New polyoxygenated briarane diterpenoids, briaexcavatolides O-R, from the gorgonian Briareum excavatum

Four new polyoxygenated briarane-type diterpenoids, briaexcavatolides O-R (1-4), have been isolated from a gorgonian octocoral Briareum excavatum. Their structures were determined using spectroscopic and chemical methods. Metabolites 1-3 were found to contain oxygenated substituents at C-2, C-3, and C-4, and the relative configurations were assigned as 2R*,3R*,4R* at these three positions. Briaranes containing this type of stereochemistry are reported for the first time. The structures of metabolites 1 and 2 were further confirmed by single-crystal X-ray analyses. Compound 2 has been shown to exhibit significant cytotoxicity toward P-388 and HT-29 cancer cells.

Role for transcription Pax5A factor in maintaining commitment to the B cell lineage by selective inhibition of granulocyte-macrophage colony-stimulating factor receptor expression

During early B lymphopoiesis, developing B cells maintain lineage commitment despite the local presence of myeloid lineage-promoting cytokines such as GM-CSF and IL-3. Previous observations suggest that the B cell-specific transcription factor Pax5A (paired box 5A transcription factor) plays a role in maintaining B cell lineage commitment by limiting expansion and survival of early IL-3/GM-CSF-dependent myeloid lineage cells. To define a mechanism by which Pax5A can exert these inhibitory effects on myeloid lineage differentiation, an inducible form of the Pax5A protein was expressed in the myeloid cell line FDC-P1. This cell line models myeloid progenitors in that it responds to the survival and growth-potentiating effects of IL-3 and GM-CSF. We observed that enforced expression of Pax5A selectively suppressed proliferation in response to GM-CSF, but not IL-3. This effect was associated with specific down-regulation of GM-CSFR alpha-chain, but not beta-chain expression. These data provide a molecular mechanism to enforce commitment to the B cell lineage despite the presence of GM-CSF, a factor that has been shown to convert early developing B cells to the myeloid lineage. Furthermore, they indicate a role for B cell Pax5A expression in maintaining rather than directing commitment to the B cell lineage.

Dichloro(2,2'-diamino-4,4'-bi-1,3-thiazole-N3,N3')copper(II)

The title complex, [CuCl(2)(C(6)H(6)N(4)S(2))], has a flattened tetrahedral coordination. The Cu(II) atom is located on a twofold rotation axis and is coordinated by two N atoms from a chelating 2,2'-diamino-4,4'-bi-1,3-thiazole ligand and by two Cl atoms. Intramolecular hydrogen bonding exists between the amino groups of the 2,2'-diamino-4,4'-bi-1,3-thiazole ligand and the Cl atoms. The intermolecular separation of 3.425 (1) A between parallel bithiazole rings suggests there is a pi-pi interaction between them.

Briaexcavatolides K-N, new briarane diterpenes from the gorgonian Briareum excavatum

Four new briarane diterpenes, briaexcavatolides K-N (1-4), along with a known diterpene, 5, have been isolated from the Taiwanese gorgonian Briareum excavatum. The structures of the new metabolites were established by extensive spectral analyses. Furthermore, the structure, including the relative configuration of briaexcavatolide K (1), was confirmed by a single-crystal X-ray analysis. Briaexcavatolides K and L (1 and 2) are the only briarane diterpenes known to possess hydroxyl groups at the C-8beta and C-17alpha positions, respectively. Cytotoxicity of these metabolites toward various cancer cell lines also is described.

Junceellolides E-G, new briarane diterpenes from the West Pacific Ocean gorgonian Junceella fragilis

Three new diterpenes, junceellolides E-G (1-3), along with an unnamed known diterpene 4, possessing the briarane carbon skeleton, have been isolated from the gorgonian Junceella fragilis collected in Taiwanese tropical waters. The structures of the new metabolites 1-3 were elucidated by extensive spectral analyses. The six-membered rings in junceellolides E and F (1 and 2) were found to exist in boat conformations. The structure, including the relative configuration of junceellolide E (1) was further confirmed by a single-crystal X-ray analysis.

