Membrane trafficking of CD98 and its ligand galectin 3 in BeWo cells − implication for placental cell fusion

Abstract

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 Commun308, 847–851].

Identification of Cell Surface Straight Chain Poly-N-Acetyl-Lactosamine Bearing Protein Ligands for VH4-34–Encoded Natural IgM Antibodies

“…terminal SC-PNAL chains does not alter the overall protein mass (data not shown). Nonetheless, the presence of PNAL glycans on CD147 and CD98 proteins has been described in other studies (66,67). Our studies using TL also confirm PNAL on CD147 and CD98 proteins individually immunoprecipitated by Abs to CD147 or CD98, respectively, using protein-G (data not shown).…”

Essential Roles of L-Type Amino Acid Transporter 1 in Syncytiotrophoblast Development by Presenting Fusogenic 4F2hc

“…We therefore suggest that some common mechanisms involving 4F2hc underlie such physiological and pathological cell fusions. A previous study indicated that galectin-3, a member of lectin family, is a ligand for 4F2hc and binds to the extracellular domain of 4F2hc to promote BeWo cell fusion (6). In that study, based on the observation that lactose, a disaccharide ligand of galectin-3, interfered with the forskolin-induced cell fusion, galectin-3 was suggested to recognize N-linked sugar chains in the extracellular domain of 4F2hc.…”

“…Two retrovirusderived murine proteins, syncytins, have been identified to mediate syncytialization of trophoblastic cells in the developing placenta (3,4). Although the in vivo relevance has not been well addressed, several other proteins, including the single-membranespanning type II membrane glycoprotein 4F2hc/CD98hc/FRP-1, have been also suggested to be involved in the cell fusion of trophoblastic cells (5)(6)(7)(8)(9)(10)(11)(12). 4F2hc is the heavy chain subunit of 4F2 antigen (CD98) and is covalently linked to a nonglycosylated light chain.…”

Functions of Galectin-3 and Its Role in Fibrotic Diseases

“…Independently, increased Gal-3 expression may also play a special role in tissue remodeling because of its adhesive and growth-regulative effects (Pricci et al, 2000). CD98, known to be important for cell fusion, adhesion, and amino acid transport, is also a demonstrated receptor for Gal-3 (Dong and Hughes, 1997;Dalton et al, 2007). The mechanistic link among interleukin (IL)-4, Gal-3, and CD98 can drive alternative macrophage activation and chronic inflammatory and fibrotic diseases (Dong and Hughes, 1997).…”