Either chick embryo dermis or retinoid-treated mouse dermis can initiate glandular morphogenesis from mammalian epidermal tissue

Excess retinoids can cause developing mouse vibrissa follicles to be transformed into mucous glands in organ culture. The objective was to test the hypothesis that retinoids act in this system by altering morphogenetic properties of the dermis. After inititation by retinoic acid (RA) in organ culture, glands were shown to develop further in embryonic skin grafted to the chick chorioallantoic membrane (CAM). Recombinants of 12.5 day mouse epidermis with untreated or RA-treated mouse or chick dermis were then grafted to CAM for 7 days. For homospecific recombinants, 13.5 day mouse dermis originated from 11.5 day skin cultured for 2 days, with or without 5.2 microgram/ml RA. For heterospecific recombinants, 12 day dermis came from chick embryos, previously injected with 250 microgram RA. Glands were absent from the homospecific recombinants including untreated mouse dermis, but appeared in 26% of those with RA-treated dermis. Among heterospecific recombinants, 75% of those with RA-treated chick dermis and 29% of those with untreated dermis had glands. Untreated 10-12 day chick skin contained two forms of endogenous vitamin A, retinol (4.5 microgram/g protein) and dehydroretinol (3.7 microgram/g protein), while 13-14 day mouse skin contained only retinol (1.8 microgram/g protein), as shown by high performance liquid chromatography. RA injection increased retinol and dehydroretinol in chick skin, while RA was undetectable. Thus RA can act through mouse dermis to form epithelial glands and through chick dermis to increase the incidence of glands. The glands in recombinants with untreated chick dermis may result from the higher levels of endogenous retinoids in chick skin, compared with mouse skin.     

Duct,exocrine, and endocrine components of cultured fetal mouse pancreas

Summary Twenty to twenty-two days postcoitum mouse fetal pancreas organ bits were cultured on the dermal surface of irradiated pigskin as a substrate. The medium used for long term culture consisted of Eagle’s Minimum Essential Medium with the addition of 10% bovine serum, 0.02 U/ml insulin, 0.025 μg/ml glucagon, 3.63 μg/ml hydrocortisone, 100 μg/ml soybean trypsin inhibitor or 10⁻⁸ M atropine. When the medium lacked trypsin inhibitor or atropine but contained the three hormones, the pigskin support began to be destroyed after 2 to 4 wk in culture. Thereafter, the cultured cells could not grow and survive on the digested pigskin. When 10⁻⁶ M atropine was added to the medium, amylase secretion from cultured cells and destruction of pigskin were inhibited completely but pancreas cells could not grow or survive. In contrast, 100 μg/ml soybean trypsin inhibitor or 10⁻⁸ M atropine permitted cell growth, permitted amylase secretion from the cultured acinar cells, and prevented the destruction of pigskin. Under these conditions pancreas cells migrated or grew or both from the organ bits onto the surface of the pigskin dermis and organoid aggregations formed. Hydrocortisone was needed to permit growth for more than 2 wk. Glucagon and insulin had additive effects. Light and electron microscopic observations indicated the culture of at least five kinds of cells, i.e., duct, acinar, centroacinar, endocrine, and mesenchymal. The majority of cultured cells were duct cells and acinar cells. There were few mesenchymal cells. Mouse pancreas cells were cultured for at least 12 wk by this method. This investigation was supported by PHS Grant CA 30220 awarded by the National Cancer Institute, DHHS, Grant 1203M awarded by the Council for Tobacco Research, Inc., and Grant RD-65 (for equipment) awarded by the American Cancer Society. Nude mice were provided by Dr. Wendall M. Farrow of Life Sciences, Inc., Resource Laboratory N01, CP6-1005 of the National Cancer Institute.     

Relative resistance to methothexate by proliferating normal rabbit epidermal cells in vitro

Summary Primary cell cultures of normal rabbit epidermal cells (keratinocytes) were established without the use of enzymatic techniques. Six experiments were carried out on cells from six different rabbits. When these cells were exposed to methotrexate (MTX) for 24 h at 1 μg/ml, proliferation, as measured by cells entering mitosis, was significantly inhibited (P<0.05) in only one experiment. When the dose of MTX was elevated to 100 μg/ml, only two experiments showed significant inhibition of mitosis. This minimal inhibition of mitosis by MTX was contrasted by the dramatic inhibitory effect of this antimetabolite on DNA synthesis. At 1 μg/ml MTX for 24 h, DNA synthesis, as measured by [³H]deoxyuridine uptake, was inhibited >95%. We can conclude that under certain conditions, the rabbit keratinocyte may represent a normal cell type that is inherently resistant to the antiproliferative effects of methotrexate. The research was supported by National Cancer Institute Grant CA 11536.     

