The first stereoselective total synthesis of quinine.
The first entirely stereoselective total synthesis of (-)-quinine is reported.
Antimalarials↗
Biomedical subjects
J R Tata
Publications and source records attributed to J R Tata.
Characterization of Xenopus cytosolic thyroid-hormone-binding protein (xCTBP) with aldehyde dehydrogenase activity.
Multiple cytosolic thyroid-hormone-binding proteins (CTBPs) with varying characteristics, depending on the species and tissue, have been reported. We first purified a 59-kDa CTBP from Xenopus liver (xCTBP), and found that it is responsible for major [125I]T(3)-binding activity in Xenopus liver cytosol. Amino acid sequencing of internal peptide fragments derived from xCTBP demonstrated high identity to the corresponding sequence of mammalian aldehyde dehydrogenases 1 (ALDH1). To confirm whether or not xCTBP is identical to xALDH1, we isolated cDNAs encoding xALDH1 from an adult Xenopus hepatic cDNA library. The amino acid sequences deduced from the two isolated xALDH1 cDNAs were very similar to those of mammalian ALDH1 enzymes. The recombinant xALDH1 protein exhibited both T(3)-binding activity and ALDH activity converting retinal to retinoic acid (RA), which were similar to those of xCTBP purified from liver cytosol. The T(3)-binding activity was inhibited by NAD, while the ALDH activity was inhibited by thyroid hormones. Our results demonstrate that xCTBP is identical to ALDH1 and suggest that this protein might modulate RA synthesis and intracellular concentration of free T(3). Communications between thyroid hormone and retinoid pathways are discussed.
Aldehyde Dehydrogenase↗
P450 interaction with HIV protease inhibitors: relationship between metabolic stability, inhibitory potency, and P450 binding spectra.
More than 60 human immunodeficiency virus protease inhibitors were examined for the structure-activity relationship between metabolic stability, CYP3A4 inhibitory potency, and substrate-induced binding spectra with a ferric form of P450 in human liver microsomes. A positive relationship was found between CYP3A4 inhibitory potency and metabolic stability; namely, compounds that were more potent for the CYP3A4 inhibition generally were more metabolically stable. In addition, the compounds formed two clusters defined by the distinct type of substrate-induced P450 binding spectra: the compounds with type II binding spectra were more stable metabolically and more potent for the CYP3A4 inhibition than those with type I binding spectra. The structure-activity relationship suggested that the presence and position of heterocyclic nitrogen on the pyridine moiety play an important role in determining the manner of interaction with P450 and the magnitude of CYP3A4 inhibition/metabolic stability in the series of structurally related human immunodeficiency virus protease inhibitors under development.
Anti-HIV Agents↗
Combinatorial diversification of indinavir: in vivo mixture dosing of an HIV protease inhibitor library.
An efficient combination solution-phase/solid-phase route enabling the diversification of the P1', P2', and P3 subsites of indinavir has been established. The synthetic sequence can facilitate the rapid generation of HIV protease inhibitors possessing more favorable pharmacokinetic properties as well as enhanced potencies. Multiple compound dosing in vivo may also accelerate the identification of potential drug candidates.
Animals↗
A brief history of developmental biology at the National Institute for Medical Research.
Explore the source record for details and available documents.
Academies and Institutes↗
Xenopus cytosolic thyroid hormone-binding protein (xCTBP) is aldehyde dehydrogenase catalyzing the formation of retinoic acid.
Amino acid sequencing of an internal peptide fragment derived from purified Xenopus cytosolic thyroid hormone-binding protein (xCTBP) demonstrates high similarity to the corresponding sequence of mammalian aldehyde dehydrogenase 1 (ALDH1) (Yamauchi, K., and Tata, J. R. (1994) Eur. J. Biochem. 225, 1105-1112). Here we show that xCTBP was co-purified with ALDH and 3,3',5-triiodo-L-thyronine (T3) binding activities. By photoaffinity labeling with [125I]T3, a T3-binding site in the xCTBP was estimated to reside in amino acid residues 93-114, which is distinct from the active site of the enzyme but present in the NAD+ binding domain. The amino acid sequences deduced from the two isolated xALDH1 cDNAs (xALDH1-I and xALDH1-II) were 94.6% identical to each other and very similar to those of mammalian ALDH1 enzymes. The two recombinant xALDH1 proteins exhibit both T3 binding activity and ALDH activity converting retinal to retinoic acid (RA), which are similar to those of xCTBP. The mRNAs were present abundantly in kidney and intestine of adult female Xenopus. Interestingly, their T3 binding activities were inhibited by NAD+ and NADH but not by NADP+ and NADPH, whereas NAD+ was required for their ALDH activities. Our results demonstrate that xCTBP is identical to ALDH1 and suggest that this protein might modulate RA synthesis and intracellular level of free T3.
