Cloning of the porcine Calbindin-D9k complementary deoxyribonucleic acid by anchored polymerase chain reaction technique

Biological significance of calbindin-D9k within duodenal epithelium

Calbindin-D_9k (CaBP-9k) binds calcium with high affinity and regulates the distribution of free calcium in the cytoplasm. The expression of CaBP-9k is detected primarily in intestine that is vitamin D target tissue, and accumulates in the enterocytes of the duodenal villi. These enterocytes are the clearest example of vitamin D responsive cells, and the presence of CaBP-9k within them accentuates calcium absorption mediated by active transcellular calcium transport. It has been well established that the expression of CaBP-9k is mediated with vitamin D response element on its promoter and it regulates the amount of intracellular calcium in order to prevent cell death from reaching the toxicity of free calcium. There is now little doubt that glucocorticoid also decreases CaBP-9k expression in duodenal epithelial cells. In addition, it was reported that the level of CaBP-9k gene in enterocytes is increased in pregnancy when the plasma estradiol concentration is generally associated with a concomitant increase. Although calcium homeostasis was not disturbed in mice lacking the CaBP-9k gene, we found that CaBP-9k has a buffering role of free calcium in the cytosolic environment beyond that of calcium transfer. To expand our knowledge of the biological functions of CaBP-9k, our research has focused on defining the biological significance of intracellular CaBP-9k. Our findings suggest that the CaBP-9k gene is involved in compensatory induction of other calcium transporter genes in duodenal epithelial cells. This article summarizes the findings from recent studies on the expression and the functions of CaBP-9k in the small intestine.

Calcium transport genes are differently regulated in maternal and fetal placenta in the knockout mice of calbindin-D(9k) and -D(28k)

Calbindin-D(9k) (CaBP-9k) and -D(28k) (CaBP-28k) are cytosolic proteins with EF-hand motifs that have a high affinity for calcium ions. Many types of calcium channels and intracellular calcium binding proteins, such as sodium/calcium exchangers (NCXs) and transient receptor potential cation channels (TRPVs), have been detected in the placenta. In this study, the expression of calcium channels involved in maternal-fetal calcium transport were investigated in wild-type mice versus CaBP-9k, CaBP-28k, and CaBP-9k/28k double knockout (KO) mouse models. The expression of calcium transport genes in three dissected sections of the placenta (maternal, central, and fetal) was examined on gestational day 19 (GD 19). The expression of CaBP-9k, TRPV6, TRPV5, and NCX1 mRNA was high in fetal compared to maternal placenta, while CaBP-28k was abundant in the maternal placenta. CaBP-9k was enhanced in all sections of placenta in CaBP-28k KO mice, whereas CaBP-28k was reduced in CaBP-9k KO mice. The expression of TRPV6, TRPV5, and NCX1 were induced in both maternal and fetal placentas in CaBP-9k KO mice, but were upregulated in maternal and central placentas of CaBP-28k KO mice. The levels of these proteins showed similar patterns with those of their mRNA. Placental CaBP-9k, TRPV6, TRPV5, and NCX1 proteins were abundantly expressed in the intraplacental yolk sac located in the fetal placenta. CaBP-28k did not colocalize with other calcium transport genes, although it was enriched in the placental trophoblasts of the decidual zone in the maternal placenta. These results indicate that placental TRPV6, TRPV5, and NCX1 compensate for CaBPs in CaBP-9k and/or CaBP-28k KO mice, and may take over the roles of CaBP-9k and CaBP-28k to transfer calcium ions in the placenta. Taken together, these results indicate that TRPV6, NCX1, and CaBP-9k in the fetal placenta and CaBP-28k in the maternal placenta may play key roles in controlling calcium transport across the placenta during pregnancy.

