Structural characterization of the rat cysteine-rich intestinal protein gene and overexpression of this LIM-only protein in transgenic mice

Cysteine-rich intestinal protein (CRIP) has a double zinc-finger motif called the LIM domain. The most elementary member of the Group 2 LIM-only protein family, CRIP was initially identified as a developmentally regulated intestinal gene. Subsequently, it was found to be highly expressed in immune cells. The structural portion of the rat CRIP gene is comprised of five exons extending over i.8 kb, with the two zinc-finger motifs of the LIM domain being divided among the first three exons. In addition to transcriptional regulatory elements previously identified in the promoter, consensus sequences for AP-1, AP2, Sp-1, and a glucocorticoid response element are located within the first intron. We have developed a line of transgenic mice that overexpress the rat CRIP gene with an expression profile that mirrors that of the endogenous gene. Driven by the homologous rat CRIP promoter, expression increased threefold to sevenfold in intestine, thymus, spleen, and lung over endogenous levels. The transgenic mice had only about 50% of the white blood cell count found in nontransgenic animals. Differential leukocyte counts showed transgenic animals had proportionately fewer lymphocytes and more monocytes, eosinophils, neutrophils. Flow cytometry data suggested that mice overexpressing CRIP have more CD4+/CD8+ thymic lymphocytes. These data suggest that CRIP plays a significant role in differentiation or maturation of cells with rapid turnover such as those found in the intestine and immune system.

Metallothionein knockout and transgenic mice exhibit altered intestinal processing of zinc with uniform zinc-dependent zinc transporter-1 expression

A role for metallothionein in intestinal zinc absorption has been the subject of considerable debate. If metallothionein affects zinc absorption, then those factors that induce metallothionein synthesis (e.g., heavy metals, hormones) should alter zinc absorption and homeostasis. The present studies used metallothionein transgenic mice (overexpressing) and metallothionein knockout mice (no expression of metallothionein-1 or metallothionein-2) to examine directly the effects of metallothionein on zinc absorption, independent of secondary effects that could be caused by metallothionein inducers. Zinc absorption was examined by administering a single oral zinc dose (0.5 mmol/kg) by feeding tube to metallothionein transgenic and metallothionein knockout mice and measuring the serum zinc concentration. Two hours after the dose, the serum zinc concentration was 2.3 times higher in metallothionein knockout mice than in their control strain. Conversely, the concentration was elevated only one third as much in the metallothionein transgenic mice as in their controls after the zinc dose. We found that the serum zinc concentration was inversely related to the level of metallothionein protein. The intestinal zinc content was higher in the metallothionein knockout mice, however, suggesting that metallothionein did not reduce zinc absorption by simply sequestering zinc in the mucosa. The expression of the zinc transporter ZnT-1 was directly related to the serum zinc level and was independent of the level of metallothionein. These results further support metallothionein as an important component for reducing the efficiency of zinc absorption at elevated zinc intakes.

A role of zinc in the regulation of gene expression

Zn, without question, has important functions related to gene expression. Newer technologies applied to address these functions are providing answers relating to the importance of this micronutrient in human and animal health.

Regulation of the zinc transporter ZnT-1 by dietary zinc

The understanding of mechanisms controlling zinc absorption and metabolism at the molecular level has advanced recently. Kinetics of zinc transport have been investigated for many years, but only recently have genes coding for proteins thought to be involved in the transport process been cloned. Four putative zinc transporters, known as ZnT-1 through ZnT-4, have now been described. Among these transporters, only ZnT-1 is ubiquitously expressed. In this report, we examine the pattern of ZnT-1 expression in the intestine and analyze the regulation of ZnT-1 by dietary zinc in both the intestine and liver. Immunofluorescence demonstrated that intestinal ZnT-1 was most abundant at the basolateral surface of enterocytes lining the villi of the duodenum and jejunum. By Western blot analysis, intestinal and liver ZnT-1 protein migrated as a 42- and 36-kDa protein, respectively. Dietary zinc supplementation elevated the level of intestinal ZnT-1 mRNA and protein approximately 50% and 10%, respectively, but had no effect in the liver. In response to an acute oral zinc dose, the level of intestinal ZnT-1 mRNA was up-regulated 8-fold, without a corresponding increase in ZnT-1 protein. Conversely, the acute oral dose did not affect liver ZnT-1 mRNA, but resulted in a 5-fold increase in liver ZnT-1 protein. These results represent studies on the expression of intestinal and hepatic ZnT-1 in an intact animal model. The data suggest that ZnT-1 is at least part of the mechanism by which dietary zinc is absorbed and that, despite the zinc responsiveness of the ZnT-1 gene, additional factors may be regulating the steady-state level of ZnT-1 transporter protein.

