PRLR is a receptor for the anterior pituitary hormone prolactin (PRL). PRL participates in a variety of physiological processes in vertebrates, including reproduction, osmo-regulation, growth and development, metabolism, immuno-regulation, energy balance, and behavior. Upon ligand binding of PRL to PRLR, the Janus-activated kinase 2 (JAK2) is activated, which in turn initiates intracellular signalling cascades, including signal transducers and activators of transcription (STAT) family members STAT-1/3/5, and extracellular regulated kinases (ERK1/2) and AKT. PRLR also acts as a prosurvival factor for spermatozoa by inhibiting sperm capacitation through suppression of SRC kinase activation and stimulation of AKT. Mutations in the PRLR gene cause multiple fibroadenomas of the breast (MFAB) and hyperprolactinemia (HPRL).