Functional and evolutionary relationship between arginine biosynthesis and prokaryotic lysine biosynthesis through alpha-aminoadipate

Our previous studies revealed that lysine is synthesized through alpha-aminoadipate in an extremely thermophilic bacterium, Thermus thermophilus HB27. Sequence analysis of a gene cluster involved in the lysine biosynthesis of this microorganism suggested that the conversion from alpha-aminoadipate to lysine proceeds in a way similar to that of arginine biosynthesis. In the present study, we cloned an argD homolog of T. thermophilus HB27 which was not included in the previously cloned lysine biosynthetic gene cluster and determined the nucleotide sequence. A knockout of the argD-like gene, now termed lysJ, in T. thermophilus HB27 showed that this gene is essential for lysine biosynthesis in this bacterium. The lysJ gene was cloned into a plasmid and overexpressed in Escherichia coli, and the LysJ protein was purified to homogeneity. When the catalytic activity of LysJ was analyzed in a reverse reaction in the putative pathway, LysJ was found to transfer the epsilon-amino group of N(2)-acetyllysine, a putative intermediate in lysine biosynthesis, to 2-oxoglutarate. When N(2)-acetylornithine, a substrate for arginine biosynthesis, was used as the substrate for the reaction, LysJ transferred the delta-amino group of N(2)-acetylornithine to 2-oxoglutarate 16 times more efficiently than when N(2)-acetyllysine was the amino donor. All these results suggest that lysine biosynthesis in T. thermophilus HB27 is functionally and evolutionarily related to arginine biosynthesis.

Lack of decrease in hypothalamic and hippocampal glucocorticoid receptor mRNA during starvation

We have shown in a previous study that high corticosterone levels during repeated immobilization stress result in a reduction of glucocorticoid receptor (GR) mRNA in the hypothalamic paraventricular nucleus (PVN) and the hippocampus. The reduction of GR presumably accounts for loss of or decrease in glucocorticoid-negative feedback, and thus hyperfunction of the hypothalamic-pituitary-adrenocortical (HPA) axis persists during chronic stress. Starvation is a stress state in which the counterregulatory responses against the loss of food occur in the central nervous system. We explored the impact of starvation on the HPA axis, GR and mineralocorticoid receptor (MR) mRNAs in the hippocampus, the PVN, and the anterior pituitary (AP) of rats. Rats were starved for 4 days and sacrificed in the morning. Starved rats showed high levels of plasma corticosterone, whereas neither plasma corticotropin (ACTH), AP proopiomelanocortin (POMC) mRNA nor AP type-1 corticotropin-releasing hormone (CRH) receptor mRNA was altered in the starved rats. In the presence of high corticosterone, starvation resulted in a decrease in both CRH mRNA and type-1 CRH receptor mRNA in the PVN. Consistently, the starved rats did not show any changes in GR mRNA in the hippocampus (CA1-2, CA3, and dentate gyrus), the PVN or the AP despite the elevation of plasma corticosterone. A significant decrease in MR mRNA was seen in the dentate gyrus and the AP, but not in CA1-2, CA3 or PVN. The lack of reduction of GR may be one of the organism's counterregulatory responses during starvation, which allows an intact glucocorticoid negative feedback, thereby resulting in decreased anorectic neuropeptide levels, namely CRH, in the PVN. The results also indicate that GR mRNA in the hippocampus and other brain regions is not solely regulated by circulating glucocorticoids. The mechanism underlying the regulation of GR mRNA in the central nervous system remains to be clarified.

