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ABSTRACT
The effect of epidermal growth factor (EGF) on testicular germ cell differentiation was investigated. Testicular fragments from surgically prepared cryptorchid testes of adult mice were cultured for 9 days in serum-free media containing various concentrations of EGF. Histological sections of testis were examined under a light microscope and each type of germ cell and mitotic cell in the seminiferous tubules was counted per 1000 Sertoli cells. EGF at concentrations ranging from 100 to 200 ng/ml induced differentiation of type A spermatogonia. The observed maximal stimulatory activity of EGF at a concentration of 100 ng/ml was 30% of the positive control cultures treated with calf serum. EGF at concentrations ranging from 1 to 100 ng/ml significantly inhibited the mitotic activity of FSH, FSH plus retinol, or FSH plus fetuin on type A spermatogonia and their differentiation. The number of type A spermatogonia in testes cultured with FSH, FSH plus retinol, or FSH plus fetuin decreased when EGF was added. On the other hand, EGF stimulated the differentiation of type A spermatogonia induced with fetuin but did not influence retinol-induced differentiation. It is proposed that EGF inhibits testicular germ cell differentiation by blocking the proliferation of type A spermatogonia stimulated by FSH.
Journal of Endocrinology (1991) 128, 383–388
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ABSTRACT
A retinoic acid binding protein has been detected in salt extracts of nuclei obtained from human prostate adenoma. The binding was characterized by competition experiments, temperature/time studies and saturation analysis.
Substantial binding was only observed after sonication of nuclei and charcoal-pretreatment of a salt extract. The binding of radiolabelled all-transretinoic acid was displaced by all-trans-retinoic acid, retinol and to a lesser extent retinal and two synthetic retinoids, RO 10-1670 and RO 13-7410. Testosterone and dihydrotestosterone, at a 100-fold excess, had little effect on the binding.
The association between retinoic acid and nuclear protein was both temperature and time dependent. At 37 °C, equilibrium was rapidly reached (30 min) whereas at 4 and 25 °C, ligand binding occurred at a slower rate. Saturation analysis performed under steady-state conditions yielded a dissociation constant of 15 ±2 nmol/l.
Metabolism studies failed to show conversion of either radiolabelled all-trans-retinol or [3H]retinoic acid in vitro; these data suggest that both acid and alcohol forms of vitamin A are recognized by the extracted nuclear protein.
The effect of three enzyme inhibitors on [3H]retinoic acid binding was studied. Binding was unaltered in the presence of aprotinin and phenylmethylsulphonyl fluoride but sodium molybdate (10 mmol/l) increased binding by 18%.
The presence of a specific retinoid binding protein in prostate nuclei suggests that retinoids may play some role in the function of the gland.
J. Endocr. (1985) 105, 157–162
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The retinoids comprise a family of polyisoprenoid lipids that includes vitamin A (retinol) and structurally related compounds. The biological activity of retinoids can be modified, for example, by changes in the molecules' state of oxidation and cis/trans isomerization. Their activity is also dependent on the levels of specific types of retinoid-binding proteins which exist in extracellular, cytosolic and nuclear compartments. The role of retinoids in gene expression represents an important biological function for this family of molecules. Retinoid-dependent modulation of gene expression is critical for normal cell and tissue function in mature as well as developing animals. Despite significant advances in the understanding of retinoid biological activity, important questions remain concerning aspects of retinoid metabohsm, cellular uptake, intracellular trafficking and regulation of gene transcription. The purpose of this review is to present these topics as a compendium of retinoid endocrinology.
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ABSTRACT
Retinoids and thyroid hormones exert profound effects on the development, growth and homeostasis of vertebrates. The receptor proteins which bind retinoic acid, tri-iodothyronine (T3) or steroid hormones and, as a result of this binding, interact with DNA to stimulate expression of specific genes, belong to the same recently discovered superfamily. The functionality of thyroid and steroid hormone receptors is thought to be related to a phosphorylation-dephosphorylation cycle. In the present work, the action of two retinoids (retinol and retinoic acid) was studied on the properties of T3-nuclear receptors and on protein kinase C (PKC) activity in the rat liver (PKC is known to be a phosphorylating enzyme for various proteins). The influence of 12-O-tetradecanoyl phorbol-13-acetate (TPA; known to enhance PKC activity) on the properties of T3-nuclear receptors was also investigated. Measurements of binding characteristics and enzyme activity were performed 4 or 12 h after a single i.p. injection of retinol or retinoic acid (6 mg/kg body weight) or 1 h after a single i.p. injection of TPA (0·7 mg/kg). The activity of PKC was increased 4 h after administration of the retinoids, and the affinity of the T3-nuclear receptor protein was increased markedly after 12 h. The activity of PKC and the affinity of the nuclear T3 receptor were both increased 1 h after administration of TPA. These observations provide indirect evidence that retinoids, particularly retinoic acid, induce an increase in PKC activity and a subsequent increase in the affinity of the T3-nuclear receptor protein.
