Biomedical subjects

C Legraverend

Publications and source records attributed to C Legraverend.

At least 19 recordsLinked to original sources

PubMed2005

Spatial and temporal expression of S100B in cells of oligodendrocyte lineage.

The analysis of oligodendrocyte (OL) lineage development has been facilitated by the immunocytochemical characterization of OL-specific antigens and definition of the phenotypes sequentially acquired by differentiating OLs. The purpose of the present study was to address an enduring discrepancy between several reported cases of S100B immunodetection in CNS myelin and myelinating OLs on the one hand, and the systematic use of the S100B protein as an alleged astrocytic marker in studies of the mammalian CNS on the other. To resolve this discrepancy, we have compared the developmental distribution of EGFP+ cells in the CNS of s100b-enhanced green fluorescent protein (EGFP) (Vives et al., 2003) and cnp-EGFP (Yuan et al., 2002) mice, and examined the degree of overlap between EGFP expression and that of stage-specific markers of OL differentiation during the embryonic and postnatal phases of development. We demonstrate that the S100B protein is expressed in postnatal and adult populations of NG2+ progenitors of mouse brain, as well as in immature and mature myelinating OLs present in the brain and spinal cord of embryonic and adult mice, respectively. Comparison between EGFP and endogenous S100B expression in the s100b-EGFP and cnp-EGFP mice indicates that S100B protein expression is upregulated in immature and mature OLs. These results argue against the current view that S100B expression is restricted to the astrocytic lineage in the CNS, and indicate that the use of S100B in combination with other molecular markers will help discriminate oligodendrocytes from astrocytes.

Aging↗

PubMed2000

Purification and cloning of type A/B hnRNP proteins involved in transcriptional activation from the Rat spi 2 gene GAGA box.

The GAGA box of the rat serine protease inhibitor 2 (spi 2) genes not only acts as a basal promoter element, but also mediates transcriptional activation by growth hormone and interleukin-6. The GAGA box is separated from the TATA box by only 12 bp, and this close association is required for efficient transcription. Hence, the GAGA box may influence transcription efficiency through interactions between GAGA box binding proteins and some components of the RNA polymerase II complex. Here we report the cloning of two GAGA box-binding proteins termed p38 and p40, that belong to the type A/B heterogeneous nuclear ribonucleoprotein subgroup. GAGA box mutations that diminish the affinity for p38 and p40 decrease basal and GH-induced reporter gene expression. Furthermore, nuclear extracts depleted of p38 and p40 can no longer support GAGA box-dependent in vitro transcription. Therefore, two polypeptides previously assigned to a family of RNA processing proteins also act as DNA-binding, promoter-specific transcription factors.

Amino Acid Sequence↗

PubMed1998

Transcription of the rat serine protease inhibitor 2.1 gene in vivo: correlation with GAGA box promoter occupancy and mechanism of cytokine-mediated down-regulation.

Two GH-response elements (GHREs) and a single glucocorticoid (GC)-response element were found to regulate activity of the rat serine protease inhibitor 2.1 gene (spi 2.1) promoter in vitro. To assess the physiological relevance of these observations, we have investigated the relationship existing between the level of spi 2.1 gene transcription, structural modifications of the chromatin, and in vivo nuclear protein-promoter interactions monitored by genomic footprinting, in control, hypophysectomized, and inflamed rats. We also addressed the mechanism of inflammation-mediated gene down-regulation. We found that a high level of spi 2.1 gene transcription correlates with hypersensitivity of the promoter to deoxyribonuclease I (DNase I) and maximal occupancy of the GAGA box (GHRE-I). The failure of GAGA-box binding proteins (GAGA-BPs) to interact with the GAGA box appears to result from an impairment in GH action due to its absence (i.e. hypophysectomized animals) or to the appearance of a cytokine-mediated GH-resistant state (i.e. inflamed rats) in liver. Unlike the GAGA box, signal transducer and activator of transcription (STAT) factor-binding sites included in the GHRE-II were never found to be protected against DNase I attack but displayed a differential DNase I reactivity depending on the level of gene transcription. Alterations in DNase I reactivity of the GC-response element region suggest that GC receptor-GC complexes may associate, in a transient manner, with the promoter in the actively transcribing control state. Taken together, our studies suggest a mechanism of spi 2.1 gene activation in vivo whereby the GH-dependent chromatin remodeling caused by or concomitant to the recruitment of GAGA-box binding proteins is the first compulsory and presumably predominant step.

