Evidence for induction by cortisol in vitro of a protein inhibitor of transport and phosphorylation processes in rat thymocytes

Photoreceptor cell death and rescue in retinal detachment and degenerations

Photoreceptor cell death is the ultimate cause of vision loss in various retinal disorders, including retinal detachment (RD). Photoreceptor cell death has been thought to occur mainly through apoptosis, which is the most characterized form of programmed cell death. The caspase family of cysteine proteases plays a central role for inducing apoptosis, and in experimental models of RD, dying photoreceptor cells exhibit caspase activation; however, there is a paradox that caspase inhibition alone does not provide a sufficient protection against photoreceptor cell loss, suggesting that other mechanisms of cell death are involved. Recent accumulating evidence demonstrates that non-apoptotic forms of cell death, such as autophagy and necrosis, are also regulated by specific molecular machinery, such as those mediated by autophagy-related proteins and receptor-interacting protein kinases, respectively. Here we summarize the current knowledge of cell death signaling and its roles in photoreceptor cell death after RD and other retinal degenerative diseases. A body of studies indicate that not only apoptotic but also autophagic and necrotic signaling are involved in photoreceptor cell death, and that combined targeting of these pathways may be an effective neuroprotective strategy for retinal diseases associated with photoreceptor cell loss.

Obstructive sleep apnea in children: do intranasal corticosteroids help?

Obstructive sleep apnea (OSA) is a common condition of childhood, and is associated with significant morbidity. Prevalence of the condition peaks during early childhood, due in part to adenoidal and tonsillar enlargement within a small pharyngeal space. The lymphoid tissues regress after 10 years of age, in the context of ongoing bony growth, and there is an associated fall in the prevalence of OSA. Obstruction of the nasopharynx by adenoidal enlargement promotes pharyngeal airway collapse during sleep, and the presence of large tonsils contributes to airway obstruction. Administration of systemic corticosteroids leads to a reduction in the size of lymphoid tissues due to anti-inflammatory and lympholytic effects. However, a short course of systemic prednisone has been demonstrated not to have a significant effect on adenoidal size or the severity of OSA, and adverse effects preclude the long-term use of this therapy. Intranasal corticosteroids are effective in relieving nasal obstruction in allergic rhinitis, and allergic sensitization is more prevalent among children who snore than among those who do not snore. Intranasal corticosteroids have also been demonstrated to reduce adenoidal size, independent of the individual's atopic status. There is preliminary evidence of an improvement in the severity of OSA in children treated with intranasal corticosteroids, but further studies are needed before such therapy can be routinely recommended. Prescribing clinicians should take into account the potential benefits to the patient, the age of the child, the presence of comorbidities such as allergic rhinitis, the agent used, and the dose and duration of treatment when considering such therapy.

Programmed cell death and apoptosis: origins of the theory

Interest in the study of apoptosis grew with the recognition that it is a highly regulated process. Such a change in attitude allowed the intellectual and technical breakthroughs that led to the explosive development of this subject.

Dissociation of early glucocorticoid inhibition of ACTH secretion and glucose uptake in mouse AtT20 D16:16 corticotrophs

Adrenal glucocorticoid hormones rapidly exert powerful effects on neurons, immune and neuroendocrine cells through induction of de novo protein synthesis. In this study, we investigated, using mouse clonal anterior pituitary AtT20 D16:16 corticotrophs, whether (i) glucocorticoids rapidly inhibit glucose transport and (ii) whether this inhibition of glucose transport is directly correlated with early inhibition of ACTH secretion. Glucose uptake in AtT20 D16:16 cells was Na+-independent because the Na+-independent glucose transport inhibitor phloretin (100 microM) completely inhibited specific 14C-deoxygluose (DoG) uptake and replacement of extracellular Na+ with N-methyl D-glucamine+ had no effect. Furthermore, the Na+-independent glucose transporters, GLUTs 1 and 3 were expressed in AtT20 D16:16 cells. The synthetic type II glucocorticoid receptor agonist dexamethasone, rapidly, within 2 h, inhibited DoG uptake into AtT20 D16:16 cells through a mechanism that was dependent on de novo mRNA synthesis. Glucocorticoid inhibition of glucose transport was not correlated with early inhibition of ACTH secretion because removal of glucose from the external medium had no effect on CRF-stimulated ACTH secretion or the efficacy of early glucocorticoid inhibition of ACTH release. Although the Na+-independent glucose transport inhibitor phloretin significantly inhibited CRF-stimulated ACTH release, this effect of phloretin was a result of its potent activation of large conductance calcium-activated potassium (BK) channels. These data suggest that different molecular pathways and/or glucocorticoid induced proteins underlie the mechanism(s) of early glucocorticoid inhibition of glucose uptake and ACTH release, respectively.

