Lactoferrin as a Signaling Mediator

Lactoferrin is a metal-binding protein, secreted from glandular epithelial cells and neutrophils. As well as other growth factors and cytokines, it plays a role for regulation of cell behavior by interacting with target cells and molecules. At the surface of the cells, the sulfated chain of proteoglycans is considered as primary lactoferrin binding site. The initial binding to proteoglycans can induce lactoferrin interaction to specific receptors, such as intelectin, LDL-receptor related protein (LRP), nucleolin and CD14. Lymphocyte expresses lactoferrin receptor which molecular weight is about 105 kDa. However, molecular nature of the lymphocye lactoferrin receptor is unknown. Some of lactoferrin receptors are involved in receptor-mediated uptake of lactoferrin. Lactoferrin acts as an anabolic factor for skeletal tissue and promotes the growth and differentiation of osteoblasts and chondrocytes. Lactoferrin antagonizes bone resorption by inhibiting osteoclastic differentiation. It inhibits the tumor cell growth by regulating the expression of and phosphorylation of cyclin-dependent kinase inhibitors (CKIs). The signal transduction pathways induced by lactoferrin is partially understood.