Analysis of rat vitamin D-dependent calbindin-D28k gene expression

Localization of gene expression of calbindin in the brain of adult rats

Localization of gene expression of calbindin, a cytosolic calcium-binding protein, was examined throughout the adult rat brain by in situ hybridization with cDNA probes. The gene was expressed most intensely in the Purkinje cells in the cerebellum, intensely in the granule cells of the dentate gyrus, and moderately in the inferior olivary nucleus, in the nuclei of the trapezoid body, in the medial part of the lateral habenular nuclei, entorhinal cortex and in the mammillary nuclei. In addition, weak expression of the gene was widespread in the forebrain and brainstem gray matter, and also in small cells in the spinal posterior horn as well as the ependymal cells. The widespread and heterogeneous expression of the gene in the brain suggests that calbindin is differentially involved in calcium-regulated phenomena in different neurons.

Calbindin-D28K-containing neurons in animal models of neurodegeneration: possible protection from excitotoxicity

Brain levels of the calcium binding protein Calbindin-D28K (CaBP28K) and CaBP28K mRNA were measured for various animal models of neurodegenerative diseases (MPTP-treated C57BL/6J mice and Sprague-Dawley rats receiving striatal/intraperitoneal kainic acid or quinolinic acid into the nucleus basalis magnocellularis). Brain areas were tested (radioimmunoassay, Western blot, slot blot, and Northern blot) for levels of CaBP28K and CaBP28K mRNA. The various models did not exhibit any changes in protein or mRNA levels from the controls, suggesting that CaBP28K-containing neurons were not lost after exposure to these neurotoxins. Immunocytochemical characterization of the substantia nigra of the MPTP-treated mice revealed that there was significant dopaminergic cell loss in this brain area after MPTP treatment. The majority of dopaminergic neurons that degenerated did not contain CaBP28K. The small percentage of surviving neurons were CaBP28K-positive. These results suggest that the presence of CaBP28K may protect neurons from calcium-mediated neurotoxicity.

Transient appearance of Ca-binding protein (spot 35-calbindin) in bronchial epithelial cells, thyroid parafollicular cells and thymic epithelial cells during the development of rats

Tracheobronchial epithelium, thyroid organ, thymus, of the developing rats were examined by immunohistochemistry using anti-spot 35 calbindin-antiserum. At E 14, weak to moderate immunoreactivity for spot 35-calbindin was detected in the airway epithelia of the distal half of the trachea and the extrapulmonary bronchus. The immunoreactive cells increased in intensity at E 16-E 21, but decreased markedly after birth. These cells were non-ciliated cells and comprised a majority of the epithelial cells especially in the ventral/cartilaginous portion of the airway. They were characterized by microvilli, vacuoles, granular and agranular endoplasmic reticulum. Typical ciliated cells, which were much less numerous than the immunopositive non-ciliated cells, were immunonegative. In thyroid gland, calbindin-immunoreactive cells first appeared at E 18. They increased in number at E 20-P 1 and decreased gradually after P 7. These cells were the parafollicular cells characterized by numerous secretory granules and situated in close proximity to the basal surface of the follicular cells. In the thymus, immunoreactive cells appeared in the thymic medulla at E 20. They increased in number at P 1, but decreased gradually after P 7. They were stellate in shape and had vesicles, vacuoles, intermediate filaments and represented a subpopulation of thymic reticular epithelial cells. Such a transient appearance of spot 35-calbindin in these cells suggests that this protein may be involved in the regulation of differentiation or may be involved in the process of secretion during the limited developmental period.

