Distinct expression pattern of early- and late-response genes in normal and osteoarthritic human synovial membranes

The significance of activating proteins (AP-1), c-fos, c-jun and jun B relative to the AP-1 responsive metallothionein, collagenase and stromelysin gene expression in the pathophysiology of osteoarthritis (OA) was investigated. The 'early' c-fos, c-jun and jun-B mRNAs were ubiquitously expressed in normal and OA human knee synovial membranes. There was no strict correlation between expression of these and the AP-1 responsive, collagenase and stromelysin gene expression. Interestingly, the total metallothionein (MT) and the AP-1 responsive, MT-IIA gene-specific mRNAs were greatly diminished in OA compared with normal synovial membranes. The possible role of reduced expression of MT and trace metals in OA pathophysiology is discussed. Collectively, these data demonstrate a discoordinate expression of AP-1 encoding and their target genes in synovium.

An upstream region of the rat spermatogenesis-specific heat-shock-like Hst70 gene confers testis-specific expression in transgenic mice

In order to study the temporal and spatial regulation of a rat testis-specific heat-shock-like hst70 gene, an 0.8-kb fragment of its upstream DNA was fused to the lacZ gene and microinjected into one-cell murine embryos. Independent tgHST1 and tgHST2 transgenic mice strains were established, containing about 5-7 and 40-60 transgene copies/haploid genome, respectively. Enzyme assays in various tissues showed that transgene-encoded beta-galactosidase accumulates exclusively in testes of transgenic animals and cannot be detected until 16-17 days after birth. In-situ assays revealed that the enzyme accumulates mainly in pachytene primary spermatocytes. Our data complement previous studies on the endogenous rat hst70 and suggest that its 0.8-kb upstream region contains sufficient information to function as an active spermatogenesis-specific promoter.

Expression of c-fos, c-jun, jun-B, metallothionein and metalloproteinase genes in human chondrocyte

Normal and osteoarthritic (OA) human articular cartilage chondrocytes, released enzymatically in the presence of 0.5% fetal calf serum, display constitutive expression of early response activating protein (AP-1) genes; c-fos, c-jun and jun-B. Among the late AP-1 responsive genes, total metallothionein (MT) and stromelysin mRNAs were expressed at high levels in both normal and OA chondrocytes, while collagenase and hMT-IIA mRNA levels were elevated only in OA individuals. Despite the common AP-1 sequences present in their promoter regions, the three late genes were differentially expressed.

Molecular cloning and characterization of a constitutively expressed heat-shock-cognate hsc71 gene from rainbow trout

A rainbow trout major heat-shock-protein-like gene (hsp 70) and corresponding cDNA clones were isolated by hybridization to heterologous hsp70 probes. DNA sequencing revealed that this gene is structurally similar to a mammalian heat-shock-cognate hsc70 gene and consists of eight introns. Northern blot and primer extension analyses showed that the corresponding mRNA is constitutively abundant in different trout tissues and salmonid cell lines. Fragments of the isolated gene containing the -900 - +30 and -217 - +58 sequence were linked to a bacterial chloramphenicol acetyltransferase reporter gene and transiently transfected into salmonid cells. The expression pattern of these constructs supports our conclusion that the isolated genomic and cDNA clones correspond to a trout heat-shock-cognate hsc70 gene.

Functional analyses of promoter elements responsible for the differential expression of the human metallothionein (MT)-IG and MT-IF genes

