Rat duodenal calcium-binding protein messenger RNA: induction by 1,25-dihydroxyvitamin D3

Expression of calbindin-D9k messenger ribonucleic acid in the gastrointestinal tract of dairy cattle

The calcium demands of pregnancy and lactation are known to up-regulate expression of Calbindin-D9k (CaBP-9k) mRNA in the intestines. The gastrointestinal CaBP-9k mRNA expressions has not been studied in dairy cows, which are bound to experience several pregnancies and lactation stages. In this study, the CaBP-9k mRNA expression were examined in the gastrointestinal tract of Holstein dairy cattle by Northern blot analysis. Detectable expression of CaBP-9k mRNA was localized in the proximal portion of the small intestines. These expressions were higher at the most proximal region of the duodenum and gradually decreased distally. The duodenal CaBP-9k mRNA was detected in all dairy cattle from 0.4 to 83.4 months old, but was not detectable in foetuses. There were no significant correlations between the age and the levels of CaBP-9k mRNA expression or between the plasma 1,25-(OH)2D3 concentrations and the levels of CaBP-9k mRNA expression.

Calcium absorption--a paradigm for mineral absorption

Intestinal calcium absorption proceeds by two mechanisms, an active transcellular process that takes place in the duodenum and a passive paracellular process throughout the small intestine. This article characterizes the three steps of transcellular calcium movement-entry, intracellular diffusion and extrusion-and identifies conditions that must be satisfied for other mineral ions to move transcellularly as part of a transepithelial transport process. Passive calcium movement is down a chemical gradient with the amount absorbed by this pathway determined in large measure by the sojourn time, most of which is spent in the ileum. Because transcellular movement of most mineral ions other than calcium, where measured, is either small or negligible, passive transport is likely to be the major route of intestinal absorption, the nature of which, however, has not been well established experimentally.

The rat vitamin-D-dependent calcium-binding protein (9-kDa CaBP) gene. Complete nucleotide sequence and structural organization

The structural organization of the entire rat vitamin-D-dependent calcium-binding protein (9-kDa CaBP) gene was determined by analysis of overlapping genomic clones isolated from a rat genomic library using the rat 9-kDa CaBP cDNA [Desplan C., Heidmann O., Lillie J., Auffray C. and Thomasset M. (1983) J. Biol. Chem. 258, 13502-13505]. These clones together span 30 kbp of rat genomic DNA, with the rat 9-kDa CaBP gene lying in the middle. The 9-kDa CaBP gene is 2.5 kbp long and contains three exons interrupted by two introns. The first exon contains almost the entire 5' untranslated region. The second exon codes for the calcium-binding site I, the third exon codes for site II and the 3' untranslated region. Therefore each of the calcium-binding domains is encoded by single, separate exons. The transcription initiation site was identified by S1 nuclease mapping and primer extension. A consensus sequence TATAAA is localized 31 bp upstream from the cap site and the 'CCAAT-box' lies upstream from the transcription start. Single (AC)25 and (AG)23 repeats are present in the second intron together with an Alu-like sequence. Repetitive elements are present 5 kbp upstream from the cap site and in the 3' flanking region. Comparison of the known rat CaBP sequences (9-kDa CaBP, 28-kDa CaBP, S100 protein) shows that the 9-kDa CaBP is more closely related to the S100 protein than to the 28-kDa CaBP. There is no evidence to indicate that 9-kDa CaBP has arisen from the 28-kDa CaBP.

1 alpha,25(OH)2 vitamin D3: a steroid hormone capable of producing pleiotropic receptor-mediated biological responses by both genomic and nongenomic mechanisms

Vitamin D3 is now considered a pro-hormone and its biological activities are in a great majority due to its hormonally active derivative 1 alpha,25-dihydroxyvitamin D3. The actions of vitamin D3 have been extensively studied both in vivo and in vitro using different animal models as well as a diversity of cell types including intestinal epithelial cells, kidney cells, lymphocytes, macrophages and a number of malignant cell lines. Results thus obtained have considerably extended the number of target tissues for this vitamin and hormone far beyond its classical target organs, parathyroid gland, kidney, intestine and bone. Studies performed at the cellular, subcellular and molecular levels have led to the establishment of new concepts on the mode of action of vitamin D3 which is not believed to act through receptor-mediated genomic and nongenomic events leading to the expression of the full biological response.

Vitamin-D dependent 9 kDa calcium-binding protein gene: cDNA cloning, mRNA distribution and regulation

Cholecalciferol (calcitriol) the active hormonal form of vitamin D induces the synthesis of at least two intracellular calcium-binding proteins (Ka = 10(6) M-1), the cholecalcins (CaBP) in mammals. We used the synthesis of these proteins to study the genomic steroid-like action of vitamin D. The 9 kDa CaBP is mainly concentrated in the duodenum while 28 kDa CaBP is located in the kidney and cerebellum. Complementary DNA copies of rat intestinal 9 kDa CaBP mRNA were cloned in E. coli. The deduced amino acid sequence for 9 kDa CaBP contains two 'EF hand' domains corresponding to calcium-binding sites I and II. The homology observed suggests, after comparison with the structures of other intracellular CaBPs, that rat 9 kDa CaBP mRNA contains the remains of an untranslated calcium-binding site III-like structure seen in 28 kDa CaBP from kidney and cerebellum of rat. Northern blots showed that the cDNA sequence hybridizes to a homogeneous 500-600 nucleotide mRNA species from rat duodenum. Larger mRNA species encoding 28 kDa CaBP were undetectable in rat kidney and cerebellum even under low stringency conditions. These findings demonstrate that there is no cross-hybridization between 9 kDa and 28 kDa CaBP mRNAs, and Southern analysis indicates that there are distinct genes coding for each rat cholecalcin. The cDNA probe was used to analyze the specific 9 kDa CaBP gene expression along the intestine of growing rats and during gestation and fetal development.(ABSTRACT TRUNCATED AT 250 WORDS)

The action of 1 alpha,25-dihydroxyvitamin D3 on rat small intestine: changes in translatable mRNA species

The time course of changes in translatable mRNA from small intestinal mucosa was studied in vitamin D-deficient rats following an intrajugular dose of 1,25-dihydroxyvitamin D3. L-[35S]Methionine-labeled translation products were analyzed by high-resolution one- and two-dimensional electrophoresis. Changes were detected in two distinct proteins, Mr 14,000/pI 6.24 (Band I), and Mr 5,200/pI 4.86 (Band II). These increased to maxima of 1-2% each of the total in vitro-synthesized protein at 12 h after dosing. This represented a 3- and 10-fold increase, respectively, over control values. The time course of these changes suggests that regulation of the levels of the mRNAs coding for these proteins is not involved in the initial (6 h) peak of 1,25-dihydroxyvitamin D3-stimulated intestinal calcium transport in the rat.

Skin calcium-binding protein: effect of vitamin D deficiency and vitamin D treatment

The amount of skin calcium-binding protein, evaluated using a sensitive radioimmunoassay and indirect immunofluorescence, was decreased in vitamin-D deficient rats and increased after one week vitamin D3 or 1 alpha-hydroxyvitamin D3 treatment. In vitamin D replete and in vitamin D-deficient animals, skin calcium-binding protein was not sensitive to changes in dietary and/or serum calcium concentrations. These results indicate that this protein is different from other calcium-binding proteins such as parvalbumin and calmodulin which are not vitamin D-dependent, and also different from intestinal calcium-binding protein which, in D replete animals, is sensitive to changes in dietary and serum calcium concentrations. Skin calcium-binding protein may, therefore, represent a new class of vitamin D-dependent protein.