Membranes as sensitive targets in thymocyte apoptosis

The role of cellular membranes in thymocyte apoptosis has been examined. Trolox, a water soluble analogue of vitamin E and inhibitor of membrane damage, inhibits DNA fragmentation in thymocytes exposed to gamma-radiation. Trolox is most effective in inhibiting DNA fragmentation when added to cells within 30 min post-irradiation. Exposure to trolox only during irradiation did not prevent DNA fragmentation, suggesting that it does not work by scavenging free radicals generated during radiation exposure. Incubation of the irradiated cell suspension with trolox for 2 h post-irradiation was sufficient to prevent DNA fragmentation measured at 24 h in irradiated cells. This suggests that trolox irreversibly inhibits a cellular lesion required for apoptosis. The induction of DNA fragmentation appears to be related to a concurrent, pronounced flow of Ca2+ into the cell. At 3 h post-irradiation the amount of Ca2+ in irradiated thymocytes was more than twice that of unirradiated thymocytes. Membrane damage has been shown to affect the transport of Ca2+. Trolox treatment completely blocked the radiation-induced influx of Ca2+ into the thymocytes. These results suggest that membrane damage is a critical lesion that is involved in DNA fragmentation in thymocyte apoptosis.

Dexamethasone inhibits the hexose monophosphate shunt in activated rat peritoneal macrophages by reducing hexokinase-dependent sugar uptake

Dexamethasone decreases 2-D-deoxyglucose (2-dGlc) uptake and accumulation into rat peritoneal macrophages in vitro in a concentration- and time-dependent manner (Ki for 1 microM-dexamethasone after a 2 h exposure = 0.71 +/- 0.21 microM; Ki for 0.1 microM-dexamethasone after exposure for 4 h = 0.10 +/- 0.06 microM). The inhibition of 2-dGlc uptake is consistent with a decrease in the coupling between endofacial hexokinase activity and the sugar transporter. The evidence for this is: (1) the Km for zero-trans 2-dGlc uptake in quiescent macrophages was increased by dexamethasone, but there was no significant effect on the Vmax.; (2) dexamethasone increased the rate of exit of sugar from cells preloaded with 2-dGlc; (3). the free sugar accumulation within the cytosol of the cells above the external solution concentration was significantly decreased by dexamethasone. These effects of dexamethasone on 2-dGlc transport were antagonized by simultaneous exposure to the steroid RU 38486 (Ki = 0.04 +/- 0.01 microM; 4 h incubation). Although dexamethasone inhibited zero-trans uptake, the maximum rate of infinite-trans exchange uptake of 2-dGlc into cells preloaded with 3-O-methyl-D-glucose (40 mM) was unaltered by dexamethasone or RU 38486, indicating that the dexamethasone-dependent decrease in zero-trans uptake was not due to a change in the number of transporters in the plasma membrane. Dexamethasone also inhibited the phorbol myristate acetate-induced stimulation of hexose monophosphate shunt (HMPS) activity, and this was reversed by RU 38486. Cytochalasin B, the potent sugar-transport inhibitor, inhibited HMPS activity and 2-d[2,6-3H]Glc uptake equally, indicating a single site of action. By contrast, dexamethasone showed differential inhibition of HMPS activity and 2-d[2,6-3H]Glc uptake, suggesting that it not only acts by decreasing the coupling between hexokinase and sugar transport, but also at one or more additional points.

12-0-tetradecanoylphorbol-13-acetate and concanavalin A enhance glucose uptake in thymocytes by different mechanisms

The effects of the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) and the plant lectin concanavalin A (Con A) on glucose uptake in murine thymocytes were studied. TPA induces a rapid dose-dependent increase in the uptake of 2-deoxyglucose and in the transport of 3-0-methylglucose. Con A also elicits a time- and dose-dependent enhancement of 2-deoxyglucose uptake. The effect of Con A, however, is less pronounced. The effect of combined treatment of thymocytes with Con A and TPA is not additive. Cytochalasin B completely inhibits the basal, as well as TPA- and Con A-enhanced, 2-deoxyglucose uptake. Dexamethasone markedly inhibits basal 2-deoxyglucose uptake, but is less inhibitory to enhanced 2-deoxyglucose uptake induced by TPA and Con A. The effect of TPA on 2-deoxyglucose uptake and 3-0-methylglucose transport is refractory to inhibition by isobutyl methyl xanthine, dibutyryl cyclic AMP, and ethyleneglycol tetraacetic acid. These agents markedly inhibit the enhancement of 2-deoxyglucose (2-DOG) uptake by Con A. p-Bromophenacyl bromide, an inhibitor of phospholipase A2, also selectively inhibits Con A enhancement of 2-DOG uptake. Taken together, the results suggest that Con A and TPA exert their stimulatory effect on glucose uptake by different activating mechanisms, but they may share a final common transport pathway.