Metallothionein expression is increased in monocytes and erythrocytes of young men during zinc supplementation

The metallothionein gene is transcriptionally regulated by zinc. Consequently, metallothionein has potential for serving as an index of dietary zinc status in humans. To examine this possibility, an enzyme-linked immunoassay (ELISA) based on a sandwich approach that utilizes monoclonal and chicken egg yolk antibodies was used to compare the response of erythrocyte metallothionein protein levels with the response of monocyte metallothionein mRNA levels as measured by competitive reverse transcriptase-polymerase chain reaction (CRT-PCR) during zinc supplementation. Young male subjects participated in an 18-d supplementation study in which zinc was provided at 50 mg/d. Control subjects received a placebo. The zinc supplement resulted in significantly greater erythrocyte metallothionein levels by d 8 of supplementation compared with controls. Monocyte metallothionein mRNA levels were significantly greater than those of controls by d 2 of supplementation. Both remained elevated through d 18. They returned to base line by 8 and 4 d after supplementation, respectively. The plasma zinc concentration was significantly greater than in controls by d 6 and had returned to control levels by d 22 of supplementation. The results presented here show that both monocyte metallothionein mRNA and erythrocyte metallothionein protein concentrations change in human subjects in response to elevated dietary zinc intake and that monocyte metallothionein mRNA responds more rapidly to elevation of dietary zinc status than erythrocyte metallothionein protein. Consequently, both erythrocyte metallothionein and monocyte metallothionein mRNA may prove to be measures useful for assessment of either zinc depletion or the bioavailability of zinc supplements.

Mammalian zinc transporters

Genes that are involved in mammalian zinc transport recently have been cloned. These all predict proteins with multiple membrane spanning regions, and most have a histidine-rich intracellular loop. ZnT-1 was the first cloned and is associated with zinc efflux. It is found in all tissues examined, and, at least in some, ZnT-1 expression is regulated by dietary zinc intake. In enterocytes of the small intestine and renal tubular cells, ZnT-1 is localized to the basolateral membrane, suggesting an orientation that is consistent with zinc absorption/retention. ZnT-2 is also an exporter and may be involved in zinc efflux or uptake into vesicles in intestine, kidney, and testis. ZnT-3 is involved in zinc uptake into vesicles in neurons and possibly in testis. ZnT-4 is also an exporter and is highly expressed in mammary gland and brain. The divalent cation transporter 1 (DCT1) is regulated by iron, but exhibits transport activity for a number of trace elements including zinc. Description of a family of zinc transporters bridges the integrative and reductionist approach to the study of zinc metabolism. Other members of this transporter family may emerge. Many of these may be regulated by zinc, and some may respond to immune challenge, oxidative stress, and competing metals in the dietary supply. Collectively, description of transporters that influence cellular zinc uptake and efflux will provide a clearer understanding of the molecular events that regulate zinc absorption and homeostasis.

Competitive reverse transcriptase-polymerase chain reaction shows that dietary zinc supplementation in humans increases monocyte metallothionein mRNA levels

Zinc status is difficult to evaluate in humans. Metallothionein gene expression is transcriptionally regulated by dietary zinc and thus could serve as an assessment parameter based on zinc-dependent function. We used semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to establish that MT mRNA is increased in a human monocytic cell line by addition of zinc to the medium. To examine this response in human subjects, a dietary supplement of 50 mg zinc gluconate/d was given for 15 d. Monocytes were purified from venous blood using NycoPrep 1.068. Monocyte purity was determined by flow cytometry using fluorescent anti-human monocyte CD14 antibodies. Total monocyte RNA was extracted and converted to cDNA by reverse transcription. Competitive RT-PCR was used to analyze differences between cDNA levels that are proportional to MT mRNA levels in monocytes from zinc-supplemented and control subjects. RT-PCR oligonucleotide primers were designed to amplify both a 201 bp segment of the human MT cDNA and a 180 bp competitor cDNA template. The 180 bp competitor cDNA template was used for MT cDNA quantitation. The RT-PCR data show that there was a significant increase in monocyte MT mRNA in subjects within 6 d of zinc supplementation, which remained elevated at d 15 of supplementation. In contrast, plasma zinc was greater at d 6 of zinc supplementation, but by d 15 of supplementation, while still elevated, was close to control levels. These data suggest that monocyte MT mRNA levels respond to zinc supplementation and that the response could serve as a more useful assessment variable than plasma zinc for the measurement of zinc status in humans.