Identification of 14-hydroxy-retro-retinol and 4-hydroxy-retinol as endogenous retinoids in rats throughout neonatal development

14-Hydroxy-retro-retinol was previously described as an in vivo and in vitro metabolite of retinol. Furthermore, the retinoid 4-hydroxy-retinol was identified as an endogenous occurring retinoid in the amphibian organism and an in vitro metabolite of retinol. We describe in the present study that 14-hydroxy-retro-retinol and 4-hydroxy-retinol are present in normal neonatal rat serum as endogenous occurring retinoids in normal non-vitamin A supplemented mammals (rats). Both retinoids were detected in serum and liver of neonatal rats at days 3 and 11 after birth. The respective concentrations at day 11 after birth were 41.8 +/- 2.8 ng/ml (serum)/ 104 +/- 6 ng/g (liver) for 4-hydroxy-retinol and 23 +/- 4.6 ng/ml (serum)/ 285 +/- 5 ng/g (liver) for 14-hydroxy-retro-retinol. Both retinoids could not be detected in adult rat serum and liver. From our experiments important physiological functions of these retinoids during postnatal development could be postulated.     

An electrophysiological freeze fracture assessment of cadmium nephrotoxicity in vitro

Summary Human proximal tubule cell cultures exposed to doses of cadmium chloride (CdCl₂) between 0.05 μg/ml and 0.5 μg/ml exhibited alterations in cell membrane structure and transport function. At these Cd concentrations, cell numbers were not significantly altered from control values in either nonreplicating confluent, or actively replicating subconfluent cultures. Transmission electron microscopy revealed few alterations in cultures treated with 0.05 μg/ml Cd. Tight junctions were intact; organelles and myeloid body formation appeared normal. Freeze fracture analysis confirmed the integrity of the tight junctions as well as increased numbers of vesicles or pits along the lateral cell membrane, indicating increased endocytotic activity. Cells exposed to 0.1 μg/ml Cd were characterized by decreased numbers of microvilli and inhibited myeloid body formation. Cd doses of 0.5 μg/ml elicited nuclear chromatin condensation, fragmented sealing strands in 5 to 10% of the tight junction profiles, sparse microvilli, and inhibited myeloid body formation. Electrophysiologic assessments of transport function by Ussing chamber analysis revealed decreases in transepithelial potentials for all three concentrations, with significant differences at Cd concentrations of 0.5 to 0.1 μg/ml. Cells treated with 0.5 μg/ml Cd also exhibited slight decreases in electrical resistance, consistent with the minimal fragmentation of sealing strands observed in freeze fracture replicas. Resistance in cultures treated with 0.1 or 0.05 μg/ml Cd remained within control values and indicated that drops in potential difference and short circuit current in these cells reflected true alterations in ion transport. This paper was presented at a Symposium on the Physiology and Toxicology of the Kidney In Vitro co-sponsored by The Society of Toxicology (SOT) and the Tissue Culture Association field at the 27th annual meeting of the SOT in Dallas, Texas in 1988. This work was supported by the Johns Hopkins Center for Alternatives to Animal Testing. The Balzers Freeze Fracture Unit utilized in these studies was provided by equipment grant S10 RR02329 from the National Institutes of Health, Bethesda, MD.     

