Interferon-tau and interferon-alpha interact with the same receptors in bovine endometrium. Use of a readily iodinatable form of recombinant interferon-tau for binding studies.

Trophoblasts of ruminant species secrete multiple forms of a novel Type I interferon (IFN-tau) for a few days preceding implantation. These IFN-tau are structurally distinct from IFN-alpha, -beta, and -omega, but it remains unclear whether they have any distinguishing biological properties. It has been of interest, therefore, to study their interaction with Type I IFN receptors. However, a recombinant bovine IFN-tau (boIFN-tau 1) prepared for such use is rapidly inactivated during chemical iodination with 125I, presumably because a critical tyrosine becomes modified. Here we describe the synthesis of a novel IFN-tau 1 in which Leu169 and Leu171 in the carboxyl terminus have been replaced by 2 tyrosine residues. The recombinant product (rboIFN-tau 1Y2) can be readily iodinated without significant loss of antiviral and antiproliferative activities, provided that reaction time with 125I is minimized. Both rboIFN-tau 1Y2 and rboIFN-alpha 1 compete with each other for binding to bovine endometrial cell membranes and Madin-Darby bovine kidney cells. Dissociation constants of both IFN are quite similar (Kd = 3.7 x 10(-10) and 3.5 x 10(-10) M, respectively). Cross-linking studies reveal a single size class of receptor polypeptide on endometrium and Madin-Darby canine kidney cells whose molecular weight is reduced from approximately 130,000 to approximately 70,000 by treatment with N-glycosidase. These studies with a single recombinant form of boIFN-tau avoid the difficulties that arise from use of a mixture of naturally occurring isoforms. They provide further evidence for the presence of a receptor common to both IFN-tau and IFN-alpha in bovine tissues and no indication for a unique IFN-tau-binding polypeptide in endometrium.