Validation of DNA test for hip dysplasia failed in Danish Labrador Retrievers

Canine hip dysplasia is characterized by poor hip joint conformation and laxity. The disease is a complex trait influenced by both genetics and environment. Diagnosis and quantification of hip dysplasia are performed by radiographic examination of the hip joint and the diagnosis is used for making breeding decisions in many breeds. A prognostic genetic test (the Dysgen test) based on seven associated SNPs has been developed in a study based on Spanish Labrador Retrievers. In our study this test has been evaluated in 39 Danish Labrador Retrievers with known radiographic hip score: 14 with hip dysplasia (grade D or E) and 25 without hip dysplasia (grade A or B). There was no significant correlation between the Dysgen test results and the radiographic hip status (P = 0.3203) in these dogs, indicating that Dysgen test results obtained for Danish Labrador Retrievers have no prognostic value.

Effect of silencing the two major tomato fruit pectin methylesterase isoforms on cell wall pectin metabolism

Post-harvest storage is largely limited by fruit softening, a result of cell wall degradation. Pectin methylesterase (PE) (EC 3.1.1.11) is a major hydrolase responsible for pectin de-esterification in the cell wall, a response to fruit ripening. Two major PE isoforms, PE1 and PE2, have been isolated from tomato (Solanum lycopersicon) pericarp tissue and both have previously been down-regulated using antisense suppression. In this paper, PE1 and PE2 double antisense tomato plants were successfully generated through crossing the two single antisense lines. In the double antisense fruit, approximately 10% of normal PE activity remained and ripening associated pectin de-esterification was almost completely blocked. However, double antisense fruit softened normally during ripening. In tomato fruit, the PE1 isoform was found to contribute little to total PE activity and have little effect on the degree of esterification of pectin. In contrast, the other dominant fruit isoform, PE2, has a major impact on de-esterification of total pectin. PE2 appears to act on non-CDTA-soluble pectin during ripening and on CDTA-soluble pectin before the start of ripening in a potentially block-wise fashion.

Estrogen receptor β upregulates FOXO3a and causes induction of apoptosis through PUMA in prostate cancer

Estrogen receptor β (ERβ) is emerging as a critical factor in understanding prostate cancer biology. Although reduced in prostate cancer above Gleason grade 3, ERβ is a potential drug target at the initial stage of the disease. In human prostate cancer cells, we found that ERβ causes apoptosis by increasing the expression of pro-apoptotic factor p53-upregulated modulator of apoptosis (PUMA), independent of p53, but dependent on the forkhead transcription factor class-O family member, FOXO3a. FOXO3a has previously been shown to induce PUMA after growth factor withdrawal and inhibition of the Akt pathway. Surprisingly, the phosphorylation of FOXO3a remained unchanged, while the mRNA and total protein levels of FOXO3a were increased in response to ERβ expression or treatment of PC3, 22Rv1 and LNCaP cells with the ERβ-specific ligands 3β-Adiol (5α-androstane-3β,17β-diol), DPN (diarylpropionitrile) or 8β-VE2 (8-vinylestra-1,3,5 (10)-triene-3,17β-diol). Knockdown of FOXO3a or ERβ expression abolished the increase of PUMA in response to 3β-Adiol in LNCaP and PC3 cells, suggesting that FOXO3a mediates the apoptotic effect of 3β-Adiol-activated ERβ. Moreover, the ventral prostate of ERβ-/- mice had decreased expression of FOXO3a and PUMA compared with the ERβ+/+ mice, indicating a relationship between ERβ and FOXO3a expression. The regulation of FOXO3a by ERβ in normal basal epithelial cells indicates a function of ERβ in cell differentiation and maintenance of cells in a quiescent state. In addition, the expression of ERβ, FOXO3a and PUMA is comparable and higher in benign prostatic hyperplasia than in prostate cancer Gleason grade 4 or higher, where there is substantial loss of ERβ, FOXO3a and PUMA. We conclude that ERβ induces apoptosis of prostate cancer cells by increasing transcription of FOXO3a, leading to an increase of PUMA and subsequent triggering of apoptosis via the intrinsic pathway involving caspase-9. Furthermore, we conclude that ligands specifically activating ERβ could be useful pharmaceuticals in the treatment of prostate cancer.

