Regulation of calbindin-D28K gene expression by 1,25-dihydroxyvitamin D3 in chick kidney

We report here the use of a cloned cDNA for the avian calbindin-D28K (28 kD, vitamin D-dependent calcium binding protein, CaBP) to investigate the expression of the chick calbindin gene in the kidney. All three cal-bindin-D28K mRNA species (2000, 2600, and 3100 nucleotide transcripts) were present in the kidney tissue of chronically vitamin D-deficient (-D) chicks; this basal constitutive level of expression was, however, enhanced by administration of the vitamin D3 metabolite, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in both a time- and dose-dependent manner. D-deficient chick renal calbindin-D28K protein levels (measured by ELISA) were maximally (twofold) stimulated by 6.5 nmole per animal of 1,25-(OH)2D3 when measured 48 h later; a concomitant level of augmentation of calbindin-D28K mRNA accumulation was also observed at this time. Time course experiments showed that enhanced renal calbindin-D28K mRNA accumulation (in -D chicks) was significantly stimulated as early as 8 h and were maximal 12 h after a single pharmacologic dose of 1,25-(OH)2D3; this elevated level of gene expression was maintained for at least 72 h. Renal calbindin-D28K protein levels (constitutively expressed in the -D chick) were significantly stimulated (twofold) as early as 12 h following the single dose of steroid hormone; the level of calbindin-D28K also remained elevated for a minimum of 72 h. Collectively, these data indicate that 1,25-(OH)2D3 acts upon the renal calbindin-D28K gene in a manner similar to that operable in the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)