Inhibition of plasma membrane NADH oxidase activity and growth of HeLa cells by natural and synthetic retinoids

Several retinoids, both natural and synthetic, were evaluated for their ability to modulate NADH oxidase activity of plasma membranes of cultured HeLa cells and the growth of HeLa cells in culture. Both NADH oxidase activity and the growth of cells were inhibited by the naturally-occurring retinoids all trans-retinoic acid (tretinoin) and retinol as well as by the synthetic retinoids, trans-acitretin, 13-cis-acitretin, etretinate and arotonoid ethylester (Ro 13-6298). For all retinoids tested, inhibition of NADH oxidase activity and inhibition of growth were correlated closely. With tretinoin, etretinate and arotonoid ethylester, NADH oxidase activity and cell growth were inhibited in parallel in proportion to the logarithm of retinoid concentration over the range of concentrations 10-8 to 10-5 M. Approximately 70% inhibition of both NADH oxidase activity and growth was reached at 10 µM. With retinol, trans-acitretin and 13-cis-acitretin, inhibition of NADH oxidase activity and growth also were correlated but maximum inhibition of both was about 40% at 10 µM. The possibility is suggested that inhibition of the plasma membrane NADH oxidase activity by retinoids may be related to their mechanism of inhibition of growth of HeLa cells in culture. (Mol Cell Biochem 166: 101-109, 1997)     

Primary and long term epithelial cell cultures from human fetal normal colonic mucosa

Summary Primary and passaged cultures of normal colon epithelial cells, derived from human fetuses (13 to 17 wk of conceptual age) have been established. These cultures have been passaged 16 times thus far. The cultures have been initiated and maintained in medium consisting of 50% Dulbecco's minimum essential medium and 50% Ham's F12 medium and supplemented with antibiotics (penicillin, 100 U/ml; streptomycin, 100 μg/ml); ascorbic acid, 40 μg/ml;l-isoleucine, 50 μg/ml; epidermal growth factor, 20 ng/ml; insulin, 5 μg/ml; cholera toxin, 5 ng/ml; transferrin, 1 μg/ml; fetal bovine serum (10%); and HEPES, 25 mM final concentration, and incubated at 37°C in humidified gas containing 5% CO₂: 95% air. The cellular and subcellular characteristics of primary and passaged cultures were defined using light microscopy and scanning and transmission electron microscopy. The cells exhibited microvilli on cell surfaces and showed junctional complexes and interdigitations between cells. Indented nuclei with dense chromatin and marginated heterochromatin, numerous mitochondria, rough endoplasmic reticulum, polysomes, and extensive Golgi zones were conspicuous. Also, periodic acid Schiff's reagent-positive staining of the cells suggests the active synthesis of complex mucopolysaccharides in the cytoplasm. This study was supported by USPHS Grant CA-30185 from the National Large Bowel Cancer Project, National Cancer Institute.     

In vitro inhibition of murine hematopoietic progenitors and stromal cells by vinorelbine

Hematopoietic progenitor colony assays were used to establish the effects of the vinca alkaloid vinorelbine (VRB) on murine bone marrow. The in vitro growth of colony-forming units–granulocyte/macrophage (CFU-GM), burst forming units–erythroid (BFU-E) and colony-forming units–mix (CFU-mix) was dose-dependently inhibited by VRB. The highest dose assayed (0.02 μg/ml) suppressed all of the different progenitor cells by 100%. A comparison of the dose–response curves showed that CFU-GM, BFU-E, and CFU-mix exhibited similar patterns of sensitivity to the cytotoxic action of VRB. Long-term bone marrow cultures have provided a valuable in vitro model for studying the role of the microenvironment of bone marrow. Cellularity of stromal layers was reduced with increasing doses of VRB. The appearence of these layers was altered minimally with the lowest dose used; a gradual loss of cellularity was seen in cultures exposed to 0.05 and 0.075 μg/ml; and a marked loss at the dose of 0.1 μg/ml. Our results show that VRB has an important effect on hematopoietic progenitors at the highest dose tested, while the stromal cells were not affected at a similar dose (0.025 μg/ml), suggesting that the stroma is more resistant to this drug. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of lipid peroxidation products on the activity of human retinol dehydrogenase 12 (RDH12) and retinoid metabolism