Phytoestrogen-mediated inhibition of proliferation of the human T47D breast cancer cells depends on the ERalpha/ERbeta ratio

This study investigates the importance of the intracellular ratio of the two estrogen receptors ERalpha and ERbeta for the ultimate potential of the phytoestrogens genistein and quercetin to stimulate or inhibit cancer cell proliferation. This is of importance because (i) ERbeta has been postulated to play a role in modulating ERalpha-mediated cell proliferation, (ii) genistein and quercetin may be agonists for both receptor types and (iii) the ratio of ERalpha to ERbeta is known to vary between tissues. Using human osteosarcoma (U2OS) ERalpha or ERbeta reporter cells it was shown that compared to estradiol (E2), genistein and quercetin have not only a relatively greater preference for ERbeta but also a higher maximal potential for activating ERbeta-mediated gene expression. Using the human T47D breast cancer cell line with tetracycline-dependent ERbeta expression (T47D-ERbeta), the effect of a varying intracellular ERalpha/ERbeta ratio on E2- or pythoestrogen-induced cell proliferation was characterised. E2-induced proliferation of cells in which ERbeta expression was inhibited was similar to that of the T47D wild type cells, whereas this E2-induced cell proliferation was no longer observed when ERbeta expression was increased. With increased expression of ERbeta the phytoestrogen-induced cell proliferation was also reduced. These results point at the importance of the cellular ERalpha/ERbeta ratio for the ultimate effect of (phyto)estrogens on cell proliferation.

A genome-wide study of the repressive effects of estrogen receptor beta on estrogen receptor alpha signaling in breast cancer cells

Transcriptional effects of estrogen result from its activation of two estrogen receptor (ER) isoforms; ERalpha that drives proliferation and ERbeta that is antiproliferative. Expression of ERbeta in xenograft tumors from the T47D breast cancer cell line reduces tumor growth and angiogenesis. If ERbeta can halt tumor growth, its introduction into cancers may be a novel therapeutic approach to the treatment of estrogen-responsive cancers. To assess the complete impact of ERbeta on transcription, we have made a full transcriptome analysis of ERalpha- and ERbeta-mediated gene regulation in T47D cell line with Tet-Off regulated ERbeta expression. Of the 35 000 genes and transcripts analysed, 4.1% (1434) were altered by ERalpha activation. Tet withdrawal and subsequent ERbeta expression inhibited the ERalpha regulation of 998 genes and, in addition, altered expression of 152 non-ERalpha-regulated genes. ERalpha-induced and ERbeta-repressed genes were involved in proliferation, steroid/xenobiotic metabolism and ion transport. The ERbeta repressive effect was further confirmed by proliferation assays, where ERbeta was shown to completely oppose the ERalpha-E2 induced proliferation. Additional analysis of ERbeta with a mutated DNA-binding domain revealed that this mutant, at least for a quantity of genes, antagonizes ERalpha even more strongly than ERbeta wt. From an examination of the genes regulated by ERalpha and ERbeta, we suggest that introduction of ERbeta may be an alternative therapeutic approach to the treatment of certain cancers.

Estrogen receptor β represses breast tumor growth and angiogenesis in vivo

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Background: Estrogens are well known stimulators of breast cancer cell growth in vitro as well as in vivo. Two different estrogen receptors exist, namely estrogen receptor (ER) α and β. ERα mediates the proliferative effect of estrogen in breast cancer cells and we have earlier shown that ERβ inhibits cell-cycle progression in vitro. Estrogens are well known stimulators of in vivo breast cancer cell growth as well as angiogenesis, and the effect is mediated through ERα. The function of ERβ in this context is not well understood. Methods: We have used ERα-positive T47D breast cancer cells stably transfected with a Tet/Off regulated ERβ expression vector system. The ERβ-inducible tumor cells are studied in vitro as well as in vivo. Results: By transplanting ERβ-inducible breast cancer cells into SCID-mice, we show that ERβ inhibits tumor growth and reduces the volume of established tumors. Furthermore, we show by immunohistochemistry, that the number of blood microvessels in the tumor periphery is decreased by ERβ expression, counteracting the well-known pro-angiogenic effect of ERα. By Western blot analysis on tumor extracts, we show that the concentration of the important pro-angiogenic growth factors VEGF and bFGF, normally expressed by breast tumor cells, is decreased in the ERβ-expressing tumors compared to the normal tumors. To exclude that the observed anti-angiogenic effect is just a result of reduced tumor growth, we incubated Tet/Off regulated ERβ expressing cells in vitro, during non-hypoxic conditions. We found that the expression of ERβ leads to decreased expression of VEGF and PDGFβ at the mRNA and protein-levels. In transient transfection assays, we found estrogen-ERα mediated up regulation of VEGF, PDGFβ and bFGF-promoter activities in T47D cells, and these activities were all suppressed following co-transfection with an ERβ-expression vector. Conclusions: We conclude that ERβ inhibits growth factor expression at transcriptional level in breast cancer cells; taken together, our data indicates that ERβ inhibits growth and angiogenesis of tumors formed by T47D breast cancer cells. This makes ERβ an interesting therapeutic target in breast cancer and perhaps treatment with the newly designed ERβ-selective ligands might work as a new anti-proliferative and anti-angiogenic therapy.

