A 16-kDa protein has been identified that is secreted by the bovine endometrium 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 regulated by IFN, we suspected that they might be related. To test this hypothesis, uterine flushings, medium from cultured endometrium, and endometrial tissues were examined for the presence of ubiquitin-immunoreactive proteins. Immunoreacting proteins were detected through use of one-dimensional (1D)-PAGE and Western blotting with ubiquitin and hUCRP antiserum (1:500). A 16-kDa protein that cross-reacted with ubiquitin and hUCRP antisera was released by the endometrium and was present in uterine flushings from all Day 18 pregnant females examined (n = 12). The immunoreacting 16-kDa protein was absent in all nonpregnant females examined (n = 23). Regulation of this uterine protein by recombinant type I IFNs (rbIFN-tau, rbIFN-alpha, and roIFN-tau), using 0, 0.5, 5, and 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 protein into medium was negligible in controls (0 nm IFN). For each IFN, a dose-dependent increase (p < 0.05) in release of the immunoreacting 16-kDa protein was noted. We conclude that the 16-kDa protein that is produced 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.

Bovine interferon-tau (bIFN-tau) is secreted by the developing conceptus and initiates antiluteolytic events by interacting with uterine membrane receptors. We have identified three endometrial proteins (approximately 8, 16, and 28 kDa; P8, P16, and P28; respectively) that are secreted in response to recombinant (r) bIFN-tau. The objective of this study was to determine whether or not secretion of these proteins was a unique response to IFN-tau during early pregnancy. Three experiments were designed to examine secretion of endometrial proteins as a function of time in culture (0, 3, 6, 12, 18, 24 h), stage of the estrous cycle and pregnancy (Days 15, 18, 0/21), and dose of Type I IFN (0, 0.5, 5, and 25 nM; rbIFN-tau, rbIFN-alpha, and roIFN-tau). Endometrium was cultured for times specified with L-[3H]leusine to generate radiolabeled proteins. Secreted proteins were quantitated by using one-dimensional (1D)-PAGE, fluorography, and densitometry. Secretion of P8, P16, and P28 increased over time (p < 0.0001) in culture and in response to 25 nM rbIFN-tau (p < 0.05). Secretion of P8 in response to rbIFN-tau was higher (p < 0.05). Secretion of P8 in response to rbIFN-tau was higher (p < 0.0005) in endometrium collected from pregnant than nonpregnant heifers, but did not differ across the days examined. Although secretion of P8 was higher (p < 0.0001) in the presence than in the absence of rbIFN-tau, it was not affected by rbIFN-alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

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