Overexpression of the human neonatal Fc-receptor alpha-chain in trophoblast-derived BeWo cells increases cellular retention of beta2-microglobulin.
Major histocompatibility complex (MHC) class I and MHC class I-type molecules such as the neonatal Fcgamma-receptor, FcRn, are heterodimers consisting of a transmembrane alpha-chain non-covalently associated with beta2-microglobulin (beta2m). Human placental villous syncytiotrophoblast (STB) lacks MHC class I molecules, but express hFcRn that mediates materno-fetal transmission of immunoglobulin G (IgG). Trophoblast-derived BeWo cells that are used to study placental IgG transport likewise express beta2m and low levels of hFcRn alpha-chain. The contribution of FcRn alpha-chain in retention and subcellular distribution of beta2m in STB and BeWo cells is unclear. To investigate this issue, we increased expression of hFcRn alpha-chain in BeWo cells (BeWo/hFcRn) by cDNA transfection. Overexpressed hFcRn protein exhibited the characteristic pH-dependent IgG binding and association with beta2m. In comparison to parental BeWo cells, beta2m mRNA levels in BeWo/hFcRn cells were not significantly altered, but total cell-associated beta2m protein was increased by 120%. Treatment of BeWo and BeWo/hFcRn cells with brefeldin A, an inhibitor of the secretory pathway, abrogated this effect, demonstrating that hFcRn alpha-chain expression retained otherwise secreted beta2m. Flow cytometry revealed that beta2m plasma membrane expression was unaffected by alpha-chain overexpression whereas by fluorescence microscopy a preferential staining of beta2m in peripheral endosomes was observed.
Ellinger
I
I
Department of Pathophysiology, Medical University of Vienna, Vienna, Austria.
Reischer
H
H
Lehner
C
C
Leitner
K
K
Hunziker
W
W
Fuchs
R
R
D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D020126:Brefeldin A / Q000494:pharmacology; D002460:Cell Line; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I; D006801:Humans; D007112:Immunity, Maternally-Acquired; D007074:Immunoglobulin G / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011961:Receptors, Fc / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*; D001613:beta 2-Microglobulin / Q000378:metabolism*
D015703:Antigens, CD; C036832:Fc(alpha) receptor; D015395:Histocompatibility Antigens Class I; D007074:Immunoglobulin G; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D011961:Receptors, Fc; D001613:beta 2-Microglobulin; D020126:Brefeldin A; C100688:Fc receptor, neonatal