No significant financial relationships to disclose.

Extracellular matrix components in atherosclerotic arteries of Apo E/LDL receptor deficient mice: an immunohistochemical study

During accelerated vascular remodeling such as in atherosclerosis, the composition of the extracellular matrix becomes altered. The matrix components of the diseased artery influence cellular processes such as adhesion, migration and proliferation. Furthermore, in atherosclerosis, the inability of the cells within the lesion to produce a mechanically stable matrix may lead to plaque rupture. In this immunohistochemical study of atherosclerotic mice aorta, we have reviewed the presence of ECM components with roles in maintaining tissue structure and function. These components include osteopontin and COMP as well as the leucine rich repeats proteins decorin, PRELP, and fibromodulin. Immunohistochemistry demonstrated presence of osteopontin, COMP, decorin, PRELP and fibromodulin in lesion areas of ApoE/LDLr deficient mice. Some advanced lesions exhibited areas of cartilage-like morphology and were shown to represent cartilage by their content of the cartilage specific proteins collagen II and aggrecan. The results suggest that cartilage-associated cell/collagen binding ECM proteins may be involved in the pathogenesis of atherosclerosis.

The Hairy and Enhancer of Split homologue-1 (HES-1) mediates the proliferative effect of 17beta-estradiol on breast cancer cell lines

The mechanism behind hormone dependent growth of breast cancer is presently not well understood. We show that the HES-1 protein level in the breast cancer cell lines T47D and MCF-7 is down regulated by 17beta-estradiol treatment. This regulation could be reversed by addition of the anti-estrogens 4OH tamoxifen, raloxifen and Imperial Chemical Industries (ICI) 182,780. In T47D cells with inducible exogenous HES-1 expression, induced expression of HES-1 protein prevented the proliferative effect of 17beta-estradiol and subsequent up regulation of proliferating cell nuclear antigen (PCNA). An inverse correlation between the HES-1 and PCNA protein levels respectively was found in colon cancer cell lines. These findings point to a potential role of HES-1 as a tumor suppressor in epithelial cells, and as a mediator of 17beta-estradiols proliferative effect on breast cancer cells.

Estrogen receptor beta mRNA in colon cancer cells: growth effects of estrogen and genistein

Knowledge regarding the expression of the recently cloned estrogen receptor beta (ERbeta) in colonic mucosa is limited. In this study, we demonstrated that five human colon cancer cell lines, HT29, Colo320, Lovo, SW480, and HCT116, expressed ERbeta mRNA, but lacked ERalpha mRNA. Results from a cell growth assay demonstrated that these colon cancer cells were not influenced by estrogen, while genistein possessed slight growth inhibitory effects on HT29, Colo320 and Lovo cells at 10 microM, at which concentration is stimulated the growth of ERalpha-positive human breast cancer MCF-7 cells. Tamoxifen inhibited the growth of HT29 and Colo320 cells, dose-dependently, as well as MCF-7 cells. A transfected reporter plasmid containing a vitellogenin estrogen response element could be activated by estradiol in Colo320 cells. Taken together with previous reports, these data suggest that ERalpha and ERbeta may have different biological functions in colon cells.

