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Calreticulin associates with non‐HLA‐A,‐B class I proteins in the human choriocarcinoma cell lines JEG‐3 and BeWo
Author(s) -
S.D. Wainwright,
K L Simpson,
C H Holmes
Publication year - 1998
Publication title -
immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.297
H-Index - 133
eISSN - 1365-2567
pISSN - 0019-2805
DOI - 10.1046/j.1365-2567.1998.00439.x
Subject(s) - calreticulin , biology , human leukocyte antigen , trophoblast , mhc class i , microbiology and biotechnology , choriocarcinoma , major histocompatibility complex , antigen , endoplasmic reticulum , immunology , genetics , fetus , placenta , pregnancy
Human placental trophoblast expresses an 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 β 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 β 2 ‐microglobulin and calreticulin. However, calreticulin‐β 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.