SECRETION OF BOVINE UTERINE PROTEINS IN RESPONSE TO TYPE-I INTERFERONS

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 (similar to 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-[H-3]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 < 0.0005) 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. Secretion of P16 was higher (p < 0.0001) in endometrium collected from pregnant than from nonpregnant heifers, but did not differ across the days examined. Both rbIFN-tau and rbIFN-alpha stimulated (p < 0.0005) secretion of P16, but this effect was significant only in tissues collected during the estrous cycle. Pregnancy status, day of collection, and treatment with rbIFN-alpha did not affect secretion of P28. However, rbIFN-tau stimulated (p < 0.001) secretion of P28. Dose-response studies revealed that secretion of P8 and P28 was stimulated in a dose-dependent manner only by rbIFN-tau (p < 0.005). Secretion of P16 was stimulated by all Type I IFNs examined (p < 0.01). These data may be interpreted to mean that the endometrium has the ability to distinguish between closely related Type I IFNs.