Fusion proteins containing a minimal GPI-attachment signal are apically expressed in transfected MDCK cells

We have shown that addition of the C-terminal 37 amino acids of decay-accelerating factor (DAF) to secretory proteins leads to glycosyl-phosphatidyl-inositol (GPI) anchoring and apical surface expression in MDCK cells. Theoretically, transferred apical sorting information may reside in the glycolipid-anchor moiety or the DAF sequence (9 amino acids) that remains after signal cleavage and GPI attachment. We show here that removal of eight of these nine remaining amino acids, thereby creating a minimal GPI-attachment signal, results in apical expression of GPI-anchored human growth hormone. These data argue that the apical sorting information conveyed by the C terminus of DAF is related to its ability to direct GPI attachment, rather than to a specific sequence that remains in the fusion protein.