Mediation of NGF signaling by post-translational inhibition of HES-1, a basic helix-loop-helix repressor of neuronal differentiation

The induction of neurite outgrowth by NGF is a transcription-dependent process in PC12 cells, but the transcription factors that mediate this process are not known. Here we show that the bHLH transcriptional repressor HES-1 is a mediator of this process. Inactivation of endogenous HES-1 by forced expression of a dominant-negative protein induces neurite outgrowth in the absence of NGF and increases response to NGF. In contrast, expression of additional wild-type HES-1 protein represses and delays response to NGF. Endogenous HES-1 DNA-binding activity is post-translationally inhibited during NGF signaling in vivo, and phosphorylation of PKC consensus sites in the HES-1 DNA-binding domain inhibits DNA binding by purified HES-1 in vitro. Mutation of these sites generates a constitutively active protein that strongly and persistently blocks response to NGF. These results suggest that post-translational inhibition of HES-1 is both essential for and partially mediates the induction of neurite outgrowth by NGF signaling.

Characterization of orphan nuclear receptor binding elements in sex-differentiated members of the CYP2C gene family expressed in rat liver

The HepG2-specific P450 2C factor motif (HPF1-motif) is conserved in many hepatic cytochrome P450 genes (CYP). Its functional importance for rabbit CYP2C genes has led to the proposal that the HPF1 motif acts as a common regulator for the liver-specific expression of CYP2 genes with hepatic nuclear factor (HNF)-4 being the corresponding trans-activator. The HPF1-like elements in the rat CYP2C genes 2C7, 2C11, 2C12, and 2C13 have been studied with regard to functional importance and binding of the orphan receptors HNF-4, apoAI regulatory protein-1 (ARP-1), and v-erbA-related receptors (EAR) 3 and 2. Binding activity in rat liver nuclear extracts includes these orphan receptors as judged from electromobility supershift experiments and from results obtained with expressed receptors, although the element in CYP2C11 did not bind HNF-4. Mutations of the HPF1-like elements in the CYP2C7, CYP2C11, and CYP2C12 promoters had marginal effects on the expression of luciferase reporter gene constructs transiently transfected into HepG2 cells, whereas for CYP2C13 the activity was reduced to 60% of the wild type construct. Coexpression of HNF-4 in COS-7 cells had limited effect on the luciferase activity generated from the 2C promoters, maximally 3-fold. Our data indicate that the HPF1 elements in the rat CYP2C genes have limited functional importance and that HNF-4 is not a major trans-activator for any of these genes.

Increased expression of c-jun, junB, AP-1, and preproenkephalin mRNA in rat striatum following a single injection of caffeine

The effect of a single injection of caffeine on the expression of c-fos, c-jun, junB, and junD, on activator protein 1 (AP-1) and on the levels of preproenkephalin mRNA in rat striatum was studied. Male rats were given caffeine (25 mg/kg, 50 mg/kg, or 100 mg/kg, i.p.) and sacrificed at different times (0.5, 1, 2, 4, or 8 hr) after administration. By using in situ hybridization of adjacent sections we found a rapid, transient, and dose-dependent increase of c-fos, c-jun, and junB by caffeine in striatum, especially in the lateral part. The induction peaked after 1 hr, but persisted for 2 hr, and in the case of junB for 4 hr. No induction of junD was found. A strong induction of junB, a weak induction of c-fos and c-jun, but not of junD, was seen in nucleus accumbens. Furthermore, by using gel shift assay we found an induction of AP-1 by caffeine (100 mg/kg) in striatum, which peaked 2 hr after administration and was clearly increased after 4 hr. c-Fos, c-Jun, and JunB proteins were components of the AP-1. There was also a dose-dependent induction of preproenkephalin mRNA, which was most pronounced in the lateral and caudal part of striatum; the level peaked 4 hr after injection and was still significantly increased after 8 hr. In a complementary study we could not find increased binding to the AP-1-like site in the 5'-flanking sequence of proenkephalin following caffeine treatment. The data show that a single dose of caffeine induces a temporally and spatially characteristic pattern of c-fos, c-jun, and junB induction, followed by changes in AP-1 and preproenkephalin mRNA. Thus, a single dose of caffeine causes changes in gene transcription in the brain that may be related to the adaptive changes that occur after caffeine administration. However, a direct causal link between the immediate early genes and enkephalin could not be proven.