Aldehyde Dehydrogenase↗
Amphibian metamorphosis as a model for studying the developmental actions of thyroid hormone.
The thyroid hormones L-thyroxine and triiodo-L-thyronine have profound effects on postembryonic development of most vertebrates. Analysis of their action in mammals is vitiated by the exposure of the developing foetus to a number of maternal factors which do not allow one to specifically define the role of thyroid hormone (TH) or that of other hormones and factors that modulate its action. Amphibian metamorphosis is obligatorily dependent on TH which can initiate all the diverse physiological manifestations of this postembryonic developmental process (morphogenesis, cell death, re-structuring, etc.) in free-living embryos and larvae of most anurans. This article will first describe the salient features of metamorphosis and its control by TH and other hormones. Emphasis will be laid on the key role played by TH receptor (TR), in particular the phenomenon of TR gene autoinduction, in initiating the developmental action of TH. Finally, it will be argued that the findings on the control of amphibian metamorphosis enhance our understanding of the regulation of postembryonic development by TH in other vertebrate species.
Amphibians↗
Amphibian metamorphosis as a model for studying the developmental actions of thyroid hormone.
The thyroid hormones L-thyroxine and triiodo-L-thyronine have profound effects on postembryonic development of most vertebrates. Analysis of their action in mammals is vitiated by the exposure of the developing foetus to a number of maternal factors which do not allow one to specifically define the role of thyroid hormone (TH) or that of other hormones and factors that modulate its action. Amphibian metamorphosis is obligatorily dependent on TH which can initiate all the diverse physiological manifestations of this postembryonic developmental process (morphogenesis, cell death, re-structuring, etc.) in free-living embryos and larvae of most anurans. This article will first describe the salient features of metamorphosis and its control by TH and other hormones. Emphasis will be laid on the key role played by TH receptor (TR), in particular the phenomenon of TR gene autoinduction, in initiating the developmental action of TH. Finally, it will be argued that the findings on the control of amphibian metamorphosis enhance our understanding of the regulation of postembryonic development by TH in other vertebrate species.
Amphibians↗
Structural requirements for the activation of the human growth hormone secretagogue receptor by peptide and nonpeptide secretagogues.
Antibodies raised against an intracellular and extracellular domain of the GH secretagogue receptor (GHS-R) confirmed that its topological orientation in the lipid bilayer is as predicted for G protein-coupled receptors with seven transmembrane domains. A strategy for mapping the agonist-binding site of the human GHS-R was conceived based on our understanding of ligand binding in biogenic amine and peptide hormone G protein-coupled receptors. Using site-directed mutagenesis and molecular modeling, we classified GHS peptide and nonpeptide agonist binding in the context of its receptor environment. All peptide and nonpeptide ligand classes shared a common binding domain in transmembrane (TM) region 3 of the GHS-R. This finding was based on TM-3 mutation E124Q, which eliminated the counter-ion to the shared basic N+ group of all GHSs and resulted in a nonfunctional receptor. Restoration of function for the E124Q mutant was achieved by a complementary change in the MK-0677 ligand through modification of its amine side-chain to the corresponding alcohol. Contacts in other TM domains [TM-2 (D99N), TM-5 (M213K, S117A), TM-6 (H280F), and extracellular loop 1 (C116A)] of the receptor revealed specificity for the different peptide, benzolactam, and spiroindolane GHSs. GHS-R agonism, therefore, does not require identical disposition of all agonist classes at the ligand-binding site. Our results support the hypothesis that the ligand-binding pocket in the GHS-R is spatially disposed similarly to the well characterized catechol-binding site in the beta2-adrenergic receptor.
Amino Acid Sequence↗
Amphibian metamorphosis as a model for studying the developmental actions of thyroid hormone.