Upregulation of rat intestinal uroguanylin mRNA by dietary zinc restriction

A cDNA for the rat uroguanylin precursor was identified, by differential display of intestinal mRNA, as upregulated in zinc-deficient rats and subsequently was cloned. The cDNA and deduced amino acid sequences show a high degree of homology to human and opossum preprouroguanylin sequences. When used as a probe for Northern blot analysis of RNA from rat intestinal mucosa, the uroguanylin cDNA hybridized to a single species of mRNA that was 2.5-fold more abundant in zinc deficiency. A tissue distribution survey indicates that although the small intestine expresses a disproportionately high level of preprouroguanylin, this hormone precursor is also expressed in the colon, stomach, kidney, thymus, and testis. The induction by zinc deficiency is the first reported case of gene regulation for this hormone. These results also suggest a potential mechanism to explain, at least in part, the beneficial effects of zinc supplementation for secretory diarrhea prevalent in many areas of the world.

Human cysteine-rich intestinal protein: cDNA cloning and expression of recombinant protein and identification in human peripheral blood mononuclear cells

Cysteine-rich intestinal protein (CRIP) is a small, 8.5-kDa protein with one double zinc-finger motif called a LIM domain. It is very abundant in intestine and some immune cells in rodents, and expression is influenced by development and the immune response. We have cloned a human CRIP cDNA from human small intestine poly(A)+ RNA by RT-PCR. Through sequencing, we found that the human intestinal CRIP protein (hCRIP) differed from the previously cloned rat CRIP by two amino acids (residues 8 and 58). hCRIP was expressed with the pET vector/bacterial system and isolated by gel filtration and ion-exchange chromatography. The protein was purified to homogeneity as confirmed by PAGE, Western blotting, and immunodetection. Recombinant hCRIP has a molecular mass of 8390 Da based on mass spectrum analysis. Southern analysis suggests that there are three copies of the CRIP gene in the human genome. hCRIP mRNA was detected by RT-PCR in human monocytes purified from peripheral blood and THP-1 cells, a human monocytic cell line. Incubation of THP-1 cells with 65Zn and chromatography of the cytosol show that a significant amount of the radioactivity is associated with CRIP as was shown previously for rat intestine. The results are consistent with a functional role for CRIP in proliferation/differentiation of specific cell types, particularly those associated with host defense.

Immunohistochemical localization of cysteine-rich intestinal protein in rat small intestine

Cysteine-rich intestinal protein (CRIP) is a LIM (cysteine-rich motif of leu-11, isl-1, and mec-3 genes) domain protein with a double zinc finger motif. The protein is abundantly expressed in the intestine, peritoneal macrophages, and peripheral blood mononuclear cells. The function of CRIP is not known. The purpose of this study was to determine the cellular distribution of CRIP in rat intestine, as an initial step toward eventual determination of a function. Immunohistochemical and immunogold labeling electron microscopy using a purified polyclonal rabbit antibody to a synthetic peptide representing a zinc finger domain of rat CRIP were carried out on sections of rat duodenum. Western blotting was used to detect signal specificity of the antibodies. These immunohistochemical and electron microscopy studies showed particularly high abundance of CRIP in the cytoplasmic granules of Paneth cells of the intestine. Some evidence of CRIP expression was also found in cells of the villus tip, but abundance was less than that found in the Paneth cells. The localization of CRIP in Paneth cells and its presence in mononuclear cells suggests that CRIP may be involved in host defense mechanisms and/or tissue differentiation/remodeling processes common to these cell types.

