Inhibition of Na-K-ATPase activity and gene expression by a myeloma light chain in proximal tubule cells.
BACKGROUND
Light chain nephrotoxicity is frequently associated with Fanconi syndrome characterized by amino-aciduria, glycosuria, phosphaturia, and bicarbonaturia. The mechanisms of these transport abnormalities are unknown. To determine the role of Na-K-ATPase, we examined the effects of a lambda-light chain on both the activity and gene expression of Na-K-ATPase in primary cultures of rat proximal tubule cells.


METHODS
The lambda-light chain used here was isolated from urine of a patient with multiple myeloma and previously shown to inhibit sodium-dependent phosphate and glucose transport in proximal tubule cells. Na-K-ATPase was determined spectrophotometrically and the gene expression by Northern analysis in cells exposed to light chain.


RESULTS
In cells exposed to 200 mumol/L light chain Na-K-ATPase activity was reduced significantly, up to 73%, at 2, 24, and 48 hours compared with control cells (N = 12, P < 0.001). Northern analysis showed that in cells exposed to light chain for 24 and 48 hours the message for the alpha-1 isoform of Na-K-ATPase was suppressed significantly compared with control cells. The messages for GAPDH, beta-actin, and 28 S RNA in light chain exposed cells were also depressed in comparison with control cells. This light chain also significantly inhibited thymidine incorporation by proximal tubule cells in a dose-dependent manner.


CONCLUSIONS
These data suggest a general toxicity to cells by this light chain and indicate that inhibitory effects on both the activity and gene expression of Na-K-ATPase may be an important mechanism of light chain cytotoxicity on proximal tubule cells.
Guan
S
S
Department of Medicine, Nephrology Section, Tulane University School of Medicine, New Orleans, LA 70112, USA.
el-Dahr
S
S
Dipp
S
S
Batuman
V
V
D000818:Animals; D001536:Bence Jones Protein / Q000494:pharmacology*; D015152:Blotting, Northern; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000652:urine; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000235:genetics
D012333:RNA, Messenger; D001536:Bence Jones Protein; D000254:Sodium-Potassium-Exchanging ATPase