Mutations in human Retinol Dehydrogenase 12 (RDH12) are known to cause photoreceptor cell death but the physiological function of RDH12 in photoreceptors remains poorly understood. In vitro, RDH12 recognizes both retinoids and medium-chain aldehydes as substrates. Our previous study suggested that RDH12 protects cells against toxic levels of retinaldehyde and retinoic acid [S.A. Lee, O.V. Belyaeva, I.K. Popov, N.Y. Kedishvili, Overproduction of bioactive retinoic acid in cells expressing disease-associated mutants of retinol dehydrogenase 12, J. Biol. Chem. 282 (2007) 35621-35628]. Here, we investigated whether RDH12 can also protect cells against highly reactive medium-chain aldehydes. Analysis of cell survival demonstrated that RDH12 was protective against nonanal but not against 4-hydroxynonenal. At high concentrations, nonanal inhibited the activity of RDH12 towards retinaldehyde, suggesting that nonanal was metabolized by RDH12. 4-Hydroxynonenal did not inhibit the RDH12 retinaldehyde reductase activity, but it strongly inhibited the activities of lecithin:retinol acyl transferase and aldehyde dehydrogenase, resulting in decreased levels of retinyl esters and retinoic acid and accumulation of unesterified retinol. Thus, the results of this study showed that RDH12 is more effective in protection against retinaldehyde than against medium-chain aldehydes, and that medium-chain aldehydes, especially 4-hydroxynonenal, severely disrupt cellular retinoid homeostasis. Together, these findings provide a new insight into the effects of lipid peroxidation products and the impact of oxidative stress on retinoid metabolism.     

Exogenous fibronectin is not required for organogenesis in vitro

Summary The biological effect of plasma fibronectin on the differentiation of embryonic mouse kidney and tooth was studied in organ cultures. Transferrin (50μg/ml) was a strong mitogen for kidney cells, whereas, the addition of soluble fibronectin (50 to 250 μg/ml) had no detectable effect on differentiation or proliferation. The same serum-free, transferrin-containing medium did not support tooth differentiation. however, fibronectin was not a necessary serum component because fibronectin-free serum supported tooth development. It was demonstrated with antibodies specific for human fibronectin that the exogenously added human fibronectin at 50 μg/ml did not become incorporated to the cultured organs. Only minimal incorporation to the kidney basement membrane area was observed when fibronectin concentration was 250μg/ml. The mesenchymal stroma and the basement membranes of the kidney and tooth rudiments cultured in fibronectin-free media stained intensely with conventional fibronectin antibodies, indicating endogenous production of fibronectin. Outgrowing epithelial cells from isolated kidney tubules produced fibronectin as well as laminin. The results suggest that the fibronectin found in the stroma and basement membranes is an endogenous product of the developing tissues and that plasma fibronectin is not required for in vitro organogenesis. The results also indicate that it is difficult to study the effect of fibronectin on morphogenetic processes because it may not penetrate the organ explants in vitro. This work was supported by grants from the Sigrid Jusélius Foundation, Finska L?kares?llskapet, Finnish Life Insurance Companies and Grant CA 28896 and Cancer Center Support Grant CA 30199 from the National Cancer Institute, Department of Health and Human Services, Washington, D.C.     

Intracellular levels of adenosine triphosphate in hamster trachea organ cultures exposed toMycoplasma pneumoniae cells or membranes

Summary The amount of adenosine triphosphate (ATP) in hamster trachea organ cultures was determined with a technique based on light emission from a luciferin/luciferase/ATP reaction. The amount of ATP, expressed as ng per mg dry weight, was consistent in tracheal explants prepared from various animals and changed negligibly when explants were cultivated in vitro for several days. The amount of ATP was related directly to cellular activity and integrity in the epithelium since inactivation by heat or freeze-thaw rapidly depleted measurable ATP, and ciliary activity and ATP content were related directly. When tracheal explants were infected with 10⁵ to 10⁷ CFU of virulentMycoplasma pneumoniae cells, both ciliary activity and ATP content in the tissue dropped dramatically after approximately 5 to 8 days (up to 85% and 60% decreases, respectively). Exposure of explants to 50 to 200 μg per ml of purifiedM. pneumoniae membranes also caused significant decreases in ciliary activity and ATP. When explants were infected with attenuated or nonvirulent mycoplasmas, ciliary activity was only slightly decreased, while ATP values often rose slightly. The technology associated with the determination of ATP levels in tracheal explants should prove useful as a new, objective, analytical approach to cell viability in organ cultures. This investigation was supported in part by the National Institutes of Health (PHS Grant AI 12559), by a Biomedical Sciences Support Grant made to the University of Illinois School of Life Sciences, and by the University Research Board.     

