UBIQUITIN CROSS-REACTIVE PROTEIN IS RELEASED BY THE BOVINE UTERUS IN RESPONSE TO INTERFERON DURING EARLY-PREGNANCY

A 16-kDa protein has been identified that is secreted by the bovine en dometrium in response to conceptus-derived interferon (IFN)-tau during early pregnancy. Because this uterine protein was similar in size to a human ubiquitin cross-reactive protein (hUCRP) that also was regulat ed by IFN, we suspected that they might be related. To test this hypot hesis, uterine flushings, medium from cultured endometrium, and endome trial tissues were examined for the presence of ubiquitin-immunoreacti ve proteins. Immunoreacting proteins were detected through use of one- dimensional (1D)-PAGE and Western blotting with ubiquitin and hUCRP an tiserum (1:500). A 16-kDa protein that cross-reacted with ubiquitin an d hUCRP antisera was released by the endometrium and was present in ut erine flushings from all Day 18 pregnant females examined (n = 12). Th e immunoreacting 16-kDa protein was absent in all nonpregnant females examined (n = 23), Regulation of this uterine protein by recombinant t ype I IFNs (rbIFN-tau, rbIFN-alpha, and roIFN-tau), using 0, 0.5, 5, a nd 25 nm of each IFN, was evaluated in nonpregnant (Day 12) heifers (n = 5) using 1D-PAGE and Western blotting. Release of the 16-kDa protei n into medium was negligible in controls (0 nm IFN). For each IFN, a d ose-dependent increase (p < 0.05) in release of the immunoreacting 16- kDa protein was noted. We conclude that the 16-kDa protein that is pro duced by the endometrium in response to IFN-tau during early pregnancy also shares epitopes with hUCRP and ubiquitin. The 16-kDa protein has been named bovine UCRP.