The sequences responsible for heavy metal-inducible expression are situated within the proximal 437 and 160 base pairs (bp) of MT-IF and MT-IG 5'-flanking sequence, respectively. Only 105 bp of proximal MT-IG 5'-flanking sequence containing a TATA box, two metal responsive elements (MREs), and three GC motifs and 147 bp of proximal MT-IF 5'-flanking sequence containing a TATCA box, four MREs, and two GC motifs were required for heavy metal-inducible expression. However, the proximal 111 bp of MT-IF 5'-flanking sequences (a TATCA box, two MREs, and two GC motifs) was not responsive to heavy metals and competes less efficiently than the 105-bp MT-IG fragment in a competition transfection analysis. The MT-IF promoter fragment containing MREc and MREd is substantially stronger and a more efficient competitor than the MT-IG promoter fragment containing MREc and MREd. Furthermore, the proximal 160 bp of MT-IG 5'-flanking sequence functions as a strong metal-inducible promoter but not as a metal-inducible enhancer. Mobility shift analysis of MT-IF and MT-IG promoter subregions suggests a correlation between protein binding to MRE sequences and MT gene expression. These data illustrate that the overall structural and functional organization of the MT-IF and MT-IG promoters are very different and that the molecular mechanisms governing differential expression levels of human MT genes are quite complex.

5-Azacytidine increases the total cellular copper content and basal level metallothionein mRNA accumulation of human Hep G2 cells

In this study we have demonstrated the ability of 5-azacytidine to elevate the basal level expression of the metallothionein (MT)-IF and MT-IG genes and increase the basal level expression of the MT-IIA gene in Hep G2 cells, a cell line which exhibits heavy metal inducible MT gene expression. Atomic absorption analysis of 5-azacytidine treated Hep G2 cells detected a 2-fold increase in the total cellular copper content. Pretreatment of 5-azacytidine exposed cells with hydroxyurea and cycloheximide indicated that the increase in total cellular copper content was a direct response to 5-azacytidine treatment. S1 nuclease analysis illustrated that pretreatment of Hep G2 cells with KCN, a copper specific chelator and uptake inhibitor, suppressed 5-azacytidine- and copper-inducible MT-IG gene expression. Thus, the increase in MT gene expression in response to 5-azacytidine treatment can be correlated to an increase in the total cellular copper content. Possible mechanisms on how 5-azacytidine could alter the influx/efflux of copper in Hep G2 cells are discussed.

Developmental regulation of metallothionein mRNA, zinc and copper levels in rainbow trout, Salmo gairdneri

The metallothionein (MT) gene expression profile was followed in rainbow trout during early embryo development and in liver and gonads during the period of sexual maturation. The hepatic MT mRNA levels increase at the end of sexual maturation in both male and female rainbow trout. Although both isoforms of MT mRNA accumulate in the liver, there is a preferential increase in MT-A in the female liver. Concomitantly with this increase in MT there is a redistribution of zinc and copper to MT. In the juvenile female there is an abundance of MT mRNA in the ovaries. This is correlated to high levels of zinc in the MT fraction upon Sephadex G-75 chromatography. During ovary development the MT mRNA levels and the MT-bound zinc levels drop, with an increase in zinc being bound to high-molecular-mass proteins. At ovulation most of the zinc is found in the membrane portion upon centrifugation. In contrast to the ovaries, there are no apparent changes in either trace metal distribution or MT mRNA levels during testis development. In the developing embryo there is an increase in MT-bound copper at gastrulation. This is accompanied by an increase in both isoforms of MT mRNA. At hatch both the copper and zinc levels increase in the MT fraction, with a concomitant increase in mainly MT-A mRNA. These findings indicate that the variations in MT mRNA levels during development are closely associated with metal regulation.

A human metallothionein pseudogene containing AG/CT repetitive elements

A lambda phage recombinant clone, 25 S, which contains a 15.5-kb EcoRI human genomic DNA fragment, has been characterized. Restriction mapping and Southern blot hybridization indicated a 3.0-kb HindIII fragment containing metallothionein (MT)-like sequences. Several interesting features were found upon comparison of this nucleotide sequence with that of other human MT genes: (1) sequences representing the 5' regulatory region, the 5' untranslated region, and the first exon are not contained in the 3.0-kb HindIII fragment; (2) the coding sequence of the second exon (amino acids 10-31 encoding a portion of the beta-domain of the MT protein) has 11 amino acid changes out of a total of 21, whereas, the third exon (amino acids 32-61, representing the complete alpha-domain of the MT protein) has only 4 amino acid substitutions; however, all cysteine residues are conserved; (3) this MT-like gene retains intron sequences and processing signals; (4) Southern blot analysis of human genomic DNA indicated this MT-like gene is located on a 10.5-kb EcoRI genomic DNA fragment; and (5) unusual AG/CT-rich repetitive elements are located within the second intron and upstream of the second exon of this MT-like gene. This gene is not expressed in response to metal induction in two human cell lines, as shown by northern blot analyses. Based on these observations, this MT-like gene represents a unique nonprocessed pseudogene of the human MT multigene family.