The orphan nuclear receptor Tlx regulates Pax2 and is essential for vision

Although the development of the vertebrate eye is well described, the number of transcription factors known to be key to this process is still limited. The localized expression of the orphan nuclear receptor Tlx in the optic cup and discrete parts of the central nervous system suggested the possible role of Tlx in the formation or function of these structures. Analyses of Tlx targeted mice revealed that, in addition to the central nervous system cortical defects, lack of Tlx function results in progressive retinal and optic nerve degeneration with associated blindness. An extensive screen of Tlx-positive and Tlx-negative P19 neural precursors identified Pax2 as a candidate target gene. This identification is significant, because Pax2 is known to be involved in retinal development in both the human and the mouse eye. We find that Pax2 is a direct target and that the Tlx binding site in its promoter is conserved between mouse and human. These studies show that Tlx is a key component of retinal development and vision and an upstream regulator of the Pax2 signaling cascade.

Lysozyme association with nucleic acids

Lysozyme is well known for the ability to hydrolyze the cell wall of bacteria. Based on the similarity of structure between lysozyme and histones as seen from the results of X-ray crystal structure determinations, we have postulated that binding to nucleic acids may be another biological function of lysozyme. We have therefore begun a systematic study of the interactions of lysozyme and related molecules with nucleic acids, and present here a preliminary report. Binding to DNA and RNA has been demonstrated from gel electrophoresis, enzyme activity, and coprecipitation studies. We suggest that this function of lysozyme will provide an explanation why Lee-Huang et al. (1999) [Proc. Natl. Acad. Sci. USA 96, 2678-2681] were able to call lysozyme a "killer protein" against the AIDS virus, and may provide a new avenue of research on AIDS therapy.

BSAP/Pax5A expression blocks survival and expansion of early myeloid cells implicating its involvement in maintaining commitment to the B-lymphocyte lineage

Early B lymphopoiesis is marked by plasticity between the myeloid and B lineages. An attractive model for B-lineage development is that commitment to this lineage is partly determined by the ordered expression of genes that prohibit switching to the myeloid lineage. In this regard, whereas the role of the B-cell-specific transcription factor BSAP/Pax5A in regulating B-lymphoid-restricted gene expression has been well-established, its role in maintaining B-lineage commitment is unclear. Thus, BSAP/Pax5A was constitutively expressed in the multipotent EML cell line, which can be directed toward the myeloid lineage by culture with interleukin-3 (IL-3) and retinoic acid. EML cells expressing BSAP/Pax5A successfully acquired the myeloid lineage markers CD11b and F4/80 in response to IL-3 and retinoic acid, indicating differentiation to the myeloid lineage. However, these early myeloid cells failed to expand in culture with granulocyte-macrophage colony-stimulating factor and were directed instead toward an apoptotic pathway. In parallel, primary bone marrow stem cells transduced with retrovirus constitutively expressing BSAP/Pax5A began myeloid cell differentiation, but like the transformed EML model failed to expand in response to myeloid growth factors. These studies identify a role for BSAP/Pax5A in suppressing the response to myeloid growth factors, which may be a component of the regulatory processes that limit plasticity of early B-lymphoid progenitors.

Cytotoxic terpenoids from the Formosan soft coral Nephthea brassica

Two new cytotoxic cembranoid diterpenes, brassicolide (1) and brassicolide acetate (2); a new cytotoxic sesquiterpene, (-)-4alpha-O-acetyl-selin-11-en (3); and six cytotoxic terpenoids, (-)-selin-11-en-4alpha-ol (4), 2-hydroxynephthenol (5), nephthenol (6), cembrene A (7), epoxycembrene A (8), and (-)-beta-elemene (9), have been isolated from the Formosan soft coral Nephthea brassica. The structures of compounds 1-9 were determined by spectral, chemical, and X-ray crystallographic analysis.

Excavatolides U-Z, new briarane diterpenes from the gorgonian briareum excavatum

A recent study of the EtOAc extract of the gorgonian Briareum excavatum afforded six new diterpenes of the briarane skeleton, excavatolides U-Z (1-6). The structures and relative stereochemistry of metabolites 1-6 were assigned on the basis of NMR studies and chemical methods. The structure, including the relative configuration of excavatolide U (1), was further confirmed by a single-crystal X-ray analysis. Some of the excavatolides have displayed significant cytotoxicity toward P-388 and HT-29 tumor cells.

