title: Ecto-phosphorylation of CD98 regulates cell-cell interactions.
abstract: Ecto-phosphorylation plays an important role in many cellular functions. The transmembrane glycoprotein CD98 contains potential phosphorylation sites in its extracellular C-terminal tail. We hypothesized that extracellular signaling through ecto-protein kinases (ePKs) might lead to ecto-phosphorylation of CD98 and influence its multiple functions, including its role in cell-cell interactions. Our results show that recombinant CD98 was phosphorylated in vitro by ePKs from Jurkat cells and by the commercial casein kinase 2 (CK2). Alanine substitutions at serines-305/307/309 or serines-426/430 attenuated CK2-mediated CD98 phosphorylation, suggesting that these residues are the dominant phosphorylation sites for CK2. Furthermore, CD98 expressed in the basolateral membranes of intestinal epithelial Caco2-BBE cells was ecto-phosphorylated by Jurkat cell-derived ePKs and ecto-CK2 was involved in this process. Importantly, cell attachment studies showed that the ecto-phosphorylation of CD98 enhanced heterotypic cell-cell interactions and that the extracellular domain of CD98, which possesses the serine phosphorylation sites, was crucial for this effect. In addition, phosphorylation of recombinant CD98 increased its interactions with Jurkat and Caco2-BBE cells, and promoted cell attachment and spreading. In conclusion, here we demonstrated the ecto-phosphorylation of CD98 by ePKs and its functional importance in cell-cell interactions. Our findings reveal a novel mechanism involved in regulating the multiple functions of CD98 and raise CD98 as a promising target for therapeutic modulations of cell-cell interactions.
authors.affiliation: Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, United States of America. hnguye9@emory.edu
authors.forename: Hang Thi Thu
authors.initials: HT
authors.lastname: Nguyen
authors.forename: Guillaume
authors.initials: G
authors.lastname: Dalmasso
authors.forename: Yutao
authors.initials: Y
authors.lastname: Yan
authors.forename: Tracy S
authors.initials: TS
authors.lastname: Obertone
authors.forename: Shanthi V
authors.initials: SV
authors.lastname: Sitaraman
authors.forename: Didier
authors.initials: D
authors.lastname: Merlin
mesh_terms: D000818:Animals; D047390:Casein Kinase II / Q000378:metabolism; D002448:Cell Adhesion; D002450:Cell Communication; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D027261:Fusion Regulatory Protein-1 / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000378:metabolism
chemical_list: D027261:Fusion Regulatory Protein-1; D011994:Recombinant Proteins; D012694:Serine; D011494:Protein Kinases; C034454:ectoprotein kinase; D047390:Casein Kinase II