The prolactin receptor: Diverse and emerging roles in pathophysiology

• PRLR expressed on diverse cells e.g. mammary gland, pancreatic β-cells, adipocytes.
• Prolactin is produced at pituitary and extrapituitary sites.
• Pathological roles may include tumorigenesis, hyperprolactinemia, diabetes, obesity.

Investigations over two decades have revised understanding of the prolactin hormone. Long thought to be merely a lactogenic hormone, its list of functions has been extended to include: reproduction, islet differentiation, adipocyte control and immune modulation. Prolactin functions by binding cell-surface expressed prolactin receptor, initiating signaling cascades, primarily utilizing Janus kinase-signal transducer and activator of transcription (JAK-STAT). Pathway disruption has been implicated in tumorigenesis, reproductive abnormalities, and diabetes. Prolactin can also be secreted from extrapituitary sources adding complexity to understanding of its physiological functions. This review aims to describe how prolactin exerts its pathophysiological roles by endocrine and autocrine means.