Oxidation products of zeylanidine

The oxidation of zeylanidine (1) afforded two new sesquiterpene dilactones, 4 and 5, besides two known compounds, neoliacine (2) and zeylanidinone (3). The structures of the novel oxidized products were elucidated on the basis of spectroscopic techniques, and the structure of compound 5 was further confirmed by X-ray crystallographic analysis. The mechanism for the oxidation of 1 to 4 and 5 has been postulated.

Molecular structure of the amyloid-forming protein kappa I Bre

The molecular structure of the amyloid-forming Bence-Jones protein kappa I Bre has been determined by X-ray crystallography at 2.0 A resolution. The fragment from the kappa chain of immunoprotein contains 107 amino acid residues, and polymerizes in the crystal form into a giant helical spiral, surrounding a cylinder of water 50 A in diameter with a repeat of 77.56 A, containing 12 kappa molecules, plus another 12 molecules from neighboring parallel spirals. The resulting structure has many features which have been found or suggested from studies on the protein fibrils found in amyloid deposits. From the results of the X-ray crystal structure a hypothesis is presented for the structure and formation of the amyloid fibril.

An essential role for retinoid receptors RARbeta and RXRgamma in long-term potentiation and depression

Hippocampal long-term potentiation (LTP) and long-term depression (LTD) are the most widely studied forms of synaptic plasticity thought to underlie spatial learning and memory. We report here that RARbeta deficiency in mice virtually eliminates hippocampal CA1 LTP and LTD. It also results in substantial performance deficits in spatial learning and memory tasks. Surprisingly, RXRgamma null mice exhibit a distinct phenotype in which LTD is lost whereas LTP is normal. Thus, while retinoid receptors contribute to both LTP and LTD, they do so in different ways. These findings not only genetically uncouple LTP and LTD but also reveal a novel and unexpected role for vitamin A in higher cognitive functions.

Novel cytotoxic cembranoids from the soft coral Sinularia flexibilis

Three new cytotoxic cembranoid diterpenes, sinuflexolide (1), dihydrosinuflexolide (2), and sinuflexibilin (3), have been isolated from the soft coral Sinularia flexibilis. The structures of compounds 1-3 were determined by spectral and X-ray crystallographic analysis.

Novel cytotoxic diterpenes, excavatolides A-E, isolated from the Formosan gorgonian Briareum excavatum

The chemistry of Briareum excavatum, a Formosan gorgonian coral, was investigated. This study has led to the isolation of five novel marine natural products, excavatolides A-E (1-5), together with brianolide (6). The structures of the above compounds were established by spectral and chemical methods. The relative configuration of excavatolide B (2) was further confirmed by a single-crystal X-ray structure analysis. Cytotoxicity of these compounds toward various cancer cell lines also is described.

Expression of human group II PLA2 in transgenic mice results in epidermal hyperplasia in the absence of inflammatory infiltrate

Group II PLA2 has been implicated in inflammatory processes in both man and other animals and has been shown to be involved in inflammatory conditions, such as arthritis and sepsis. Transgenic mice expressing the human group II PLA2 gene have been generated using a 6.2-kb genomic fragment. These mice express the group II PLA2 gene abundantly in liver, lung, kidney, and skin, and have serum PLA2 activity levels approximately eightfold higher than nontransgenic littermates. The group II PLA2 transgenic mice reported here exhibit epidermal and adnexal hyperplasia, hyperkeratosis, and almost total alopecia. The chronic epidermal hyperplasia and hyperkeratosis seen in these mice is similar to that seen in a variety of dermatopathies, including psoriasis. However, unlike what is seen with these dermatopathies, no significant inflammatory-cell influx was observed in the skin of these animals, or in any other tissue examined. These mice provide an important tool for examining group II PLA2 expression, and for determining the role of group II PLA2 in normal and disease physiology. They serve as an in vivo model for identifying inhibitors of group II PLA2 activity and gene expression.