Acute actions of 1,25-dihydroxyvitamin D3 upon chick pancreatic calbindin-D28K

We have compared the relative responsiveness of pancreatic, intestinal and renal tissue calbindin-D28K protein content to the stimulatory actions of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in vitamin D-deficient (-D) chicks. Tissue concentrations of calbindin-D28K were undetectable in the -D chick intestine but present, albeit at low concentrations (less than 1 microgram CaBP/mg protein) in the -D kidney and pancreas. Intestinal, pancreatic and renal calbindin-D28K content was stimulated 318, 9.8 and 2.9 fold respectively, 48 hours after -D chicks received a single dose of 1,25(OH)2D3 [6.5 nmol/animal]. The pancreatic calbindin-D28K content could be significantly stimulated as early as 5 hours after 1,25(OH)2D3 administrations in vivo. These findings support the contention that the pancreas is a target for vitamin D, and is consistent with the view that calbindin-D28K plays a role in normal pancreatic functions.

Vitamin D independence of small calcium-binding proteins in nonclassical target tissues

The presence and regulation of Ca-binding proteins (CaBPs) were investigated in newly identified 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] target tissues. 45Ca(2+)-blot analysis of proteins in normal rats yielded a 45Ca2+ band comigrating with authentic calmodulin. Additionally, a parvalbumin-like band (mol mass = 15.4 +/- 0.3 kDa) was prominent in prostate, and a strong unidentified 45Ca2+ band was always evident in the testis (mol mass = 23.5 +/- 0.7 kDa). Lung, bladder, and especially prostate demonstrated 45Ca2+ bands comigrating with the intestinal vitamin D-related CaBP (CaBP-D9K; mol mass = 10.9 +/- 0.5 kDa). Most tissues (including testis, heart, and lung) exhibited low levels of a 45Ca2+ band comigrating with the renal CaBP-D28K (mol mass = 28.3 +/- 0.4 kDa). Importantly, 45Ca2+ binding to all detectable CaBPs was unchanged in these four tissues in vitamin D-deficient rats, despite substantial downregulation of the intestinal CaBP-D9K and renal CaBP-D28K. Neither immunoblot analysis (rabbit anti-rat renal CaBP-D28K) nor Northern analysis (rat brain CaBP-D28K cDNA) provided evidence for coidentity of the 28-kDa 45Ca2+ band with the CaBP-D28K. Conversely, immunoblot analysis of lung, but not prostate, cytosol provided evidence for specific immunocross-reactivity to rabbit anti-rat intestinal CaBP-D9K. Immunoblot analysis of the 9-kDa CaBP in lung further confirmed its vitamin D independence. In conclusion, the vitamin D independence of the CaBPs in these putative new 1,25(OH)2D3 targets suggests the absence of an obligatory relationship between 1,25(OH)2D3 effects and CaBP induction therein.(ABSTRACT TRUNCATED AT 250 WORDS)

Up regulation of calbindin-D28K mRNA in the rat hippocampus following focal stimulation of the perforant path

Calbindin-D28K is a constitutive Ca2(+)-binding protein expressed in hippocampal neurons that are resistant to various forms of excitotoxic injury. However, the local factors controlling calbindin-D28K expression within the central nervous system are unknown. We report that neuronal excitation via the perforant path leads to an increased expression of calbindin-D28K mRNA within dentate granule cells. This response is related specifically to stimulation that induces prolonged periods of bursting afterdischarges and precedes cellular injury. The up regulation of calbindin-D28K mRNA occurs during the type of neuronal activation associated with elevated cytosolic Ca2+ and suggests that the maintenance of Ca2+ homeostasis includes a system of feedback control at the level of gene expression.

Calcium binding protein (calbindin-D28k) and glutamate decarboxylase gene expression after kindling induced seizures

