Inhibition of Na-K-ATPase Activity and Gene Expression by a Myeloma Light Chain in Proximal Tubule Cells

Abstract

Background

Light chain nephrotoxicity is frequently associated with Fanconi syndrome characterized by aminoaciduria, 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 λ-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 µmol/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 α-1 isoform of Na-K-ATPase was suppressed significantly compared with control cells. The messages for GAPDH, β-actin, and 28 S RNA in light chain exposed cells were also depressed in comparison with control cells. This light chain also signifcantly 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.