Rnd1, a novel rho family GTPase, induces the formation of neuritic processes in PC12 cells

Rho family GTPases have been shown to be involved in the regulation of neuronal cell morphology, including neurite extension and retraction. Rho activation leads to neurite retraction and cell rounding, whereas Rac and Cdc42 are implicated in the promotion of filopodia and lamellipodia formation in growth cones and, therefore, in neurite extension. In this study, we examined the morphological role of Rnd1, a new member of Rho family GTPases, in PC12 cells, and found that expression of Rnd1 by itself caused the formation of many neuritic processes from the cell body with disruption of the cortical actin filaments, the processes having microtubules but few filamentous actin and neurofilaments. Treatment with cytochalasin D, an inhibitor of actin polymerization, could mimic the effects of expression of Rnd1, in that this inhibitor disrupted the cortical actin filaments and induced the formation of many thin processes containing microtubules. The process formation induced by Rnd1 was inhibited by dominant negative Rac1. These results suggest that Rnd1 induces the Rac-dependent neuritic process formation in part by disruption of the cortical actin filaments.

Endovascular treatment of direct carotid-cavernous fistulas using detachable coils

SUMMARY

Five direct carotid-cavernous fistulas (direct CCFs) in four patients were treated by an endovascular technique using detachable coils. The embolizations were performed according to one of two strategies. 1) By embolizing the fistula, that is the compartment of the cavernous sinus adjacent to the fistula orifice, after embolization of the draining veins. 2) By embolizing the fistula only. The former strategy was used to treat first two cases and the latter to treat other three cases. In two of the cases in which only the fistula was embolized, a microcatheter was placed in the draining vein via a transvenous route beforehand, in the event that the embolization resulted in an incomplete closure and the draining veins became inaccessible. In four cases, a complete cure was achieved with preservation of the internal carotid artery and in one case, the internal carotid artery containing the fistula was occluded. The embolization of direct CCFs with detachable coils, which are suitable for both transarterial and transvenous approaches, has several advantages over balloon embolization. We believe this procedure will become an alternative treatment.

Heparan/chondroitin sulfate biosynthesis. Structure and mechanism of human glucuronyltransferase I

Human beta1,3-glucuronyltransferase I (GlcAT-I) is a central enzyme in the initial steps of proteoglycan synthesis. GlcAT-I transfers a glucuronic acid moiety from the uridine diphosphate-glucuronic acid (UDP-GlcUA) to the common linkage region trisaccharide Gal beta 1-3Gal beta 1-4Xyl covalently bound to a Ser residue at the glycosaminylglycan attachment site of proteoglycans. We have now determined the crystal structure of GlcAT-1 at 2.3 A in the presence of the donor substrate product UDP, the catalytic Mn(2+) ion, and the acceptor substrate analog Gal beta 1-3Gal beta 1-4Xyl. The enzyme is a alpha/beta protein with two subdomains that constitute the donor and acceptor substrate binding site. The active site residues lie in a cleft extending across both subdomains in which the trisaccharide molecule is oriented perpendicular to the UDP. Residues Glu(227), Asp(252), and Glu(281) dictate the binding orientation of the terminal Gal-2 moiety. Residue Glu(281) is in position to function as a catalytic base by deprotonating the incoming 3-hydroxyl group of the acceptor. The conserved DXD motif (Asp(194), Asp(195), Asp(196)) has direct interaction with the ribose of the UDP molecule as well as with the Mn(2+) ion. The key residues involved in substrate binding and catalysis are conserved in the glucuronyltransferase family as well as other glycosyltransferases.

