title: High expression in involuting reproductive tissues of uterocalin/24p3, a lipocalin and acute phase protein.
abstract: During reproduction the mass and number of cells in the uterus and the mammary gland increase rapidly and then diminish more rapidly after their reproductive functions are completed. The diminishment of tissue mass, known as involution, involves an ordered series of events that includes apoptosis of resident cells, neutrophil invasion, the release of degradative enzymes and phagocytosis of cellular debris. Local signals are believed to regulate the progression of involution in each tissue. Here we show that the mammary gland and uterus express high levels of uterocalin, a protein that specifically induces apoptosis in neutrophils and other leucocytes. In the mammary gland, uterocalin expression is induced by weaning. In both tissues, uterocalin is expressed at extremely high levels such that it constitutes an average of 0.2-0.5% of the total extractable protein at its peak. Epithelial cells in the uterus and mammary gland produce uterocalin. In each case, the protein is secreted into the tissue lumen, with mammary-derived uterocalin being found in the milk. The period of highest uterocalin expression in vivo is consistent with the hypothesis that one of its physiological roles is to induce apoptosis of infiltrating neutrophils and thereby delay the entry of neutrophils into the tissue. It is proposed that the role of uterocalin during involution is to provide a window of time during which resident cells are protected from the degradative enzymes, free radicals and other secreted products of activated phagocytes to allow these cells to prepare to survive the processes of involution.
authors.affiliation: Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, 3206 Molecular Biology Building, Ames, IA 50011, U.S.A.
authors.forename: Joel
authors.initials: J
authors.lastname: Ryon
authors.forename: Lee
authors.initials: L
authors.lastname: Bendickson
authors.forename: Marit
authors.initials: M
authors.lastname: Nilsen-Hamilton
mesh_terms: D000209:Acute-Phase Proteins / Q000096:biosynthesis* / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D015152:Blotting, Northern; D015153:Blotting, Western; D001940:Breast / Q000378:metabolism*; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism*; D005260:Female; D005609:Free Radicals; D007962:Leukocytes / Q000378:metabolism; D000071068:Lipocalin-2; D054834:Lipocalins; D019278:Matrix Metalloproteinase 3 / Q000096:biosynthesis; D051379:Mice; D008894:Milk Proteins / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism; D015513:Oncogene Proteins / Q000096:biosynthesis* / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014599:Uterus / Q000378:metabolism*; D014886:Weaning
chemical_list: D000209:Acute-Phase Proteins; D005609:Free Radicals; D000071068:Lipocalin-2; D054834:Lipocalins; D008894:Milk Proteins; D015513:Oncogene Proteins; D012333:RNA, Messenger; C071332:Lcn2 protein, mouse; D012313:RNA; D019278:Matrix Metalloproteinase 3