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Okamoto N, Fujinaga D, Yamanaka N. Steroid hormone signaling: What we can learn from insect models. VITAMINS AND HORMONES 2023; 123:525-554. [PMID: 37717997 DOI: 10.1016/bs.vh.2022.12.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Ecdysteroids are a group of steroid hormones in arthropods with pleiotropic functions throughout their life history. Ecdysteroid research in insects has made a significant contribution to our current understanding of steroid hormone signaling in metazoans, but how far can we extrapolate our findings in insects to other systems, such as mammals? In this chapter, we compare steroid hormone signaling in insects and mammals from multiple perspectives and discuss similarities and differences between the two lineages. We also highlight a few understudied areas and remaining questions of steroid hormone biology in metazoans and propose potential future research directions.
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Affiliation(s)
- Naoki Okamoto
- Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Daiki Fujinaga
- Department of Entomology, University of California, Riverside, CA, United States
| | - Naoki Yamanaka
- Department of Entomology, University of California, Riverside, CA, United States.
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Bandzerewicz A, Gadomska-Gajadhur A. Into the Tissues: Extracellular Matrix and Its Artificial Substitutes: Cell Signalling Mechanisms. Cells 2022; 11:914. [PMID: 35269536 PMCID: PMC8909573 DOI: 10.3390/cells11050914] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 03/02/2022] [Accepted: 03/04/2022] [Indexed: 02/06/2023] Open
Abstract
The existence of orderly structures, such as tissues and organs is made possible by cell adhesion, i.e., the process by which cells attach to neighbouring cells and a supporting substance in the form of the extracellular matrix. The extracellular matrix is a three-dimensional structure composed of collagens, elastin, and various proteoglycans and glycoproteins. It is a storehouse for multiple signalling factors. Cells are informed of their correct connection to the matrix via receptors. Tissue disruption often prevents the natural reconstitution of the matrix. The use of appropriate implants is then required. This review is a compilation of crucial information on the structural and functional features of the extracellular matrix and the complex mechanisms of cell-cell connectivity. The possibilities of regenerating damaged tissues using an artificial matrix substitute are described, detailing the host response to the implant. An important issue is the surface properties of such an implant and the possibilities of their modification.
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Kang XL, Li YX, Li YL, Wang JX, Zhao XF. The homotetramerization of a GPCR transmits the 20-hydroxyecdysone signal and increases its entry into cells for insect metamorphosis. Development 2021; 148:148/5/dev196667. [PMID: 33692089 DOI: 10.1242/dev.196667] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 02/05/2021] [Indexed: 12/28/2022]
Abstract
Animal steroid hormones initiate signaling by passive diffusion into cells and binding to their nuclear receptors to regulate gene expression. Animal steroid hormones can initiate signaling via G protein-coupled receptors (GPCRs); however, the underlying mechanisms are unclear. Here, we show that a newly discovered ecdysone-responsive GPCR, ErGPCR-3, transmits the steroid hormone 20-hydroxyecdysone (20E) signal by binding 20E and promoting its entry into cells in the lepidopteran insect Helicoverpa armigera Knockdown of ErGPCR-3 in larvae caused delayed and abnormal pupation, inhibited remodeling of the larval midgut and fat body, and repressed 20E-induced gene expression. Also, 20E induced both the interaction of ErGPCR-3 with G proteins and rapid intracellular increase in calcium, cAMP and protein phosphorylation. ErGPCR-3 was endocytosed by GPCR kinase 2-mediated phosphorylation, and interacted with β-arrestin-1 and clathrin, to terminate 20E signaling under 20E induction. We found that 20E bound to ErGPCR-3 and induced the ErGPCR-3 homodimer to form a homotetramer, which increased 20E entry into cells. Our study revealed that homotetrameric ErGPCR-3 functions as a cell membrane receptor and increases 20E diffusion into cells to transmit the 20E signal and promote metamorphosis.
