Identification of chicken calbindin D28K pre-messenger RNA sequences by polymerase chain reaction

Influence of feeding and UVB exposition on the absorption mechanisms of calcium in the gastrointestinal tract of veiled chameleons (Chamaeleo calyptratus)

The purpose of this study was to investigate the influence of feeding and UVB exposition on the occurrence and distribution patterns of vitamin D receptors (VDR) and calbindin D28k (Cb-D28k) in the gastrointestinal tract of veiled chameleons. Thus, 56 veiled chameleon hatchlings were divided into six treatment groups: UV (with UVB exposure); No (no supplements, no UVB exposure); CaAUV (with calcium (Ca), vitamin A supplementation, UVB exposure); CaA (with Ca, vitamin A supplementation); CaADUV (with Ca, vitamin A, vitamin D supplementation, UVB exposure); and CaAD (with Ca, vitamin A, vitamin D supplementation). Animals were reared under the suspected conditions for 6 months on locust-based diets. Tissue samples of stomach, duodenum, ileum and colon were taken, and semi-quantitative immunohistochemical methods (IHC) were performed to detect Cb-D28k and VDR. VDR immunoreactions were higher in the luminal epithelium of the duodenum than in that of the ileum. VDR immunoreactions in the luminal epithelium were higher at the base of the villi of the duodenum as compared to the tip. Cb-D28k immunoreactions were mainly observed in the luminal epithelium of the duodenum. The two groups treated with all dietary supplements (CaADUV, CaAD) exhibited a higher Cb-D28k immunoreaction as those with no supplements and UVB exposure only. No immunoreaction for both proteins could be detected in the stomach. This study suggests that the duodenum plays an important role in the active transcellular absorption of Ca in veiled chameleons as shown by the immunohistochemical detection of VDR and Cb-D28k. Expression of Cb-D28k, in particular, appears to be regulated by dietary supplementation of vitamin D and vitamin A. VDRs, however, tended to be upregulated when animals were not supplemented with Ca, vitamin D and vitamin A. This may be due to the decreased Ca concentrations which caused vitamin D activation in the skin without any supplementation, but UVB exposure.

Reversible stepwise negative regulation of CYP1A1 in cultured rat epidermal cells

When serially passaged, rat epidermal keratinocytes lose the inducibility of CYP1A1 gene expression in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. In present experiments, loss of CYP1A1 inducibility occurred in a stepwise fashion, with some keratinocyte lines progressing through a transiently inducible state before becoming completely uninducible. The negative regulation occurred at the level of transcription, but the aryl hydrocarbon receptor (AhR) pathway appeared fully functional. Transient and stable transfection of uninducible cells with reporter constructs containing up to 4.2kb of the CYP1A1 5'-flanking region resulted in a TCDD-inducible increase in luciferase activity, despite no induction of the endogenous gene. Co-treatment with protein synthesis inhibitors and TCDD restored responsiveness of the endogenous CYP1A1 gene, indicating that the negative regulation was reversible and likely mediated by a labile protein. Together, these results demonstrate a novel mechanism of CYP1A1 transcriptional repression that does not involve any previously reported negative regulatory elements for CYP1A1.

Induction of CYP1A1 by serum independent of AhR pathway

CYP1A1 is implicated in the bioactivation of procarcinogens such as polycyclic aromatic hydrocarbons. To date, no physiological compounds have been described as inducers of this gene. In this study, we have examined the role of serum in the regulation of CYP1A1 gene expression. After treatment of CaCo-2 cells with fetal bovine serum, CYP1A1 mRNA level increased to the same extent as that observed after 3-methylcholanthrene induction. The same effect was obtained after treatment with adult bovine or human serum. Evaluation of hnRNA level performed on CaCo-2 cells indicates that CYP1A1 induction by serum acts at least in part through transcriptional activation. Promoter region containing the XRE (1.56 kb) was tested in the CAT assay. No stimulation of this reporter gene was detected after serum treatment. These results demonstrate for the first time that physiological compound(s) contained in serum induces CYP1A1 gene expression by transcriptional activation independent of the AhR pathway.

Transcriptional suppression of estrogen receptor gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