Histone deacetylase as a new target for cancer chemotherapy

Trichostatin A (TSA) and trapoxin (TPX), inhibitors of the eukaryotic cell cycle and inducers of morphological reversion of transformed cells, inhibit histone deacetylase (HDAC) at nanomolar concentrations. Recently, FK228 (also known as FR901228 and depsipeptide) and MS-275. antitumor agents structurally unrelated to TSA, have been shown to be potent HDAC inhibitors. These inhibitors activate the expression of p21Waf1 in a p53-independent manner. Changes in the expression of regulators of the cell cycle, differentiation, and apoptosis with increased histone acetylation may be responsible for the cell cycle arrest and antitumor activity of HDAC inhibitors. TSA has been suggested to block the catalytic reaction by chelating a zinc ion in the active site pocket through its hydroxamic acid group. On the other hand, an epoxyketone has been suggested to be the functional group of TPX capable of alkylating the enzyme. We synthesized a novel TPX analogue containing a hydroxamic acid instead of the epoxyketone. The hybrid compound, called cyclic hydroxamic-acid-containing peptide 1 (CHAP1) inhibited HDAC at low nanomolar concentrations. The HDAC1 inhibition by CHAPI was reversible, as is that by TSA, in contrast to irreversible inhibition by TPX. Interestingly, HDAC6, but not HDAC1 or HDAC4, was resistant to TPX and CHAP1, while TSA inhibited these HDACs to a similar degree. CHAP31, the strongest HDAC inhibitor obtained from a variety of CHAP derivatives, exhibited antitumor activity in BDF1 mice bearing B16/BL6 tumor cells. These results suggest that CHAP31 is promising as a novel therapeutic agent for cancer treatment, and that CHAP may serve as a basis for new HDAC inhibitors and be useful for combinatorial synthesis and high-throughput screening.

Cloning of full-length genomic DNA encoding human FcepsilonRI alpha-chain and its transcriptional regulation

Two novel exons, named exon 1A and exon 2A, were found at 18.4 and 12.6 kb upstream from the exon known as the first exon of human FcepsilonRI alpha-chain gene. Transcription from the promoter present in the upstream of exon 1A was decreased by mutations introduced into the "first intron" between exon 1A and exon 2A, suggesting the presence of an intronic regulatory element in the intron. Consistent with this, electrophoretic mobility shift assay revealed the presence of a nuclear factor which bound the region in FcepsilonRI alpha-chain positive cells.

Glucocorticoid effects on the diurnal rhythm of circulating leptin levels

It is known that circulating leptin shows diurnal variation with a nocturnal rise; however, the mechanisms generating this rhythm have not been fully elucidated. Glucocorticoids are a potent stimulator of leptin secretion, and there is a reciprocal relationship between circulating leptin and glucocorticoid levels. We hypothesized that glucocorticoids could modulate the diurnal rhythm of circulating leptin. We therefore explored the diurnal variation of leptin under situations in which subjects showed no or some shift of glucocorticoid diurnal rhythm, such as prednisolone-administered humans, and adrenalectomized and corticosterone-replaced (ADX+B) rats. The peak level of plasma cortisol immunoreactivity was shifted from early morning to noon by prednisolone administration. The nocturnal increment of plasma leptin in prednisolone-administered patients (71.2 +/- 14.2% from 08:00 h value) was significantly greater than that in normal volunteers (12.2 +/- 7.5% from 08:00 h value), but the timing of nadir and the peak of plasma leptin was not shifted. In normal rats, the plasma concentration of leptin showed the diurnal rhythm with the bottom at 16:00 h and the top between midnight and early morning. The amplitude of leptin diurnal rhythm was significantly reduced in ADX+B rats (08:00 h: 3.0 +/- 0.2, 16:00 h: 2.7 +/- 0.2, 00:00 h; 3.7 +/- 0.2 ng/ml) compared with sham operated rats (08:00 h: 3.0 +/- 0.2, 16:00 h 2.2 +/- 0.2, 00:00 h: 4.7 +/- 0.4 ng/ml); but ADX+B rats still retained similar timing of nadir and the peak of plasma leptin as observed in sham rats. These results indicate that glucocorticoids enhance the amplitude of leptin diurnal rhythm, and are consistent with previous findings showing that glucocorticoids increase leptin secretion. Glucocorticoids appear to play modulatory, but not essential roles in generating leptin diurnal rhythm.