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Affiliation(s)
- Xin-Le Kang
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao 266237, China
| | - Yan-Xue Li
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao 266237, China
| | - Yan-Li Li
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao 266237, China
| | - Jin-Xing Wang
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao 266237, China
| | - Xiao-Fan Zhao
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao 266237, China
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Okamoto N, Viswanatha R, Bittar R, Li Z, Haga-Yamanaka S, Perrimon N, Yamanaka N. A Membrane Transporter Is Required for Steroid Hormone Uptake in Drosophila. Dev Cell 2018; 47:294-305.e7. [PMID: 30293839 PMCID: PMC6219898 DOI: 10.1016/j.devcel.2018.09.012] [Citation(s) in RCA: 80] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 08/06/2018] [Accepted: 09/09/2018] [Indexed: 02/08/2023]
Abstract
Steroid hormones are a group of lipophilic hormones that are believed to enter cells by simple diffusion to regulate diverse physiological processes through intracellular nuclear receptors. Here, we challenge this model in Drosophila by demonstrating that Ecdysone Importer (EcI), a membrane transporter identified from two independent genetic screens, is involved in cellular uptake of the steroid hormone ecdysone. EcI encodes an organic anion transporting polypeptide of the evolutionarily conserved solute carrier organic anion superfamily. In vivo, EcI loss of function causes phenotypes indistinguishable from ecdysone- or ecdysone receptor (EcR)-deficient animals, and EcI knockdown inhibits cellular uptake of ecdysone. Furthermore, EcI regulates ecdysone signaling in a cell-autonomous manner and is both necessary and sufficient for inducing ecdysone-dependent gene expression in culture cells expressing EcR. Altogether, our results challenge the simple diffusion model for cellular uptake of ecdysone and may have wide implications for basic and medical aspects of steroid hormone studies.
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Affiliation(s)
- Naoki Okamoto
- Department of Entomology, Institute for Integrative Genome Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Raghuvir Viswanatha
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Riyan Bittar
- Department of Molecular, Cell and Systems Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Zhongchi Li
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Sachiko Haga-Yamanaka
- Department of Molecular, Cell and Systems Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Norbert Perrimon
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA; Howard Hughes Medical Institute, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Naoki Yamanaka
- Department of Entomology, Institute for Integrative Genome Biology, University of California, Riverside, Riverside, CA 92521, USA.
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van Alem CMA, Boonstra M, Prins J, Bezhaeva T, van Essen MF, Ruben JM, Vahrmeijer AL, van der Veer EP, de Fijter JW, Reinders ME, Meijer O, Metselaar JM, van Kooten C, Rotmans JI. Local delivery of liposomal prednisolone leads to an anti-inflammatory profile in renal ischaemia–reperfusion injury in the rat. Nephrol Dial Transplant 2017; 33:44-53. [DOI: 10.1093/ndt/gfx204] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Accepted: 05/03/2017] [Indexed: 02/07/2023] Open
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Alléra A, Wildt L. Glucocorticoid-recognizing and -effector sites in rat liver plasma membrane. Kinetics of corticosterone uptake by isolated membrane vesicles--I. Binding and transport. J Steroid Biochem Mol Biol 1992; 42:737-56. [PMID: 1504012 DOI: 10.1016/0960-0760(92)90115-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
To gain insight into the mechanisms governing cellular uptake of glucocorticoids, we studied the binding and membrane transport of corticosterone (B) on a highly purified plasma membrane fraction from rat liver that was homogenized using a gentle, isotonic procedure. The fraction was mostly in the form of right-side out and osmotically active vesicles that were free of intracellular glucocorticoid receptors (GCR), transcortin (CBG) and ATP. Our uptake and binding studies carried out at 22 degrees C with [3H]B in physiological concentrations resulted in the following findings: (1) unlabeled B competed with [3H]B for uptake by the membrane vesicles; half-maximal competition of specific uptake was achieved with a 10- to 11-fold molar excess of unlabeled B. (2) [3H]B uptake was a saturable process of unusual kinetics (multiple sigmoidity); modified Scatchard plots revealed three significantly different apparent Kd-values of 1.3, 4.7 and 17.3 nM, corresponding to free B in the blood of non-stressed rats (4-16 nM). (3) Osmotic shrinkage of the vesicles led to a linear decrease in specific uptake, while non-specific uptake was independent of vesicle volume. Passive diffusion of [3H]B took place in leaky, but not in intact, vesicles. Reversible binding to, and mediated transport through, the membrane were interdependent parts of a strongly linked process. B was accumulated inside the vesicle up a concentration gradient by an active transport that followed first-order kinetics (Kt:3.9 nM); for its statistically reliable mathematical formulation and kinetic analysis, a replot was developed that revealed that relative accumulation increased with decreasing external hormone concentration. (4) Comparative binding studies disclosed that the apparent Kd-values (86.5 +/- 7.3 and 77.0 +/- 14.3 nM, respectively) of the [3H]B interactions with CBG and GCR did not differ (P greater than 0.3). These findings permit the conclusion that a plasma membrane-inserted carrier for B, effectively operating at physiological concentrations in the blood, is involved in a functional and regulatory manner in the biological action of glucocorticoids.