Characterization of corticosterone-induced protein synthesis in hippocampal slices

Corticosterone significantly increases the incorporation of [3H]leucine into specific cytosol protein(s) isolated from in vitro hippocampal slices prepared from adult male albino rats. The present study showed that in slices coincubated with glucocorticoid plus a protein synthesis inhibitor (1 mM-cycloheximide), no such enhancement of amino acid incorporation was observed, suggesting that the hormone acts in the hippocampus to increase de novo protein synthesis. Further experiments demonstrated that the steroid-induced protein synthesis was first detectable (+ 5.7%) following a 30-min exposure of slices to corticosterone; slices incubated for 1 or 2 h both showed a 12% increase in synthesis of the affected protein(s) when compared with controls. In an attempt to determine whether the glucocorticoid alteration of protein metabolism was receptor-mediated, hippocampal slices were also incubated with 10 nM-progesterone, a steroid known to compete for corticosterone binding to its cytosol receptor. Progesterone alone, which does not translocate cytoplasmic receptors to the nucleus, did not alter hippocampal protein metabolism and effectively blocked the induction by corticosterone of the 54K protein(s). These studies provide evidence that in the rat hippocampus corticosterone interacts with high-affinity steroid receptors to regulate the synthesis of specific protein(s).

The suppression of cellular proliferation in SV40-transformed 3T3 cells by glucocorticoids

Glucocorticosteroids, when added two hours after cell plating to SV40-transformed, 3T3 mouse fibroblasts in low serum (0.3% v/v), biotin-supplemented medium, suppress cellular proliferation by 24 hours. While some cell death probably occurs, the growth inhibition is not primarily due to cytotoxicity and cytolysis. This conclusion is supported by the following: 1) both dead and viable cell numbers are suppressed, 2) little cell debris is evident in the medium, and 3) very high concentrations of glucocorticoids do not cause an increase in the dead cell count. Furthermore, this growth suppression, which is specific for glucocorticoids since several non-glucocorticoid steroids have no inhibitory effect, is not permanent nor irreversible. Removal of the glucocorticoid and replacement with 10% serum restore rapid proliferation. Although higher concentrations (1% and 10%) of serum afford some protection against glucocorticoid inhibition, this protection is not simply a consequence of faster growth rates. SV3T3 cells can be grown in serum-free medium supplemented with biotin, transferrin, insulin, and epidermal growth factor (EGF). Under these conditions growth rates are comparable to high serum media, yet glucocorticoids are still powerful inhibitors. However, the omission of insulin from serum-free, glucocorticoid cultures does result in observable cell death and lysis. Flow microfluorometry and autoradiographic studies have determined that glucocorticoid-inhibited cells are partially blocked in G1. The proportions of S phase and G2 + M cells are greatly reduced with an accompanying accumulation of G1 cells. These results suggest that glucocorticoids regulate a biochemical step(s) in G1 which is critical for DNA initiation.

Mouse lymphoma cells: mechanisms of resistance to glucocorticoids

S49, an established line of mouse lymphoma cells, has several characteristics useful for the genetic analysis of glucocorticoid action: (1) a stable pseudodiploid karyotype; (2) an efficient cytolytic effect of glucocorticoids, which appears to follow the same biochemical pathway as steroid hormone action in other systems; (3) appearance of rare steroid-insensitive clones that exhibit stable, heritable resistance to further glucocorticoid treatment; (4) rapid growth in suspension culture and high cloning efficiency in soft agar, allowing facile isolation of variant clones. Two hundred individual steroid-resistant clones of S49 cells have been isolated and analyzed to determine the origin of their resistance. Most of these variant clones (55 %) fail to bind [3H]dexamethasone at levels above background; 70--75 percent bind less than 30 % of the wild-type level. The remaining clones fall into three general groups with respect to the efficiency with which receptors are translocated to the nucleus following dexamethasone treatment: one class transfers less than 10 percent of labeled receptors to the nucleus, another transfers normal amounts, and a third localizes virtually all of the receptors in the nucleus. The four variant phenotypes have been respectively designated r-, receptor activity deficient; nt-, nuclear transfer deficient; d-, deathless (appears normal in binding and nuclear transfer); and nti, increased nuclear transfer. Physical characterization by sucrose gradient sedimentation and gel permeation chromatography reveals that wild-type receptors are approximately 90,000 daltons and nti receptors about 50,000 daltons. The affinities of variant and wild-type receptors for purified DNA in vitro are consistent with their respective nuclear binding characteristics in vivo. Genetic studies with these and other cell lines, combined with recently developed methods for purification and structural analysis of minute quantities of proteins, can provide the level of biochemical resolution required for a fundamental understanding of the molecular mechanism of steroid hormone action.