Friend erythroleukemia cell differentiation: induction by retinoids

Abstract. Growth in the presence of retinoids was found to induce erythroid differentiation in Friend murine erythroleukemia (MEL) cells in culture. The program of differentiated functions expressed by retinoid-treated cells was quite similar to that promoted by other inducers of MEL cell differentiation. For example, 70% or more of induced cells synthesized hemoglobin which accumulated to a level of 8 μg–10 μg per 10⁶ cells. The level of acetylcholinesterase activity increased two to five-fold in induced cells, and induction by retinoids, like induction by dimethylsulfoxide (DMSO), promoted the appearance of cell surface lumps or 'blebs'. All-trans retinaldehyde, which promoted maximum hemoglobin and acetylcholinesterase synthesis at a concentration of 5 × 10⁻⁷ M, was found to be a more potent inducer than all-trans retinoic acid or retinol, which both showed maximum induction at 1 × 10⁻⁵ M. Like differentiation promoted by DMSO, retinoid-induced differentiation was inhibited by 10⁻⁷ M dexamethasone.     

Hepatic retinol secretion and storage are altered by dietary CLA: common and distinct actions of CLA c9,t11 and t10,c12 isomers

Conjugated linoleic acid (CLA) is a polyunsaturated fatty acid obtained from ruminant products. Previous studies in rats and pigs showed that a dietary equimolar mixture of c9,t11 and t10,c12 CLA isomers induces changes in serum and tissue levels of retinoids (vitamin A derivatives). However, the mechanism(s) responsible for these actions remain(s) unexplored. Given the numerous crucial biological functions regulated by retinoids, it is key to establish whether the perturbations in retinoid metabolism induced by dietary CLA mediate some of the beneficial effects associated with intake of this fatty acid or, rather, have adverse consequences on health. To address this important biological question, we began to explore the mechanisms through which dietary CLA alters retinoid metabolism. By using enriched preparations of CLA c9,t11 or CLA t10,c12, we uncoupled the effects of these two CLA isomers on retinoid metabolism. Specifically, we show that both isomers induce hepatic retinyl ester accumulation. However, only CLA t10,c12 enhances hepatic retinol secretion, resulting in increased serum levels of retinol and its specific carrier, retinol-binding protein (RBP). Dietary CLA t10,c12 also redistributes retinoids from the hepatic stores toward the adipose tissue and possibly stimulates hepatic retinoid oxidation. Using mice lacking RBP, we also demonstrate that this key protein in retinoid metabolism mediates hepatic retinol secretion and its redistribution toward fat tissue induced by CLA t10,c12 supplementation.     

Cellular retinoic acid-binding protein and its relationship to the biological activity of four synthetic retinoids in hamster tracheal organ culture

Summary The mechanism of action of retinoid in reversing keratinization in hamster trachea is yet unknown. The purpose of this study was to determine if cellular retinoic acid binding protein (CRABP) is present in tracheal epithelium following incubation in serum-free, vitamin A-deficient culture medium for 10 days, and if the effectiveness of a retinoid in reversing keratinization in organ culture is correlated with its ability to compete for CRABP sites. The cytosol prepared from tracheal cultures contained CRABP at a concentration of 2.61 pmoles per mg protein. Of the four retinoids with carboxyl end group selected for the study, two of the biological active retinoids competed for the CRABP sites. However, no correlation was observed between the biological activity of the inactive retinoids and their ability to associate with the CRABP sites. These results indicate that even though the action of retinoid may be mediated by retinoid binding protein, it cannot be used as a sole predicator of retinoid response in hamster trachea. This investigation was supported by Contract N01-CP-31012 and U. S. P. H. Grants CA30512 and CA32428, which were awarded by the Division of Cancer Etiology, National Cancer Institute, DHHS. Editor's Statement Tracheal organ cultures provide a useful model for the study of epithelial differentiation and carcinogenesis. Much attention has been given to the action of retinoids in this process. Mehta et al. demonstrate a lack of correlation between biological activity and specific cytosolic binding of members of this class of compounds, pointing out the need for a more complete biochemical understanding of the mechanism of action and active forms of retinoids in this and other systems in vivo and in vitro. David W. Barnes     

Evaluation of the sensitive step of inhibition of chondrogenesis by retinoids in limb mesenchymal cells in vitro