In order to determine whether calcium binding protein (calbindin-D28k or CaBP) and glutamate decarboxylase (GAD) may be involved in the process underlying the generation of seizure activity, changes in CaBP protein and mRNA and in GAD mRNA were examined in the kindling model of epilepsy. Following amygdaloid (AK) and commissure (CK) kindling significant decreases in the concentration of CaBP of 20% and 30%, respectively, were specifically observed in the hippocampal formation. However, using a cDNA specific to mammalian CaBP, Northern analysis of poly(A+) RNA and slot blot analysis of total RNA revealed no changes in the levels of CaBP mRNA in hippocampus, subcortical area (including amygdala, substantia nigra and striatum) or cerebellum of rats sacrificed 30 min, 1 h, 6 h or 24 h after the last kindled seizure. Similarly when these blots were reprobed with a cDNA specific to mammalian GAD, no changes in GAD gene expression were observed. However, fos gene expression was markedly enhanced at 1 h after seizure. We also tested whether changes in CaBP or GAD mRNA could be detected at any of the various stages of the kindling process. Slot blot analysis of cortex, subcortical structures and hippocampus revealed no changes in CaBP or GAD mRNA during the course of commissure kindling. In situ hybridization studies with GAD and CaBP 35S-labeled antisense probes also indicated no obvious changes upon visual analysis of autoradiographs. However, when silver grains were counted, significant changes in GAD mRNA in individual cells in hippocampus and substantia nigra were noted after kindling induced epilepsy. Our results indicate that, unlike fos gene expression, prominent alterations in GAD and CaBP mRNA in gross brain regions (as measured by slot blot and Northern blot analyses) are not observed in the kindling process. However, our in situ hybridization studies suggest that changes in GAD mRNA in individual cells may be involved in the process underlying kindling induced seizure activity.

Modulation of quail intestinal and egg shell gland calbindin (Mr 28,000) gene expression by vitamin D3, 1,25-dihydroxyvitamin D3 and egg laying

The effects of vitamin D3 sources, egg production and egg cycle on the genomic expression of calbindin (Mr 28,000) in the intestine and egg shell gland (ESG) of quail were characterized by Northern blot and solution hybridization, using synthetic oligonucleotide probe. In vitamin D3- or 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)-fed quail, onset of egg production induced duodenal and ESG calbindin mRNA and calbindin synthesis. Duodenal calbindin mRNA was slightly higher during the period of shell calcification as compared with the period during which shells were not formed (ESG inactivity). ESG calbindin mRNA was markedly higher during the period of shell calcification than of ESG inactivity. Increasing dietary intake of [3H]1 alpha-hydroxyvitamin D3 increased the duodenal, but not ESG, content of 1,25-(OH)2D3 and calbindin. Duodenal calbindin and its mRNA were absent in vitamin D-deficient quail and were not affected by egg laying. ESG calbindin in the vitamin D-deficient quail was not affected by egg laying, but calbindin mRNA increased in the vitamin D-deficient birds during shell calcification. The results suggest that: (a) intestinal calbindin mRNA and calbindin are induced and/or regulated, either directly or indirectly, by 1,25-(OH)2D3; (b) intestinal calbindin and its mRNA are further induced at the onset of egg laying by an additional stimulator besides 1,25-(OH)2D3; (c) 1,25-(OH)2D3 is required for the expression of the latter stimulator; (d) ESG calbindin mRNA and calbindin are induced in egg-laying birds by a stimulator associated with the egg cycle; and (e) the induction of ESG calbindin mRNA does not need vitamin D metabolites, but 1,25-(OH)2D3 is required for the translation of the mRNA.

Vitamin D-independent expression of chick brain calbindin-D28K

A combination of calbindin-D28K-specific cDNA probes and polyclonal antisera were used to investigate expression of the calbindin-D28K in the vitamin D-deficient avian brain in vivo in response to pharmacological doses of the vitamin D3 metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Serum calcium levels were stimulated (2-fold) and intestinal calbindin-D28K expression (between 10- and 30-fold) by 1,25(OH)2D3 (6.5 nmol/animal) after 12 h. In marked contrast, steady-state whole brain levels of calbindin-D28K as judged by enzyme-linked immunoassay (ELISA) remained constant. Northern gel analysis revealed that three species of calbindin-D28K mRNA (2.0, 2.6 and 3.1 kb) were present a priori in the vitamin D-deficient chick brain and that administration of pharmacological doses (6.5 nmol/animal) of 1,25(OH)2D3 failed to influence their relative abundance. Separate but parallel dot blot hybridization analyses also confirmed that brain calbindin-D28K-mRNA levels were not influenced by 1,25(OH)2D3. These experiments demonstrate at the molecular level that, in contrast to the intestine, the gene encoding calbindin-D28K in the brain is regulated by mechanism(s) or factors which are independent of vitamin D status.

