Placental ribonuclease inhibitor distribution in human placenta and decidua; expression by trophoblastic cells

Objectives Placental ribonuclease inhibitor (PRI) is a 50-kDa leucine-rich repeat protein characterised by its property to inhibit ribonucleases (RNase) of the pancreatic type. PRI is a tight-binding inhibitor of angiogenin (RNase 5), a 14-kDa secreted protein with ribonucleolytic and angiogenic activities that promotes cell growth and survival. PRI inhibits angiogenesis and blocks tumour growth and metastasis. PRI was first purified to homogeneity from human placenta but is largely expressed [1]. Angiogenin is associated with tumour development but is also present in normal biological fluids and tissues [2]. Its expression has been previously mapped in human placentas and shown associated with blood vessel formation [3-5]. To address the physiological role of PRI, we studied its expression in situ and in vitro, during human placental development.