Sinugibberol, a new cytotoxic cembranoid diterpene from the soft coral Sinularia gibberosa

Bioactivity-guided fractionation of a chloroform extract of the soft coral Simularia gibberosa afforded a new cytotoxic cembranoid diterpene, sinugibberol [1]. The structure of 1 was determined by spectral and X-ray crystallographic analysis.

Sequence specific inhibition of human type II phospholipase A2 enzyme activity by phosphorothioate oligonucleotides

Phosphorothioate oligonucleotides were identified which directly inhibited human type II phospholipase A2 (PLA2) enzyme activity in a sequence specific manner. The minimum pharmacophore common to all oligonucleotides which inhibited PLA2 enzyme activity consisted of two sets of three or more consecutive guanosine residues in a row. These oligonucleotides appear to form G quartets resulting in the formation of oligonucleotide aggregates. Additionally, a phosphorothioate backbone was required to be effective inhibitors of type II PLA2. The activity of one oligodeoxynucleotide, IP 3196 (5'-GGGTGGGTATAGAAGGGCTCC-3') has been characterized in more detail. IP 3196 inhibited PLA2 enzyme activity when the substrate was presented in the form of a phospholipid bilayer but not when presented in the form of a mixed micelle with anionic detergents. Human type II PLA2 was 50-fold more sensitive to inhibition by IP 3196 than venom and pancreatic type I enzymes. These data demonstrate that phosphorothioate oligonucleotides can specifically inhibit human type II PLA2 enzyme activity in a sequence specific manner.

Inhibition of endothelial cell adhesion molecule expression with antisense oligonucleotides

In response to inflammatory stimuli, expression of a group of proteins that bind circulating leukocytes (endothelial-leukocyte adhesion molecules) are induced on the luminal surface of vascular endothelium. A series of phosphorothioate oligonucleotides 18 to 21 bases in length were designed and synthesized to hybridize selectively to the mRNA, which encodes three such endothelial-leukocyte adhesion molecules; human intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. Antisense oligonucleotides were identified that selectively inhibited ICAM-1, VCAM-1, and E-selectin expression in HUVEC. Oligonucleotides that hybridized to the 3'-untranslated region of either ICAM-1, VCAM-1, or E-selectin mRNAs promoted a selective reduction in the respective mRNA levels. In contrast, oligonucleotides that hybridized to 5'-untranslated sequences did not significantly reduce target mRNA levels, although they did promote a reduction in protein expression. With the use of flow cytometry to measure cell surface expression, ICAM-1 and E-selectin were selectively inhibited by their respective antisense oligonucleotide. At low concentrations of oligonucleotides, only VCAM-1 antisense oligonucleotides inhibited VCAM-1 expression. However, at an oligonucleotide concentration of 50 nM or greater, phosphorothioate oligonucleotides not predicted to hybridize to VCAM-1 mRNA also reduced VCAM-1 expression. The sequence-independent inhibition of VCAM-1 expression by phosphorothioate oligonucleotides could be the result of a perturbation in the transcriptional regulation of the VCAM-1 gene. ICAM-1, VCAM-1, and E-selectin antisense oligonucleotides reduced adhesion of HL-60 cells to TNF-activated HUVEC. These data demonstrate that phosphorothioate oligonucleotides are capable of selectively inhibiting the expression of ICAM-1, VCAM-1, and E-selectin in HUVEC.

Inhibition of endothelial cell adhesion molecule expression with antisense oligonucleotides