Estrogen activation of the nuclear orphan receptor CAR (constitutive active receptor) in induction of the mouse Cyp2b10 gene

The nuclear orphan receptor CAR (constitutively active receptor or constitutive androstane receptor) can be activated in response to xenochemical exposure, such as activation by phenobarbital of a response element called NR1 found in the CYP2B gene. Here various steroids were screened for potential endogenous chemicals that may activate CAR, using the NR1 enhancer and Cyp2b10 induction in transfected HepG2 cell and/or in mouse primary hepatocytes as the experimental criteria. 17beta-Estradiol and estrone activated NR1, whereas estriol, estetrol, estradiol sulfate, and the synthetic estrogen diethylstilbestrol did not. On the other hand, progesterone and androgens repressed NR1 activity in HepG2 cells, and the repressed NR1 activity was fully restored by estradiol. Moreover, estrogen treatment elicited nuclear accumulation of CAR in the mouse livers, as well as primary hepatocytes, and induced the endogenous Cyp2b10 gene. Ovariectomy did not affect either the basal or induced level of CAR in the nucleus of the female livers, while castration slightly increased the basal and greatly increased the induced levels in the liver nucleus of male mice. Thus, endogenous estrogen appears not to regulate CAR in female mice, whereas endogenous androgen may be the repressive factor in male mice. Estrogen at pharmacological levels is an effective activator of CAR in both female and male mice, suggesting a biological and/or toxicological role of this receptor in estrogen metabolism. In addition to mouse CAR, estrogens activated rat CAR, whereas human CAR did not respond well to the estrogens under the experimental conditions.

Phenobarbital-elicited activation of nuclear receptor CAR in induction of cytochrome P450 genes

Phenobarbital (PB) increases metabolic capability of hepatocytes by its ability to activate numerous genes encoding various xenochemical-metabolizing enzymes such as cytochrome P450s and specific transferases. More than 35 years since PB induction was first reported, the key nuclear receptor CAR that mediates the induction has now been identified, and the molecular/cellular mechanism involving multiple signal transduction pathways has begun to be unraveled. In response to PB exposure, CAR in the cytoplasm translocates into the nucleus, forms a heterodimer with the retinoid X receptor, and activates the PB response enhancer element leading to the concerted induction of numerous genes.

Small GTPase RhoG is a key regulator for neurite outgrowth in PC12 cells

The Rho family of small GTPases has been implicated in cytoskeletal reorganization and subsequent morphological changes in various cell types. Among them, Rac and Cdc42 have been shown to be involved in neurite outgrowth in neuronal cells. In this study, we examined the role of RhoG, another member of Rho family GTPases, in nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. Expression of wild-type RhoG in PC12 cells induced neurite outgrowth in the absence of NGF, and the morphology of wild-type RhoG-expressing cells was similar to that of NGF-differentiated cells. Constitutively active RhoG-transfected cells extended short neurites but developed large lamellipodial or filopodial structures at the tips of neurites. RhoG-induced neurite outgrowth was inhibited by coexpression with dominant-negative Rac1 or Cdc42. In addition, expression of constitutively active RhoG elevated endogenous Rac1 and Cdc42 activities. We also found that the NGF-induced neurite outgrowth was enhanced by expression of wild-type RhoG whereas expression of dominant-negative RhoG suppressed the neurite outgrowth. Furthermore, constitutively active Ras-induced neurite outgrowth was also suppressed by dominant-negative RhoG. Taken together, these results suggest that RhoG is a key regulator in NGF-induced neurite outgrowth, acting downstream of Ras and upstream of Rac1 and Cdc42 in PC12 cells.

Receptor isoform-specific interaction of prostaglandin EP3 receptor with muskelin

By using the yeast two-hybrid system, muskelin was found to bind with the carboxy-terminal tail of the prostaglandin EP3 receptor alpha isoform but not with either the beta or gamma isoform. A direct interaction between the carboxy-terminal tail of the alpha isoform and muskelin was confirmed in vitro using recombinant fusion proteins. Analysis by confocal microscopy indicated that the isoform and muskelin were distributed at the plasma membrane in transfected cells. When the isoform was stimulated by agonist, the receptor was internalized in the cells expressing the receptor alone, but this internalization was partially inhibited by the cotransfection with muskelin. Furthermore, muskelin enhanced the Gi activity of the isoform. Thus, muskelin appears to be an isoform-specific anchoring protein for the EP3 receptor.