Interaction of different organic and inorganic zinc and copper sources fed to rats

A study was conducted to compare bioavailability, interactions and retention of different sources of Zn and Cu fed to rats. Sixty-three male CD rats were fed individually a purified diet and deionized water ad libitum. The nine treatments included were all combinations of three Zn (ZnMet, ZnLys, ZnSO4) and three Cu (CuLys, CuSO4, CuO) sources added to the basal diet at 30 mg/kg of Zn and 6 mg/kg of Cu forming a 3' 3 factorial experiment. After the four-week supplementation phase, four randomly selected rats from each treatment were sacrificed (Phase 1). The remaining rats were fed the purified, unsupplemented diet for an additional week (Phase 2) and then sacrificed. Mineral (Zn and Cu) concentrations were determined in plasma, liver, kidney, bone and muscle, and metallothionein (MT) content was determined in liver and kidney. Plasma Cu concentrations were lower (p < 0.05) for CuO-than CuSO4- and CuLys-supplemented rats. Bone Zn concentrations were higher (p < 0.05) for CuLys-than for CuO-supplemented rats. In all tissues where Cu was measured, CuO was the lowest (p < 0.05) available source of Cu. Furthermore, in muscle, CuSO4-supplemented rats had higher (p < 0.05) Cu concentrations than CuLys-supplemented rats. Kidney MT concentrations followed the same pattern as Cu concentrations, with CuO-fed rats having the lowest (p < 0.05) MT concentrations. Plasma Cu concentrations of depleted rats were lower (p < 0.05) for CuO-than CuLys-supplemented rats. Kidney Zn concentrations were lower (p < 0.05) for CuSO4-than for CuO-supplemented rats after depletion. In liver, CuO supplemented rats had the lowest (p < 0.05) Cu concentration. Copper oxide was less available than CuLys and CuSO4 when added in adequate dietary levels. However, organic (ZnMet and ZnLys) and inorganic (ZnSO4) sources of Zn were similar.

Differential display of intestinal mRNAs regulated by dietary zinc

Regulation of gene expression by zinc is well established, especially through the metal response elements of the metallothionein genes; however, most other aspects of the functions of zinc in gene expression remain unknown. We have looked for intestinal mRNAs that are regulated by dietary zinc status. Using the reverse transcriptase-PCR method of mRNA differential display, we compared intestinal mRNA from rats that were maintained for 18 days in one of three dietary groups: zinc-deficient, zinc-adequate, and pair-fed zinc-adequate. At the end of this period, total RNA was prepared from the intestine and analyzed by mRNA differential display. Under these conditions, only differentially displayed cDNA bands that varied in the zinc-deficient group, relative to the zinc-adequate groups, were selected. Utilizing two anchored oligo-dT3' PCR primers and a total of 27 arbitrary decamers as 5' PCR primers, our results yielded 47 differentially displayed cDNA bands from intestinal RNA. Thirty were increased in zinc deficiency, and 17 were decreased. Nineteen bands were subcloned and sequenced. Eleven of these were detectable on Northern blots, of which four were confirmed as regulated. Three of these have homology to known genes: cholecystokinin, uroguanylin, and ubiquinone oxidoreductase. The fourth is a novel sequence as it has no significant homology in GenBank. The remainder of those cloned included novel sequences, as well as matches to reported expressed sequence tags, and functionally identified genes. Further characterization of the regulated sequences identified here will show whether they are primary or secondary effects of zinc deficiency.

Apolipoprotein B mRNA editing is preserved in the intestine and liver of zinc-deficient rats

Apolipoprotein B (apo B) mRNA editing is a site-specific, post transcriptional cytidine deamination reaction that generates apo B48 in the mammalian small intestine and in the liver of certain animals. This reaction is mediated by an enzyme complex that includes the catalytic subunit apobec-1, a zinc-dependent cytidine deaminase. To determine the importance of zinc status to apo B mRNA editing in vivo, we examined the effects of experimentally induced zinc deficiency in rats upon hepatic and serum lipid levels and several indices of apo B gene expression. Rats were either given unlimited access to or were pair-fed a semipurified zinc-supplemented (30 mg Zn/kg) diet or were fed a zinc-deficient diet (approximately 1 mg Zn/kg) for 17 d. Significant differences were detected in the ratio of serum apo B100/B48 in the unlimited access, zinc-supplemented group compared with either zinc-deficient rats or pair-fed controls. There were no alterations in hepatic triglyceride and cholesterol concentrations, hepatic apo B mRNA abundance or apo B mRNA editing in either the small intestine or liver. Taken together, these data suggest that the altered ratios of serum apo B isomorphs seen in zinc deficiency are not mediated through changes in hepatic or intestinal apo B mRNA editing.

