Triiodithyronine (T3) enhances the stimulatory effect of 1,25-dihydroxyvitamin D3 on calbindin-D28K mRNA expression in kidney and intestine but not in cerebellum of the chick
The present study was conducted to investigate the role of thyroid hormones in the regulation of gene expression of calbindin-D28k(CaBP-D28K) in the chicken. By employing slot blot and RIA analyses, levels of CABP-D28K mRNA and CaBP-D28K protein in the intestine, kidney, cerebellum and liver were measured 6 and 12 h after i.m. injection of 1, 25-dihydroxyvitamin D3[1, 25 (OH)2D3; 250 ng/chick] and 3, 5, 3-triiodothyronine(T3; 500 ng/chick) in one-day-old chicks. The abundant messages of CaBP-D28K mRNA were detected in the intestine, kidney and cerebellum while there was little message in the liver. After 1, 25 (OH)2D3 treatment (6 + 12 hours),, levels of CaBP-D28K mRNA increased in the intestine, but there was no change in the mRNA levels in the kidney and cerebellum. Although T3 alone had no effect on CaBP-D28K mRNA levels, simultaneous administration of T3 enhanced the 1, 25 (OH)2D3 effect of levels of CaBP-D28K mRNA in the intestine both 6 and 12 h post-treatment, and in the kidney 12 h post-treatment. At a protein level, co-treatment with 1, 25 (OH)2D3 and T3 elicited a significant increase in CaBP-D28K expression in the intestine 12 h post-treatment, as compared to treatment with only 1, 25 (OH)2D3, whereas no differences were observed in the CaBP-D28K protein levels in the kidney and cerebellum. These results suggest that thyroid hormones may play a synergistic role with 1, 25 (OH)2D3 for CaBP-D28K gene expression in the intestine and kidney in chicks