Characterization of aspartate kinase III of Bacillus subtilis

A search in the Bacillus subtilis genome sequence found that the gene designated yclM encode(s) a protein showing significant identity in amino acid sequence to aspartate kinases. When yclM was introduced into Escherichia coli cells deficient in all three aspartate kinase genes, production of a protein with molecular size 50 kDa, which was similar to the value deduced from the nucleotide sequence of the gene, was observed. Expectedly, the protein purified to homogeneity had aspartate kinase activity. The enzyme was significantly inhibited by simultaneous addition of both threonine and lysine, which is a typical feature of aspartate kinase III of B. subtilis. The enzyme was very unstable in 10 mM tris-HCl (pH 7.5) buffer, but was stabilized by addition of 500 mM ammonium sulfate. Although all the aspartate kinases so far investigated are oligomeric enzymes, this aspartate kinase was suggested to be a monomer.

A Study of Familial Occurrence of Behçet's Disease With and Without Ocular Lesions

PURPOSE

To examine retrospectively the features of Behçet's disease patients with familial occurrence and make a comparison between familial Behçet's patients with ocular lesions and those without ocular lesions.

METHODS

We sent questionnaires about Behçet's disease patients with familial occurrence to 114 hospitals that reported treating such patients in previous nationwide hospital surveys, and to 341 hospitals selected at random in Japan.

RESULTS

We obtained reports on 83 Behçet's patients with familial occurrence. The positive rate of HLA-B51 was 53.1%. The positive rate of HLA-B51 among patients with ocular lesions was 64.0%, that in patients without ocular lesions was 14.3%, and that in patients with genital ulcers was 40.9%. The mean birth year and onset year of the patients with ocular symptoms was significantly lower than that of the patients without ocular symptoms. Although there was no significant difference between these two groups, parent-child involvement was more common among the patients without ocular lesions than in those with ocular lesions.

CONCLUSIONS

The findings of this study suggest that the number of familial Behçet's disease patients with ocular lesions and high HLA-B51 positivity has been decreasing recently. To elucidate the etiology of familial occurrence, larger scale epidemiological studies and further molecular studies of Behçet's disease are needed.

Active transepithelial transport of irinotecan (CPT-11) and its metabolites by human intestinal Caco-2 cells

Irinotecan (CPT-11) is a camptothecin analog with low (about 10--20%) and variable oral bioavailability in animal models. Here, Caco-2 cells were used to evaluate the transepithelial transport of CPT-11 and its metabolites. Caco-2 cells demonstrated significant expression of P-glycoprotein (P-gp), multidrug resistance-associated protein and canalicular multispecific organic anion transporter. Both the lactone and carboxylate forms of CPT-11 and SN-38 were actively transported across the cell monolayers, mainly by the apical-localized P-gp pump. Cellular permeability of CPT-11 at a concentration of 17 microM converted from active to passive-diffusional transport between the 2 and 6 h exposure time points. Antiproliferative effects of CPT-11 were related to permeability of the lactone form, whereas for SN-38 efficacy was dependent on lactone accumulation. Exposure of CPT-11 with cyclosporin A significantly enhanced its efficacy, whereas this was not observed with verapamil and R101933. In contrast, SN-38 efficacy decreased in the presence of P-gp inhibitors due to active transport toward the basolateral side, thereby reducing drug accumulation. Hence, multiple-active transport systems could be demonstrated to be responsible for not only accumulation profiles but also cytotoxic efficacy of CPT-11 and SN-38 in the intestinal Caco-2 cells. It is suggested that CPT-11 might act in a time-dependent manner and that SN-38-mediated cytotoxicity relates to (dose-dependent) lactone kinetics. The results detailed in this report could contribute toward the development of a clinically useful oral formulation of CPT-11 with improved absorption characteristics and suggest that cyclosporin A is a suitable agent for further research of this concept.