Animals↗

PubMed1996

A novel growth hormone response element unrelated to STAT (signal transducer and activator of transcription)-binding sites is a bifunctional enhancer.

Regulation of gene expression by GH has so far been shown to be mediated by a few cis-acting elements, most of which are signal transducer and activator of transcription (STAT)-binding sites. Here we have characterized a novel GH-response element present in the promoter of rat serine protease inhibitor (spi) genes. It consists of a 13 nucleotide-long GAGA box containing two GAGGAG repeats separated by a G, structurally unrelated to STAT-binding sites. In hepatocytes, the spi GAGA box behaves as a position-dependent bifunctional enhancer controlling basal and GH-dependent transcription. In addition, spi GAGA box oligonucleotides inhibit cell-free transcription driven by GAGA box-containing as well as GAGA box-less promoters, suggesting that the spi GAGA box interacts directly or indirectly with component(s) of the basic transcriptional machinery. Mobility shift assays showed that this GAGA box is specifically recognized by nuclear factors that are unrelated to previously characterized proteins binding to purine-rich elements or to GH-activated STATs. Finally, experiments performed with cells expressing wild type, truncated, or mutated forms of the GH receptor indicate that protein kinase Janus kinase 2 is involved in the GH-dependent activation of the spi GAGA box. These studies reveal the existence of an as yet unidentified Janus kinase-2-dependent, STAT-independent pathway in GH activation of gene expression.

Animals↗

PubMed1995

Transcriptional repression, a novel function for 3' untranslated regions.

The transcription rates of the rat serine protease inhibitor 2.3 and 2.1 genes (spi 2.3 and spi 2.1), which are normally very low and high, respectively, are inversely modulated during inflammation. Two growth-hormone-response elements (GHRE-I and GHRE-II) maintain the spi 2.1 gene under the stringent control of growth hormone [Le Cam, A., Pantescu, V., Paquereau, L., Legraverend, C., Fauconnier, G. & Asins, G. (1994) J. Biol. Chem. 269, 21532-21539], whereas spi 2.3 appears to escape control by this hormone, despite the presence in its promoter of a functional GHRE-I. A major difference between these two otherwise very similar genes is the presence in spi 2.3 of a specific 348-bp extension of the 3' untranslated region (3' UTR). Inserting this 3' UTR element downstream of the polyadenylation signal or upstream of the spi 2.3 promoter in constructs containing the chloramphenicol acetyltransferase gene strongly decreases basal transcription and inhibits growth-hormone-stimulated transcription, but poorly affects transcriptional stimulation by dexamethasone or interleukin-6. The spi 2.3 3' UTR extension also inhibits, basal and growth-hormone-induced transcription from the spi 2.1 promoter. Repressor activity appears to be distributed throughout the specific extension of the 3' UTR and seems to involve interactions with two types of 5' cis-acting promoter elements. The first is the GAGA box, a key control spi promoter element, whose mutation faithfully reproduces the effects of the 3' UTR silencer on spi 2.1 and spi 2.3 promoters. The second is represented by CCAAT enhancer-binding-protein-(C/EBP)-binding sites, whose functions are severely impaired by the spi 2.3-specific 3' UTR extension. The presence of this silencer in the spi 2.3 gene very likely accounts for the lack of basal of transcription in vivo and for induction of the gene during acute inflammation.

Animals↗

PubMed1994

cis-Acting elements controlling transcription from rat serine protease inhibitor 2.1 gene promoter. Characterization of two growth hormone response sites and a dominant purine-rich element.

The cis-acting elements that are functionally important for the basal, the growth hormone (GH), and the glucocorticoid hormone (GC) regulation of expression of the rat serine protease inhibitor 2.1 gene (spi 2.1) were mapped. Normal rat hepatocytes were transiently transfected with constructs harboring deleted or mutated versions of the spi 2.1 proximal promoter region fused to the chloramphenicol acetyltransferase gene. A purine-rich sequence (GAGA box, nucleotides -57 to -45), whose mutation or deletion almost completely knocks out both basal and hormone-stimulated promoter activities, plays the role of a key control element. A positive GC response element, spanning nucleotides -88 to -74, confers GC responsiveness to a heterologous promoter. Two structurally unrelated GH-response elements (GHRE) were identified. GHRE-II (nucleotides -136 to -104) contains a CCAAT enhancer binding protein binding site whose mutation completely abolishes its GH-dependent enhancer function. GHRE-I, which spans nucleotides -61 to +8, is not an enhancer element. Its GH-dependent activity depends on the preservation of the distance separating the GAGA box and elements of the basic transcriptional machinery. Taken together, these results have revealed the existence of an apparently new type of promoter functioning that strictly depends on the integrity of a key regulatory (G + A) motif.