Evidence for calcium-reducing and excito-protective roles for the calcium-binding protein calbindin-D28k in cultured hippocampal neurons

Neuronal systems for calcium homeostasis are crucial for neuronal development and function and may also contribute to selective neuronal vulnerability in adverse conditions such as exposure to excitatory amino acids or anoxia, and in neurodegenerative diseases. Previous work demonstrated the presence and differential distribution of calcium-binding proteins in the CNS. We now report that a subpopulation of neurons in dissociated cell cultures of embryonic rat hippocampus expresses calbindin-D28k (Mr 28,000 calcium-binding protein) immunoreactivity and that these neurons are relatively resistant to neurotoxicity induced by either glutamate or calcium ionophore. Direct comparisons of dynamic aspects of intracellular calcium levels and calbindin-D28k immunoreactivity in the same neurons revealed that calbindin-D28k-positive neurons were better able to reduce free intracellular calcium levels than calbindin-D28k-negative neurons. These findings indicate that the differential expression of calbindin-D28k in hippocampal neurons occurs early in development and may be one determinant of selective neuronal vulnerability to excitotoxic insults.

Calcium binding protein (calbindin-D28k) gene expression in the developing and aging mouse cerebellum

Calbindin-D28k (CaBP28k) protein and gene expression were examined in the mouse cerebellum during development and aging utilizing slot and Northern blot hybridization analyses for mRNA levels, Western blot analysis and radioimmunoassay (RIA) for protein levels, and by in situ studies using immunocytochemistry and hybridization cytochemistry on prepared tissue sections. Samples were obtained and analyzed from C57BL/6J mice aged day of birth and postnatal weeks 1, 2, 4, 8, and 120. A specific cDNA and antibody for CaBP28k were utilized in these studies. Analysis of mRNA levels showed a steady rise in CaBP28k mRNA from birth to a peak at postnatal week (3.4-fold increase) and then a decline to steady-state levels at postnatal weeks 4 and 8 (47% reduction of peak level) followed by a reduction of CaBP28k mRNA to birth levels at postnatal week 120. The specificity of the changes observed was tested by reprobing blots with beta-actin cDNA. Analysis of CaBP28k protein levels by both Western blot and RIA showed a similar pattern. In situ analysis of CaBP28k mRNA levels, based on hybridization signal (silver grains per cell), demonstrated a rise in cellular CaBP28k mRNA levels which peaked at postnatal week 2 (416.9 +/- 52.1) and then declined to steady-state levels by postnatal weeks 4 and 8 (267.4 +/- 35.8). Cellular CaBP28k mRNA levels exhibited a dramatic reduction in the aged cerebellum (postnatal week 120; 78.3 +/- 16.0). The levels of cellular CaBP28k mRNA corresponded to the intensity of immunoreactive CaBP28k localized by immunocytochemistry. The results are consistent with the hypothesis that CaBP28k may play a critical role in Purkinje cell maturation and maintenance.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular gene expression for calbindin-D28k in mouse kidney

Gene expression for calbindin-D28k, the 28,000 relative molecular mass vitamin D-dependent calcium-binding protein, was measured in cells of the murine nephron by in situ hybridization on tissue sections (hybridization cytochemistry). Radiolabeled (35S-UTP), single-stranded RNA complementary to calbindin-D28k-mRNA (probe RNA) was prepared from linearized cDNA template and used for the hybridizations. Autoradiography was carried out and cellular levels of hybridization signal (silver grains) were quantified. After correction for background the concentration of silver grains was more than 350% greater in the distal tubule than in either the proximal tubule or the glomerulus. The relative cellular level of mRNA in the cytoplasm, as reflected in silver grains/cell, of the distal tubules with probe RNA was 3.4 times greater than that with control RNA. Cells of the distal tubule were the only apparent sites of specific hybridization with probe RNA. The presence of calbindin-D28k-mRNA in the distal tubule corresponded to the localization of calbindin-D28k by immunocytochemistry.