In response to inflammatory stimuli, expression of a group of proteins that bind circulating leukocytes (endothelial-leukocyte adhesion molecules) are induced on the luminal surface of vascular endothelium. A series of phosphorothioate oligonucleotides 18 to 21 bases in length were designed and synthesized to hybridize selectively to the mRNA, which encodes three such endothelial-leukocyte adhesion molecules; human intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. Antisense oligonucleotides were identified that selectively inhibited ICAM-1, VCAM-1, and E-selectin expression in HUVEC. Oligonucleotides that hybridized to the 3'-untranslated region of either ICAM-1, VCAM-1, or E-selectin mRNAs promoted a selective reduction in the respective mRNA levels. In contrast, oligonucleotides that hybridized to 5'-untranslated sequences did not significantly reduce target mRNA levels, although they did promote a reduction in protein expression. With the use of flow cytometry to measure cell surface expression, ICAM-1 and E-selectin were selectively inhibited by their respective antisense oligonucleotide. At low concentrations of oligonucleotides, only VCAM-1 antisense oligonucleotides inhibited VCAM-1 expression. However, at an oligonucleotide concentration of 50 nM or greater, phosphorothioate oligonucleotides not predicted to hybridize to VCAM-1 mRNA also reduced VCAM-1 expression. The sequence-independent inhibition of VCAM-1 expression by phosphorothioate oligonucleotides could be the result of a perturbation in the transcriptional regulation of the VCAM-1 gene. ICAM-1, VCAM-1, and E-selectin antisense oligonucleotides reduced adhesion of HL-60 cells to TNF-activated HUVEC. These data demonstrate that phosphorothioate oligonucleotides are capable of selectively inhibiting the expression of ICAM-1, VCAM-1, and E-selectin in HUVEC.

Regulation of 5-lipoxygenase and 5-lipoxygenase-activating protein expression in HL-60 cells

5-Lipoxygenase performs the first two enzymic reactions in the biosynthetic pathway for the leukotrienes. We have utilized HL-60 cells to study the mechanisms regulating expression of 5-lipoxygenase and the recently described 18 kDa membrane protein, 5-lipoxygenase-activating protein (FLAP). Differentiation of HL-60 cells into granulocyte-like cells with dimethyl sulphoxide (Me2SO), retinoic acid or dibutyryl cyclic AMP (Bt2-cAMP) resulted in a 2-3-fold increase in 5-lipoxygenase enzyme activity and a 4-fold increase in leukotriene B4 synthesis. Differentiation of HL-60 cells into monocyte-like cells with 1,25-dihydroxyvitamin D3 induced 5-lipoxygenase activity 5-fold, but leukotriene B4 production was only increased 2-fold. Differentiation of HL-60 cells with phorbol 12-myristate 13-acetate (PMA) into macrophage-like cells failed to induce 5-lipoxygenase or leukotriene B4 production. Examination of the levels of the transcript encoding 5-lipoxygenase and FLAP demonstrated that differentiation of HL-60 cells into granulocytes resulted in a co-ordinate induction of 5-lipoxygenase and FLAP mRNA. In contrast, differentiation of HL-60 cells into monocytes resulted in discordant regulation of 5-lipoxygenase and FLAP mRNA. Treatment with 1,25-dihydroxyvitamin D3 resulted in a 6-fold increase in 5-lipoxygenase mRNA and a 1.3-fold increase in FLAP mRNA, while treatment with phorbol ester did not induce 5-lipoxygenase mRNA but did increase FLAP mRNA 2-fold. The transcriptional rate of the 5-lipoxygenase and FLAP genes did not change upon Me2SO or 1,25-dihydroxyvitamin D3 treatment, suggesting that the increase of the mRNA coding for these proteins was not due to transcriptional activation of their respective genes. The mRNA half-life for 5-lipoxygenase did not change significantly upon treatment with Me2SO or 1,25-dihydroxyvitamin D3. The FLAP mRNA half-life increased from approx. 3.5 h to 4.5 h in cells treated with either Me2SO or 1,25-dihydroxyvitamin D3. These data suggest that expression of 5-lipoxygenase and FLAP is controlled by a post-transcriptional event other than stabilization of the mRNA.

Cationic lipids enhance cellular uptake and activity of phosphorothioate antisense oligonucleotides