Suppression of the constitutive expression of cytochrome P-450 2C11 by cytokines and interferons in primary cultures of rat hepatocytes: comparison with induction of acute-phase genes and demonstration that CYP2C11 promoter sequences are involved in the suppressive response to interleukins 1 and 6

Hepatic expression of various members of the cytochrome P-450 (CYP) superfamily is suppressed during inflammatory responses. We have shown that the specific expression of P-450 2C11 in male rat liver is suppressed transcriptionally by endotoxin treatment. To investigate the molecular mechanisms underlying this phenomenon, we studied the effects of the inflammatory cytokines interleukin (IL)-1, IL-6, tumor necrosis factor-alpha (TNF), interferon (IFN)-alpha, and IFN-gamma on the expression of P-450 2C11 and the mRNAs of two typical acute-phase protein genes, alpha 1-acid glycoprotein (AGP) and fibrinogen, in primary hepatocyte cultures. IL-1, IL-6, TNF, and IFN-alpha all suppressed P-450 2C11 mRNA, whereas IFN-gamma had no effect. IL-1 and TNF were more effective than IL-6 in the suppression of P-450 2C11 mRNA. Whereas IL-1 and IL-6 effects on P-450 2C11 were accompanied by induction of AGP and fibrinogen mRNAs, IFN-alpha and TNF treatments had no effects on AGP. The suppression of P-450 2C11 and the induction of AGP by IL-1 showed similar time courses. The combination of IL-1 and IL-6 showed additivity in suppression of P-450 2C11, at maximally effective concentrations of cytokines. The effects of IL-1 on P-450 2C11 and AGP expression were blocked by IL-1 receptor antagonist protein. We also studied the effects of IL-1 and IL-6 on the transient expression of chloramphenicol acetyl-transferase reporter gene constructs containing 200 or 1287 base pairs of the 5' flanking region of the CYP2C11 gene, transfected into primary hepatocytes. The chloramphenicol acetyltransferase activities in cells transfected with the 200-base pair construct were reduced to about 33% and 58% of control levels by treatment with IL-1 or IL-6, respectively, suggesting that sequences important for cytokine down-regulation lie within the proximal promoter region of the CYP2C11 gene.

The human spiral ganglion

The adult normal human spiral ganglion (SG) was analyzed with regard to ultrastructure and immunohistochemistry. The cytoskeleton of the SG cells was found to comprise F-actin, intermediate filaments (IFs) and microtubules (MTs). The IF subgroups (cytokeratins, Cks; neurofilaments, NFs, vimentin, glial fibrillary acidic proteins, GFAP; desmin) displayed characteristic staining patterns. Ck No. 8 was found in all SG cells, whereas vimentin was lacking. GFAP stained only a small subpopulation of SG cells (type 2?). The light (68 kD) and medium-sized chains of NFs occurred in all SG cells and axons, whereas the 200-kD NF subunit was only found in the axonal hillock of (type 2?) SG cells, but in no other part of the cytoplasm, and regionally in nerve fibres. MAP-1 and MAP-2 occurred in all SG cells but only MAP-1 was found in the nerve fibres. The calcium-binding protein synaptophysin (SY) was expressed only in SG cells, in contrast to the S-100 which occurred more generally in the labyrinth. The neuropeptides VIP and substance P were identified in all SG cells, in contrast to NPY which was expressed in a small subpopulation of SG cell (type 2?). Staining for neuron-specific enolase (NSE) identified most (type 1?) but not all SG cells. The cell surface glycoprotein Thy-1 was expressed in SG cells in a way similar to that described for neurons in the CNS. The SG cells express a high degree of cytoskeletal complexity, allowing one to distinguish between type 1 and type 2 cells. The cell bodies and their adjacent nerve fibres show characteristic features of calcium-binding proteins, surface membrane glycoproteins, NSE and neuropeptides but the basic pattern is still similar to neurons in the CNS.

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.

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.

The role and mechanism of growth hormone in the regulation of sexually dimorphic P450 enzymes in rat liver

The determination of sexually dimorphic hepatic steroid metabolism in rat liver has been shown to involve growth hormone. However, the mechanisms by which growth hormone controls the cytochrome P450 enzymes responsible for this dimorphic steroid metabolism is largely unknown. In this review we discuss different levels of growth hormone signal transduction, including receptor binding, signal transduction and activation of target genes by growth hormone.

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.

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.

