Evolution and cellular biology of the uterine serpins

Uterine serpins (US) are a unique group of progesterone-induced glycoproteins in a restricted group of mammals that belong to the serine proteinase inhibitor superfamily and which are secreted in large quantities into the uterus during pregnancy. The US gene has been identified in species with epitheliochorial placentation of the Ruminantia and Suidae orders of the Laurasiatheria superorder of eutherian mammals.One goal of this dissertation was to examine the evolution of the US gene in mammals. A US gene was identified in horses and dogs and found expressed in the uterus during pregnancy. The dog is a species with endotheliochorial placenta, suggesting that the US gene is not restricted to species with epitheliochorial placentation. However, its absence in other mammals, and apparent loss in the cat, suggests that the US gene evolved only within the Laurasiatheria superorder.The US do not appear to be functional proteinase inhibitors and to have species-specific functions. The most studied member of the group, ovine uterine serpin (OvUS), inhibits proliferation of several cell types including activated lymphocytes, bovine pre-implantation embryos and some tumor cell lines. A second goal was to evaluate the mechanism by which OvUS inhibits cell proliferation. Ovine US blocked cell cycle progression of human prostate 15 cancer (PC-3) cells, causing an accumulation of cells at G_2/M at 12 h and at G_0/G_1 at 24 h after treatment addition. Additionally, OvUS blocked the cell cycle progression in phytohemagglutinin-stimulated lymphocytes increasing the number of cells at the G_0/G_1 stage at 96 h after treatment. Blocking of the cell-cycle progression by OvUS was caused specifically by the up-regulation of cell cycle checkpoint and arrest genes such as CDKN1A (p21), CDKN2B (p15) and CCNG2 (cyclin G2), and down-regulation of genes involved in DNA synthesis and cell cycle regulation and progression.The finding that the US gene is only retained in a limited group of mammals suggests its importance for successful pregnancies in these species. It is also possible that the US gene evolved a distinct and specie-dependent function from an ortholog serpin gene, rather than the typical anti-proteolytic activity conserved in most members of the superfamily.