The sensitive step of inhibition of chondrogenesis in vitro by retinoids was investigated in modified micromass cultures of limb bud mesenchymal cells from mouse embryos of day 11 and 12. Evaluation of chondrogenesis was performed after alcian blue staining, using a simple random hit counting of cartilage nodules. All-trans-retinoic acid, 13-cis-retinoic acid, and a newly developed arotinoid, RO 13-6298, were tested for their ability to inhibit chondrogenesis. We found that inhibition of chondrogenesis depended on the dosage and the duration of treatment with the different retinoids. Further analysis showed that chondrogenesis in limb bud mesenchymal cells from the proximal part was irreversibly inhibited after one hour of treatment, whereas distal cells showed a reduction of cartilage development only after a treatment period of 12 and more hours. In respect to the doses of the retinoids, proximal cells were about one magnitude more vulnerable than distal cells. These proximo-distal differences were obtained with 13-cis-retinoic acid at 10 micrograms/ml, with all-trans-retinoic acid at 1 microgram/ml and with arotinoid RO 13-6298 with 10 ng/ml. It is supposed that the late blastemal stage of chondrogenic differentiation before the onset of matrix synthesis is the step which is most vulnerable to retinoid treatment.     

Clonal growth of human keratinocytes with small amounts of dialyzed serum

Summary A survey of commercially availabla media revealed that medium F-12 was superior to medium 199 for clonal growth of human epidermal keratinocytes (HK) when supplemented with 10 μg/ml hydrocortisone (HC) plus dialyzed fetal bovine serum protein (FBSP), rather than the whole serum used in previous studies. Qualitative and quantitative adjustment of the medium composition for optimal clonal growth with minimal amounts of FBSP generated a new medium, MCDB 151, which supports clonal growth of HK with 10 μg/ml HC and as little as 1 mg/ml FBSP (equivalent in protein concentration to 2.0% whole serum). MCDB 151 differs significantly from MCDB 105, previously developed in this laboratory for normal human fibroblasts, and each medium selectively favors growth of its own type of cell in primary cultures of disaggregated human neonatal foreskin cells. Differences in the amounts of calcium and adenine in the two media appear to be among the most influential factors mediating the selective growth. Optimal growth of HK occurs at a very low level of Ca²⁺ that causes the colonies to remain as monolayers rather than stratifying as they do in the presence of higher levels of calcium. However, keratin synthesis, which was examined through use of highly specific fluorescent antibodies, is not affected by the Ca²⁺ concentration. Agents that increase intracellular cyclic AMP levels appear to have no effect on HK growth in MCDB 151 with 10 μg/ml HC and 1.0 mg/ml FBSP. This paper contains material from a thesis submitted to the Graduate School of the University of Colorado, Boulder, by Donna M. Peehl in partial fulfillment of the requirements for the Ph.D. degree. This work was supported by Grant CA 15305 from the National Cancer Institute and Grant AG 00310 from the National Institute on Aging.     

In vitro effects of retinoids on murine thymus-dependent and thymus-independent mitogenesis

The effects of three retinoids: all-trans-retinoic acid (RA), 13-cis-retinoic acid (13-cis-RA), and N-(4-hydroxyphenyl)retinamide (4-HPR) on murine splenic lymphocyte proliferative responses to mitogens were evaluated. The responses to T-cell mitogens, PHA and Con A, and a T-cell-dependent B-cell mitogen, PWM were significantly potentiated by these retinoids. However proliferative responses to a B-cell mitogen, Escherichia coli LPS were unaffected or inhibited. All three retinoids at concentrations ranging from 10(-6) to 10(-15) M significantly potentiated Con A-induced proliferative responses. In response to PWM, 10(-13) M RA, 10(-12) M 13-cis RA, and 10(-11) M 4-HPR were the lowest concentrations producing significant potentiation. Endpoint concentrations of retinoids significantly potentiating responses to PHA were; 10(-9) M RA, 10(-8) M 13-cis RA, and 10(-6) M 4-HPR. These responses were independent of retinol contained in fetal calf serum supplemented medium since responses were reproduced in serum-free medium devoid of retinol. Optimal potentiation by retinoids of responses to these T-cell-dependent mitogens were found at superoptimal concentrations of mitogen suggesting a selective inhibition of T-suppressor cells. Thus, potentiation of T-cell-dependent mitogen responses provides the most sensitive biological assay yet described for detection of retinoid activity and is a reproducible system to explore the cellular and molecular mechanisms of retinoid-mediated immunopotentiation.     