Expression of vascular endothelial growth factor by synovial fluid neutrophils in rheumatoid arthritis (RA)

Most of the leucocytes infiltrating rheumatoid synovial fluid (SF) are neutrophils capable of producing a variety of inflammatory mediators known to contribute significantly to the disease process during active RA. In the present study, we investigated the contribution made by SF neutrophils to the elevated levels of vascular endothelial growth factor (VEGF) seen in rheumatoid SF. Rheumatoid SF neutrophils were found to contain significantly larger amounts of both VEGF protein and its mRNA than peripheral blood neutrophils from either RA patients or healthy controls. Levels of cell-associated VEGF were well correlated with free VEGF in SF, which was significantly higher than in SF from osteoarthritis patients. Levels of SF neutrophil-associated VEGF also correlated with RA disease activity and cell surface integrin expression. Thus, SF neutrophil-associated VEGF may be considered an indicator of both local and systemic inflammation of RA, contributing to the neovascularization seen during RA synovitis.

ATF6 activated by proteolysis binds in the presence of NF-Y (CBF) directly to the cis-acting element responsible for the mammalian unfolded protein response

Transcription of genes encoding molecular chaperones and folding enzymes in the endoplasmic reticulum (ER) is induced by accumulation of unfolded proteins in the ER. This intracellular signaling, known as the unfolded protein response (UPR), is mediated by the cis-acting ER stress response element (ERSE) in mammals. In addition to ER chaperones, the mammalian transcription factor CHOP (also called GADD153) is induced by ER stress. We report here that the transcription factor XBP-1 (also called TREB5) is also induced by ER stress and that induction of CHOP and XBP-1 is mediated by ERSE. The ERSE consensus sequence is CCAAT-N(9)-CCACG. As the general transcription factor NF-Y (also known as CBF) binds to CCAAT, CCACG is considered to provide specificity in the mammalian UPR. We recently found that the basic leucine zipper protein ATF6 isolated as a CCACG-binding protein is synthesized as a transmembrane protein in the ER, and ER stress-induced proteolysis produces a soluble form of ATF6 that translocates into the nucleus. We report here that overexpression of soluble ATF6 activates transcription of the CHOP and XBP-1 genes as well as of ER chaperone genes constitutively, whereas overexpression of a dominant negative mutant of ATF6 blocks the induction by ER stress. Furthermore, we demonstrated that soluble ATF6 binds directly to CCACG only when CCAAT exactly 9 bp upstream of CCACG is bound to NF-Y. Based on these and other findings, we concluded that specific and direct interactions between ATF6 and ERSE are critical for transcriptional induction not only of ER chaperones but also of CHOP and XBP-1.

Regulatory DNA elements of phenobarbital-responsive cytochrome P450 CYP2B genes

This article reviews recent progress in characterizing cis-acting DNA elements of the phenobarbital-inducible CYP2B genes. Whereas proximal DNA elements such as the C/EBP binding site regulate basal transcription activity, phenobarbital-responsive enhancer activity is governed by the distal element (designated phenobarbital-responsive enhancer module, PBREM) residing about -2.3 kbp upstream from the transcription start site. Proximal elements are not required to enhance the phenobarbital-inducible transcription, since the PBREM can confer the inducibility to several heterologous promoters. Repression of the basal transcription by a negative element upstream of the -0.8 kbp region, however, may be necessary for the proper regulation of the CYP2B genes.