Differential expression of cysteine-rich intestinal protein in liver and intestine in CCl4-induced inflammation

Cysteine-rich intestinal protein (CRIP) is a double zinc finger (LIM domain) protein that is developmentally regulated but has an unknown function. CRIP is highly expressed in the intestine, but expression is low in liver. To determine if CRIP expression is regulated under altered physiological status, we used CCl4-induced injury as a model to produce hepatic injury and systemic effects associated with inflammation. Since CRIP is a zinc finger protein and zinc decreases the hepatic response to CCl4, the effect of supplemental dietary zinc (300 mg/kg diet) was also examined. Our results show that this supplemental level of dietary zinc did not affect the index of hepatic injury (plasma alanine aminotransferase), indicating zinc did not have a protective effect. Liver CRIP mRNA increased with CCl4 and CRIP protein was shown by immunohistochemistry to be localized in hepatocytes near the vascular supply. In the intestine, CCl4 caused a transient decrease in CRIP mRNA, but supplemental dietary zinc treatment prevented this decrease. These current results show that CRIP expression changes in response to cellular damage due to acute hepatic injury and are consistent with a functional role for CRIP in proliferation, differentiation, or turnover.

Lipopolysaccharide regulates cysteine-rich intestinal protein, a zinc-finger protein, in immune cells and plasma

Cysteine-rich intestinal protein (CRIP), a double zinc-finger LIM protein, is expressed in great abundance in the intestine. We have found comparable levels of CRIP mRNA in peritoneal macrophages, peripheral blood mononuclear cells (PBMC), and lesser amounts in thymus and spleen. Because CRIP expression was high in immune cells, rats were challenged with lipopolysaccharide (LPS) to determine whether expression was altered during the acute-phase immune response. Immunocytochemistry showed that, in adherent mononuclear cells, CRIP protein was localized in the cytoplasm. CRIP mRNA levels increased over time after LPS injection in peritoneal macrophages, PBMC, spleen, and intestine. No changes in CRIP mRNA level were seen in either liver or thymus. In PBMC, the level of CRIP mRNA decreased before increasing later in the acute-phase immune response. CRIP protein was found in the plasma. Shortly after LPS administration plasma CRIP decreased, suggesting that CRIP was either passively diffused out of capillaries or was actively shunted into tissues to execute its function. Increased CRIP expression seen in response to LPS suggests that CRIP may play a role in immune cell activation or differentiation or in processes associated with cellular repair.

Relative bioavailability of two organic and two inorganic zinc sources fed to sheep

A study was conducted to compare supplemental Zn lysine (ZnLys), Zn methionine (ZnMet), ZnSO4, and ZnO on Zn, Cu, and metallothionein (MT) concentrations in various fluids and tissues of 40 wether lambs. Supplemental Zn (360 mg/kg) was fed for 3 wk, withdrawn for 4 wk, and then resumed for another week. Mineral (Zn and Cu) concentrations were determined in serum, liver, pancreas, kidney, bone, bone marrow, hoof, and leg muscle, and only Zn was determined in skin and cornea. Metallothionein concentration was determined in liver, pancreas, and kidney. By d 49 serum Zn had increased less (P < .05) for controls than for all lambs except those fed ZnMet, and on d 55 it had increased more (P < .05) for ZnLys than for all but ZnSO4. There were no treatment effects in serum Cu concentration, but overall Cu concentration fell slightly for all treatments from d 0. The ZnLys-treated lambs had the highest (P < .05) Zn accumulation (581, 389, and 340 mg/kg) in kidney, liver, and pancreas, respectively. Both ZnSO4- and ZnMet-treated lambs had higher (P < .05) liver Zn concentrations (195 and 198 mg/kg, respectively) than the control lambs (127 mg/kg). Mean Zn concentration of bone, bone marrow, cornea, skin, hoof, and muscle was not different (P > .05) for lambs among treatments. The ZnLys-treated lambs had the highest (P < .05) MT concentrations (79, 167, and 68 micrograms MT/g for liver, kidney, and pancreas, respectively). Mean muscle Cu concentration was highest (P < .05) for controls (10 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Zinc status is not adversely affected by folic acid supplementation and zinc intake does not impair folate utilization in human subjects

Changes in zinc status in response to folic acid supplementation and the effect of zinc intake on folate utilization were evaluated in 12 men (20-34 y old) consuming a diet containing 3.5 or 14.5 mg zinc/d for two 25-d intervals. Deuterium-labeled folic acid (800 micrograms/d) or a placebo was administered orally during each phase. No differences in plasma zinc, erythrocyte zinc, urinary zinc, erythrocyte metallothionein or serum alkaline phosphatase, due to supplemental folic acid, were detected at either level of zinc intake. Differences in the response to folic acid supplementation, due to the level of zinc intake, were not detected for serum, erythrocyte or urinary (labeled and unlabeled) folate. Within the constraints of this short-term folic acid supplementation study, adverse effects on zinc status were not observed and our data suggest that folic acid utilization was not influenced by level of zinc intake.