TCDD, the most potent congener of the polychlorinated dioxins, has been shown to be an antiestrogen. The mechanisms of TCDD-induced antiestrogenicity are still under investigation. In this study, we investigated the effects of TCDD on the expression of the estrogen receptor (ER) gene. We studied the levels of un-spliced ER transcript (hnRNA) as well as the ER mRNA in ovary, uterus and liver of TCDD-treated mice with different genetic backgrounds. To quantitate the ER hnRNA levels, the intron and exon boundary of ER hnRNA was amplified by competitive RT-PCR. The ER mRNA from these mice was quantitated by competitive RT-PCR amplifying exons separated by an intron. ER hnRNA and ER mRNA levels were quantitated 4 days after a single i.p. dose of TCDD (5 microg/kg) in female C57BL/6J (B6) mice, which carry the responsive allele to TCDD. TCDD treatment significantly (p < 0.05) suppressed the levels of ER hnRNA in the ovary (27.4%) and uterus (21.9%). The decreases in ER hnRNA were coordinated with significant (p < 0.01) decreases in ER mRNA in ovary (57.7%) and uterus (37.6%). There was a significant decrease (20.3%, p < 0.05) in liver ER mRNA, however, the changes of ER hnRNA in liver were not significant. The coordinated decreases in ER hnRNA and mRNA in TCDD-treated mice suggest a suppression of transcription of the ER gene. We performed the same study on DBA/2J (D2) mice, which possess the "non-responsive" allele of the aryl hydrocarbon receptor (AhR). These mice demonstrated no significant decrease in either the ER mRNA or hnRNA after TCDD treatment. Overall, these results suggest that TCDD suppresses the gene expression of the ER receptor by decreasing its transcription, and the AhR plays an important role in mediating this response.

1,25(OH)2D3-dependent regulation of calbindin-D28k mRNA requires ongoing protein synthesis in chick duodenal organ culture

Organ culture of 19-day-old chick embryo duodena was utilized to evaluate the mechanism of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-dependent calbindin-D28k (CaBP) expression. Duodenal CaBP and 1,25(OH)2D3 receptor (VDR) expression were assessed by Western blot analysis, while CaBP and VDR mRNA levels were determined by Northern blot analysis. In untreated duodena, both VDR protein and mRNA were present, while CaBP protein and mRNA were undetectable. Treatment of cultured duodena with 25 nM 1,25(OH)2D3 resulted in detectable CaBP mRNA after 4 h which continued to increase during a 24 h time period. Under these conditions, localization of [3H-1 beta]1 alpha,25(OH)2D3 in duodenal chromatin is rapid (< or = 30 min). Thus, the delayed accumulation of detectable CaBP mRNA cannot be explained by slow nuclear binding of 1,25(OH)2D3. The inclusion of 1.6 microM actinomycin D in the organ culture partially inhibited the 1,25(OH)2D3-regulated increase in CaBP mRNA, which implies that there is a transcriptional component involved in the increased CaBP mRNA levels. Similarly, quantitative polymerase chain reaction studies allowed the detection of CaBP pre-mRNA and mRNA sequences 1 h after hormone treatment, suggesting that CaBP gene transcription is initiated rapidly. Treatment of cultures with 36 microM cycloheximide 1 h prior to 1,25(OH)2D3 addition resulted in superinduction of VDR mRNA levels but sharply reduced CaBP steady-state mRNA levels. This dramatic reduction in CaBP mRNA reveals that 1,25(OH)2D3-mediated CaBP expression is dependent on ongoing protein synthesis. Thus, we propose that a labile auxiliary protein or other cofactor, which may or may not be 1,25(OH)2D3-dependent, is necessary for 1,25(OH)2D3-mediated CaBP gene transcription in chick duodena.

Different mechanisms of regulation of the human stromelysin and collagenase genes. Analysis by a reverse-transcription-coupled-PCR assay

Tissue-remodeling processes are largely controlled by matrix metalloproteinases that degrade the extracellular components of connective tissues. In this study, gene regulation of two human matrix metalloproteinases, stromelysin and collagenase, was investigated by a reverse-transcription-coupled (RT)-PCR assay. Here, signals from both the heterogenous nuclear RNA (hnRNA) and mRNA are amplified, allowing the regulation of gene expression to be divided between transcriptional and/or post-transcriptional control. In confluent human lung fibroblast cultures, tumor-necrosis factor-alpha and 12-O-tetradecanoyl-phorbol 13-acetate induce stromelysin and collagenase genes transcriptionally. Interleukin-1 beta (IL-1 beta) induces stromelysin gene transcription but has little, if any, effect on the collagenase gene transcription in cells cultured in the presence of 10% serum. By a competitive RT-PCR assay, the IL-1 beta-reated cultures contain an average of 60 molecules of stromelysin mRNA/cell and the untreated cultures about 1.9 molecules/cell. In serum-starved cells, both IL-1 beta and serum induce transcription of the collagenase gene. Also, in serum-starved cells type II collagen can induce collagenase mRNA but not stromelysin mRNA. Inhibition of protein synthesis with cycloheximide induces stromelysin gene transcription but has no effect on the collagenase gene. These data indicate different mechanisms of regulation of the human stromelysin and collagenase genes in cultured cells.

