FXYD2 and Na,K-ATPase expression in isolated human proximal tubular cells: disturbed upregulation on renal hypomagnesemia?
Autosomal dominant renal hypomagnesemia (OMIM 154020), associated with hypocalciuria, has been linked to a 121G to A mutation in the FXYD2 gene. To gain insight into the molecular mechanisms linking this mutation to the clinical phenotype, we studied isolated proximal tubular cells from urine of a patient and a healthy subject. Cells were immortalized and used to assess the effects of hypertonicity-induced overexpression of FXYD2 on amount, activity and apparent affinities for Na(+), K(+) and ATP of Na,K-ATPase. Both cell lines expressed mRNA for FXYD2a and FXYD2b, and patient cells contained both the wild-type and mutated codons. FXYD2 protein expression was lower in patient cells and could be increased in both cell lines upon culturing in hyperosmotic medium but to a lesser extent in patient cells. Similarly, hyperosmotic culturing increased Na,K-ATPase protein expression and ATP hydrolyzing activity but, again, to a lesser extent in patient cells. Apparent affinities of Na,K-ATPase for Na(+), K(+) and ATP did not differ between patient and control cells or after hyperosmotic induction. We conclude that human proximal tubular cells respond to a hyperosmotic challenge with an increase in FXYD2 and Na,K-ATPase protein expression, though to a smaller absolute extent in patient cells.
Department of Biochemistry, Radboud University Nijmegen Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands.
Edinio R
ER
Cairo
Herman G P
HG
Swarts
Martijn J G
MJ
Wilmer
Peter H G M
PH
Willems
Elena N
EN
Levtchenko
Jan Joep H H M
JJ
De Pont
Jan B
JB
Koenderink
D000328:Adult; D015153:Blotting, Western; D002478:Cells, Cultured; D002648:Child; D006801:Humans; D007668:Kidney / Q000378:metabolism* / Q000473:pathology*; D008275:Magnesium Deficiency / Q000378:metabolism*; D008297:Male; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
C499076:ATP1A1 protein, human; C416502:FXYD2 protein, human; D000254:Sodium-Potassium-Exchanging ATPase