Membrane trafficking of CD98 and its ligand galectin 3 in BeWo cells--implication for placental cell fusion.
CD98 heavy chain (CD98hc), expressed at high levels in developing human trophoblasts, is an integral membrane protein with multiple N-linked glycosylation sites and known to be important for cell fusion, adhesion, and amino acid transport. Western blotting and flow cytometry were used to study the effect of brefeldin A, an inhibitor of protein translocation through the Golgi, on CD98hc in the human placental trophoblast cell line BeWo. Although brefeldin A treatment caused increased cell surface expression of CD98hc, a novel partially glycosylated form of the protein was found and, concomitantly, cell fusion was reduced. Western blotting showed that CD98 and galectin 3, a proposed ligand for the glycosylated extracellular domain of CD98hc, co-immunoprecipitated, and double-label immuno-electron microscopy confirmed that CD98hc associated with galectin 3. Furthermore, cell fusion was reduced (specifically) by the disaccharide lactose, a known ligand for the carbohydrate recognition domain of galectin 3, suggesting that the association was functional. Taken together, the data suggest that N-glycosylation of CD98 and subsequent interaction with galectin 3 is critical for aspects of placental cell biology, and provides a rationale for the observation that, in the mouse, truncation of the CD98hc extracellular domain leads to early embryonic lethality [Tsumura H, Suzuki N, Saito H, Kawano M, Otake S, Kozuka Y, Komada H, Tsurudome M & Ito Y (2003) Biochem Biophys Res Commun 308, 847-851].
Dalton
Paola
P
Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK. paoladalton@yahoo.co.uk
Christian
Helen C
HC
Redman
Christopher W G
CW
Sargent
Ian L
IL
Boyd
C A R
CA
D020126:Brefeldin A / Q000494:pharmacology; D002459:Cell Fusion; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D027261:Fusion Regulatory Protein-1 / Q000096:biosynthesis / Q000502:physiology*; D037502:Galectin 3 / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D010920:Placenta / Q000166:cytology; D021381:Protein Transport / Q000187:drug effects; D014327:Trophoblasts; D014415:Tunicamycin / Q000494:pharmacology
D027261:Fusion Regulatory Protein-1; D037502:Galectin 3; D014415:Tunicamycin; D005576:Colforsin; D020126:Brefeldin A