Calreticulin associates with non-HLA-A,-B class I proteins in the human choriocarcinoma cell lines JEG-3 and BeWo.
Human placental trophoblast expresses as unusual repertoire of major histocompatibility complex (MHC) class I products that appears to reflect the unique role of this epithelium in mediating feto-maternal relations during pregnancy. Trophoblast is devoid of human leucocyte antigen (HLA)-A,-B antigens but can express one or more non-HLA-A,-B class I proteins. The human choriocarcinoma cell lines JEG-3, BeWo and JAR are widely used as models to study trophoblast. During attempts to isolate non-HLA-A,-B class I from JEG-3 and BeWo by immunoaffinity chromatography using a monoclonal antibody to beta 2-microglobulin we observed a 55,000 MW protein co-purifying with class I. N-terminal amino acid sequencing and immunoblotting using a specific antiserum identified this product as calreticulin, a molecule recently shown to be involved in the assembly of classical class I in human B-lymphoblastoid cells. In our hands JEG-3 and BeWo were found to express 45,000 MW non-HLA-A,-B class I proteins while the 40,000 MW HLA-G product was identified only in JEG-3. Our data suggest that calreticulin associates with non-HLA-A,-B class I heterodimers and with free 45,000 MW non-HLA-A,-B class I H chains in JEG-3. JAR was found to be devoid of detectable class I H chains but contained beta 2-microglobulin and calreticulin. However, calreticulin-beta 2-microglobulin complexes were not detected in JAR. Calreticulin and class I were apparently co-localized within the endoplasmic reticulum of JEG-3 cells whereas only class I was expressed at the cell surface. These studies demonstrate that calreticulin is associated with non-HLA-A,-B class I products in human choriocarcinoma cells.
Wainwright
S D
SD
University of Bristol, Department of Clinical Medicine, St. Michael's Hospital, UK.
Simpson
K L
KL
Holmes
C H
CH
D001324:Autoantigens; D002135:Calcium-Binding Proteins / Q000032:analysis*; D037282:Calreticulin; D002822:Choriocarcinoma / Q000378:metabolism*; D002846:Chromatography, Affinity; D005260:Female; D006680:HLA Antigens / Q000032:analysis; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000032:analysis*; D006801:Humans; D015151:Immunoblotting; D037102:Lectins; D018613:Microscopy, Confocal; D012261:Ribonucleoproteins / Q000032:analysis*; D014327:Trophoblasts / Q000276:immunology*; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*
D001324:Autoantigens; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D037102:Lectins; D012261:Ribonucleoproteins