Interferon-induced Proteins: Identification of Mx Proteins in Various Mammalian Species

Mx protein controls influenza virus pathogenicity in mice in vivo. It is an abundant protein synthesized in response to interferon-alpha/beta. Searches for homolog proteins in various animal species have been conducted using several methods: (1) radioactive labeling of proteins induced by interferon and analysis by 2-D gel electrophoresis, (2) immunoprecipitation, (3) protoblot-ELISA analysis of cell-protein extracts, and (4) immunostaining of fixed cells. All mammalian species tested so far (including human, horse, and pig, which are prone to influenza virus infection) responded to interferon-alpha by synthesizing one or two Mx proteins differing in relative molecular weight and pl. The expression of Mx proteins within one species differed sometimes between primary cultures of diploid cells and established cell lines. Mx proteins were detected in all species in the cytoplasm and, in some rodents only, also in the nucleus. This study indicates that the site of action of the Mx gene family might be cytoplasmic. The conservation and ubiquity of this family of proteins reflects a more general and essential cellular function than was initially considered.