A new diagnostic method for the detection of endogenous Rous-associated virus-type provirus in chickens

A quick and simple method has been developed to detect the presence or absence of the endogenous Rous-associated virus (RAV) element ev1 in chickens. The procedure consists of a one-tube multiplex polymerase chain reaction (PCR) involving three oligonucleotide primers that are specific for the upstream flanking region, the long terminal repeat (LTR), and the downstream flanking region of the proviral insert, respectively. The multiplex reaction allows for the unambiguous discrimination between ev1+/ev1+ homozygote, ev1-/ev1- homozygote, and ev1+/ev1- heterozygote birds. The method works best with purified genomic DNA as substrate, but can also be used with rapidly prepared, "crude" DNA samples. The combination of speed with the safety of a nonradioactive procedure, and the ability to perform large numbers of assays by a semi-automated procedure, make this method attractive for large-scale screening projects. The ev1 locus has been used as a model system to demonstrate the feasibility of the PCR diagnostic approach. However the same principle should be applicable to the analysis of other RAV-type ev loci, as well as endogenous elements belonging to other families of viruses as sequence information for the flanking regions of these inserts becomes available.

Induction of Calbindin-D28K by 1,25-dihydroxyvitamin D3 in cultured chicken intestinal cells

Intestinal cells from chicken embryos were grown in chemically defined, serum-free medium. The majority of cultured cells exhibits an epithelial-like morphology. As demonstrated by indirect immunofluorescence, the epithelial cells, and not the contaminating fibroblasts, express Calbindin-D28K only after 1,25-dihydroxyvitamin D3, the hormonally active form of vitamin D, is added to the culture medium. The highly sensitive reverse transcriptase-polymerase chain reaction shows that both Calbindin-D28K mRNA and the corresponding primary unprocessed transcripts (pre-mRNA) are dramatically increased in cultured intestinal cells treated with 1,25-dihydroxyvitamin D3, thus indicating that Calbindin-D28K is induced by the increased rate of transcription of the corresponding gene.

Evaluation of a putative vitamin D response element in the avian calcium binding protein gene

A primary response of the avian intestine to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] is increased synthesis of a 28-kD calcium-binding protein, calbindin-D28k (CaBP). This study examined whether 1,25-(OH)2D3 regulates CaBP gene transcription by an interaction of the vitamin D receptor (VDR) with a vitamin D-responsive element (VDRE) in the CaBP promoter. A genomic clone of CaBP containing about 1 kb of 5'-flanking DNA and 13 kb of the structural gene was isolated. 5'-Flanking DNA from -320 to -306 had considerable sequence similarity to VDREs identified in other genes. Indeed, a portion of the CaBP gene containing this region (-743 to +47) linked to a growth hormone reporter construct elicited a 1,25-(OH)2D3-dependent, VDR-dependent increase in reporter expression in transiently transfected chicken embryo fibroblasts. However, deletion analysis demonstrated that the sequences responsible for this induction reside 3' to -133 and the putative VDRE at -320 to -306 was not involved in the response. Furthermore, transfection of heterologous promoter constructs consisting of a Ban I fragment (-354 to -252) linked to the Herpes simplex thymidine kinase promoter revealed no effect of this region on reporter expression. Gel mobility shift analysis confirmed that this putative VDRE in the CaBP promoter was not a high-affinity binding site for VDR. Consequently, functional significance with respect to the primary induction of CaBP by 1,25-(OH)2D3 cannot be ascribed to this region of the CaBP promoter.

Dietary restriction of calcium, phosphorus, and vitamin D elicits differential regulation of the mRNAs for avian intestinal calbindin-D28k and the 1,25-dihydroxyvitamin D3 receptor

We investigated the regulation of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-induced calbindin-D28k (CaBP) and of the vitamin D receptor (VDR) by evaluating CaBP protein, CaBP mRNA, and VDR mRNA under conditions of altered intake of vitamin D, calcium, or phosphorus. Chickens were maintained for 10 days on one of four diets: vitamin D-deficient, normal (1.0% Ca and 1.1% P), low calcium (0.1% Ca and 1.2% P), and low phosphorus (1.1% Ca and 0.3% P). CaBP was undetectable in D-deficient duodena and was elevated above normal values by low-calcium (3.1-fold) and low-phosphorus (2.3-fold) intake. Contradictory to published data, we observed a correlation between CaBP protein and mRNA levels in that the CaBP mRNA was absent in D-deficient intestine and augmented threefold and twofold in low-calcium and low-phosphate duodena, respectively. In contrast, VDR mRNA concentrations were identical in vitamin D-deficient and normal duodena, implying that intestinal VDR is not dependent upon 1,25-(OH)2D3 for basal expression. Chickens fed a low-phosphorus diet displayed a twofold increase in VDR mRNA, but those fed a low-calcium diet exhibited a dramatic decrease in VDR mRNA. These data show that CaBP mRNA and protein levels are modulated in a tightly coupled fashion, and they are consistent with previous conclusions that augmented circulating 1,25-(OH)2D3 stimulates CaBP expression when dietary calcium or phosphorus is limiting. However, a more complex regulation of VDR expression occurs in that low-phosphorus restriction enhances VDR mRNA levels, possibly via increased circulating 1,25-(OH)2D3. Conversely, reduced dietary calcium diminishes VDR mRNA despite increased circulating 1,25-(OH)2D3, indicating that another factor, such as parathyroid hormone, is a predominant downregulator of VDR.