed in the central and peripheral is_associated_with::nervous system and also in several non-neural tissues, notably is_associated_with::lung, is_associated_with::kidney, gut and is_associated_with::bone. Pleiotrophin is also expressed by several is_associated_with::tumor cells and is thought to be involved in tumor is_associated_with::angiogenesis. In the adult is_associated_with::central nervous system, pleiotrophin is expressed in an activity-dependent manner in the is_associated_with::hippocampus where it can suppress is_associated_with::long term potentiation induction. Pleiotrophin expression is low in other areas of the adult is_associated_with::brain, but it can be induced by is_associated_with::ischemic insults. or targeted neuronal damaged in the is_associated_with::entorhinal cortex or in the substantia nigra pars compacta.

Clinical significance
Pleiotrophin binds to cell-surface is_associated_with::nucleolin as a low affinity receptor. This binding can inhibit HIV infection.