Poly- and monoclonal antibodies against recombinant rat brain calbindin D-28K were produced to map its selective distribution in the central nervous system

Many processes in the CNS depend on calcium. The calcium signal is transduced into an intracellular response via Ca2(+)-binding proteins, including calbindin D-28K. In many laboratories, polyclonal antibodies against chicken intestinal calbindin D-28K have been used to study its localization in the brain (normal and degenerated) of various species, including humans, but some of these antisera cross-reacted with other proteins, including calretinin. We purified recombinant rat brain calbindin D-28K to raise antisera in rabbits and purified a recombinant rat-chicken calbindin D-28K hybrid protein to immunize mice for the generation of monoclonal antibodies. These antisera were highly specific for calbindin D-28K, as demonstrated by two-dimensional Western blotting analysis. Immunohistochemical analyses combined with in situ hybridization studies demonstrated that calbindin D-28K in the Purkinje cells of the cerebellum is independent of vitamin D. The antibodies described here will be important tools for studying the regulation of expression of calbindin D-28K and its biological function in the brain and in the PNS.

Evolution of EF-hand calcium-modulated proteins. I. Relationships based on amino acid sequences

The relationships among 153 EF-hand (calcium-modulated) proteins of known amino acid sequence were determined using the method of maximum parsimony. These proteins can be ordered into 12 distinct subfamilies--calmodulin, troponin C, essential light chain of myosin, regulatory light chain, sarcoplasmic calcium binding protein, calpain, aequorin, Stronglyocentrotus purpuratus ectodermal protein, calbindin 28 kd, parvalbumin, alpha-actinin, and S100/intestinal calcium-binding protein. Eight individual proteins--calcineurin B from Bos, troponin C from Astacus, calcium vector protein from Branchiostoma, caltractin from Chlamydomonas, cell-division-cycle 31 gene product from Saccharomyces, 10-kd calcium-binding protein from Tetrahymena, LPS1 eight-domain protein from Lytechinus, and calcium-binding protein from Streptomyces--are tentatively identified as unique; that is, each may be the sole representative of another subfamily. We present dendrograms showing the relationships among the subfamilies and uniques as well as dendrograms showing relationships within each subfamily. The EF-hand proteins have been characterized from a broad range of organismal sources, and they have an enormous range of function. This is reflected in the complexity of the dendrograms. At this time we urge caution in assigning a simple scheme of gene duplications to account for the evolution of the 600 EF-hand domains of known sequence.

Comparison of receptor binding, biological activity, and in vivo tracer kinetics for 1,25-dihydroxyvitamin D3, 1,25-dihydroxyvitamin D2, and its 24 epimer

Scatchard analyses of 1,25-dihydroxyvitamin D receptors (VDR) from chick and rat intestine, bovine thymus, pig kidney cells (LLC-PK1), and human breast cancer cells (T-47D) demonstrated that 1,25-dihydroxyvitamin D3 (1,25-D3) and 1,25-dihydroxyvitamin D2 (1,25-D2) had equal affinities for VDR. 24-Epi-1,25-dihydroxyvitamin D2 (24-epi-1,25-D2) exhibited affinities for VDR equal to that of 1,25-D2 and 1,25-D3 in most of these tissues. Scatchard analysis with 24-epi-[3H]1,25-D2 underestimated total VDR by 50-70% in rat intestine, LLC-PK1, and T-47D cells. The biological activity of 24-epi-1,25-D2 was found to be only 30-70% of 1,25-D3 and 1,25-D2 as determined by in vivo induction of intestinal calcium transport and bone calcium resorption in the rat and in vitro induction of 23- and 24-hydroxylase activities in T-47D cells. In vivo tracer kinetic studies demonstrated that in the rat 1,25-D3 and 1,25-D2 kinetics were similar, whereas 24-epi-1,25-D2 had a 25% shorter plasma half-life and was cleared from the body 2.8 times faster than the natural hormones. This more rapid clearance of 24-epi-1,25-D2 along with reduced VDR binding appears to explain the reduced biological activity of 24-epi-1,25-D2. Our data clearly demonstrate that although there are differences in side chain structure between 1,25-D2 and 1,25-D3, the VDR binding, biological activity, and whole body tracer kinetics of these two metabolites are virtually identical. However, movement of the 28 methyl of 1,25-D2 from its natural S configuration to the R configuration significantly alters the activity of this hormone.