Galpha(12) and galpha(13) inhibit Ca(2+)-dependent exocytosis through Rho/Rho-associated kinase-dependent pathway

The release of neurotransmitters is known to be regulated by activation of heterotrimeric G protein-coupled receptors, although precise mechanisms have not yet been elucidated. To assess the role of the G(12) family of heterotrimeric G proteins in the regulation of neurotransmitter release, we established PC12 cell lines that expressed constitutively active Galpha(12) or Galpha(13) using an isopropyl-beta-D-thiogalactoside-inducible expression system. In the cells, expression of constitutively active Galpha(12) or Galpha(13) inhibited the high K(+)-evoked [(3)H]dopamine release without any effect on the high K(+)-induced increase in intracellular Ca(2+) concentration. A Ca(2+) ionophore ionomycin-induced [(3)H]dopamine release was also inhibited by the expression of active Galpha(12) or Galpha(13). These inhibitory effects of Galpha(12) and Galpha(13) on [(3)H]dopamine release were mimicked by the expression of constitutively active RhoA. In addition, Y-27632, and inhibitor of Rho-associated kinase, a downstream Rho effector, completely abolished the inhibition of [(3)H]dopamine release by Galpha(12), Galpha(13), and RhoA. These results indicate that Ca(2+)-dependent exocytosis is regulated by Galpha(12) and Galpha(13) through a Rho/Rho-associated kinase-dependent pathway.

Immunohistochemical localization of prostaglandin EP3 receptor in the rat nervous system

The prostaglandin EP3 receptor (EP3R) subtype is believed to mediate large portions of diverse physiologic actions of prostaglandin E2 in the nervous system. However, the distribution of EP3R protein has not yet been unveiled in the peripheral or central nervous systems. The authors raised a polyclonal antibody against an amino-terminal portion of rat EP3R that recognized specifically the receptor protein. In this study, immunoblotting analysis with this antibody showed several immunoreactive bands with different molecular weights in rat brain extracts and in membrane fractions of recombinant EP3R-expressing culture cells, and treatment with N-glycosidase shifted those immunoreactive bands to an apparently single band with a lower molecular weight, suggesting that EP3R proteins are modified posttranslationally with carbohydrate moieties of various sizes. The authors performed immunohistochemical investigation of EP3R in the rat brain, spinal cord, and peripheral ganglia by using the antibody. EP3R-like immunoreactivity was observed in many and discrete regions of the rostrocaudal axis of the nervous system. The signals were particularly strong in the anterior, intralaminar, and midline thalamic nuclear groups; the median preoptic nucleus; the medial mammillary nucleus; the superior colliculus; the periaqueductal gray; the lateral parabrachial nucleus; the nucleus of the solitary tract; and laminae I and II of the medullary and spinal dorsal horns. Sensory ganglia, such as the trigeminal, dorsal root, and nodose ganglia, contained many immunopositive neurons. Neuronal cells in the locus coeruleus and raphe nuclei exhibited EP3R-like immunoreactivity. This suggests that EP3R plays regulatory roles in the noradrenergic and serotonergic monoamine systems. Autonomic preganglionic nuclei, such as the dorsal motor nucleus of the vagus nerve, the spinal intermediolateral nucleus, and the sacral parasympathetic nucleus, also contained neuronal cell bodies with the immunoreactivity, implying modulatory functions of EP3R in the central autonomic nervous system. The characteristic distribution of EP3R provides valuable information on the mechanisms for various physiologic actions of prostaglandin E2 in the central and peripheral nervous systems.

Crystal structure of SULT2A3, human hydroxysteroid sulfotransferase

The crystal structure of SULT2A3 human hydroxysteroid sulfotransferase has been solved at 2.4 A resolution in the presence of 3'-phosphoadenosine 5'-phosphate (PAP). The overall structure is similar to those of SULT1 enzymes such as estrogen sulfotransferase and the PAP binding site is conserved, however, significant differences exist in the positions of loops Pro14-Ser20, Glu79-Ile82 and Tyr234-Gln244 in the substrate binding pocket. Moreover, protein interaction in the crystal structure has revealed a possible dimer-directed conformational alteration that may regulate the SULT activity.