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Affiliation(s)
- A Alléra
- Department of Clinical Biochemistry, University of Bonn, Germany
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Howell GM, Po C, Lefebvre YA. Identification of dexamethasone-binding sites on male-rat liver plasma membranes by affinity labelling. Biochem J 1989; 260:435-41. [PMID: 2764881 PMCID: PMC1138687 DOI: 10.1042/bj2600435] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Binding studies with [3H]dexamethasone identified two binding sites on plasma membranes prepared from the male rat liver, a low-capacity site with a KD of 7.0 nM and a higher-capacity site with a KD of 90.1 nM. Both sites exhibited glucocorticoid responsiveness and specificity for glucocorticoids and progestins. Triamcinolone acetonide, which competes well for the binding of dexamethasone to the cytosolic glucocorticoid receptor, did not compete well for the binding of [3H]dexamethasone to the plasma-membrane binding sites. The binding sites were sensitive to protease and neuraminidase treatment, and resistant to extraction with NaCl, but were extracted with the detergent Triton X-100. As these experiments indicated the presence of plasma-membrane protein components which bind glucocorticoids at physiological concentrations, affinity-labelling experiments with dexamethasone mesylate were conducted. Two peptides were specifically labelled, one at approx. Mr 66,000 and one at Mr 45,000. The Mr-66,000 peptide was not sensitive to glucocorticoids, and was extracted by NaCl, and so did not correspond to either of the sites identified in the dexamethasone-binding studies. The Mr-45,000 entity, on the other hand, resembled the dexamethasone-binding sites in its response to glucocorticoid manipulation of the animal and in its resistance to salt extraction. This peptide was not present in rat serum. Thus we have identified a plasma-membrane peptide which binds dexamethasone. Whether this peptide is involved in transport of the glucocorticoid across the plasma membrane remains to be determined.
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Affiliation(s)
- G M Howell
- Department of Medicine, University of Ottawa, Ottawa Civic Hospital, Ont., Canada
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Boudinot FD, D'Ambrosio R, Jusko WJ. Receptor-mediated pharmacodynamics of prednisolone in the rat. JOURNAL OF PHARMACOKINETICS AND BIOPHARMACEUTICS 1986; 14:469-93. [PMID: 2879901 DOI: 10.1007/bf01059656] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A pharmacokinetic/pharmacodynamic model describing receptor-mediated effects of prednisolone is presented. The basis of the model is the generally accepted mechanism of action of steroid hormones in which corticosteroids bind to cytosolic receptors forming steroid-receptor complexes, which are activated and translocated into the nucleus. There the complexes associate with specific DNA sequences and modulate the rate of transcription of DNA into specific RNAs that code for the synthesis of proteins that elicit biological responses. Prednisolone, 5 or 50 mg/kg, was administered intravenously to adrenalectomized rats. Total plasma, free plasma, CBG-free plasma, and liver prednisolone concentrations were measured simultaneously with free hepatic cytosolic glucocorticoid receptor concentrations and tyrosine aminotransferase (TAT) activity of the liver as a function of time. The association/dissociation kinetics of prednisolone binding to the glucocorticoid receptor were measured separately in vitro at 37 degrees C. Total plasma, free plasma, and CBG-free plasma prednisolone concentrations could be used equally well in the model to account for the time course of receptor concentrations and TAT activity. However, use of liver steroid concentrations resulted in an overestimation of receptor depletion. Steroid concentrations in plasma increased 20 to 30-fold with a tenfold increase in dose, but receptor occupancy and TAT activity over time increased about threefold. While prednisolone pharmacokinetics were dose-dependent, parameters describing receptor kinetics and TAT activity were constant at each prednisolone dose. The major determinants of receptor-mediated glucocorticoid activity are confirmed to be the availability of the receptor, drug-receptor dissociation rate, and corticosteroid persistence in the biophase.