Animals↗

PubMed1994

Transactivation of the rat CYP2C13 gene promoter involves HNF-1, HNF-3, and members of the orphan receptor subfamily.

The rat CYP2C13 gene (2C13) encodes one of the constitutive male forms of cytochrome P-450 that are involved in steroid metabolism. In addition to being developmentally regulated, the expression of 2C13 is restricted to the liver and suppressed by the female pattern of growth hormone (GH) secretion at the transcriptional initiation level. In this study, we show that the liver-specific expression, but not the regulation by GH, can be reconstituted with 117 bp to 2 kb of 2C13 5' flank. Transactivation of the 2C13 promoter requires both HNF-1 and HNF-3 and is influenced by members of the orphan receptor subfamily of transcription factors. Although HNF-4, ARP-1, EAR-2, and COUP-TF bind to the 2C13 promoter in vitro, overexpression of EAR-2 and COUP-TF, but not of HNF-4 or ARP-1, results in the potentiation of the HNF-3- and HNF-1-supported activity in non-liver cells.

Animals↗

PubMed1994

Characterization of the proximal promoter and two silencer elements in the CYP2C11 gene expressed in rat liver.

The cytochrome P450 gene CYP2C11, expressed in the liver of male rats, is transcriptionally regulated in a dual fashion by the sexually dimorphic secretion pattern of growth hormone. To enable analysis of transcriptional regulatory DNA elements, rat genomic sequences were cloned. DNase I hypersensitivity analysis of rat liver nuclei revealed the existence of two hypersensitive sites whose presence in the vicinity of the transcription start site correlates to high transcriptional activity of the gene. Deletion mutants of the 5' flank were fused to reporter genes and transiently transfected into HepG2 cells or into primary adult rat hypatocytes. Transfection experiments in combination with DNase I footprinting analysis in vitro led to the identification of two negative regulatory regions spanning nucleotides -1,230 to -1,188 and -409 to -368 and designated (SIL1200) and (SIL400), respectively. When placed in front of the heterologous thymidine kinase promoter, SIL1200 and SIL400 reduced the activity of the chloramphenicol acetyl transferase reporter gene to 13% and 23% of the control value, respectively. No sex-dependent binding of liver nuclear extracts to the two silencers could be detected by in vitro footprinting or gel retardation assays. However, a sex-dependent footprint consistently stronger with male liver nuclear extracts than with female extracts was observed in the -320 to -294 region. A significant level of identity was found between the DNA sequence corresponding to this footprint and that of orphan steroid receptor elements as well as with that of a basal transcription element common to several CYP2C genes. However, the identity of a potential trans-acting factor binding between -320 and -294 or response of this element to growth hormone is as yet unknown. A sex- and GH secretory profile-dependent protein-DNA interaction in vitro was observed in the -107 to -95 region. In spite of the sequence similarity that exists between this region and the consensus binding site for HNF-1, this region does not bind HNF-1 alpha. This element acted as a repressor on the heterologous thymidine kinase promoter. To date, the two silencer elements and possibly also the HNF-1-like element are the only functional elements defined in the CYP2C11 gene, and it is conceivable that induction of the gene involves derepression of the silencer elements.

Animals↗

PubMed1993

High level activity of the mouse CCAAT/enhancer binding protein (C/EBP alpha) gene promoter involves autoregulation and several ubiquitous transcription factors.