Vascular endothelial growth factor expression and regulation of murine collagen-induced arthritis

We have examined the expression and function of the angiogenic factor, vascular endothelial growth factor (VEGF) during the evolution of type II collagen-induced arthritis (CIA). Biologically active VEGF was expressed along a time course that paralleled the expression of two specific VEGF receptors, Flk-1 and Flt-1, and the progression of joint disease. Moreover, levels of VEGF expression correlated with the degree of neovascularization, as defined by vWF levels, and arthritis severity. Macrophage- and fibroblast-like cells, which infiltrated inflamed sites and were then activated by other inflammatory mediators, are probably important sources of VEGF and may thus regulate angiogenesis during the development of CIA. Administration of anti-VEGF antiserum to CIA mice before the onset of arthritis delayed the onset, reduced the severity, and diminished the vWF content of arthritic joints. By contrast, administration of anti-VEGF antiserum after the onset of the disease had no effect on the progression or ultimate severity of the arthritis. These data suggest that VEGF plays a crucial role during an early stage of arthritis development, affecting both neovascularization and the progression of experimentally induced synovitis.

Different membrane targeting of prostaglandin EP3 receptor isoforms dependent on their carboxy-terminal tail structures

Mouse prostaglandin EP3 receptor consists of three isoforms, EP3alpha, beta and gamma, with different carboxy-terminal tails. To assess the role of their carboxy-terminal tails in membrane targeting, we examined subcellular localization of myc-tagged EP3 isoforms expressed in MDCK cells. Two isoforms, EP3alpha and EP3beta, were localized in the intracellular compartment but not in the plasma membrane, while the EP3gamma isoform was found in the lateral plasma membrane and in part in the intracellular compartment. Mutant EP3 receptor lacking the carboxy-terminal tail was localized in the intracellular compartment but not in the plasma membrane. Thus, EP3 isoforms differ in subcellular targeting, and the carboxy-terminal tails play an important role in determination of the membrane targeting of EP3 receptor.

Regulation of cytochrome P450 (CYP) genes by nuclear receptors

Members of the nuclear-receptor superfamily mediate crucial physiological functions by regulating the synthesis of their target genes. Nuclear receptors are usually activated by ligand binding. Cytochrome P450 (CYP) isoforms often catalyse both formation and degradation of these ligands. CYPs also metabolize many exogenous compounds, some of which may act as activators of nuclear receptors and disruptors of endocrine and cellular homoeostasis. This review summarizes recent findings that indicate that major classes of CYP genes are selectively regulated by certain ligand-activated nuclear receptors, thus creating tightly controlled networks.

Molecular decipherment of Rho effector pathways regulating tight-junction permeability

We reported recently that the activation of RhoA induced an increase in transepithelial electrical resistance (TER). To clarify effectors of Rho for this RhoA-induced regulation of tight-junction permeability, we introduced two effector-loop mutants of constitutively active RhoA(V14), RhoA(V14/L40) and RhoA(V14/C42), into Mardin-Darby canine kidney cells in an isopropyl beta-D-thiogalactoside-inducible expression system. RhoA(V14) and the two effector-loop mutants interacted in vitro with the Rho-binding domain of Rho-associated kinase, ROKalpha. Next we examined two parameters of Rho functions, stress-fibre formation and TER elevation, induced by RhoA(V14). Stress-fibre formation was induced by RhoA(V14/C42) but not by RhoA(V14/L40). On the other hand, TER elevation was induced by neither RhoA(V14/L40) nor RhoA(V14/C42). RhoA-associated kinase inhibitor, Y-27632, inhibited both stress-fibre formation and TER elevation induced by RhoA(V14). These results demonstrated that RhoA-induced regulation of tight-junction permeability is mediated by Rho-associated kinase and at least one other unidentified effector, the coupling to RhoA being disrupted by mutation at position 40 or 42 in the effector loop.