We have investigated the use of a cationic lipid preparation to enhance antisense oligonucleotide activity in human umbilical vein endothelial cells. A liposomal preparation containing the cationic lipid N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) was found to increase by at least 1000-fold the potency of an antisense oligonucleotide (ISIS 1570) that hybridizes to the AUG translation initiation codon of human intercellular adhesion molecule-1. In the presence of 8 microM DOTMA, 6-15-fold more 35S-ISIS 1570 associated with cells, at oligonucleotide concentrations from 0.01 to 5 microM, than did in the absence of DOTMA. Both 35S-ISIS 1570 association with cells and antisense activity were increased as a function of DOTMA concentration and with increasing time of incubation with the cationic lipid. Fluorescein-labeled ISIS 1570 was used to assess the intracellular distribution of the oligonucleotide in the presence and absence of DOTMA. In the absence of DOTMA, the oligonucleotide localized to discrete structures in the cytoplasm of the cell, resulting in a punctate fluorescence pattern. In the presence of DOTMA, cellular fluorescence markedly increased and the oligonucleotide localized within the nucleus, as well as to discrete structures in the cytoplasm. Accumulation of the oligonucleotide in the nucleus in the presence of DOTMA was time and temperature dependent. Nuclear accumulation was inhibited by preincubation of the cells with monensin but not chloroquine, NH4Cl, nocodazole, colcemid, or brefeldin A. These data demonstrate that cationic lipids increase antisense activity by increasing the amount of oligonucleotide associated with cells and altering intracellular distribution of the oligonucleotide.

Antisense oligonucleotides inhibit intercellular adhesion molecule 1 expression by two distinct mechanisms

Intercellular adhesion molecule 1 (ICAM-1) is a glycoprotein expressed on the surface of both hemopoietic and nonhemopoietic cells that mediates, in part, the emigration of leukocytes out of the vasculature. Expression of ICAM-1 on the surface of human umbilical vein endothelial cells and a human lung carcinoma cell line (A549) was increased by interleukin-1 beta, tumor necrosis factor alpha, and interferon gamma in a concentration-dependent manner. Phosphorothioate antisense oligonucleotides designed to hybridize to 10 target sites on the human ICAM-1 mRNA were tested for inhibition of ICAM-1 expression in both cell lines by an ICAM-1 enzyme-linked immunosorbent assay. Based upon potency and unique mRNA target sites, two oligonucleotides were studied in greater detail: ISIS 1570, which targeted the AUG translation initiation codon, and ISIS 1939, which targeted specific sequences in the 3'-untranslated region of the mRNA. Both oligonucleotides specifically inhibit expression of ICAM-1 as analyzed by immunoprecipitation of 35S-labeled proteins. Treatment of cells with ISIS 1939 promoted a reduction in ICAM-1 mRNA, whereas ISIS 1570 did not change the level of ICAM-1 mRNA, suggesting that the two oligonucleotides may be inhibiting ICAM-1 expression by two different mechanisms. The activity of both oligonucleotides was blocked by hybridization of the oligonucleotide to its complementary sense strand prior to addition to the cells. Neither ISIS 1570 nor ISIS 1939 changed the transcriptional rate of the ICAM-1 gene, demonstrating that both oligonucleotides were working through a post-transcriptional mechanism. 2'-O-Methyl phosphorothioate analogs, which do not support RNase H-mediated cleavage of target mRNA, were used to determine if the active antisense oligonucleotides inhibited ICAM-1 expression by an RNase H-dependent mechanism. The 2'-O-methyl phosphorothioate analog of ISIS 1939 did not significantly reduce interleukin-1 beta-induced ICAM-1 expression, whereas the 2'-O-methyl phosphorothioate analog of ISIS 1570 did inhibit ICAM-1 expression, suggesting that the reduction of ICAM-1 mRNA following treatment with ISIS 1939 was due, in part, to RNase H-mediated hydrolysis. Adherence of HL-60 cells to human umbilical vein cell monolayers was inhibited by ISIS 1570 and ISIS 1939, demonstrating that the reduced levels of ICAM-1 impact on ICAM-1-associated function.

Leukotriene receptors and mechanisms of signal transduction

To better understand the mechanisms by which leukotriene tone is regulated, we have characterized the mechanisms of genetic regulation of 5-lipoxygenase in HL60 cells induced to differentiate with dimethyl sulfoxide (DMSO) and compared a number of rat and human 5-lipoxygenase introns. We demonstrate that differentiation of HL60 cells with DMSO results in coordinate induction of 5-LO and 5-LO activating protein (FLAP). The production of LTB4, 5-LO protein, 5-LO mRNa and FLAP RNA increased coordinately. However, two approaches demonstrated no increase in the initiation of transcription of 5-LO and FLAP pre-mRNA and no changes in the mRNA half lives. Moreover, cycloheximide inhibits the induction of the mRNAs and proteins. Thus, we suggest that 5-LO and FLAP are coordinately regulated in HL60 cells via mechanisms involving changes in RNA processing. To better understand potential mechanisms involved, we have cloned and sequenced several human 5-LO introns and compared them to analogous rat 5-LO introns. A number of regions of potential regulatory significances are conserved and may be important in controlling the rate of pre-mRNA processing.

