Regulation of gp330/megalin expression by vitamins A and D.
BACKGROUND
A membrane-bound 550-kD Ca2+-binding glycoprotein belonging to the low-density lipoprotein (LDL) receptor superfamily has recently been identified as a putative calcium-sensing molecule. This molecule, known as gp330/megalin, is among several tissues present in the proximal tubule, parathyroid and placental cytotrophoblasts, in which a Ca2+-sensing function has been demonstrated.


METHODS
Regulation of mRNA and protein expression of gp330/megalin were studied in a recently established cell line derived from rat kidney proximal tubule cells (IRPTCs), in human JEG-3 cells and in the mouse embryonal carcinoma cell line F9.


RESULTS
In IRPTCs, quantification of mRNA and protein expression demonstrated two- to five-fold increases after addition of 10(-6) mol L(-1) all-trans-retinoic acid, 9-cis-retinoic acid or 1,25-dihydroxyvitamin D3, alone or in combination. Similarly, an increase in gp330/megalin mRNA expression was seen in JEG-3 cells cultured with vitamin D and retinoids, as well as when F9 cells were differentiated by incubation with retinoic acid and cAMP. The IRPTCs were immortalized by viral infection with the SV40 genome preceded by a temperature-sensitive promoter. Thus, by culture of the cells at 41 degrees C, SV40 genome transcription is inhibited and the IRPTC phenotype is reversed towards non-infected proximal tubule cells. At 41 degrees C, gp330/megalin mRNA expression was significantly increased compared with cells incubated at 34 degrees C.


CONCLUSIONS
The results indicate a correlation between exposure to retinoic acid or vitamin D or induction of cell differentiation (by retinoic acid/cAMP in F9 cells or inhibition of SV40 transcription in IRPTCs) and an increase in gp330/megalin protein and mRNA expression.
Liu
W
W
University Hospital, Uppsala, Sweden.
Yu
W R
WR
Carling
T
T
Juhlin
C
C
Rastad
J
J
Ridefelt
P
P
Akerström
G
G
Hellman
P
P
D000818:Animals; D015152:Blotting, Northern; D002118:Calcium / Q000032:analysis; D002461:Cell Line, Transformed; D003593:Cytoplasm / Q000737:chemistry; D005786:Gene Expression Regulation / Q000187:drug effects; D026541:Heymann Nephritis Antigenic Complex; D006801:Humans; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000276:immunology; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D051379:Mice; D012313:RNA / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D051381:Rats; D013194:Staining and Labeling; D013696:Temperature; D014407:Tumor Cells, Cultured; D014801:Vitamin A / Q000494:pharmacology*; D014807:Vitamin D / Q000494:pharmacology*
D026541:Heymann Nephritis Antigenic Complex; D008562:Membrane Glycoproteins; D012334:RNA, Neoplasm; D014801:Vitamin A; D014807:Vitamin D; D012313:RNA; D002118:Calcium