Expression of the interferon tau inducible ubiquitin cross-reactive protein in the ovine uterus

Ubiquitin cross-reactive protein (UCRP) is a 17-kDa protein that shows cross-reactivity with ubiquitin antisera and retains the carboxyl-terminal Leu-Arg-Gly-Gly amino acid sequence of ubiquitin that ligates to, and directs degradation of, cytosolic proteins. It has been reported that bovine endometrial UCRP is synthesized and secreted in response to conceptus-derived interferon-tau (IFNτ). In the present studies, UCRP mRNA and protein were detected in ovine endometrium. Ovine UCRP mRNA was detectable on Day 13, peaked at Day 15, and remained high through Day 19 of pregnancy. The UCRP mRNA was localized to the luminal epithelium (LE), stromal cells (ST) immediately beneath the LE, and shallow glandular epithelium (GE) on Day 13, but it extended to the deep GE, deep ST, and myometrium of uterine tissues by Day 15 of pregnancy. Western blotting revealed induction of UCRP in the endometrial extracts from pregnant, but not cyclic, ewes. Ovine UCRP was also detected in uterine flushings from Days 15 and 17 of pregnancy and immunoprecipitated from Day 17 pregnant endometrial explant-conditioned medium. Treatment of immortalized ovine LE cells with recombinant ovine (ro) IFNτ induced cytosolic expression of UCRP, and intrauterine injection of roIFNτ into ovariectomized cyclic ewes induced endometrial expression of UCRP mRNA. These results are the first to describe temporal and spatial alterations in the cellular localization of UCRP in the ruminant uterus. Collectively, UCRP is synthesized and secreted by the ovine endometrium in response to IFNτ during early pregnancy. Because UCRP is present in the uterus and uterine flushings, it may regulate endometrial proteins associated with establishment and maintenance of early pregnancy in ruminants.