The promoter region of the mouse CCAAT-Enhancer Binding Protein (C/EBP alpha) gene is capable of directing high levels of expression of reporter constructs in various cell lines, albeit even in cells that do not express their endogenous C/EBP alpha gene. To understand the molecular mechanisms underlying this ubiquitous expression, we have characterized the promoter region of the mouse C/EBP alpha gene by a variety of in vitro and in vivo methods. We show that three sites related in sequence to USF, BTE and C/EBP binding sites and present in promoter region -350/+3, are recognized by proteins from rat liver nuclear extracts. The sequence of the C/EBP alpha promoter that includes the USF binding site is also capable of forming stable complexes with purified Myc+Max heterodimers and mutation of this site drastically reduces transcription of C/EBP alpha promoter luciferase constructs both in liver and non liver cell lines. In addition, we identify three novel protein-binding sites two of which display similarity to NF-1 and a NF kappa B binding sites. The region located between nucleotides -197 and -178 forms several heat-stable complexes with liver nuclear proteins in vitro which are recognized mainly by antibodies specific for C/EBP alpha. Furthermore, transient expression of C/EBP alpha and to a lesser extent C/EBP beta expression vectors, results in transactivation of a cotransfected C/EBP alpha promoter-luciferase reporter construct. These experiments support the notion that the C/EBP alpha gene is regulated by C/EBP alpha but other C/EBP-related proteins may also be involved.

Animals↗

PubMed1992

Hepatic steroid hydroxylating enzymes are controlled by the sexually dimorphic pattern of growth hormone secretion in normal and dwarf rats.

In rats, the onset of the sexually dimorphic pattern of growth hormone (GH) secretion and increased hepatic GH-binding capacity at puberty are temporally correlated with the sex-dependent expression of some hepatic cytochrome P450 enzymes involved in steroid metabolism. There are indications that the expression of the GH receptor gene itself is dependent on the sexually differentiated pattern of GH secretion. However, the molecular mechanisms by which a given pattern of GH secretion turns on a specific set of genes in the hepatocyte are not yet understood. Studies of the cytochrome P450 2C gene subfamily in hypophysectomized rats and isolated hepatocytes suggest that one major mechanism of GH action in the liver occurs through modulation of gene transcriptional initiation. The occurrence, in dwarf rats and in rats treated neonatally with monosodium glutamate, of sex differences in GH secretion and liver steroid metabolism typical of normal rats, in spite of a 95% reduction in pituitary GH levels, is compatible with the notion that extremely low levels of circulating GH are sufficient to regulate the expression of liver steroid-metabolizing enzymes. This, together with the fact that single daily subcutaneous injections of GH are sufficient to masculinize the liver of a hypophysectomized rat, indicates that neither the amplitude nor the frequency of the GH pulse is recognized as male or female by the hepatocyte, but rather the complete and prolonged suppression (in males) or the persistence (in females) of circulating GH during the trough period after a GH surge.

Animals↗

PubMed1992

Constitutive expression and hormonal regulation of male sexually differentiated cytochromes P450 in primary cultured rat hepatocytes.

Experiments, predominantly performed in vivo, have shown that the pattern of growth hormone (GH) release from the pituitary gland is a major regulator of sex-specific cytochromes P450 (P450) in rats and other rodents. However, difficulty in constitutively expressing male-specific forms of P450 using in vitro models, such as primary cell culture, has impeded efforts to examine the direct actions of hormones on these enzyme forms. In the present study mRNA species for the male-specific P450 2C11 and 2C13, but not 3A2, were successfully expressed in primary hepatocytes cultured on a laminin-rich extracellular matrix (matrigel) in a serum-free, chemically defined medium containing insulin as the only hormone. When cells were exposed to GH (100 ng/ml), 2C11 mRNA expression was virtually abolished and 2C13 expression decreased to approximately 50% of control values, demonstrating that the negative regulation of these P450 forms by GH is a direct action on hepatocytes. Dexamethasone (DEX, 10(-8) M) increased the expression of 2C11 to 195% while decreasing 2C13 expression to 25% of control values. When GH and DEX were administered concurrently 2C11 was downregulated, indicating that GH is the dominant regulatory hormone for this form. L-Triiodothyronine (T3) (10(-9) M) suppressed 2C11 (46% of control) but had no effect on 2C13 mRNA expression. The positive regulatory effect of glucocorticoids on 2C11 was also found to occur in vivo and demonstrated to operate predominantly at the transcriptional level. This study demonstrates that primary cultures of hypatocytes are a suitable in vitro model for studies on regulation of some male-specific P450 forms and that GH, DEX, and T3 act directly on hepatocytes at a pretranslational level to regulate these forms.

Animals↗

PubMed1992

Growth hormone regulation of hepatic cytochrome P450 expression in the rat.