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Boudinot FD, Jusko WJ. Dose-dependent pharmacokinetics of prednisolone in normal and adrenalectomized rats. JOURNAL OF PHARMACOKINETICS AND BIOPHARMACEUTICS 1986; 14:453-67. [PMID: 3806371 DOI: 10.1007/bf01059655] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The pharmacokinetics of prednisolone after 5- and 50-mg/kg doses given as the sodium succinate salt was examined in normal and adrenalectomized rats. Prednisolone, prednisone, and corticosterone concentrations in plasma were determined by HPLC and free prednisolone measured by equilibrium dialysis. Prednisolone sodium succinate was rapidly and completely hydrolyzed to prednisolone as indicated by the absence of the ester from plasma within 5 min after intravenous injection. Prednisolone was rapidly metabolized to prednisone, while corticosterone concentrations in normal rats declined rapidly and were undetectable by 1 hr. Adrenalectomy had no effect on the disposition and protein binding of prednisolone. Dose, however, had a marked effect on prednisolone pharmacokinetics, with mean plasma clearance decreasing from 6.18 to 3.07 L/h per kg and mean steady-state volume of distribution decreasing from 2.14 to 1.05 L/kg from the lower to higher steroid dose. Half-life (0.50 hr) and mean residence time (0.35 hr) were unaffected by dose. Prednisolone plasma protein binding was nonlinear due to saturation of transcortin binding. Changes in pharmacokinetic parameters were not related to the nonlinear plasma binding, but were more likely caused by saturation of elimination pathways and tissue binding sites.
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Ponec M, Kempenaar JA. Biphasic entry of glucocorticoids into cultured human skin keratinocytes and fibroblasts. Arch Dermatol Res 1983; 275:334-44. [PMID: 6197938 DOI: 10.1007/bf00417208] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The uptake of glucocorticoids by cultured human skin keratinocytes and fibroblasts was found to be a rapid, temperature-sensitive process. All glucocorticoids tested accumulated in the cells, and the ratio between the intracellular and extracellular concentrations (ci/co ratio) was higher than 1. For most of the glucocorticoids under study there was good correlation between the lipophilicity and the rate of uptake. Since the uptake of glucocorticoids seems to be unsaturable in the concentration range used and no competition was observed between these compounds for entry into the cells, it may be assumed that the uptake of glucocorticoids is essentially a simple diffusion process based on a distribution of glucocorticoids between a lipid-rich phase and water. The analysis of the uptake process revealed that the entry of glucocorticoids into cultured human skin fibroblasts and keratinocytes is a non-mediated passive diffusion process that involves two distinct steps: a rapid, non-specific, high-capacity association to the cell membrane followed by a slower internalization process associated with a stronger binding of glucocorticoids within the cell.
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Duval D, Durant S, Homo-Delarche F. Non-genomic effects of steroids. Interactions of steroid molecules with membrane structures and functions. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 737:409-42. [PMID: 6309233 DOI: 10.1016/0304-4157(83)90008-4] [Citation(s) in RCA: 207] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Harrison RW. Cellular factors which modulate hormone responses: glucocorticoid action in perspective. INTERNATIONAL REVIEW OF CYTOLOGY. SUPPLEMENT 1983; 15:1-16. [PMID: 6343280 DOI: 10.1016/b978-0-12-364376-6.50007-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Virtually all glucocorticoid effects are mediated through changes in gene transcription. Steroid binding to the receptor and nuclear binding of the steroid-receptor complex are pivotal events in this process, but may be modified by the ability of a given steroid to traverse the cell membrane or cause receptor activation. The physical nature of the receptor, its precise subcellular location, and the process by which gene activation is accomplished are unknown. Preparation of purified receptor and further characterization of the nuclear binding sites will be crucial to a better understanding of this process.