The role of intravascular embolization prior to radiosurgery of cerebral arteriovenous malformations. from the standpoint of hemorrhage and early obliteration after gamma knife radiosurgery

The role of intravascular embolization prior to radiosurgery of cerebral arteriovenous malformations was evaluated based on the basis of the results of gamma knife radiosurgery in relation to hemorrhage and early obliteration after treatment. Nine of 213 patients experienced hemorrhage 4 to 42 months after radiosurgery. All AVMs in these patients had dilated feeding arteries, and the flow of the AVM was rapid and/or high. An intranidal aneurysm was seen in one patient. Drainage of all AVMs consisted of a single and/or deep draining veins, and venous obstruction was found in six. Sixty-three of 87 patients followed for more than four years after radiosurgery were examined angiographically, and total obliteration of AVM was observed in 52 of them (82.5%). Early obliteration was found in 19 of the 34 patients examined within 12 months. The obliteration rate was significantly higher in slow- and low-flow AVMs (73.9%) than in rapid- and/or high-flow AVMs (18.2%). It is concluded that the role of intravascular embolization prior to radiosurgery is not only decreasing the size of the AVM but decreasing the risk of hemorrhage and shortening the latency period by decreasing their flow rate and flow volume.

Crystal structure of human catecholamine sulfotransferase

Sulfonation, like phosphorylation, can modify the activity of a variety of biological molecules. The sulfotransferase enzymes sulfonate neurotransmitters, drugs, steroid hormones, dietary carcinogens and proteins. SULT1A3 specifically sulfonates catecholamines such as dopamine, adrenaline and noradrenaline. The crystal structure of SULT1A3 with a sulfate bound at the active site, has been determined at 2.4 A resolution. Although the core alpha/beta fold is like that of estrogen and heparan sulfotransferases, major differences occur in and around the active site. Most notably, several regions surrounding the active site, including a section of 40 residues, are disordered in SULT1A3. Regions that are topologically equivalent to the disordered parts of SULT1A3 are involved in substrate and cofactor binding in estrogen and heparan sulfotransferase. Flexibility in these regions suggests that ligand binding elicits a disorder-order transition in and around the active site of sulfotransferases and might contribute to the broad substrate specificity of these enzymes.

Substrate gating confers steroid specificity to estrogen sulfotransferase

Estrogen sulfotransferase (EST) exhibits a high substrate specificity and catalytic efficiency toward estrogens such as estradiol (E2) but insignificant ability to sulfate hydroxysteroids such as dehydroepiandrosterone (DHEA). To provide the structural basis for this estrogen specificity, we mutated amino acid residues that constitute the substrate-binding site of EST. Among these mutants, only Tyr-81 decreased E2 and increased DHEA sulfotransferase activities. Substitution for Tyr-81 by smaller hydrophobic residues increased K(m(E2)) for E2 activity, whereas the k(cat(E2)) remained relatively constant. The Y81L mutant exhibited the same DHEA activity as wild-type hydroxysteroid sulfotransferase, for which K(m(DHEA)) remained relatively constant, and k(cat(DHEA)) was markedly increased. The side chain of Tyr-81 is directed at the A-ring of the E2 molecule in the substrate-binding pocket of EST, constituting a steric gate with Phe-142 sandwiching E2 from the opposite side. The present mutagenesis study indicates that the 3beta-hydroxyl group of the DHEA molecule is excluded from the catalytic site of EST through steric hindrance of Tyr-81 with the C-19 methyl group of DHEA. Thus, this stricture-like gating caused by steric hindrance appears to be a structural principle for conferring estrogen specificity to EST.

Structure and function of HNK-1 sulfotransferase. Identification of donor and acceptor binding sites by site-directed mutagenesis