GH by means of its sexually differentiated secretory pattern is the predominant regulator of the expression of cytochrome P450 enzymes responsible for a sexual dimorphism of hepatic steroid metabolism. Other hormones, such as gonadal, thyroid and glucocorticoid hormones, as well as insulin appear to modulate the sexually differentiated expression of these enzymes. The major constitutively expressed sex specific forms of P450, belonging to the P4502C-subfamily, have been shown to be regulated by GH at the level of transcription. However, the GH postreceptor events leading to increased or decreased transcriptional activity are essentially unknown. Neither is the functional role of the soluble GH binding protein yet resolved. On-going protein synthesis is a prerequisite for GH transcriptional activation of the female specific P4502C12 but not for all GH effects in the hepatocyte. With regard to signalling mechanisms PKC activity appears to be permissive for the GH induction of P4502C12 but some as yet unidentified factor/kinase(s) may also be activated. The transcriptional control exerted on the rat P4502C-gene subfamily by the pattern of GH secretion offers a versatile tool to elucidate the molecular mechanisms of GH regulation of cytochrome P450 expression.

Androgens↗

PubMed1992

Transcriptional regulation of rat P-450 2C gene subfamily members by the sexually dimorphic pattern of growth hormone secretion.

The onset of the sexually dimorphic pattern of GH secretion and increased hepatic GH-binding capacity in rats at puberty is temporally correlated with the developmental induction of three hepatic cytochrome P-450s with steroid hydroxylase activity, P-450 IIC11, P-450 IIC12, and P-450 IIC13, and one cytochrome P-450 with vitamin A hydroxylase activity, P-450 IIC7. In this study we demonstrate that expression of the 2C11, 2C12, and 2C13 genes is modulated by GH at the level of transcriptional initiation both in vivo and in primary cultures of adult hepatocytes. In an effort to define the minimum sequence responsible for the inductive effects of GH, we have analyzed the ability of a 0.7-kilobase fragment isolated from the 5'-flank of the 2C12 gene, including the natural promoter, to drive transcription of a 320-basepair G-less cassette in vitro. We were unable to detect any substantial difference in RNA polymerase-II-dependent transcriptional efficiency toward the 2C12 promoter between liver nuclear extracts from normal and hypophysectomized rats of both sexes. This observation supports the assumption that the sequence information contained between bases -700 and 1 is sufficient to support basal transcription of the 2C12 gene. Sequence information residing 5' or 3' of the 0.7-kilobase 5'-flank or a higher ordered chromatin structure may be necessary for the sex-specific transcriptional activation of the 2C12 gene.

Animals↗

PubMed1991

A role for protein kinases in the growth hormone regulation of cytochrome P4502C12 and insulin-like growth factor-I messenger RNA expression in primary adult rat hepatocytes.

GH is a major determinant of cytochrome P4502C12 and insulin-like growth factor-I (IGF-I) mRNA expression in rat liver. In the present study, a possible role for protein kinase C (PKC) in the GH-mediated regulation of these two genes was investigated. Addition of bovine GH (bGH) to cultured primary adult rat hepatocytes lead to the formation of diacylglycerol and subsequent induction of P4502C12 and IGF-I mRNA, indicating a PKC-dependent signal transduction. However, stimulation of PKC by phorbol 12-myristate 13-acetate (PMA) or sn-1,2-dioctanoylglycerol treatment, in dose and time-course experiments in the presence or absence of ionomycin, failed to induce either P4502C12 or IGF-I mRNA. On the other hand, down-regulation of PKC by PMA treatment, i.e. 24 h pretreatment, attenuated the bGH induction of both P4502C12 and IGF-I mRNA. One hundred nanomolar PMA reduced the bGH-stimulated expression of both IGF-I mRNA and P4502C12 mRNA (approximately 50%). Treatment with the potent kinase inhibitor staurosporine in combination with bGH caused a dose-dependent decrease of the bGH response with different sensitivities toward the inhibitor for the different mRNA species, IGF-I being less sensitive. These data indicate a permissive role for PKC in the GH-mediated induction of P4502C12 and IGF-I mRNA. When activators of protein kinase A, such as forskolin and 8-Br-cAMP were added to the culture medium opposite effects were observed on the mRNA levels of P4502C12 and IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaloids↗

PubMed1989

Interleukin-2 induces a rapid increase in ornithine decarboxylase mRNA in a cloned murine T lymphocytic cell line.

