title: Characterization of a novel human IgG antibody reactive with a Ca(2+)-sensitive cell-cell adhesion epitope of PtK2 epithelial cells.
abstract: We have characterized a human IgG antibody present in the serum of a patient with an autoimmune undifferentiated connective tissue disease and reactive with PtK2 epithelial cell-cell adhesions. The fluorescent staining pattern is observed only at cell-cell contacts whether cells are permeabilized or not. The serum reacts with polypeptides of 90, 48 and 45 kD by immunoblotting. IgG affinity-purified from these bands failed to reproduce the original immunofluorescence staining pattern. Treatment with cycloheximide did not abolish the staining pattern suggesting that the recognized antigen is not a newly expressed protein. However, when EGTA was used for chelating calcium ions in the culture medium the original staining pattern observed at cell-cell adhesions was affected although some fluorescence was still present at cell periphery. This was reversible when cells were reincubated with fresh medium containing Ca2+. The recognized antigen colocalizes at cell-cell adhesions with actin, the microfilament-associated proteins vinculin, alpha-actinin and myosin light chain, and with Triton-insoluble uvomorulin (E-cadherin) material. We conclude that the antibody reacts with, at least, an extracellular portion of a Ca(2+)-dependent PtK2 antigen. The characterization of this antibody based on (1) its localization at cell-cell adhesions, (2) its sensitivity to EGTA-treatment and (3) its colocalization with the epithelial cellular adhesion molecule (CAM) uvomorulin, strongly suggest that the recognized Ag is a CAM or a CAM-associated protein.
authors.affiliation: Hôpital Notre-Dame, Department of Medicine, University of Montreal School of Medicine, QUE, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Girard
authors.forename: J L
authors.initials: JL
authors.lastname: Senécal
mesh_terms: D001327:Autoimmune Diseases / Q000276:immunology*; D015820:Cadherins / Q000032:analysis*; D002118:Calcium / Q000494:pharmacology*; D002448:Cell Adhesion; D003240:Connective Tissue Diseases / Q000276:immunology*; D003513:Cycloheximide / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D000939:Epitopes; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007074:Immunoglobulin G / Q000276:immunology*; D008875:Middle Aged; D016596:Vinculin / Q000032:analysis
chemical_list: D015820:Cadherins; D000939:Epitopes; D007074:Immunoglobulin G; D016596:Vinculin; D004533:Egtazic Acid; D003513:Cycloheximide; D002118:Calcium