Transcriptional and translational expression of calbindin-D9k in the duodenum, kidney and uterus of a female canine model

Calbindin-D9k (CaBP-9k) is a cytosolic calcium-binding protein expressed in tissues in the intestine, uterus, placenta, kidney, pituitary gland and bone. Its exact function is unknown, but it is considered to regulate intracytoplasmic concentration and transport of free ions (Ca(2+)). CaBP-9k protein is involved in intestinal calcium absorption in the intestine and in the regulation of myometrial activity by intracellular calcium in the uterus. Renal CaBP-9k protein is expressed at the site of calcium re-absorption in the kidney and expressed in distal convoluted tubules, where it is thought to facilitate calcium re-absorption. Expression of the CaBP-9k gene has been explored in most mammalians except in a canine model. Presently, we elucidated the expression of CaBP-9k mRNA and protein in the duodenum, kidney and uterus in a canine model involving two adult (2.5-year-old) female beagles. To collect tissues, the dogs were euthanized and then the abdominal cavity was exposed by midline incision. The proximal duodenum, cortex of kidney and uterine horn were collected. Expression of CaBP-9k mRNA was confirmed by reverse transcriptionpolymerase chain reaction (RT-PCR) and real-time PCR. CaBP-9k protein expression and localization were ascertained by Western blot analysis and immunohistochemistry, respectively. CaBP-9k mRNA was detected in the duodenum, but not in the kidney and uterus. Its protein was expressed only in the enterocytes of the duodenum. Taken together, the results indicate that CaBP-9k mRNA and protein are highly expressed in the enterocytes of the duodenum of a canine model, consistent with findings in other mammalian species.

Molecular mechanism of regulation of the calcium-binding protein calbindin-D9k, and its physiological role(s) in mammals: a review of current research

Calbindin-D_9k (CaBP-9k) is a cytosolic calcium-binding protein that is expressed in a variety of tissues, such as uterus, placenta, intestine, kidney, pituitary gland and bone. At present, the precise role(s) of CaBP-9k remains to be clarified. CaBP-9k-null mice are normal, which indicates that other calcium-transporter genes can compensate for the lack CaBP-9k. Uterine CaBP-9k has been shown to be involved in the regulation of myometrial activity by intracellular calcium. In the uterus and placenta, CaBP-9k expression is regulated by the sex steroid hormones oestrogen (E2) and progesterone (P4). Intestinal CaBP-9k is involved in intestinal calcium absorption, and is regulated at the transcriptional and post-transcriptional levels by 1,25-dihydroxyvitamin D3, the hormonal form of vitamin D. Thus, evidence to date suggests that CaBP-9k may be regulated in a tissue-specific manner. In this review, we will summarize current data on the molecular mechanism of regulation of CaBP-9k in mammals, including recent research data generated in our laboratories.

Calcium Homeostasis in Human Placenta: Role of Calcium‐Handling Proteins

The human placenta is a transitory organ, representing during pregnancy the unique connection between the mother and her fetus. The syncytiotrophoblast represents the specialized unit in the placenta that is directly involved in fetal nutrition, mainly involving essential nutrients, such as lipids, amino acids, and calcium. This ion is of particular interest since it is actively transported by the placenta throughout pregnancy and is associated with many roles during intrauterine life. At term, the human fetus has accumulated about 25-30 g of calcium. This transfer allows adequate fetal growth and development, since calcium is vital for fetal skeleton mineralization and many cellular functions, such as signal transduction, neurotransmitter release, and cellular growth. Thus, there are many proteins involved in calcium homeostasis in the human placenta.

Biology and physiology of Calbindin-D9k in female reproductive tissues: involvement of steroids and endocrine disruptors

Although Calbindin-D9k (CaBP-9k), a cytosolic calcium binding protein which has calcium binding sites, is expressed in various tissues, i.e., intestine, uterus, and placenta, potential roles of this gene and its protein are not clearly understood. Uterine CaBP-9k may be involved in controlling myometrial activity related with intracellular calcium level and is not under the control of vitamin D despite the presence of vitamin D receptors. But, it is under the control of the sex steroid hormones, estrogen (E2) and progesterone (P4), in female reproductive systems including the uterus and placenta. Thus, in this review, we summarize recent research literature in regards to the expression and regulation of CaBP-9k in mammals and introduce the research data of recent studies by us and others.