We recently observed a 25-fold increase in the activity of ornithine decarboxylase (ODC) 6 h after treatment of G1-synchronized CTLL-2 cells with interleukin-2 (IL-2). Here we show that the ODC mRNA content increased in parallel with the ODC activity during the first hours of stimulation with IL-2, resulting in a 25-fold increase at 6 h. Between 6 and 24 h the ODC mRNA content continued to increase steadily up to 50-fold, even after the ODC activity had returned to low basal levels. In the case of density-arrested CTLL-2 cells deprived of IL-2 for 16 h, the IL-2-mediated increase in ODC mRNA was 2-fold at 1 h and 5-fold at 8 h, irrespective of the capability of the cells to resume their cycle. There was no marked increase in the rate of transcription of the ODC gene, at least during the first 2 h of stimulation with IL-2. These findings suggest that the regulation of the ODC activity by IL-2 is a primary event in IL-2-induced cell proliferation and occurs at the post-transcriptional level, possibly by stabilizing the ODC mRNA and affecting the efficiency of translation of the messenger.

Animals↗

PubMed1989

Interleukin-2 regulates the activity of ornithine decarboxylase in a cloned murine T lymphocytic cell line: evidence for a protein kinase C-dependent pathway.

The role of protein kinase C (PKC) in the regulation of ornithine decarboxylase (ODC) activity during interleukin-2 (IL-2)-dependent cell growth was investigated. A large biphasic increase in the activity of ODC was observed after treatment of IL-2-deprived CTLL-2 cells with recombinant human IL-2 (rec IL-2). The PKC activators phorbol 12-myristate 13-acetate (PMA) and 4 beta-phorbol 12,13-didecanoate (4 beta-PDD), but not the inactive analog 4 alpha-PDD, induced ODC activity in exponentially growing cultures. Unlike IL-2, however, phorbol esters were poor inducers of IL-2-depleted cultures. H-7, a potent inhibitor of PKC and cyclic nucleotide-dependent protein kinases (CN-PK), suppressed the IL-2-induced ODC activity, while HA1004, a more potent inhibitor of CN-PK than of PKC, had opposite effects depending on its concentration. The results suggest that activation of PKC is involved in but is not the sole mechanism for the induction of ODC by rec IL-2. At concentrations which suppressed the induction of ODC activity by IL-2, H-7 inhibited DNA synthesis and HA1004 did not.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1988

A third genetic locus affecting the Ah (dioxin) receptor.

We have isolated a new benzo(a)pyrene-resistant clone, c35, of the mouse hepatoma line, Hepa-1. Cytochrome P1-450 mRNA and P1-450-dependent aryl hydrocarbon hydroxylase (AHH) activity are no longer inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin in c35. The phenotype of c35 is unstable in long-term culture. A subclone, c35-1, having partially restored AHH inducibility, was studied in detail. The concentration of dioxin required to give half-maximal induction of AHH activity was 16-fold greater in c35-1 than in Hepa-1. Scatchard analysis showed that c35-1 contains reduced levels of the Ah (dioxin) receptor, which mediates induction of P1-450, but that the affinity of the receptor for dioxin is unaltered. In vivo assays confirmed that c35-1 possesses reduced levels of receptor but showed that it is even more severely affected in nuclear translocation of the receptor. Somatic cell hybridization experiments demonstrated that c35 is recessive and belongs to a new, third complementation group of mutants defective in Ah receptor activity. We propose that c35 is mutated either in the ligand-binding Ah receptor polypeptide or in another polypeptide required for receptor function and that in c35-1 partial reversion has occurred to generate a polypeptide which is still impaired in its role in promoting nuclear translocation and/or DNA binding.

Animals↗

PubMed1984

DNA binding of [14C]styrene in isolated rat hepatocytes.

Incubation of hepatocytes from phenobarbital-pretreated rats with diethylmaleate (DEM) and 1 mM [14C]styrene for 3 to 5 hours did not result in binding of styrene 7,8-oxide (SO) to DNA as determined by ion exchange chromatography of enzymatic digests of DNA. The elution of substantial amounts of radioactivity together with natural nucleosides and bases suggests that styrene is partly metabolized via splitting of the vinyl bond and that incorporation of C1 fragments into DNA is most likely the result of repair DNA synthesis following DNA damage by styrene itself or one of its metabolites.

Animals↗