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Abstract
Characteristics of the processes by which steroid and thyroid hormones enter tissues, cells and membrane vesicles are reviewed. Several authors suggest that entry is by passive diffusion: the accumulation within cells is attributed to cytoplasmic binding proteins. Other authors, however, propose a membrane-mediated process of entry. The involvement of saturability, high specificity, sensitivity to temperature, sulfhydryl and cell-surface-perturbing reagents and hydrolytic enzymes support the latter view. Purified plasma-membrane vesicle preparations retain several characteristics of entry shown by intact cells. Intracellular hormone-binding protein would not contribute to processes observed with these preparations.
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Green RD. Adenosine transport by a variant of C1300 murine neuroblastoma cells deficient in adenosine kinase. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 598:366-74. [PMID: 6246950 DOI: 10.1016/0005-2736(80)90014-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The uptake of adenosine by an adenosine kinase deficient variant of C1300 murine neuroblastoma cells has been studied in the absence and in the presence of erythro-9-(2-hydroxy-3-nonyl)adenine, a potent adenine deaminase inhibitor. Although 100 micro M inhibitor completely blocks the metabolism of adenosine under the conditions studied, the uptake of adenosine is concentrative, i.e., the intracellular adenosine concentration exceeds the extracellular concentration. This concentrative effect decreases as the concentration of adenosine increases and is hypothesized to be due to the binding of adenosine to an intracellular component. Despite this concentrative effect, we believe that the kinetics of uptake, as determined in experiments with short (10-20 s) uptake periods, reflect the kinetics of adenosine transport by a facilitated diffusion process. This nucleoside transport system appears to be nonspecific in that the transport of adenosine is competitively antagonized by thymidine. It does not appear to be necessary to inhibit adenosine deaminase in order to study transport in these cells as the Km for transport is not affected by the presence of erythro-9-(2-hydroxy-3-nonyl)adenine. However, erythro-9-(2-hydroxy-3-nonyl)adenine does depress the V for transport. This effect of the inhibitor is probably not due to the inhibition of adenosine deaminase as the transport of thymidine is similarly affected.
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Alléra A, Rao GS, Breuer H. Specific interaction of corticosteroids with components of the cell membrane which are involved in the translocation of the hormone into the intravesicular space of purified rat liver plasma membrane vesicles. JOURNAL OF STEROID BIOCHEMISTRY 1980; 12:259-66. [PMID: 7421211 DOI: 10.1016/0022-4731(80)90276-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Giorgi EP. The transport of steroid hormones into animal cells. INTERNATIONAL REVIEW OF CYTOLOGY 1980; 65:49-115. [PMID: 6993407 DOI: 10.1016/s0074-7696(08)61959-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Ballard PL. Delivery and transport of glucocorticoids to target cells. MONOGRAPHS ON ENDOCRINOLOGY 1979; 12:25-48. [PMID: 386085 DOI: 10.1007/978-3-642-81265-1_2] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Abstract
Glucocorticoid receptors are found in most mammalian tissues and have been studied in detail in a number of tissue culture systems. With cells that have not been exposed to steroids, the receptors are found in the cytoplasmic fraction from which they can be isolated and studied. Methods for studying glucocorticoid receptors depend on their high-affinity specific binding of radioactive steroids. The reversible interaction is intracellular. It follows Michaelian kinetics, at least in cell-free cytosol, and involves a thermodynamically homogeneous population of about 10 000 sites per cell. The receptor is an asymmetric, slightly acidic protein of about 100 000 daltons. It is very labile, especially in the unbound form. Binding activity depends on the integrity of thiol groups and perhaps on phosphorylation of amino acid residues. Although indirect, the evidence is overwhelmingly convincing that this protein is the physiologic glucocorticoid receptor. The time-kinetics of binding and dissociation are consistent with the sequence of events in glucocorticoid action. Various steroid analogs display binding characteristics predictable from their glucocorticoid activity. Loss of the binding protein from certain cultured cell lines is accompanied by unresponsiveness to glucocorticoids. The extensive tissue distribution of receptors parallels the extensive role of glucocorticoids in regulation. Finally, there is a strong correlation between nuclear binding of receptors and nuclear effects of the steroid. The glucocorticoid receptor can be distinguished from other glucocorticoid-binding proteins, based on their steroid specificity and physicochemical properties. There is no clear-cut demonstration that the receptor differs from tissue to tissue, and it is in fact very similar in various species. Unlike in other systems, receptor concentration does not seem to be regulated by its ligand or by other hormones. However, certain cases of hypo- as well as hypersensitivity to glucocorticoids appear to result from changes at the receptor level. The data indicate that the receptor can exist in inactive and active forms. The former predominate in the absence of steroid or when an angatonist is bound. Glucocorticoid agonists bind the active form, allowing it to be "activated" and subsequently bound to the nucleus. All of the receptors in isolated cytosol do not appear to be available for immediate occupancy by an agonist and this may be due to the time required for conversion of the receptors from inactive to active forms. The correlations between receptor binding and the glucocorticoid response indicate that the receptor is a rate-limiting factor in the magnitude and kinetics of the response, and this finding has important implications regarding mechanisms.