Effect of retinoids on growth factor-induced anchorage independent growth of human fibroblasts

Summary We have studied the effects of all-trans retinol, all-trans retinoic acid, and anhydroretinol, a biologically inactive retinoid, on anchorage-independent growth of human fibroblasts induced by purified growth factors. The anchorage-independence assay was, conducted in medium supplemented with serum that had had its peptide growth factors inactivated by treatment with dithiothreitol and iodoacetamide. Physiologic concentrations of either all-trans retinol (0.5 μM) or all-trans retinoic acid (1.0 nM) but not anhydroretinol (0.5 μM) reduced the frequency of anchorage-independent growth of normal human fibroblasts induced by platelet-derived growth fator (PDGF). All-trans retinol was also tested for its effect on the frequency of anchorage-independent growth induced by basic fibroblast growth factor (bFGF) and was found to decrease this growth. All-trans retinol also reduced the frequency of anchorage-independent growth of the human fibrosarcoma-derived cell, line, HT1080, which grew in semisolid medium without added growth factors. Inasmuch as these retinoids reduced the frequency of anchorage-independent growth induced by either PDGF or bFGF and because PDGF and bFGF bind to independent cell membrane receptors and are known to stimulate different pathways leading to DNA synthesis, the data suggest that physiologically active retinoids, have an effect on a step that is common to both signal pathways. This research was supported in part by Department of Energy, Washington, DC, grant DE-F602-87ER-60524 and by DHHS grants CA21289 and, CA32490 from the National Cancer Institute, Bethesda, MD.     

Effects of cyclic adenosine 3′:5′-monophosphate-elevating agents and retinoic acid on differentiation in retinoid-deficient tracheal cultures

Summary The ability of cyclic AMP-elevating agents to induce normal differentiation has been investigated in retinoid-deficient hamster tracheal epithelium in organ culture. Dibutyryl cAMP (dbcAMP) and other cAMP-regulating agents alone caused disappearance of keratin and regeneration of normal mucociliary epithelium in retinoid-deficient cultures. Incubation of retinoid-deficient cultures with dbcAMP, isoproterenol, and cholera toxin (CT) (without addition of exogenous retinoid) reversed keratinization in a dose-dependent manner. The ED₅₀ of cultures treated with dbcAMP was 4×10⁻⁶ M; ED₅₀ of isoproterenol was 7×10⁻⁵ M; and CT, 0.6 μg/ml. Phosphodiesterase inhibitors and other cAMP analogs were inactive. Dibutyryl cAMP in combination with theophylline enhanced normal differentiation. Retinoid-deficient tracheas pretreated for 20 h with 10⁻⁹ M all-trans-retinoic acid (RA) responded to 10⁻⁶ M dbcAMP by potentiating normal differentiation; this concentration of dbcAMP alone was inactive. Isoproterenol showed a similar response but to a lesser degree. These cAMP-elevating agents applied in combination with theophylline did not increase activity. This investigation was supported by National Cancer Institute Contract NO1-CP-31012.     

Retinol uptake and metabolism,and cellular retinol binding protein expression in an in vitro model of hepatic stellate cells

Liver is a major site of retinoid metabolism and storage, and more than 80% of the liver retinoids are stored in hepatic stellate cells. These cells represent less than 1% of the total liver protein, reaching a very high relative intracellular retinoid concentration. The plasma level of retinol is maintained close to 2 M, and hepatic stellate cells have to be able both to uptake or to release retinol depending upon the extracellular retinol status. In view of their paucity in the liver tissue, stellate cells have been studied in primary cultures, in which they loose rapidly the stored lipids and retinol, and convert spontaneously into the activated myofibroblast phenotype, turning a long-term study of their retinol metabolism impossible. We have analyzed the retinol metabolism in the established GRX cell line, representative of stellate cells. We showed that this cell line behaves very similarly, with respect the retinol uptake and release, to primary cultures of hepatic stellate cells. Moreover, we showed that the cellular retinol binding protein (CRBP-I) expression in these cells, relevant for both uptake and esterification of retinol, responds to the extracellular retinol status, and is correlated to the retinol binding capacity of the cytosol. Its expression is not associated with the overall induction of the lipocyte phenotype by other agents. We conclude that the GRX cell line represents an in vitro model of hepatic stellate cells, and responds very efficiently to wide variations of the extracellular retinol status by autonomous controls of its uptake, storage or release.