Differential regulation of metallothionein genes in rainbow trout fibroblasts, RTG-2

Exposure of a trout gonadal fibroblast (RTG-2) cell line to ZnCl2, CdCl2 and CuCl2 resulted in differential levels of accumulation of metallothionein (MT) mRNA. ZnCl2 being the most effective agent induced MT mRNA in 3 h, with 172-fold induction after 48 h and continued accumulation up to 144 h. Following CdCl2 treatment, mRNA could be detected after 24 h, reaching peak levels at 72 h. Furthermore, trout MT mRNA could be detected up to 8 days after withdrawal of extraneous ZnCl2. Using a novel technique of primer extension and DNA sequencing with total RNA as template, specificity of the trout MTa and MTb gene-specific primers was established. Primer extension studies revealed a higher response of MTa to ZnCl2 and CdCl2 compared to MTb. Insensitivity of MT mRNA induction to cycloheximide suggested that induction by the metals was independent of de novo protein synthesis. However, simultaneous exposure of cells to actinomycin D and metals completely inhibited MT mRNA synthesis implying control at the transcriptional level.

Differences in metallothionein gene expression in primary cultures of rainbow trout hepatocytes and the RTH-149 cell line

Primary cultures of rainbow trout, Salmo gairdneri, hepatocytes were used to study the expression of metallothionein (MT) genes in response to steroid hormone treatment. The expression pattern was compared to that of an immortal cell line (RTH-149). MT mRNA accumulated in both cell cultures after exposure to zinc while 17 beta-oestradiol had no effect in either system. Treatment with cortisol and corticosterone resulted in a 2-fold increase of metallothionein mRNA levels in the primary cultures but had no effect in the RTH-149 cell culture. Primary cultures that were exposed to zinc or cortisol showed a high temporal correlation (r = 0.974) between MT mRNA and MT protein levels. The basal level expression was 3-4-fold higher in primary cultures than in RTH-149 cells. The present study demonstrates the inducibility of rainbow trout MT genes in response to glucocorticoids. It further indicates that primary cultures are to be preferred to immortal cell lines when investigating the inducibility of MT mRNA.

Cell-type specific and differential regulation of the human metallothionein genes. Correlation with DNA methylation and chromatin structure

The expression of three human metallothionein genes, MT-IIA, MT-IF, and MT-IG was studied in the human hepatoblastoma (HepG2), the hepatocarcinoma (Hep3B2), the embryonic kidney (Hek 293), and the lymphoblastoid-derived (Wi-L2) cell lines. The pattern of expression of each specific MT gene in response to various heavy metals was different among the four cell lines studied indicating differential regulation of MT gene expression. The MT-IF or MT-IG and the MT-IIA genes were regulated in a cell-type specific manner in response to heavy metals and dexamethasone, respectively. DNA methylation was shown to be correlated to cell-type specific regulation of MT gene expression since 5-azacytidine treatment resulted in the expression of the MT-IF and MT-IG genes in response to cadmium and zinc in Wi-L2 cells, of the MT-IIA gene in response to dexamethasone in Wi-L2 cells, and of the MT-IG in response to zinc and copper in Hek 293 cells. Furthermore, transfection studies indicated that all the trans-acting factors necessary for the expression of these genes were present and functional in Wi-L2 and Hek 293 cells. The differential level of expression of the MT-IF and MT-IG genes in response to heavy metals in the Hek 293 cell line was shown to be correlated to their chromatin structure.