Dominant expression of porcine Calbindin-D9k in the uterus during a luteal phase

Calbindin-D9k (CaBP-9k) is a member of intracellular calcium binding proteins, which have a high affinity to calcium. CaBP-9k is mainly expressed in the mammalian intestine, uterus and placenta, and is regulated in tissue- and species-specific manners. Previous studies have shown that CaBP-9k expression is mainly controlled by steroid hormones and their receptors. Thus, we further investigated the expression and regulation of CaBP-9k during an estrus cycle in the pig uterus by Northern blot and immunoblot analysis in this study. In addition, serum levels of estrogen (E2) and progesterone (P4) were measured using ELISA. The CaBP-9k mRNA is highly expressed in the porcine uterus during a luteal phase compared to a follicular phase, and its mRNA level in a luteal phase is increased up to 10-fold compared to a follicular phase. In parallel to the level of CaBP-9k mRNA, the CaBP-9k protein is also dominantly expressed in the porcine uterus, and strongly expressed in the epithelium and glands of the porcine uterus during a luteal phase. Although, the localization of the CaBP-9k protein is scarcely detected at follicular phase, it is dominantly expressed in the porcine uterus during a luteal phase. In addition, the serum P4 level was significantly increased during a luteal phase compared to a follicular phase, whereas no difference was observed in E2 levels between follicular and luteal phases, indicating that the ratio of P4/E2 is remarkably increased in porcine uterus during a luteal phase compared to a follicular phase. In conclusion, these results suggest that P4 may play an important role in the up-regulation of CaBP-9k gene in the porcine uterus in a luteal phase, which is unlike the condition in the rat uterus. In addition, the porcine CaBP-9k may be dominantly expressed in the epithelium and glandular structure of pig uterus during a luteal phase. It may also be differentially regulated during this cycle presumably by steroid hormones, especially up-regulated P4 levels in this tissue.

The baboon expresses the calbindin-D9k gene in intestine but not in uterus and placenta: implication for conservation of the gene in primates

Expression of the Calbindin-D9k (CaBP-9k) gene was studied in the baboon. Northern blot analysis using a human CaBP-9k cDNA probe detected expression in duodenum but not in uterus and placenta. Reverse transcription/polymerase chain reaction (RT/PCR) confirmed this expression pattern and indicated a high degree of identity between the baboon and human CaBP-9k mRNAs. PCR was employed to amplify the intron A region of the baboon CaBP-9k gene using human-derived primers and baboon genomic DNA. The baboon intron was closely related to the human CaBP-9k intron A, including the presence a complete Alu-repetitive element. Most significantly, a 13 nucleotide long element at the 5' end of the baboon intron matched exactly the human sequence. This element represents a nonfunctional variation of an estrogen response element found at the same location in the rat CaBP-9k gene. The rat element functions as an enhancer and mediates uterine and possibly placental CaBP-9k expression in the rat and probably most other mammals. The finding of a modified ERE in baboon as in human suggests that during primate evolution the expression of this mammalian-specific gene has been eliminated in uterus and placenta. This scenario raises the question of the role of CaBP-9k in these reproductive tissues.

Isolation and N-terminal sequence of two low molecular weight calcium-binding proteins from pig granulocytes

1. Two small, abundant calcium-binding proteins were isolated from pig granulocytes. They were named p7A and p7B. Relative molecular masses were approx. 32,000 for p7A and 13,000 for p7B, when obtained by Sephadex G-75 gel filtration, while it was 7000 for both proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). 2. N-terminal sequence analysis suggests that p7A is homologous to human and mouse MRP-8 and that p7B may be related to human and mouse MRP-14, though some properties of the latter--such as mobility on SDS-PAGE--were found to be different. In addition, p7A and p7B could be resolved under native conditions, contrasting with the fact that human and mouse MRP-8/MRP-14 form noncovalent complexes.