Cellular localization and function of the antiviral protein, ovine Mx1 (oMx1): I. Ovine Mx1 is secreted by endometrial epithelial cells via an 'unconventional' secretory pathway

Problem: Embryonic loss is a major contributor to infertility. Understanding factors contributing to embryonic loss will aid in development of technologies to improve/regulate fertility in animals and humans. Method of study: We tested the hypothesis that the antiviral protein, ovine Mx1 (oMx1), is secreted by uterine epithelial cells. Uterine flushes were obtained from cyclic and early pregnant ewes and examined for levels of oMx1 protein. The pathway for ovine Mx1 secretion in ovine glandular epithelial (oGE) cells was determined using brefeldin A (BFA), an inhibitor of the conventional secretory pathway. Effects of BFA were determined using β2-microglobulin (β 2MG) as a marker for the conventional secretory pathway, and interferon stimulated gene 15 (ISG15) and Galectin-1 (Gal-1) as markers for the unconventional secretory pathways. Results: Ovine Mx1 protein levels were low in uterine flushes from cyclic ewes and levels increased in pregnant ewes after D 15. Ovine GE cells secreted oMx1 in response to interferon and secretion was not reduced by BFA, suggesting oMx1 was secreted via an unconventional secretory pathway. β2MG secretion was reduced by BFA, whereas ISG15 and Gal-1 were not. Conclusion: This is the first report that the antiviral protein, oMx1, is secreted and provides evidence that secretion occurs via unconventional secretory pathway(s).