Cloning and analysis of calbindin-D28K cDNA and its expression in the central nervous system

The vitamin D-dependent calcium-binding protein (CaBP), calbindin-D28K (CaBP28K), is present in the central nervous system (CNS), the sensory system, and kidneys of mammals and birds. Recent studies have indicated that several other CaBPs of very similar Mrs are also present in the CNS. This study was carried out to establish the relationship between CaBP28K and other CaBP, particularly spot 35, to provide a basis for further studies on the tissue-specific regulation and distribution of CaBP28K. A cloned pC28 cDNA was isolated from a rat brain expression library using synthetic oligodeoxyribonucleotides (oligos) complementary to rat spot-35 mRNA. This pC28 cDNA had an open reading frame (ORF) of 783 nucleotides (nt) coding for a 261-aa, 30-kDa protein. There was 100% homology between the pC28 sequence and that of the CaBP28K isolated from rat brain cDNA library using a chicken intestinal CaBP28K probe (Hunziker and Schrickel, 1988). Thus the aa and nt sequences of rat CaBP28K and spot 35 are identical. Primer extension studies and Northern analyses show that the major species of CaBP28K mRNA contains a 5'-untranslated region of 132 nt, a coding region of 261 codons and a 3'-untranslated region of 804 nt without the poly(A) tail. The rat CaBP28K probe hybridizes to one major RNA species (1.9 kb) and two minor ones (2.8 and 3.2 kb) in the cerebellum, hippocampus, retina and kidney. This distribution correlates well with the distribution of CaBP28K itself in these organs. Comparison of the genomic organization of the CaBP28K gene with that of other members of the 'EF-hand' CaBP family emphasizes that the CaBP28K gene diverged from the others at the first duplication of the gene encoding one CaBP domain. All the members of the 'EF-hand' gene CaBP family evolved by exon shuffling and specific genomic rearrangements.

A study of proteins in the auditory system of rabbits using two-dimensional gels: identification of glial fibrillary acidic protein and vitamin D-dependent calcium binding protein

Two-dimensional gel electrophoresis and computerized optical densitometry were employed to compare the relative content of proteins across major auditory brain regions in rabbits. Areas examined included the dorsal and ventral cochlear nuclei which receive the primary afferents from the organ of Corti, the lateral superior olivary nucleus which has strong reciprocal relationships with the cochlear nucleus, and the successively more rostral projections of the auditory pathways to inferior colliculus, medial geniculate and auditory cortex. Twelve proteins demonstrated significant decreases and 5 proteins significant increases in content at successively more rostral levels of the auditory system, including 2 proteins which were highly localized to the cochlear nuclei and 2 proteins greatest in amounts in the auditory cortex. One protein which was localized to the cochlear nuclei and lateral superior olive (molecular weight (MW) = 50.3, isoelectric point (pI) = 5.7) was identified as the glial fibrillary acidic protein by reaction of specific antisera on blots. Antisera to the vitamin D-dependent calcium binding protein reacted specifically with one protein (MW = 27.2, pI = 4.8) which was greatest in amount in the lateral superior olive (LSO) versus other auditory regions examined. The significance of these findings rests in the potential for identifying specific markers for cellular elements that are important in auditory function and which might be lost as a consequence of developmental abnormalities or other traumas.