Transcription factor MBF-I interacts with metal regulatory elements of higher eucaryotic metallothionein genes

Metallothionein (MT) gene promoters in higher eucaryotes contain multiple metal regulatory elements (MREs) that are responsible for the metal induction of MT gene transcription. We identified and purified to near homogeneity a 74-kilodalton mouse nuclear protein that specifically binds to certain MRE sequences. This protein, MBF-I, was purified employing as an affinity reagent a trout MRE that is shown to be functional in mouse cells but which lacks the G+C-rich and SP1-like sequences found in many mammalian MT gene promoters. Using point-mutated MREs, we showed that there is a strong correlation between DNA binding in vitro and MT gene regulation in vivo, suggesting a direct role of MBF-I in MT gene transcription. We also showed that MBF-I can induce MT gene transcription in vitro in a mouse extract and that this stimulation requires zinc.

Metal-specific posttranscriptional control of human metallothionein genes

During the initial 4 h of treatment, copper and zinc similarly activated the rates of transcription and mRNA accumulation from the two human metallothionein (MT) genes, viz., MTI-G and MTII-A, in the hepatoblastoma cell line HepG2. The levels of copper-induced MT mRNAs remained at a plateau for up to 15 h. In contrast, the levels of zinc-induced MT mRNAs gradually declined after about 4 h, despite substantial transcription. The decrease in the zinc-induced MT mRNA half-life is probably due to a posttranscriptional event(s).

Endogenous and heavy-metal-ion-induced metallothionein gene expression in salmonid tissues and cell lines

Endogenous levels of metallothionein (MT) mRNA were detected by RNA probes in several somatic and germ-line tissues of rainbow trout, such as eggs, ovaries and immature testis. These levels may be related to metal-ion homeostasis in the observed tissues. The induction kinetics of trout MT isoform B (MT-B) mRNA were studied after single intraperitoneal injections of CdCl2, CuCl2 and ZnCl2. MT-B mRNA was induced within 12 h in liver, kidney, spleen and gills. However, over the 48-h experimental period, the kinetics of MT-B mRNA accumulation differed in response to the three metal salts, possibly due to differential handling of the salts by these tissues. Multiple metal-salt injections induced high levels of MT-B mRNA in the four tissues studied. In the rainbow trout hepatoma cell line, ZnCl2 was a better inducer of the MT-B gene, as compared to CdCl2 and CuCl2. The expression of the exogenous trout MT-B promoter in Chinook salmon embryonic cell line indicates the presence of MT regulatory factors. In contrast, the endogenous MT genes in these cells are quiescent, possibly due to the methylation of their promoter region.

Calcium phosphate-mediated transfection alters metallothionein gene expression in response to Cd2+ and Zn2+

The level of expression of a transfected metallothionein (MT)-IGcat fusion gene in response to cadmium differed from that of the endogenous MT-IG gene. Atomic absorption analysis indicated that the total cellular content of cadmium and zinc increased upon calcium phosphate-mediated transfection. Thus, changes in the influx/efflux of metals may regulate the level of MT gene expression.

Heavy metal tolerant transgenic Brassica napus L. and Nicotiana tabacum L. plants

A chimeric gene containing a cloned human metallothionein-II (MT-II) processed gene was introduced into Brassica napus and Nicotiana tabacum cells on a disarmed Ti-plasmid of Agrobacterium tumefaciens. Transformants expressed MT protein as a Mendelian trait and in a constitutive manner. Seeds from self-fertilized transgenic plants were germinated on media containing toxic levels of cadmium and scored for tolerance/ susceptibility to this heavy metal. The growth of root and shoot of transformed seedlings was unaffected by up to 100 μM CdCl2, whereas control seedlings showed severe inhibition of root and shoot growth and chlorosis of leaves. The results of these experiments indicate that agriculturally important plants such as B. napus can be genetically engineered for heavy metal tolerance/sequestration and eventually for partitioning of heavy metals in non-consumed plant tissues.