Sequence and regional distribution of the mRNA encoding the alpha 2 polypeptide of rat gamma-aminobutyric acidA receptors

A cDNA from a rat hippocampal cDNA library encodes an isoform of the alpha polypeptide of the gamma-aminobutyric acid (GABA)/benzodiazepine (BZ) receptor. Its deduced amino acid sequence is 96% identical to that of the alpha 2 polypeptide of the bovine GABAA receptor. The polypeptide has features shared by all previously reported GABAA receptor alpha polypeptides and shares 71-76% identity with previously described rat alpha polypeptides. Most of the differences lie in the presumed extracellular and intracellular domains. On Northern blots, the alpha 2 cDNA detects two mRNAs, which are found in cortex, hippocampus, and striatum, brain regions enriched in pharmacologically defined "BZ type II" receptors. Other workers have previously shown that the alpha polypeptides of the GABAA receptor largely determine the BZ binding properties of reconstituted receptors. The distribution of alpha 2 mRNAs in rat brain suggests that the alpha 2 subunit may indeed be involved in the BZ type II receptors.

Independent cellular and ontogenetic expression of mRNAs encoding three alpha polypeptides of the rat GABAA receptor

Previous studies have shown that several distinct but related polypeptides can serve as alpha subunits of functional GABAA receptors. Furthermore, the diversity of these polypeptides at least partially accounts for the functional heterogeneity of GABAA receptors. In this paper, we report the results of in situ hybridization studies using probes derived from our recently reported cDNAs for alpha 1, alpha 2, and alpha 4 GABAA receptor polypeptides. We show that the mRNAs that encode these isoforms have distinct regional and cellular distributions and are present at widely varying levels within the rat brain. In addition, our Northern blot analyses indicate that each of these three alpha mRNAs has a distinct pattern of ontogenetic regulation. Differential regulation of alpha polypeptide isoforms may lead to changes in GABAA receptor function during ontogeny as well as to distinct cellular responses to GABA and GABA-related drugs.

A novel alpha subunit in rat brain GABAA receptors

Two cDNAs (alpha 1 and alpha 4) from rat brain cDNA libraries encode isoforms of the alpha subunit of the GABA/benzodiazepine receptor, which differ at 30% of their amino acid residues. Northern blot analysis and in situ hybridization histochemistry show that alpha 1 and alpha 4 mRNAs have distinct sizes and distinct regional and cellular distributions in rat brain: both mRNAs are found in the cortex and hippocampus; however, only the alpha 1 mRNA is detected in the cerebellum. We injected RNA transcribed from alpha 1 and alpha 4 cDNAs into Xenopus oocytes, together with an RNA for a rat beta subunit. We obtained GABA-dependent inward currents that were reversibly blocked by picrotoxin. Picrotoxin alone, applied to oocytes producing the alpha and beta polypeptides, elicited an outward current. We suggest that these polypeptides together produce GABA-gated ion channels that can also open spontaneously.

Absolute configuration of a chiral CHD group via neutron diffraction: confirmation of the absolute stereochemistry of the enzymatic formation of malic acid

Neutron diffraction has been used to monitor the absolute stereochemistry of an enzymatic reaction. (-)(2S)malic-3-d acid was prepared by the action of fumarase on fumaric acid in D2O. After a large number of cations were screened, it was found that (+)(R) alpha-phenylethylamine forms the large crystals necessary for a neutron diffraction analysis. The subsequent structure determination showed that (+)(R) alpha-phenylethylammonium (-)(2S)malate-3-d has an absolute configuration of R at the CHD site (i.e., the C3 carbon of malate). This result confirms the absolute stereochemistry of fumarate-to-malate transformation as catalyzed by the enzyme fumarase.