Secreted growth factor that mediates its signal through cell-surface proteoglycan and non-proteoglycan receptors (PubMed:16814777, PubMed:27671118, PubMed:9817766). Binds cell-surface proteoglycan receptor via their chondroitin sulfate (CS) groups (By similarity). Thereby regulates many processes like cell proliferation, cell survival, cell growth, cell differentiation and cell migration in several tissues namely neuron and bone (PubMed:27671118, PubMed:9817766). Also plays a role in synaptic plasticity and learning-related behavior by inhibiting long-term synaptic potentiation (By similarity). Binds PTPRZ1, leading to neutralization of the negative charges of the CS chains of PTPRZ1, inducing PTPRZ1 clustering, thereby causing the dimerization and inactivation of its phosphatase activity leading to increased tyrosine phosphorylation of each of the PTPRZ1 substrates like ALK or AFAP1L2 in order to activate the PI3K-AKT pathway (PubMed:16814777). Through PTPRZ1 binding, regulates endothelial cell migration and controls oligodendrocyte precursor cell differentiation (By similarity). Forms a complex with PTPRZ1 and integrin alpha-V/beta-3 (ITGAV:ITGB3) that stimulates endothelial cell migration through SRC dephosphorylation and activation that consequently leads to ITGB3 'Tyr-773' phosphorylation (By similarity). In adult hippocampus promotes dendritic arborization, spine development, and functional integration and connectivity of newborn granule neurons through ALK by activating AKT signaling pathway (By similarity). Binds GPC2 and chondroitin sulfate proteoglycans (CSPGs) at the neuron surface, leading to abrogation of binding between PTPRS and CSPGs and neurite outgrowth promotion (PubMed:27671118). Binds SDC3 and mediates bone formation by recruiting and attaching osteoblasts/osteoblast precursors to the sites for new bone deposition (PubMed:9817766). Binds ALK and promotes cell survival and cell proliferation through MAPK pathway activation (By similarity). Inhibits proliferation and enhances differentiation of neural stem cells by inhibiting FGF2-induced fibroblast growth factor receptor signaling pathway (By similarity). Mediates regulatory mechanisms in normal hemostasis and in hematopoietic regeneration and in maintaining the balance of myeloid and lymphoid regeneration (By similarity). In addition may play a role in the female reproductive system, auditory response and the progesterone-induced decidualization pathway (By similarity). Interacts with ALK and NEK6 (By similarity). Interacts with PTPRZ1 (via chondroitin sulfate groups); promotes formation of homooligomers; oligomerization impairs tyrosine phosphatase activity (PubMed:16814777). Forms a complex with PTPRZ1 and CTNNB1; this complex inactivates PTPRZ1 protein tyrosine phosphatase activity through PTN interaction and stimulates tyrosine phosphorylation of CTNNB1. Interacts with ITGB3 AND ITGA5. Forms a complex with PTPRZ1 and integrin alpha-V/beta-3 (ITGAV:ITGB3) that stimulates endothelial cell migration through ITGB3 'Tyr-773' phosphorylation (By similarity). Interacts with SDC3 (via heparan sulfate chains); this interaction mediates the neurite outgrowth-promoting signal from PTN to the cytoskeleton of growing neurites; this interaction mediates osteoblast recruitment (PubMed:8175719, PubMed:9817766). Interacts with GPC2 (via heparan sulfate); this interaction promotes neurite outgrowth through binding of PTN with chondroitin sulfate of proteoglycans, thereby releasing PTPRS of chondroitin sulfate proteoglycans (CSPGs) and leading to binding with heparan sulfate of GPC2 (PubMed:27671118). Expressed in brain (PubMed:2170351). Hardly expressed in bone. Abundantly expressed in the growth plate. Intensely expressed in the cartilage matrix that forms the hollow for the secondary ossification center. Is expressed selectively by the osteocytes of the lamellar bone, whereas it is hardly expressed by those of the woven bone. Is detected in the matrix surrounding the osteocytes and in the canaliculi of the osteocytes. Is distributed on the surface of lamellar bone (PubMed:9817766). Expressed at low levels in the brain in early embryonic stages. Levels increase to a maximum before or just after birth, and are lower in adult brain (PubMed:1768439). At E16 intensely expressed in the matrix of the developing cartilage and persists in the matrix of the mineralized cartilage at E20 (at protein level). Localized within the unmineralized cartilage matrix (at mRNA level) (PubMed:9817766). Phosphorylated by NEK6. Belongs to the pleiotrophin family.