prolactin receptor ( PRLR) is a type I cytokine receptor encoded in humans by the  PRLR gene on chromosome 5p13-14. The PRLR binds prolactin (PRL) as a transmembrane receptor. Thus the PRLR contains an extracellular region to bind PRL, a transmembrane region, and a cytoplasmatic region. The PRLR can also bind to and be activated by growth hormone (GH) and human placental lactogen (hPL), in addition to prolactin.
Expression of the PRLR protein is found within cells of the
mammary glands in accordance with its role in lactation, but also is the subject of attention for its diverse and emerging roles by its expression in adipose tissue,  pancreatic islet cell proliferation,  and immune responses. 
The PRLR is a
cytokine receptor and  second messenger cascades include the JAK-STAT pathway, JAK-RUSH pathway,  Ras-Raf-MAPK, and  PI3K/AKT/mTOR pathway. Disruption of PRLR signaling pathways have been linked to tumorigenesis and  breast cancer development.
The PRLR has been found to be essential for
lobuloalveolar maturation of the mammary glands during pregnancy, as evidenced by the fact that PRLR knockout mice show severely impaired development of lobuloalveolar structures. 
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