Induction of metallothionein synthesis in rainbow trout,Salmo gairdneri, during long-term exposure to waterborne cadmium

Rainbow trout were exposed to 200 μg cadmium/l in the water during four months at 6-10°C. The liver, kidney and gills were analyzed for cadmium, copper, zinc, metallothionein and metallothionein mRNA. Cadmium accumulated in all three organs and reached the highest concentration in the kidney. The tissue zine and copper concentrations showed no major alterations during the experiment. The cytosolic distribution of cadmium, copper and zinc was followed during four months of exposure by Sephadex G-75 chromatography. It was found that cadmium was predominantly associated with proteins of an apparent molecular vieght of 10,000 daltons. These proteins were further identified as metallothioneins after fast protein liquid chromatography on a Mono-Q column. The metallothionein concentration was significantly higher in liver of exposed fish than in control fish after only one month. The kidneys reached significantly elevated levels of metallothionein in the exposed group after three months. In the gills, elevated metallothionein concentrations were observed after four months of exposure. After four months of exposure, the metallothionein mRNA content of liver and kidney was analyzed using a rainbow trout anti-sense RNA probe. Elevated MT mRNA levels were observed in both kidney and liver. These results demonstrate thatde novo synthesis of metallothionein is induced by cadmium in rainbow trout after exposure to the metalvia water.

Analysis of stress-induced gene expression in fish cell lines exposed to heavy meals and heat shock

We have examined the effect of heavy metals on the expression of two major groups of stress-induced proteins in fish cell lines: the 70 kDa heat-shock proteins (hsp70) and metallothioneins (MTs). The rainbow trout hepatoma (RTH) cell line synthesized the hsp70 protein in response to zinc and heat shock, while chinook salmon embryonic (CHSE) cells synthesized this protein in response to these inducers, as well as cadmium. The synthesis of this 70 kDa protein was correlated with the accumulation of hsp70 mRNA as measured by hybridization to a trout hsp70 gene probe. Heavy metals also induced the synthesis of MT in RTH cells. However, heat shock did not result in induction of MT and its mRNA. Unlike RTH cells, CHSE cells did not synthesize MT following exposure to cadmium or zinc. When these cells were treated with 5-azacytidine prior to heavy metal treatment, accumulation of MT mRNA was observed. Northern blot analysis of total RNA from 5-azacytidine treated CHSE cells, using a trout MT (tMT-B) cDNA probe, indicated that the time-course of induction and the maximal level of MT mRNA accumulation in response to cadmium and zinc paralleled that observed in RTH cells. Copper and dexamethasone were ineffective in inducing MT mRNA in 5-azacytidine-treated CHSE cells. These results indicate that MT is specifically induced in response to heavy metal treatment, whereas the synthesis of hsp70 appears to be a general stress response. Furthermore, MT is differentially regulated by heavy metals and dexamethasone in these cell lines and the expression of MT is cell-type-specific.

A role of metallothionein in zinc regulation after oestradiol induction of vitellogenin synthesis in rainbow trout, Salmo gairdneri

The regulation of metallothionein (MT) biosynthesis in rainbow-trout liver was studied after a single intraperitoneal injection of oestradiol-17 beta. Sampling was performed after 2, 7, 14, 21, 28 and 35 days. Following induction of vitellogenin synthesis in the liver, liver somatic index (LSI) rose from 1.25 to 2.00 in 14 days. Associated with the increase in LSI was an elevation of hepatic vitellogenin mRNA and zinc concentrations. The vitellogenin mRNA concentrations peaked at 7 days after treatment. The zinc concentrations increased to a peak at day 14. MT was analysed by using differential pulse polarography and a rainbow-trout MT RNA probe. The MT mRNA concentrations rose after 14 days and remained elevated at 21 and 28 days. The MT concentrations increased after 14 days and remained elevated throughout the experimental period. The concentrations of MT-bound zinc increased in association with the elevation in MT concentrations in the oestradiol-treated rainbow trout. These findings indicate that MT is involved in the regulation of zinc during the period of vitellogenin induction and that MT may function by maintaining the pool of available zinc at an appropriate concentration.

