title: Mesothelin-MUC16 binding is a high affinity, N-glycan dependent interaction that facilitates peritoneal metastasis of ovarian tumors.
abstract: BACKGROUND
  The mucin MUC16 and the glycosylphosphatidylinositol anchored glycoprotein mesothelin likely facilitate the peritoneal metastasis of ovarian tumors. The biochemical basis and the kinetics of the binding between these two glycoproteins are not clearly understood. Here we have addressed this deficit and provide further evidence supporting the role of the MUC16-mesothelin interaction in facilitating cell-cell binding under conditions that mimic the peritoneal environment.
  
  
  RESULTS
  In this study we utilize recombinant-Fc tagged human mesothelin to measure the binding kinetics of this glycoprotein to MUC16 expressed on the ovarian tumor cell line OVCAR-3. OVCAR-3 derived sublines that did not express MUC16 showed no affinity for mesothelin. In a flow cytometry-based assay mesothelin binds with very high affinity to the MUC16 on the OVCAR-3 cells with an apparent Kd of 5-10 nM. Maximum interaction occurs within 5 mins of incubation of the recombinant mesothelin with the OVCAR-3 cells and significant binding is observed even after 10 sec. A five-fold molar excess of soluble MUC16 was unable to completely inhibit the binding of mesothelin to the OVCAR-3 cells. Oxidation of the MUC16 glycans, removal of its N-linked oligosaccharides, and treatment of the mucin with wheat germ agglutinin and erythroagglutinating phytohemagglutinin abrogates its binding to mesothelin. These observations suggest that at least a subset of the MUC16-asscociated N-glycans is required for binding to mesothelin. We also demonstrate that MUC16 positive ovarian tumor cells exhibit increased adherence to A431 cells transfected with mesothelin (A431-Meso+). Only minimal adhesion is observed between MUC16 knockdown cells and A431-Meso+ cells. The binding between the MUC16 expressing ovarian tumor cells and the A431-Meso+ cells occurs even in the presence of ascites from patients with ovarian cancer.
  
  
  CONCLUSIONS
  The strong binding kinetics of the mesothelin-MUC16 interaction and the cell adhesion between ovarian tumor cells and A431-Meso+ even in the presence of peritoneal fluid strongly support the importance of these two glycoproteins in the peritoneal metastasis of ovarian tumors. The demonstration that N-linked glycans are essential for mediating mesothlein-MUC16 binding may lead to novel therapeutic targets to control the spread of ovarian carcinoma.
authors.affiliation: Department of Obstetrics and Gynecology, University of Wisconsin-Madison, Madison, USA. arens@wisc.edu
authors.forename: Jennifer A A
authors.initials: JA
authors.lastname: Gubbels
authors.forename: Jennifer
authors.initials: J
authors.lastname: Belisle
authors.forename: Masanori
authors.initials: M
authors.lastname: Onda
authors.forename: Claudine
authors.initials: C
authors.lastname: Rancourt
authors.forename: Martine
authors.initials: M
authors.lastname: Migneault
authors.forename: Mitchell
authors.initials: M
authors.lastname: Ho
authors.forename: Tapan K
authors.initials: TK
authors.lastname: Bera
authors.forename: Joseph
authors.initials: J
authors.lastname: Connor
authors.forename: Bangalore K
authors.initials: BK
authors.lastname: Sathyanarayana
authors.forename: Byungkook
authors.initials: B
authors.lastname: Lee
authors.forename: Ira
authors.initials: I
authors.lastname: Pastan
authors.forename: Manish S
authors.initials: MS
authors.lastname: Patankar
mesh_terms: D001667:Binding, Competitive / Q000502:physiology; D018394:CA-125 Antigen / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology; D045744:Cell Line, Tumor; D005260:Female; D005434:Flow Cytometry; D058851:GPI-Linked Proteins; D006801:Humans; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D000090204:Mesothelin; D008954:Models, Biological; D010051:Ovarian Neoplasms / Q000378:metabolism / Q000473:pathology; D010534:Peritoneal Neoplasms / Q000378:metabolism / Q000556:secondary; D011134:Polysaccharides / Q000378:metabolism*
chemical_list: D018394:CA-125 Antigen; D058851:GPI-Linked Proteins; C451759:MUC16 protein, human; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011134:Polysaccharides; D000090204:Mesothelin