Phototrophic N2 fixation suppressed by activated sulfate reduction in anoxic rice soil slurries

Interactions between sulfate reduction (SR) and phototrophic nitrogenase activities were investigated in rice soil slurries mixed with rice straw. Activation of SR by adding exogenous sulfate suppressed acetylene-reducing activity (ARA) of the slurries, which was associated with phototrophic purple bacteria (PB) enumerated to 108-109 MPN g-1 dry weight (dw) soil. Adding 5 mm sodium molybdate, an inhibitor of SR, markedly increased ARA. However, in the slurries receiving both molybdate and exogenous sulfate, the effects declined simultaneously with partial recovery of SR. These results indicate outcompetition of sulfate-reducing bacteria (SRB) with PB in rice soil, when sulfate concentrations are high enough to support SR. The increasing effects of molybdate on ARA continued during the incubation in the sulfate-depleted condition, probably because of absence of SR and toxicity of molybdate to methanogenesis. Accordingly, stopping activities of the competitive microorganisms may be efficient to increase N2 fixation in rice soil.

Chiral helicity induced by hydrogen bonding and chirality of podand histidyl moieties

[structure: see text] The single-crystal X-ray structure determination of N,N'-bis[(S)-(+)-1-methoxycarbonyl-2-(4-imidazolyl)ethyl]-2,6-pyridinedicarboxamide (L-BHisPA) and the D-isomer (D-BHisPA) derived from the corresponding chiral histidine revealed a left- and right-handed helical conformation, respectively, through intramolecular hydrogen bonding and chirality of the podand histidyl moieties. Furthermore, each helical molecule is connected by continuous intermolecular hydrogen bonds to afford a left- or right-handed helical assembly, respectively, in the crystal packing.

Evidence for the presence of DNA-binding proteins involved in regulation of the gene expression of indole-3-pyruvic acid decarboxylase, a key enzyme in indole-3-acetic acid biosynthesis in Azospirillum lipoferum FS

We isolated the ipdc gene coding for indole-3-pyruvic acid decarboxylase (IPDC), a key enzyme in the indole-3-pyruvic acid pathway for indole-3-acetic acid biosynthesis, in the plant growth-promoting rhizobacterium Azospirillum lipoferum FS. Gel mobility-shift assay showed the presence of two DNA-binding proteins that might be involved in regulation of the ipdc gene expression.

Replacements of amino acid residues at subsites and their effects on the catalytic properties of Rhizomucor pusillus pepsin, an aspartic proteinase from Rhizomucor pusillus

Site-directed mutagenesis was carried out to investigate the functional roles of amino acid residues of Rhizomucor pusillus pepsin (RMPP) in substrate-binding and catalysis. Mutations of two amino acid residues, E13 in the S3 subsite and N219 in the S3/S4 subsites, caused marked changes in kinetic parameters for two substrate peptides with different sequences. Further site-directed mutagenesis at E13 suggested that E13 plays a critical role in forming the correct hydrogen bond network around the active center. In the crystal structure of Rhizomucor miehei pepsin (RMMP), which is an aspartic proteinase produced by Rhizomucor miehei and shows 81% amino acid identity to RMPP, the Oepsilon atom of N219 forms a hydrogen bond with the N-H of isovaline in pepstatin A, a statine-type inhibitor, at the P3 position, suggesting that the loss of the hydrogen bond causes an unfavorable arrangement of the P3 residue. Among the mutants constructed, the E13A mutant showed a 5-fold increase in the ratio of clotting versus proteolytic activity without significant loss of clotting activity. This mutant may present a promising candidate for a useful milk coagulant.