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Fain JN. Inhibition of glucose transport in fat cells and activation of lipolysis by glucocorticoids. MONOGRAPHS ON ENDOCRINOLOGY 1979; 12:547-60. [PMID: 226873 DOI: 10.1007/978-3-642-81265-1_29] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The major effects of glucocorticoids on white fat are shown in Fig. 1. The glucocorticoid diffuses into the cytosol of fat cells where it binds to a soluble receptor. The steroid-receptor complex then enters the nucleus where RNA synthesis is increased. The next step may be a selective increase in synthesis of protein(s). In any event, there is an inhibition of the membrane-bound glucose transport system and an increase in the ability of lipolytic agents to activate triglyceride lipolysis. There is also a decrease in phosphoenolpyruvate carboxykinase, lipoprotein lipase, and fatty acid synthetase that occurs after a somewhat longer lag period than is required for inhibition of glucose transport or lipolysis activation. Whether these effects are independent or secondary to the glucose transport inhibition and lipolysis activation remains to be established.
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Wohlhueter RM, Marz R, Graff JC, Plagemann PG. A rapid-mixing technique to measure transport in suspended animal cells: applications to nucleoside transport in Novikoff rat hepatoma cells. Methods Cell Biol 1978; 20:211-36. [PMID: 692430 DOI: 10.1016/s0091-679x(08)62020-8] [Citation(s) in RCA: 115] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Rao ML, Rao GS, Eckel J, Breuer H. Factors involved in the uptake of corticosterone by rat liver cells. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 500:322-32. [PMID: 588595 DOI: 10.1016/0304-4165(77)90024-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Isolated rat liver cells take up corticosterone rapidly; the initial rates increase with increasing temperature. A plot of the initial rates against the concentration of corticosterone indicated the presence of saturable and nonsaturable uptake systems. The Eadie-Hofstee plot showed the presence of two saturable and one nonsaturable uptake components. The apparent Kt values of the saturable systems were 64 +/- 40 nM (n = 3) and 1085 +/- 313 nM (n = 12). The nonsaturable system, probably diffusion, contributed 12% to the total uptake between 15 and 72 nM corticosterone, the physiological concentration of the free corticosterone in rat serum. Metabolic inhibitors did not influence the uptake of corticosterone. N-Ethylmaleimide, 1-fluoro-2,4-dinitrobenzene and sodium ethyl mercurithiosalicylate (1 mM each) decreased the uptake by 40%. Iodoacetate did not have any influence. Treatment of cells with phospholipase A inhibited the uptake 35--45%. In the presence of cortisone, cortisol, dexamethasone, aldosterone, testosterone, estradiol-17beta and estrone (2 muM each) the uptake decreased 30--50%. The presence of serum proteins in the external medium inhibits the uptake of corticosterone. These results suggest that corticosterone is transported into the cell and is accumulated. Only the free hormone is available for uptake which in turn may be regulated by protein and lipid components in the plasma membrane of the liver cell.
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Graff JC, Wohlhueter RM, Plagemann PG. Effect of temperature and of cytochalasin B and persantin on the nonmediated permeation of non-electrolytes into cultured Novikoff rat hepatoma cells. J Biol Chem 1977. [DOI: 10.1016/s0021-9258(17)40249-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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