High level expression and secretion of Fc-X fusion proteins in mammalian cells.

We have developed a general expression system that enhances the production and secretion of proteins in mammalian cells. The protein of interest is expressed as a fusion to a signal peptide and the Fc fragment of immunoglobulin as the N-terminal fusion partner, which can direct the cellular processes into expressing and secreting high levels of many different types of proteins. These include secretory proteins, enzymes and soluble domains of membrane proteins, as well as nuclear and regulatory proteins. Typical expression levels of these proteins from stable cell lines ranged from several to 100 microg/ml in conditioned media. The Fc domain helps to solubilize hydrophobic proteins and provides a handle for easy detection and purification of the fusion proteins; and it can be cleaved off by treatment with protease if desired.