Inhibition of methanogens increases photo-dependent nitrogenase activities in anoxic paddy soil amended with rice straw

The interaction between phototrophic dinitrogen fixers and methanogens was examined in soil slurries amended with rice straw using 2-bromoethanesulfonic acid (BES), a specific methanogenic inhibitor. Slurries incubated in light increased phototrophic nitrogenase activity (acetylene reducing activity), and showed growth of phototrophic purple bacteria and reduction of CH(4) emission, indicating outcompetition of purple bacteria with methanogens in photic zones. Adding BES effectively inhibited methane production and markedly increased phototrophic acetylene reducing activity accompanied with acetate accumulation, but did not affect populations of purple bacteria in the slurries. More acetate accumulated in the inhibited slurries incubated in dark. We suggest that increased availability of organic substrates for purple bacteria after stopping methanogenic consumption by BES caused the increased phototrophic acetylene reducing activity. These results indicate that, after purple bacteria grow enough, performance of their N(2) fixation may be limited by substrate availability, which methanogenesis may profoundly influence.

Substeps within the 8-nm step of the ATPase cycle of single kinesin molecules

Kinesin is a molecular motor that moves processively by regular 8-nm steps along microtubules. The processivity of this movement is explained by a hand-over-hand model in which the two heads of kinesin work in a coordinated manner. One head remains bound to the microtubule while the other steps from the alphabeta-tubulin dimer behind the attached head to the dimer in front. The overall movement is 8 nm per ATPase cycle. To investigate elementary processes within the 8-nm step, we have developed a new assay that resolves nanometre displacements of single kinesin molecules with microsecond accuracy. Our data show that the 8-nm step can be resolved into fast and slow substeps, each corresponding to a displacement of approximately 4 nm. The substeps are most probably generated by structural changes in one head of kinesin, leading to rectified forward thermal motions of the partner head. It is also possible that the kinesin steps along the 4-nm repeat of tubulin monomers.

Titanium casting: the surface reaction layer of castings obtained using ultra-low-temperature molds

To examine whether the surface reaction layer of titanium castings can be reduced by lowering the mold temperature during casting, we cast titanium at three mold temperatures, including an ultra-low temperature produced by cooling the mold with liquid nitrogen, then measured the tensile strength and elongation of the castings. The titanium was cast using a centrifugal casting machine, and the molds were incinerated according to the manufacturers' instructions. Castings were then made with the molds at 200 degrees C, 600 degrees C, and an ultra-low temperature (-196 degrees C). The castability of titanium cast in the mold at the ultra-low temperature was good. The Vickers hardness near the surface layer of castings decreased as the mold temperature decreased.

Characterization of RGS5 in regulation of G protein-coupled receptor signaling

RGS proteins (regulators of G protein signaling) serve as GTPase-activating proteins (GAPs) for G alpha subunits and negatively regulate G protein-coupled receptor signaling. In this study, we characterized biochemical properties of RGS5 and its N terminal (1-33)-deleted mutant (deltaN-RGS5). RGS5 bound to G alpha(i1), G alpha(i2), G alpha(i3), G alpha(o) and G alpha(q) but not to G alpha(s) and G alpha13 in the presence of GDP/AIF4-, and accelerated the catalytic rate of GTP hydrolysis of G alpha(i3) subunit. When expressed in 293T cells stably expressing angiotensin (Ang) AT1a receptors (AT1a-293T cells), RGS5 suppressed Ang II- and endothelin (ET)-1-induced intracellular Ca2+ transients. The effect of RGS5 was concentration-dependent, and the slope of the concentration-response relationship showed that a 10-fold increase in amounts of RGS5 induced about 20-25% reduction of the Ca2+ signaling. Furthermore, a comparison study of three sets of 293T cells with different expression levels of AT1a receptors showed that RGS5 inhibited Ang II-induced responses more effectively in 293T cells with the lower density of AT1a receptors, suggesting that the degree of inhibition by RGS proteins reflects the ratio of amounts of RGS proteins to those of activated G alpha subunits after receptor stimulation by agonists. When expressed in AT1a-293T cells, deltaN-RGS5 was localized almost exclusively in the cytosolic fraction, and exerted the inhibitory effects as potently as RGS5 which was present in both membrane and cytosolic fractions. Studies on relationship between subcellular localization and inhibitory effects of RGS5 and deltaN-RGS5 revealed that the N terminal (1-33) of RGS5 plays a role in targeting this protein to membranes, and that the N terminal region of RGS5 is not essential for exerting activities.

