1,25-Dihydroxycholecalciferol Regulates Rat Intestinal Calbindin D9k Posttranscriptionally

Abstract

To determine whether calbindin D9k (CaBP) is subject to posttranscriptional control, 6-wk-old Sprague Dawley-derived rats were fed one of three purified diets, 1.5% Ca and 3.0% Ca, mostly as carbonate, and 2.9% Ca, mostly as gluconate. Two weeks later, 5-cm segments of duodenum, jejunum, ileum, cecum and colon were obtained and analyzed for CaBP and CaBP-mRNA. Analysis of the steady-state distribution of CaBP-mRNA and of CaBP revealed a statistically significant (r = 0.95; P < 0.01) linear relationship between CaBP-mRNA and CaBP. When, however, animals that had been fed the 1.5% Ca diet received by intrajugular injection 1.2 nmol 1,25-dihydroxycholecalciferol [1.25-(OH)2-D3] and their CaBP-mRNA and CaBP were analyzed as a function of time after 1,25-(OH)2-D3 administration, the kinetic response of the two molecules differed. The CaBP-mRNA increased linearly by approximately 68% for 4 h after administration and then declined over the next 6 h to a concentration below the preinjection value. Thus, appearance and disappearance of CaBP-mRNA approximated 17% x h(-1). The CaBP, however, increased steeply to 80% above preinjection concentration until 2 h postinjection, i.e., at a rate of 40% x h(-1). Thereafter, CaBP decreased to 35% above the preinjection value between 5 and 10 h postinjection (2.5% x h(-1)). These findings are consistent with a 1,25-(OH)2-D3-mediated posttranscriptional regulation of CaBP concentrations, because the 1,25-(OH)2-D3-mediated increase in CaBP-mRNA is not reflected in an immediately changed CaBP level.

Transcriptional Regulation of Rat Calbindin Expression during Development Determined by Bacterially Expressed Protein.

“…At weaning time, calcium availability changes from repletion to deficiency, so the beginning of calbindin-D9k synthesis is thought to be an adaptation to and protection against this transition (11,15). This hypothesis is consistent with the previous findings of down-regulation of the expression of calbindin-D9k with a high-calcium diet and up-regulation with a low-calcium diet (10,14,17,18). Although Brehier and Thomasset (25) showed the increased expression of calbindin-D9k as the result of high-calcium content in an organ culture of fetus tissue, the mechanism of response against the concentration of calcium may be different between fetal and adult tissues.…”

“…Its expression is highest in the duodenum (12)(13)(14) and reveals a unique pattern during neonatal development with a peak shortly after weaning (11,12,15,16). Regarding the effects of calcium intake from food, up-regulation has been suggested by a low-calcium diet and down regulation by a high-calcium diet (10,14,17,18).…”

The Specific Expression Patterns of Lactase, Sucrase and Calbindin-D9k in Weaning Rats Are Regulated at the Transcriptional Level

“…Dietary sucrose enhances SI and LPH gene expression at a transcription level in rats (8,9). mRNA expression of CaBP fluctuates during 1 ,25-dihydroxyvitamin D3 deficiency and repletion (5) and might be up and 266 FUKTJSHIMA A et al down-regulated by low and high-calcium diets, respec tively, in rats (10,11). The expression of CaBP is re stricted to a very low level in VDR-ablated mice but recovered by a high-lactose, high Ca and high-phos phate diet to the level of non-ablated mice (12 Western blot analysis.…”

Aluminum Toxicity Alters the Regulation of Calbindin-D28k Protein and mRNA Expression in Chick Intestine

“…There is evidence that aluminum binds to nucleic acids and calcium-binding proteins (9,30), but little is known about how this may alter their function or turnover. There is also evidence that 1,25(OH) 2 D and calcium can upregulate posttranscriptional steps in calbindin production (18), but the mechanisms are unclear and no studies have been performed to determine whether aluminum can influence this regulation. It is possible that the decrease in serum calcium and phosphorous induced by aluminum intake in the control group stimulated calbindin synthesis without a corresponding increase in calbindin mRNA.…”

“…Its concentration is also thought to be regulated at both transcriptional and posttranscriptional levels by 1,25(OH) 2 D, in cooperation with other regulatory factors (18,19). In both rats and chicks, aluminum toxicity inhibits the classic ability of injected 1,25(OH) 2 D to upregulate the concentration of intestinal calbindin (11,20).…”