PREGNANCY AND INTERFERON-TAU INDUCE CONJUGATION OF BOVINE UBIQUITIN CROSS-REACTIVE PROTEIN TO CYTOSOLIC UTERINE PROTEINS

Conceptus-derived interferon-tau (IFN-tau) induces bovine endometrial ubiquitin cross-reactive protein (UCRP) mRNA and protein on Days 15-21 of pregnancy. Bovine UCRP retains the Leu-Arg-Cly-Cly C-terminal sequ ence of ubiquitin that ligates to and directs degradation of cytosolic proteins. The objectives of the present experiments were to determine whether UCRP became conjugated to endometrial cytosolic proteins duri ng early pregnancy and in response to recombinant bovine (rbo) IFN-tau . Ubiquitin (8 kDa), UCRP (17 kDa), and conjugates thereof (greater th an or equal to 30 kDa) were quantitated using Western blotting and den sitometry. Endometrial ubiquitin and its conjugates did not differ bet ween Day 18 pregnant and nonpregnant cows, or between control and rboI FN-tau-treated (25 nM) explant cultures (Day 14; nonpregnant). Bovine UCRP was induced in endometrium from pregnant as compared with nonpreg nant cows. Conjugation of endometrial proteins to UCRP was induced in pregnant as compared to nonpregnant cows. Recombinant boIFN-tau induce d UCRP and its conjugates in cultured endometrial explants from nonpre gnant cows. It is concluded that UCRP, in response to rboIFN-tau becom es conjugated to endometrial cytosolic proteins during early pregnancy . The regulation of uterine proteins by UCRP may be integral to the ma intenance of early pregnancy in ruminants.