Physiological roles of corticotropin-releasing hormone receptor type 2

Recent investigations of the physiological roles of CRH-R2 are reviewed and summarized in Fig. 5. VMH CRH-R2 is more important than CRH-R1 in mediating anorexic effect of CRH or urocortin (UCN) and stress-induced reduction of food intake. CRH-R2 mediates a central anxiolytic response, opposing the anxiogenic effect of CRH mediated by CRH-R1. Hippocampal CRH-R1 mediates stress-induced enhancement of learning, while CRH-R2 in the lateral intermediate septum may act to impair learning. CRH-R1 mediates CRH-induced blood pressure elevation, while peripheral CRH-R2 mediates the hypotensive effect of systemically administered UCN and CRH. It is likely that CRH-R2 does not play an important role in hypothalamic-pituitary adrenal axis regulation, though it has been reported that CRH-R2-deficient mice showed hyperresponse of ACTH and corticosterone. Peripheral CRH-R2 mediates UCN-induced mast cell degranulation, vascular permeability, and abdominal surgery-induced gastric stasis. These recent investigations have revealed that the existence of two CRH receptors, which mediate some opposite effects, provides the CRH and UCN systems a high flexibility and dynamic role in the adaptation of the body to environmental challenge.

A complex composed of USF1 and USF2 activates the human FcepsilonRI alpha chain expression via a CAGCTG element in the first intron

The high-affinity IgE receptor, FcepsilonRI, is a key regulatory molecule in the allergic reaction. During the course of studies to find cis-acting elements for FcepsilonRI alpha chain gene expression, a CAGCTG sequence located in the first intron was revealed to serve as a crucial enhancer element. Electromobility shift assays using antibodies and in vitro translation products showed that the CAGCTG element was recognized by the USF1/USF2 complex. As was the case for other intronic cis-elements, the CAGCTG element regulated the promoter in an orientation- and position-dependent manner. Overexpression of USF2 antisense repressed the FcepsilonRI alpha chain gene promoter and decreased the amount of alpha chain mRNA in mast cell lines. All these results indicated that the USF1/USF2 complex activates the human FcepsilonRI alpha chain gene expression via the CAGCTG element in the first intron.

Sodic soils reclaimed with by-product from flue gas desulfurization: corn production and soil quality

Interest is growing in the use of by-product from flue gas desulfurization (FGD) to reclaim sodic soils by controlling the pH and excessive Na+. This study evaluated the effects on corn (Zea mays) production and pH and electrical conductivity (EC) of calcareous sodic soil during four times of cultivation when the by-product was applied once at the first cultivation (Study I) and the impacts on plant and soil quality at first cultivation when the by-product was applied to the soil at 23,000 kg ha-1 (Study II). In Study I, the germination rate and corn production increased by applying the by-product (0, 5,800, 11,600, and 23,100 kg ha-1), and the greatest total amounts of corn production during the four times of cultivation was when the by-product was applied at 23,100 kg ha-1. In Study II, the pH, exchangeable sodium percentage (ESP), clay dispersion and soluble Na+ in the soil decreased and soluble Mg2+ and soluble K+ in the soil increased. The soil pH was reduced from 9.0 to 7.7 by applying the by-product. However, the by-product decreased the concentrations of total N and P in corn leaves in this study. No significant difference in the concentrations of Mo, Zn, Pb, Ni, Cd, Mn, Cr, Cu, and Al in corn leaves and the soil was observed between the by-product addition and the control except for B in the soil and Fe in corn leaves. The concentration of B in the soil was reduced from 28.7 mg kg-1 to 25.4 mg kg-1 and the concentration of Fe in corn leaves increased from 17.5 mg kg-1 to 22.6 mg kg-1 by applying the by-product in our study.

