Sorting and function of the human folate receptor is independent of the caveolin expression in Fisher rat thyroid epithelial cells.
Caveolae are small, flask-shaped, non-clathrin coated invaginations of the plasma membrane of many mammalian cells. Caveolae have a coat that includes caveolin. They have been implicated in numerous cellular processes, including potocytosis. Since the human folate receptor (hFR) and other glycosyl-phosphatidylinositol GPI)-tailed proteins have been co-localized to caveolae, we studied the caveolin role in the hFR function by transfecting hFR and/or caveolin cDNA into Fisher rat thyroid epithelial (FRT) cells that normally do not express detectable levels of either protein. We isolated and characterized stable clones as follows: they express (1) high levels of caveolin alone, (2) hFR and caveolin, or (3) hFR alone. We discovered that hFR is correctly processed, sorted, and anchored by a GPI tail to the plasma membrane in FRT cells. No difference in the total folic acid binding or cell surface folic acid binding activity were found between the FRT cells that were transfected with hFR, or cells that were transfected with hFR and caveolin. The hFR that was expressed on the cell surface of clones that were transfected with hFR was also sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC) release, and incorporated radiolabeled ethanolamine that supports the attachment of a GPI-tail on hFR. We conclude that the processing, sorting, and function of hFR is independent on the caveolin expression in FRT cells.
Kim
Chong-Ho
CH
Department of Clinical Pathology, Wonkwang Health Science College, Iksan 570-750, Korea. chkim@wkhc.ac.kr
Park
Young-Soon
YS
Chung
Koong-Nah
KN
Elwood
Patrick C
PC
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D051242:Caveolin 1; D022461:Caveolins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D002999:Clone Cells; D018076:DNA, Complementary / Q000235:genetics; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D051381:Rats; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism; D014162:Transfection
C495540:CAV1 protein, human; D002352:Carrier Proteins; C495537:Cav1 protein, rat; D051242:Caveolin 1; D022461:Caveolins; D018076:DNA, Complementary; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D005492:Folic Acid