A salient feature of the thyroid hormones. L-thyroxine (T4) and triiodo-L-thyronine (T3), is the multiplicity of their physiological and biochemical actions in a wide variety of vertebrates. Important among these is their profound effects on postembryonic development. Analysis of their developmental action in mammals is vitiated by the exposure of the developing foetus to a number of maternal factors which do not allow one to specifically define the role of thyroid hormone (TH) or that of other hormones and factors that modulate its action. Amphibian metamorphosis is obligatorily dependent on TH which can initiate all the diverse physiological manifestations of this postembryonic developmental process (morphogenesis, cell death, re-structuring, etc.) in free-living embryos and larvae of most anurans. It is therefore an ideal model for studying the mechanisms underlying the hormonal regulation of postembryonic development. This article will first summarize the key features of metamorphosis and its control by TH and other hormones. Emphasis will be laid on the important role played by TH receptor (TR), in particular the phenomenon of TR gene autoinduction, in initiating the developmental action of TH. Finally, it will be argued that the findings on the control of amphibian metamorphosis enhance our understanding of the regulation of postembryonic development by TH in mammals and other vertebrate species.
Amphibians↗
Differential responses to ligands of overexpressed thyroid hormone and retinoid X receptors in a Xenopus cell line and in vivo.
In an attempt to explain the contrasting patterns of expression of Xenopus thyroid hormone (xTR) and retinoid X (xRXR) receptor genes and to extend our understanding of the role of heterodimerization of these receptors during amphibian metamorphosis, we have investigated the response to their respective ligands of cells in which xTR and xRXR were overexpressed. Results obtained with two separate approaches are now described. In the first, 3,3'5-triiodothyronine (t3) was found to strongly upregulate xTR beta mRNA in XTC-2 cells, but not of xTR alpha or xRXR alpha mRNAs, while xRXR gamma transcripts could not be detected. 9-cis-retinoic acid (9-cis-RA) did not substantially influence the expression of any of these four receptor genes. When transcription from three different thyroid response elements (TREs) (a palindromic TREpal, an inverted repeat +6 [F2] and a direct repeat +4[DR+4] as present in the promoter of xTR beta gene) was measured in XTC-2 cells in which xTR beta and xRXR alpha were overexpressed, only T3 upregulated transcription while 9-cis-RA, alone or together with T3, was ineffective. 9-cis-RA however enhanced transcription from an RXR responsive element (RXR-RE). THe second approach involved overexpression of xTR beta and xRXR alpha in premetamorphic Xenopus tadpole tail muscle followed by measuring the response of the tails to T3 in organ culture. After validating the microinjection/culture procedure histochemically, we found that T3 enhanced transcription from the xTR beta DR +4 TRE in tails in which xTR beta was overexpressed but the overexpression of xRXR alpha failed to modify this response. It is concluded that in both XTC cells and tadpole tails, overexpressed xRXR fails to modify the enhanced transcriptional response of endogenous and overexpressed xTR beta to T3 and that exogenous 9-cis-RA is ineffective.
Alitretinoin↗
Thyroid hormone receptor genes of neotenic amphibians.
Since thyroid hormones play a pivotal role in amphibian metamorphosis we used PCR to amplify DNA fragments corresponding to a portion of the ligand-binding domain of the thyroid hormone receptor (TR) genes in several neotenic amphibians: the obligatory neotenic members of the family Proteidea the mudpuppy Necturus maculosus and Proteus anguinus as well as two members of the facultative neotenic Ambystoma genus: the axolotl Ambystoma mexicanum and the tiger salamander Ambystoma tigrinum. In addition, we looked for TR genes in the genome of an apode Typhlonectes compressicaudus. TR genes were found in all these species including the obligatory neotenic ones. The PCR fragments obtained encompass both the C and E domains and correspond to alpha and beta genes. Their sequences appear to be normal, suggesting that there is no acceleration of evolutionary rates in the TR genes of neotenic amphibians. This result is not surprising for Ambystomatidae, which are known to respond to T3 (3,3',5-triiodothyronine) but is not in agreement with biochemical and biological data showing that Proteidea cannot respond to thyroid hormones. Interestingly, by RT-PCR analysis we observed a high expression levels of TRalpha in gills, intestine, and muscles of Necturus as well as in the liver of Ambystoma mexicanum, whereas TRbeta expression was only detected in Ambystoma mexicanum but not in Necturus. Such a differential expression pattern of TRalpha and TRbeta may explain the neoteny in Proteidea. The cloning of thyroid-hormone-receptor gene fragments from these species will allow the molecular study of their failure to undergo metamorphosis.
