ATYPICAL PORCINE TYPE-I INTERFERON - BIOCHEMICAL AND BIOLOGICAL CHARACTERIZATION OF THE RECOMBINANT PROTEIN EXPRESSED IN INSECT CELLS

A recombinant baculovirus was designed to express short porcine type I interferon (spI interferon), a novel and atypical type I interferon t hat was recently described as the product of a gene transcribed in pig trophoblast at the time of implantation in the uterus [Lefevre, F. an d Boulay, V. C. (1993) J. Biol. Chem. 268, 19760-19768]. The recombina nt protein, secreted into the culture medium of Sf9 cells at 3 days po st infection (60000 IU/ml), was purified by ion-exchange and reverse-p hase HPLC. N-terminal sequencing confirmed the predicted signal peptid e cleavage site and therefore the size of the mature protein (149 amin o acids), the shortest of all reported type I interferons. Purified sp I interferon, with a specific antiviral activity using Madin-Darby bov ine kidney cells of 3.7X10(7) IU/mg, is an N-glycosylated monomer of 1 9 kDa that possesses several physicochemical characteristics of interf erons: (a) disulfide bonds are necessary for bioactivity; spI interfer on is thermolabile, stable at pH 2, and able to renature after complet e denaturation (1% 2-mercaptoethanol, 1% SDS, and 5 M urea); (b) the c arbohydrate chain is not essential for bioactivity since no loss of an tiviral activity is observed following complete deglycosylation. In th is study, antiviral and anti-proliferation activities of spI interfero n in cell culture were compared with those of other interferons, espec ially with porcine type 1 interferon-alpha. A major difference with po rcine type 1 interferon-alpha was that spI interferon was not active o n human cells in either test, and it was relatively more active on pig cells compared to bovine cells than porcine type 1 interferon-alpha. Serological cross-neutralization results obtained with anti-(spI inter feron) serum confirmed that several members of interferon families are not antigenically related to spI interferon, in agreement with previo us observations; this provides further evidence that spI interferon co uld represent a new family of type I interferon.