Synthesis of Lanostane-Type Triterpenoid N-Glycosides and Their Cytotoxicity against Human Cancer Cell Lines.

Seventeen lanostane-type triterpenoid derivatives (2 - 18), including 11N-glycosides (8 - 18), were synthesized from the natural triterpenoid, lanosterol (1), and were evaluated for their cytotoxicity against the human cancer cell lines, HL-60, A549, and MKN45, as well as the normal human lung cells, WI-38. Among them, N-ß-d-2-acetamido-2-deoxyglucoside (10) showed cytotoxicity against HL-60, A549, MKN45, and WI-38 cells (IC50 0.0078 - 2.8 µm). However, N-ß-d-galactoside (12) showed cytotoxicity against HL-60 and MKN45 cells (IC50 0.0021 - 4.0 µm), but not the normal WI-38 cells. Furthermore, Western blot analysis suggested that 12 induces apoptosis by activation of caspases-3, 8, and 9. These results will be useful for the synthesis of other tetracyclic triterpenoids or steroid N-glycosides to increase their cytotoxicity and apoptosis-inducing activities.

Quality-controlled ceramide-based GPI-anchored protein sorting into selective ER exit sites.

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) exit the endoplasmic reticulum (ER) through a specialized export pathway in the yeast Saccharomyces cerevisiae. We have recently shown that a very-long acyl chain (C26) ceramide present in the ER membrane drives clustering and sorting of GPI-APs into selective ER exit sites (ERES). Now, we show that this lipid-based ER sorting also involves the C26 ceramide as a lipid moiety of GPI-APs, which is incorporated into the GPI anchor through a lipid-remodeling process after protein attachment in the ER. Moreover, we also show that a GPI-AP with a C26 ceramide moiety is monitored by the GPI-glycan remodelase Ted1, which, in turn, is required for receptor-mediated export of GPI-APs. Therefore, our study reveals a quality-control system that ensures lipid-based sorting of GPI-APs into selective ERESs for differential ER export, highlighting the physiological need for this specific export pathway.

Structural analysis of the GPI glycan.

Glycosylphosphatidylinositol (GPI) anchoring of proteins is an essential post-translational modification in all eukaryotes that occurs at the endoplasmic reticulum (ER) and serves to deliver GPI-anchored proteins (GPI-APs) to the cell surface where they play a wide variety of vital physiological roles. This paper describes a specialized method for purification and structural analysis of the GPI glycan of individual GPI-APs in yeast. The protocol involves the expression of a specific GPI-AP tagged with GFP, enzymatic release from the cellular membrane fraction, immunopurification, separation by electrophoresis and analysis of the peptides bearing GPI glycans by mass spectrometry after trypsin digestion. We used specifically this protocol to address the structural remodeling that undergoes the GPI glycan of a specific GPI-AP during its transport to the cell surface. This method can be also applied to investigate the GPI-AP biosynthetic pathway and to directly confirm predicted GPI-anchoring of individual proteins.