Amino Acid Sequence↗
Tissue-dependent and developmentally regulated cytosolic thyroid-hormone-binding proteins (CTBPs) in Xenopus.
Xenopus cytosolic thyroid-hormone-binding proteins (CTBPs) were examined by a photoaffinity labeling and [125I]T3-binding assay. An affinity-labeled protein of 59 kDa, which was responsible for the major T3-binding activity in adult tissues, was predominant in liver. The 59-kDa CTBP first appeared in significant amounts at the metamorphic climax stage in liver cytosol and continued to be expressed after metamorphosis. Another affinity-labeled CTBP of 38 kDa appeared at the metamorphic climax stage in cytosol from head region, but disappeared after this stage. T3-binding assay using whole cytosol showed that a distinct CTBP, although not photoaffinity-labeled, was present in cytosol from hindlimb bud and gradually disappeared as the hindlimb grew. The cytosol from liver, head region, and hindlimb bud contained high affinity binding sites for T3 with Kd values ranging from 10(-9) to 10(-8) M. These results suggest that there are at least three distinct CTBPs in Xenopus cytosol, which are expressed in a tissue-dependent and developmentally regulated manner.
Animals↗
An immunocytochemical analysis of the expression of thyroid hormone receptor alpha and beta proteins during natural and thyroid hormone-induced metamorphosis in Xenopus.
Amphibian metamorphosis is characterized by the upregulation of thyroid hormone receptor (TR) mRNA in all tissues of tadpole during both the natural and thyroid hormone (TH)-induced development. The two TR genes, termed alpha and beta, are members of a large multigene family of nuclear receptors related to the cellular homolog of the oncogene c-erbA. The phenomenon of upregulation is more marked for the beta than the alpha isoform. To determine whether or not the auto-induction of the transcripts is paralleled by that of TR proteins, non-cross-reacting monoclonal antibodies were prepared against Xenopus laevis TR alpha and beta (xTR alpha, beta) in order to analyze immunocytochemically their expression and localization. Three tadpole tissues that exemplify three major consequences of gene re-programing during natural and TH-induced metamorphosis were studied: (i) Liver that undergoes extensive functional switching; (ii) small intestinal epithelium that exhibits substantial cell death prior to major structural and biochemical modifications; and (iii) hind limb-bud as an example of de novo morphogenesis. It was shown that xTR alpha protein is generally more abundant in these tissues, and its expression is developmentally and hormonally less regulated, than is xTR beta. The auto-induction of xTR beta was particularly intense at 5 days after administration of triiodo-thyronine (T3) to both pre-metamorphic (stage 52) tadpoles and at the onset of natural metamorphosis (stage 55). In the developing hind limb-bud at both stages the upregulation of TR beta is topologically restricted, being particularly intense in dense pockets of cells, presumably rich in chondrocytes. It was concluded that the distribution and expression of xTR alpha and beta proteins match partially, but not fully, those of their transcripts during natural and hormone-induced metamorphosis.
Amino Acid Sequence↗
Dominant-negative mutant thyroid hormone receptors prevent transcription from Xenopus thyroid hormone receptor beta gene promoter in response to thyroid hormone in Xenopus tadpoles in vivo.