Cloning and initial characterization of the promoter region of the rat cysteine-rich intestinal protein gene

Cysteine-rich intestinal protein (CRIP) is an intestinal Zn(2+)-binding protein containing a single copy of the double Zn(2+)-finger arrangement known as the LIM motif. CRIP is developmentally regulated and can be induced by glucocorticoid hormones during the early suckling period. In this report we show that CRIP mRNA levels are induced by dexamethasone in cultured rat intestinal epithelial cells (IEC-6). Analysis of the 2644 bp of the 5'-flanking region of the CRIP gene revealed that the CRIP promoter lacks classical CAAT and TATA boxes but contains GC-rich regions in the proximal end of the promoter that probably function in transcription initiation. In addition to binding sites for transcription factors such as Sp-1, AP-2, OCT and GATA-2, there are multiple glucocorticoid-response elements. CRIP promoter constructs fused to the chloramphenicol acetyltransferase reporter gene and transfected into IEC-6 cells confirmed glucocorticoid responsiveness and the presence of negative acting elements. Mobility-shift assays revealed the presence of nuclear factors that bind to the CRIP promoter as a result of dexamethasone treatment. These experiments provide the initial data required to explore further the regulation of this tissue-specific developmentally regulated Zn(2+)-finger protein.

Metal elements and gene expression

The transcriptional regulation of genes by metals is a biological function separate from structural and catalytic roles for metals in gene expression. Each of these functions relies on metals that enter cells from metabolic compartments derived from and influenced by the dietary metal supply. The intracellular metal pools provide an available source for binding to metalloregulatory proteins for transcriptional regulation. These proteins bind MRE sequences found in the promoters of some genes. The distribution of MRE sequences and of metalloregulatory proteins extends from microbial to mammalian systems. The bulk of the data on metal regulation of mammalian gene expression is from the perspective of positive transcriptional regulation. Nevertheless, negative regulation by metals could potentially occur. Transcriptional regulation of genes by nutritionally important metals must be viewed in the context of the other roles of metals in cellular structure and function. Investigators are rapidly delineating the involvement of metals in molecular biology in general and in gene expression in particular.

Purification and properties of rat cysteine-rich intestinal protein

Cysteine-rich intestinal protein (CRIP) is a zinc-binding protein where the binding domain is in the so-called LIM double zinc finger motif. Methods are described for the preparation of CRIP from rat small intestine. Gel-filtration and ion-exchange chromatography and preparative PAGE gave homogeneous CRIP, based upon analytical PAGE, mass spectrometry and microsequencing. Initial localization of CRIP during chromatography was based on binding of 65Zn radioisotope introduced into the intestine. The stoichiometry of binding by CRIP is less than 2 atoms of zinc per molecule. The metal-binding affinity in vitro is zinc > cadmium > copper > iron, at low metal concentrations. Zinc is the predominant metal bound when these metals are taken up from the intestinal lumen. Zinc binding was not influenced by pH between values of 4.5 to 7.5. Metallothionein has a much greater zinc-binding affinity than CRIP. The tissue concentration of CRIP is of the order of 15-20 micrograms/g of mucosal tissue, suggesting that the protein is more abundant than zinc-finger-containing transcription factors. The metal-binding properties of CRIP are consistent with proposed zinc-related functions for this cytoplasmic protein, which is expressed in the small intestine during the postnatal period.