Journal of Endocrinology (1991) 128, 245–251
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and methods (page 689), and the heading of the first results subsection (page 690), which should all read cellular retinol binding protein, CRBP1 and not as published.
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Introduction Vitamin A is an essential nutrient consumed in the diet in the form of retinyl esters or beta carotene. Retinyl esters are transported by chylomicrons to the liver where they are converted to retinol and bound to retinol
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). Retinol-binding protein 4 (RBP4) is both an adipokine and liver-derived protein that transports retinol (vitamin A) in the blood ( Tamori et al . 2006 ). It has been implicated in the metabolic syndrome and adipose tissue inflammation ( Kovacs et al
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National Institute of Nutrition and Seafood Research, Department of Animal Physiology, School of Biological Sciences, PO Box 2029 Nordnes, N-5817 Bergen, Norway
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increased collagenase mRNA expression and collagen degradation in rat ( Varghese et al . 1994 ). Skeletal deformities in fish have been causally associated with dietary retinol levels ( Dedi et al . 1995 , Ørnsrud et al . 2002 ). Data from mammalian
Institute for Molecular and Cell Biology, Rua do Campo Alegre, Porto, Portugal
ICBAS, University of Porto, Largo Professor Abel Salazar, Porto, Portugal
Molecular Endocrinology Unit, Instituto de Investigaciones Biomédicas Alberto Sols, CSIC & UAM, Madrid, Spain
Department of Production & Systems Engineering, University of Minho, Campus Gualtar, Braga, Portugal
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Institute for Molecular and Cell Biology, Rua do Campo Alegre, Porto, Portugal
ICBAS, University of Porto, Largo Professor Abel Salazar, Porto, Portugal
Molecular Endocrinology Unit, Instituto de Investigaciones Biomédicas Alberto Sols, CSIC & UAM, Madrid, Spain
Department of Production & Systems Engineering, University of Minho, Campus Gualtar, Braga, Portugal
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Institute for Molecular and Cell Biology, Rua do Campo Alegre, Porto, Portugal
ICBAS, University of Porto, Largo Professor Abel Salazar, Porto, Portugal
Molecular Endocrinology Unit, Instituto de Investigaciones Biomédicas Alberto Sols, CSIC & UAM, Madrid, Spain
Department of Production & Systems Engineering, University of Minho, Campus Gualtar, Braga, Portugal
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Institute for Molecular and Cell Biology, Rua do Campo Alegre, Porto, Portugal
ICBAS, University of Porto, Largo Professor Abel Salazar, Porto, Portugal
Molecular Endocrinology Unit, Instituto de Investigaciones Biomédicas Alberto Sols, CSIC & UAM, Madrid, Spain
Department of Production & Systems Engineering, University of Minho, Campus Gualtar, Braga, Portugal
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Institute for Molecular and Cell Biology, Rua do Campo Alegre, Porto, Portugal
ICBAS, University of Porto, Largo Professor Abel Salazar, Porto, Portugal
Molecular Endocrinology Unit, Instituto de Investigaciones Biomédicas Alberto Sols, CSIC & UAM, Madrid, Spain
Department of Production & Systems Engineering, University of Minho, Campus Gualtar, Braga, Portugal
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thyroxine (T 4 ) and the retinol-binding protein–retinol complex. TTR synthesis is a phylogenetically conserved event ( Harms et al. 1991 ), and starts early during embryonic development. It has for a long time been suggested that TTR is involved in
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: 770 µg *RAE Lactation: 1300 µg *RAE Clostridiales ⊣ Retinoic acid → IL-22 → Antimicrobial responses in intestinal epithelial cells Dysbiosis → ↑Proteobacteria → ↓Retinoic acid → ↑ S. typhiumurium colonization Germ Free vs Conventional Mice: Retinol
