Adverse effect of cadmium on binding of transcription factor Sp1 to the GC-rich regions of the mouse sodium-glucose cotransporter 1, SGLT1, promoter

Exposure of the kidney to cadmium can cause glucosuria. Effect of cadmium on sodium-glucose cotransporter 1, (SGLT1) mRNA molecules in cultured mouse kidney cortical cells was determined by quantitative competitive RT-PCR. SGLT1 mRNA molecules decreased from 58 x 10(4)mug(-1) total RNA in untreated cells to 29 x 10(4) mug(-1) total RNA in cells exposed to 5 muM cadmium. Increasing cadmium to 7.5 and 10 muM, reduced mRNA molecules to 21 X 10(4) and 12 x 10(4)mug(-1) total RNA, respectively. The half-life of SGLT1 mRNA in control and in cells exposed to 7.5 muM cadmium were almost the same and calculated to be 9.1 h (S.E +/-2.7) for the former and 8.5 h (S.E.+/-2.2) for the latter. We also analyzed mouse SGLT1 promoter sequences and identified two conserved Sp I binding sites. The Sp I binding sequences were used as probes in electrophoretic mobility shift assay (EMSA) with nuclear proteins from cultured cells. Intensity of complexes of the 5' and the 3' Spl probes with nuclear Spl from cells treated with 7.5 muM cadmium were 84% (S.E.+/-4) and 6 1 % (S.E.+/-14) of controls, respectively. Cadmium had no effect on expression of Sp I mRNA or protein level. Cadmium-induced inhibition of glucose uptake in kidney may be the result of transcriptional down-regulation of SGLT1 mediated through modification of Sp 1 binding to its promoter. (C) 2004 Elsevier Ireland Ltd. All rights reserved.