Splice isoforms of transcription factor Elf-1 affecting its regulatory function in transcription-molecular cloning of rat Elf-1

To elucidate the role of Elf-1 in Fc epsilonRI alpha chain expression, rat Elf-1 cDNAs were isolated and characterized. The rat Elf-1 cDNA of 2744 bp contained an open reading frame of 1848 bp. In addition to the full length rat Elf-1 cDNA (named type 1), two splice isoforms were isolated. One of the two isoforms lacked the amino acid residues from 85th to 120th (type 2), and the other from 85th to 175th (type 3). Similar isoforms were also observed in human tissue. Overexpression of rat Elf-1 (type 1) using a transient coexpression system inhibited of the alpha chain promoter activity. The inhibition activity was different between the isoforms; the inhibition activity of type 2 was lower than that of type 1, and type 3 did not have an inhibitory effect. This observation suggested that each Elf-1 isoform played a different role in the gene expression under its control.

Calcium stores regulate the polarity and input specificity of synaptic modification

Activity-induced synaptic modification is essential for the development and plasticity of the nervous system. Repetitive correlated activation of pre- and postsynaptic neurons can induce persistent enhancement or decrement of synaptic efficacy, commonly referred to as long-term potentiation or depression (LTP or LTD). An important unresolved issue is whether and to what extent LTP and LTD are restricted to the activated synapses. Here we show that, in the CA1 region of the hippocampus, reduction of postsynaptic calcium influx by partial blockade of NMDA (N-methyl-D-aspartate) receptors results in a conversion of LTP to LTD and a loss of input specificity normally associated with LTP, with LTD appearing at heterosynaptic inputs. The induction of LTD at homo- and heterosynaptic sites requires functional ryanodine receptors and inositol triphosphate (InsP3) receptors, respectively. Functional blockade or genetic deletion of type 1 InsP3 receptors led to a conversion of LTD to LTP and elimination of heterosynaptic LTD, whereas blocking ryanodine receptors eliminated only homosynaptic LTD. Thus, postsynaptic Ca2+, deriving from Ca2+ influx and differential release of Ca2+ from internal stores through ryanodine and InsP3 receptors, regulates both the polarity and input specificity of activity-induced synaptic modification.

Regulation of type-2 corticotropin-releasing hormone receptor mRNA in rat heart by glucocorticoids and urocortin

A novel subtype of corticotropin-releasing hormone (CRH) receptor, designated type-2 CRH receptor (CRHR-2), has been cloned by a number of laboratories, and its mRNA has been found to be distributed not only in the brain but in peripheral tissues such as heart and skeletal muscle. To date, however, the regulation of CRHR-2 mRNA is poorly understood. Therefore, we examined the effect of glucocorticoid treatment, adrenalectomy, and systemic administration of urocortin, a possible endogenous ligand for CRHR-2, on heart CRHR-2 mRNA levels in male Wistar rats, using in situ hybridization histochemistry. CRHR-2 mRNA in the heart was significantly decreased 9 h after systemic administration of urocortin (5 microg/kg b.w.). Systemic administration of corticosterone (CORT; 10 mg/rat/day for 12 days) or CORT pellet (200 mg) implant for 7 and 14 days also decreased CRHR-2 mRNA in the heart, whereas it was unchanged 7 days after adrenalectomy. Thus, similar regulation of CRHR-2 mRNA in the rat heart by its ligand and glucocorticoids was observed. The precise mechanism of the regulation of CRHR-2 mRNA in the heart and the physiologic significance of cardiac CRHR-2 remains to be elucidated.