HNK-1 glycan, sulfo-->3GlcAbeta1-->3Galbeta1-->4GlcNAc-->R, is uniquely enriched in neural cells and natural killer cells and is thought to play important roles in cell-cell interaction. HNK-1 glycan synthesis is dependent on HNK-1 sulfotransferase (HNK-1ST), and cDNAs encoding human and rat HNK-1ST have been recently cloned. HNK-1ST belongs to the sulfotransferase gene family, which shares two homologous sequences in their catalytic domains. In the present study, we have individually mutated amino acid residues in these conserved sequences and determined how such mutations affect the binding to the donor substrate, adenosine 3'-phosphate 5'-phosphosulfate, and an acceptor. Mutations of Lys(128), Arg(189), Asp(190), Pro(191), and Ser(197) to Ala all abolished the enzymatic activity. When Lys(128) and Asp(190) were conservatively mutated to Arg and Glu, respectively, however, the mutated enzymes still maintained residual activity, and both mutant enzymes still bound to adenosine 3',5'-diphosphate-agarose. K128R and D190E mutant enzymes, on the other hand, exhibited reduced affinity to the acceptor as demonstrated by kinetic studies. These findings, together with those on the crystal structure of estrogen sulfotransferase and heparan sulfate N-deacetylase/sulfotransferase, suggest that Lys(128) may be close to the 3-hydroxyl group of beta-glucuronic acid in a HNK-1 acceptor. In contrast, the effect by mutation at Asp(190) may be due to conformational change because this amino acid and Pro(191) reside in a transition of the secondary structure of the enzyme. These results indicate that conserved amino acid residues in HNK-1ST play roles in maintaining a functional conformation and are directly involved in binding to donor and acceptor substrates.

Phenobarbital-responsive nuclear translocation of the receptor CAR in induction of the CYP2B gene

The constitutively active receptor (CAR) transactivates a distal enhancer called the phenobarbital (PB)-responsive enhancer module (PBREM) found in PB-inducible CYP2B genes. CAR dramatically increases its binding to PBREM in livers of PB-treated mice. We have investigated the cellular mechanism of PB-induced increase of CAR binding. Western blot analyses of mouse livers revealed an extensive nuclear accumulation of CAR following PB treatment. Nuclear contents of CAR perfectly correlate with an increase of CAR binding to PBREM. PB-elicited nuclear accumulation of CAR appears to be a general step regulating the induction of CYP2B genes, since treatments with other PB-type inducers result in the same nuclear accumulation of CAR. Both immunoprecipitation and immunohistochemistry studies show cytoplasmic localization of CAR in the livers of nontreated mice, indicating that CAR translocates into nuclei following PB treatment. Nuclear translocation of CAR also occurs in mouse primary hepatocytes but not in hepatocytes treated with the protein phosphatase inhibitor okadaic acid. Thus, the CAR-mediated transactivation of PBREM in vivo becomes PB responsive through an okadaic acid-sensitive nuclear translocation process.

Developmental action of estrogen receptor-alpha feminizes the growth hormone-Stat5b pathway and expression of Cyp2a4 and Cyp2d9 genes in mouse liver

We have studied the roles of estrogen receptor-alpha (ERalpha) and the Stat5b form of STAT (signal transducers and activators of transcription) in sex-specific expression of Cyp2a4 (steroid 15alpha-hydroxylase) and Cyp2d9 (steroid 16alpha-hydroxylase) genes using ERalpha-deficient mice. ERalpha deficiency resulted in the repression of the female-specific Cyp2a4 and expression of the male-specific Cyp2d9 genes, respectively in females. In ERalpha-deficient males, the Cyp2d9 gene continued to be expressed. Nuclear localization of Stat5b occurs in both sexes of ERalpha-deficient mice, although it is normally observed in only wild-type males. Nuclear localization of Stat5b correlates with the repression of Cyp2a4 and expression of Cyp2d9, respectively. Because Stat5b was not detectable in liver nuclear extracts prepared from hypophysectomized ERalpha-deficient females, the regulation by ERalpha appeared to be mediated through a pituitary hormone (i.e., growth hormone). Thus, ERalpha appears to play a key role in the mechanism that inhibits nuclear localization of Stat5b in female mice, leading to feminization of a ERalpha-GH-Stat5b pathway and Cyp expression. Defaulting to this ERalpha-dependent mechanism results in localization of Stat5b to nuclei, which masculinizes the expression of Cyp genes in male mice.