Gene structure and expression of the rat cytochrome P450IIC13, a polymorphic, male-specific cytochrome in the P450IIC subfamily

The male-specific CYP2C13 gene has been isolated from two independent rat genomic libraries. This gene spans more than 50 kb and contains eight introns which are subject to the GT-AG rule. Two allelic forms of the CYP2C13 gene were identified. Determination of the exonic sequences revealed that one of them encodes cytochrome P450(+g) and the other encodes cytochrome P450(-g). Using allele-specific restriction enzyme sites, a good correlation between the genotype and the phenotype of CYP2C13 was shown. Nucleotide substitutions between the (+g) and the (-g) genes exist not only in the exons but also in the introns and the 5'-flanking region. Although five nucleotide differences were identified within 287 base pairs of the (+g) and (-g) 5'-flanking regions, the transcription initiation sites were identical. In addition to a canonical TATA box located 31 base pairs upstream of the start site of transcription, putative binding sites for the liver-enriched and liver-specific transcription factors HNF1/LF-B1/APF, HNF3, HNF4/AF-1, C/EBP, LAP, and eH-TF/TGT3 and the ubiquitous factors NF-1 and OTF-1 were identified.

Growth hormone regulation of the cytochrome P-450IIC subfamily in the rat: inductive, repressive, and transcriptional effects on P-450f (IIC7) and P-450PB1 (IIC6) gene expression

The effects of growth hormone (GH) on two constitutively expressed rat liver cytochrome P-450 (P-450) enzymes, namely P-450f (IIC7) and P-450PB1 (IIC6), have been investigated. Hypophysectomy of both male and female rats results in low expression of P-450f. Single daily injections of GH cannot restore expression of P-450f but further repress it. Continuous administration of GH, on the other hand, increases expression of P-450f to levels comparable to those of the normal male and female rat. P-450PB1 is minimally affected by hypophysectomy or GH treatment, although a weak but significant repression by continuous administration of GH can be detected. Run-on analysis shows that continuous GH treatment increases transcription of P-450f. In addition, the sequence of the 5' flanking region of this gene reveals DNA segments that might have a putative role in the transcriptional regulation of P-450f by GH.

Structural and regulatory analysis of a cytochrome P450 gene (CYP2C12) expressed predominantly in female rat liver

Cytochrome P450 15 beta is a female-specific gene product that catalyzes the hydroxylation of steroid sulfates at the 15 beta position. Isolation and analysis of the gene for rat P450 15 beta reveals nine coding exons and encompasses more than 35 kb of chromosomal DNA. The intron-exon junctions are at similar positions with the P450 genes of the II family, whose gene structure has been determined. Sequencing of about 2 kb of the 5'-flanking region indicates the presence of the Alu-like R.dre.1 repetitive sequence, a GA-rich stretch that is also found in the 5'-flanking DNA of the male-specific cytochrome P450 16 alpha gene, the enhancer octamer sequence ATGCAAAT, and three CAAAGTT repeats just upstream from the TATA box. Primer extension reveals a major and a minor transcription start site located 22 and 26 bases 5' to the translation initiation codon, respectively. This gene is developmentally regulated and transcriptional activation accounts, at least partly, for the sexually differentiated expression of cytochrome P450 15 beta.

Structural and regulatory analysis of the male-specific rat liver cytochrome P-450 g: repression by continuous growth hormone administration

Complementary DNA clones encoding the male-specific rat liver cytochrome P-450 g have been isolated by cross-hybridization with sequences from the female-specific rat liver cytochrome P-450 15 beta. Tissue distribution analysis indicates the liver as the organ with major expression of this cytochrome P-450 gene. Minimal P-450 g expression was also detected in prostate, kidney, heart, and brain. A developmental analysis reveals liver expression in the 8-week-old male and to a lesser extent in the 4-week-old male, but no detectable expression is seen in females of these ages or in 1- and 2-week-old rats from both sexes. Hypophysectomy of female rats dramatically increases hepatic expression of P-450 g, whereas continuous GH administration represses hepatic expression in male or female hypophysectomized rats. In similarity to P-450 15 beta and P-450 16 alpha, therefore, the cytochrome P-450 g gene in liver is GH regulated.