Structure of the rainbow trout metallothionein B gene and characterization of its metal-responsive region

The trout metallothionein (MT) genes consist of two members. We describe the structure of the first fish MT (tMT-B) gene which shows an overall resemblance but some remarkable differences with mammalian MT genes. The similarities included (i) tripartite structure of the gene, (ii) conservation of cysteine residues, and (iii) a TATAAA signal and two copies of metal-responsive elements (MREs). The differences consisted of (i) an AT-rich tMT-B promoter compared with highly GC-rich mammalian MT promoters and (ii) a lack of SP1-binding sites in the tMT-B promoter. Functional analysis of the tMT-B 5'-flanking region following fusion with the bacterial chloramphenicol acetyltransferase gene and its transfection into the rainbow trout hepatoma cell line revealed that sequences from positions -600 to +8 are sufficient for regulation by metals. Further deletion analyses of this fragment suggested that a minimum of 100 nucleotides upstream of the transcription initiation site are required for induction by cadmium and zinc. The tMT-B promoter was also functional in the human hepatoblastoma cell line, suggesting that an MT regulatory factor(s) is conserved in phylogenetically distant species like humans and fish.

Structure and expression of the human metallothionein-IG gene. Differential promoter activity of two linked metallothionein-I genes in response to heavy metals

The human metallothionein (MT)-IG gene (hMT-IG) is tandemly linked in a head-to-head fashion with the hMT-IF gene. The hMT-IG gene encodes a MT-I polypeptide and has a tripartite structure. The 5'-flanking region of the hMT-IG gene has a TATAA box, four GC motifs, and at least four metal responsive elements. The 3'-untranslated region has a variation of the polyadenylation signal, AATTAA, and the 3'-flanking region a YGTGTTYY RNA processing signal. This gene is expressed in hepatoma-derived cell lines (Hep G2 and Hep3B2) in response to the heavy metals (cadmium, copper, and zinc) but not to the glucocorticoid analogue dexamethasone. In contrast, the lymphoblastoid cell line (Wi-L2) does not express the hMT-IG gene. These results suggest that the hMT-IG gene is regulated differentially and in a cell type-specific manner. Transient expression studies of the chloramphenicol acetyltransferase (CAT) gene under the transcriptional control of either the hMT-IG or hMT-IF promoter in Hep G2 cells has demonstrated that both promoters contain all the necessary cis-acting elements to elicit a similar pattern of heavy metal inducibility. However, the hMT-IG promoter in all instances is five times more active than the hMT-IF promoter. The differences in promoter activity of these genes could possibly be due to inherent differences in their basal level regulatory sequences. The expression of MT-IGcat in transfected Wi-L2 cells demonstrates that the hMT-IG promoter is not cell type-specific.

Inosine incorporation in GC rich RNA probes increases hybridization sequence specificity

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Pairwise linkage analysis of 11 loci on human chromosome 4

New RFLPs are described for INP10 and interleukin 2. The 55 pairwise genetic linkage relationships for these two loci and nine additional loci on the long arm of chromosome 4 (4q) are reported. Fifteen new linkages are established, and new data are added to the four previously reported linkages on 4q. Tight linkage of interleukin 2 (T-cell growth factor), epidermal growth factor, and alcohol dehydrogenase is described. Significant differences were observed between male and female recombination rates. The female rate was estimated to be 1.27 times the male rate. On the basis of these pairwise results, the order for the 11 loci is D4S35-GC-(ALB/AFP)-MT2P1-D4S1-INP10-ADH3-( EGF/IL2)-(FBB/FBA/FBG)-MNS. This preliminary order can serve as a starting point for more detailed multipoint analysis.