Retinoids modulate expression of the endocytic partners megalin, cubilin, and disabled-2 and uptake of vitamin D-binding protein in human mammary cells.
The major circulating form of vitamin D, 25-hydroxycholecalciferol (25D3), circulates bound to vitamin D-binding protein (DBP). Prior to activation to 1,25-dihydroxycholecalciferol in the kidney, the 25D3-DBP complex is internalized via receptor-mediated endocytosis, which is absolutely dependent on the membrane receptors megalin and cubilin and the adaptor protein disabled-2 (Dab2). We recently reported that mammary epithelial cells (T-47D) expressing megalin, cubilin, and Dab2 rapidly internalize DBP via endocytosis, whereas cells that do not express all 3 proteins (MCF-7) do not. The objectives of this study were to characterize megalin, cubilin, and Dab2 expression and transport of DBP in human mammary epithelial cells. Using immunoblotting and real-time PCR, we found that megalin, cubilin, and Dab2 were expressed and dose dependently induced by all-trans-retinoic acid (RA) in T-47D human breast cancer cells and that RA-treated T-47D cells exhibited enhanced DBP internalization. These are the first studies to our knowledge to demonstrate that mammary epithelial cells express megalin, cubilin, and Dab2, which are enhanced during differentiation and may explain, at least in part, our finding that receptor-mediated endocytosis of DBP is upregulated in differentiated mammary epithelial cells.
Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011, USA.
Timothy M
TM
Chlon
David A
DA
Taffany
Joellen
J
Welsh
Matthew J
MJ
Rowling
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D001940:Breast / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins; D014809:Vitamin D-Binding Protein / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C102885:DAB2 protein, human; D017931:DNA Primers; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D025521:Tumor Suppressor Proteins; D014809:Vitamin D-Binding Protein; C029486:intrinsic factor-cobalamin receptor; D014212:Tretinoin