A dual role of growth hormone as a feminizing and masculinizing factor in the control of sex-specific cytochrome P-450 isozymes in rat liver

The effects of GH on the major constitutive sex-specific forms of cytochrome P-450 (P-45015 beta and P-45016 alpha) were studied in hypophysectomized rats at the mRNA level. Time-course experiments were performed with or without simultaneous treatment with thyroxine and cortisol. Intermittent administration of GH, mimicking the male secretory pattern, caused complete masculinization of the male specific P-45016 alpha at a pretranslational level in the absence and presence of thyroxine and cortisol. When GH was administered continuously, mimicking the female secretory pattern, the female specific P-45015 beta was induced, an effect that was dramatically potentiated by simultaneous treatment with thyroxine and cortisol. A synergistic effect of thyroxine and cortisol at a pretranslational level was demonstrated, although the major potentiating effect could be attributed to thyroxine. Thus it was concluded that GH, depending on its secretory pattern is the sole masculinizing factor for cytochrome P-450, and that it is also a feminizing factor, although this activity requires the synergistic action of thyroid hormones and glucocorticoids to reach its full effect.

cDNA cloning, sequence, and regulation of a major female-specific and growth hormone-inducible rat liver cytochrome P-450 active in 15 beta-hydroxylation of steroid sulfates

cDNA clones encompassing the complete coding sequence for the female-specific rat liver microsomal 15 beta-hydroxylase have been isolated and sequenced. This cytochrome P-450 species (P-450 15 beta) has a total of 490 amino acid residues, and its deduced amino acid sequence as well as direct sequencing of the amino-terminal portion of the purified protein revealed its identity with P-450 i. P-450 15 beta was found to be 66% similar to the male-specific rat liver microsomal 16 alpha-hydroxylase, P-450 16 alpha. Furthermore, P-450 15 beta is 47% similar to the major phenobarbital-inducible cytochrome P-450 in rat liver, P-450 b, while its structural similarity to P-450 c, P-450 pregnenolone-16a-carbonitrile, and P-450 lauric acid omega-hydroxylase is less than 30%. However, the developmentally regulated cytochromes P-450 f and P-450 PB-1 both have 68% similarity to P-450 15 beta. It is therefore concluded that P-450 15 beta belongs to the same gene subfamily (P450IIC) that also includes cytochromes P-450 f, PB-1, and 16 alpha. The plasma pattern of growth hormone (GH) is known to be a major determinant for the sex-specific expression of P-450 15 beta and P-450 16 alpha. Continuous infusion of GH to hypophysectomized male rats causes an increase in P-450 15 beta mRNA after 6 days of treatment, while intermittent injections have no effect. On the other hand, no effect on P-450 16 alpha mRNA is observed after continuous administration of GH, while intermittent injections cause an increase after 2 days of treatment. This relatively long period before P-450 15 beta and P-450 16 alpha mRNA induction is seen might indicate that protein factors mediating GH action are involved.

Cloning and pretranslational hormonal regulation of testosterone 16 alpha-hydroxylase (P-45016 alpha) in male rat liver

cDNA clones for P-45016 alpha were isolated from a male liver lambda gt11 expression library using antibodies against P-45016 alpha. The clones encompassed 1633 and 1791 bp, respectively. The latter clone contained the whole coding sequence. The 20 deduced NH2-terminal amino acids were identical to those of P-450h and the cDNA sequence was in complete agreement with that of P-450 (M-1). Northern blots showed that P-45016 alpha in the rat liver is pretranslationally regulated by the growth hormone secretory pattern. Southern blots indicated that few genes belong to the same P-450 gene family as P-45016 alpha.

Analysis of sister-chromatid exchanges and tumorigenicity in cell hybrids

The relationship between the ‘spontaneous’ frequency of sister-chromatid exchanges (SCE) and tumorigenicity was studied in a series of hybrids between a C57BL melanoma cell line and diploid cells, but no correlation was found between the 2 variables. Hybrids in which malignancy was suppressed and malignant segregants derived from them showed virtually identical SCE frequencies. Variation of SCE frequencies was observed, however, between the different hybrid clones, and most hybrids showed consistently less SCE per chromosome than the corresponding parental cell types did under similar growth conditions. The lower SCE frequencies could neither be related to a higher number of chromosomes in the hybrid nor could they be related to the method of hybrid selection. These findings suggest that cell fusion might have induced epigenetic SCE frequency changes possible in the same way as modulation of SCE frequencies is known to occur in the humam leukocyte series.