Expression of cysteine-rich intestinal protein in rat intestine and transfected cells is not zinc dependent

The cysteine-rich intestinal protein (CRIP) is a member of a superfamily of proteins containing the LIM motif (a double zinc finger) that has been shown to bind zinc. The role of zinc in the regulation of CRIP was examined in adult rats, cultured intestinal epithelial cells and in a transient transfection system. When adult male rats were fed diets with various amounts of zinc, the amount of ileal CRIP mRNA was only 19% lower in rats fed a zinc-deficient diet (1 mg Zn/kg) and was not different in the zinc-supplemented group (180 mg Zn/kg) compared with the zinc-adequate group (30 mg Zn/kg). In contrast, metallothionein mRNA levels were 76% lower and 80% greater than control levels in the zinc-deficient and zinc-supplemented groups, respectively. Using the chloramphenicol acetyltransferase (CAT) reporter gene, 5'-deletion products of the CRIP genomic promoter were tested for basal and zinc-induced CAT activity in transiently transfected IEC-6 cells. Treatment of the cells with zinc did not alter CAT activity of any construct. These results suggest that CRIP is not directly regulated by zinc in the intestine of rats.

Malabsorption of zinc in rats with acetic acid-induced enteritis and colitis

Acute intestinal inflammation was established in rats by intraluminal administration of acetic acid into loops of distal ileum, proximal jejunum or ascending colon. The study included two control groups of intact (untreated) rats and sham-operated (saline-treated) rats for each intestinal segment. A third group of rats received acetic acid. Histological evaluation demonstrated that acetic acid treatment induced a mild inflammatory response. Two days after treatment, zinc absorption was measured using ligated 10-cm loops of each segment in which 65Zn was injected intraluminally. 65Zn absorption by the ileum, jejunum and colon was markedly reduced in those rats in which inflammation was induced by acetic acid. The liver showed the highest uptake of radioisotope, but the relative tissue distribution generally followed the amount of absorption. The surgical procedure itself seemed to reduce zinc absorption. No changes in [3H]leucine absorption were observed between sham-operated and acetic acid-treated controls. There was no significant serosal-->luminal secretion of intramuscularly injected 65Zn in any of the studied segments. Therefore, based upon the data obtained, we conclude that acetic acid-induced intestinal inflammation reduces absorption of zinc by the small and large intestine, and that a surgical procedure (laparotomy) also reduces zinc absorption. The mechanism of this inflammation is such that malabsorption shows some specificity.

Zinc metabolism and metallothionein expression in bone marrow during erythropoiesis

Zinc metabolism and metallothionein induction in rat bone marrow were investigated during induced erythropoiesis. Redistribution of body zinc was measured with 65Zn after acute blood loss in rats fed zinc-restricted or zinc-adequate diets. Uptake of 65Zn by bone marrow was related to time after blood loss, metallothionein induction, and dietary zinc status. Increased 65Zn uptake by marrow of zinc-restricted rats suggests a minimal amount of zinc is necessary to support expansion of the erythrocytic compartment. Zinc induction of marrow metallothionein also occurred in rats in which anemia was produced using phenylhydrazine. Anemic rats which were administered zinc had higher concentrations of marrow metallothionein compared with control rats. Induction of marrow metallothionein by zinc in nonanemic rats required prior treatment with erythropoietin. Percoll fractionation showed marrow metallothionein was most abundant in erythroblasts. These experiments suggest metallothionein synthesis occurs in erythropoietin-sensitive precursor cells in the marrow in response to increased zinc accessibility.

Metallothionein expression in rat bone marrow is dependent on dietary zinc but not dependent on interleukin-1 or interleukin-6

The comparative influence of dietary zinc status and recombinant human interleukin-1 alpha (rhIL-1 alpha) and recombinant human interleukin-6 (rhIL-6) on metallothionein (MT) gene expression was examined in rat bone marrow and liver. Growing male rats were fed a diet with 5 (restricted), 30 (control), or 180 (supplemented) mg Zn/kg for 14 d. On d 15, rats were injected with 5 micrograms of rhIL-1 alpha or rhIL-6. Marrow metallothionein responded directly to dietary zinc but did not respond to these cytokines. Significantly less zinc accumulated in marrow from the zinc-restricted rats compared with control or supplemented rats. Analysis of metallothionein isoform mRNA expression showed MT-1 is the primary gene expressed in marrow. A significant interaction between dietary zinc and cytokine treatment was observed in the liver. Hepatic metallothionein induction following both rhIL-1 alpha and rhIL-6 injection was directly related to dietary zinc intake. Expression of hepatic metallothionein isoform mRNAs suggested MT-1 responded to zinc and MT-2 responded to cytokines. These results indicate that metallothionein gene expression in both the marrow and the liver responds to dietary zinc status. In contrast, liver metallothionein expression can be altered by these cytokines, which are known to act on many cell types. Furthermore, these results suggest that bone marrow metallothionein could be of importance in the development of marrow cells.