We describe a dominant-negative approach in vivo to assess the strong, early upregulation of thyroid hormone receptor beta (TR beta) gene in response to thyroid hormone, characteristic of the onset of natural and thyroid hormone-induced amphibian metamorphosis, 3,3',5-Triiodo-thyronine (T3) treatment of organ cultures of premetamorphic Xenopus tadpole tails coinjected in vivo with the wild-type Xenopus TR beta (wt-xTR beta) and three different thyroid responsive element chloramphenicol acetyltransferase (TRE-CAT) reporter constructs, including a direct repeat +4 (DR +4) element in the -200/+87 fragment of the xTR beta promoter, resulted in a 4- to 8-fold enhancement of CAT activity. Two human C-terminal TR beta 1 mutants (delta-hTR beta 1 and Ts-hTR beta 1), an artificial Xenopus C-terminal deletion mutant (mt-xTR beta), and the oncogenic viral homology v-erbA, none of which binds T3, inhibited this T3 response of the endogenous wt-xTR in Xenopus XTC-2 cells cotransfected with the -1600/+87 xTR beta promoter-CAT construct, the potency of the dominant-negative effect of these mutant TRs being a function of the strength of their heterodimerization with Xenopus retinoid X receptor gamma. Coinjection of the dominant-negative Xenopus and human mutant TR beta s into Xenopus tadpole tails totally abolished the T3 responsiveness of the wt-xTR beta with different TREs, including the natural DR +4 TRE of the xTR beta promoter.
Amino Acid Sequence↗
Metamorphosis: an exquisite model for hormonal regulation of post-embryonic development.
Metamorphosis in invertebrates and vertebrates, a process highly conserved throughout evolution, is an ideal model for studying mechanisms of post-embryonic development regulated by external signals. Amphibian metamorphosis also shares many similarities with mammalian development in the perinatal period. The precocious induction in vivo and in culture of insect and amphibian metamorphosis by exogenous thyroid hormones, and its retardation or inhibition by prolactin (PRL), have allowed the analysis of such characteristic features of post-embryonic development as morphogenesis, tissue remodelling, gene reprogramming, and programmed cell death. Recent studies on metamorphosis have revealed the important role played by such processes as auto-and cross-regulation of thyroid hormone receptor (TR) genes and by cell death or apoptosis, as in the maturation of the central nervous system, tissue restructuring and organolysis.
Animals↗
Contrasting patterns of expression of thyroid hormone and retinoid X receptor genes during hormonal manipulation of Xenopus tadpole tail regression in culture.
The precocious induction of amphibian metamorphosis is an ideal system for analyzing the developmental action of TH, while the hormonal activation of tadpole tail regression offers the further advantage of studying programmed cell death. One of the striking features of thyroid hormone (TH)-induced tail regression (as with morphogenetic responses of all tadpole tissues) in Xenopus is the rapid autoinduction of TRbeta gene, but it is not known how TH would affect the expression of the genes encoding TR's heterodimeric partner, retinoid X receptor (RXR). Here we first show that the synthetic glucocorticoid dexamethasone (Dex) potentiates and prolactin (PRL) suppresses, 3,3',5-triiodothyronine (T3)-induced regression of pre-metamorphic Xenopus tadpole tails in organ culture. T3 strongly upregulated (11-35-fold) the concentration of Xenopus TRbeta (xTRbeta) mRNA in these cultures while downregulating by 50% that of Xenopus RXRgamma (xRXRgamma) mRNA in the same samples of tail RNA. DEX and PRL enhanced or diminished the T3-regulated expression of these two transcripts, respectively, which parallels their other effects in whole tadpoles or cultured tails. The contrasting effects of the three hormones on the steady-state levels of xTRbeta and XRXRgamma mRNAs were time- and dose-dependent. T3 and DEX also strongly upregulated the transcription of xTRbeta gene transfected into Xenopus XTC-2 cells but PRL failed to prevent this autoinduction. The actions of these three hormones involved in amphibian metamorphosis, as judged by the expression of xTRbeta and xRXRgamma genes, reveal a new facet of hormonal interplay underlying their developmental actions.
Animals↗
Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue.
A potent, orally active growth hormone (GH) secretagogue L-163,191 belonging to a recently synthesized structural class has been characterized. L-163,191 releases GH from rat pituitary cells in culture with EC50 = 1.3 +/- 0.09 nM and is mechanistically indistinguishable from the GH-releasing peptide GHRP-6 and the prototypical nonpeptide GH secretagogue L-692,429 but clearly distinguishable from the natural GH secretagogue, GH-releasing hormone. L-163,191 elevates GH in dogs after oral doses as low as 0.125 mg/kg and was shown to be specific in its release of GH without significant effect on plasma levels of aldosterone, luteinizing hormone, thyroxine, and prolactin after oral administration of 1 mg/kg. Only modest increases in cortisol were observed. Based on these properties, L-163,191 has been selected for clinical studies.
Administration, Oral↗