[Phagocytosis--a central mechanism in inflammatory reaction (author's transl)]

It is attempted to describe the complex pathogenesis of the inflammatory reaction by analysing the mechanisms of several reactions involved. Phagocytosis is a central phenomenon of host defense mechanisms responding to an invasion of foreign bodies. The induction of secondary reactions following phagocytosis is looked at. Several pathogenetic mechanisms responsible for a switch from acute to chronic inflammation are suggested. Known principles of the autonomous regulation of cell effector functions are discussed in relation to their participation in inflammatory reactions.

Effect of methylprednisolone on the nucleoside metabolism of a human lymphoblastoid cell line

Concentrations of methylprednisolone which have lethal effects on human lymphoblastoid cell lines in vitro cause a reduction both in the uptake of uridine and thymidine into acid-soluble material and their incorporation into acid-insoluble material. These effects are virtually instantaneous, which indicates that they do not depend on alterations in gene activity. Normal uptake of nucleosides into cells is by both simple and facilitated diffusion, and methylprednisolone appears to act directly on the cell surface to inhibit only facilitated diffusion uptake.

Calcium dependence of glucocorticoid-induced lymphocytolysis

A potent glucocorticoid, triamcinolone acetonide (9alpha-fluoro-11beta, 16alpha,17alpha, 21-tetrahydroxypregna-1,4-diene-3,20-dione-16,17-acetonide) and a divalent cation ionophore (A23187) had similar effects in vitro on [3H]uridine uptake and on lysis of thymocytes of adrenalectomized rats. Removal of Ca2+ from the medium blunted the cytolytic action of triamcinolone acetonide and virtually eliminated that of A23187. In Ca2+-free media, treatment of the thymocytes for 15 hr with triamcinolone acetonide or A23187 followed by re-introduction of Ca2+ resulted in a rapid decrease in cell survival. Based on the time courses of the responses, triamcinolone acetonide and A23187 evoked proportionate increases in 45Ca uptake and lysis of the thymocytes. These findings implicate enhanced Ca2+ uptake in glucocorticoid-dependent lymphocytolysis.

Glucocorticoid receptors and lymphocytolysis in normal and neoplastic lymphocytes

When cells of the thymus or mouse leukemias P288 and L1210 are exposed in vitro to the potent synthetic glucocorticoid, 3H-Triamcinolone acetonide, the steroid enters the cells passively and binds to macromolecules in the cytoplasm. At 37 degrees C this hormone-receptor complex enters the nucleus and associates with the chromatin. The association with chromatin occurs not only in the corticosteroid-sensitive rat thymocytes and mouse tumors P288 and P1798S but also in the corticosteroid-resistant mouse tumors L1210 and P1798R. An apparent correlation, although not absolute, exists between the content of glucocorticoid-binding macromolecule and the sensitivity of the lymphocytes studied to the lytic effect of glucocorticoids; the sensitive cells having more receptor than the resistant cells. The process of lysis is attributed to the release from the much larger stores of triglyceride in thymus and sensitive lymphoma cells, of a large pool of FFA which causes focal damage to the nuclear membrane resulting in karyorrhexis and, subsequently, to cytolysis. Resistance is attributed to the capacity for preventing the accumulation of greater than about 0.5 fmole FFA/cell. Resistant cells induced to accumulate greater amounts, even for a few minutes, ultimately undergo lysis. Most effective in accomplishing this are branched chain fatty acids of C-8 and higher, which block FFA metabolism, causing accumulation which results in cytolysis.

Glucocorticoid-binding proteins in human acute lymphoblastic leukemic blast cells

The first known step in steroid hormone action is the association of the steroid with specific cytoplasmic steroid-binding proteins (SBP). Using a competitive binding assay, we detected, quantified, and partially characterized such a SBP in cytosol from glucocorticoid-sensitive human lymphoblastic leukemic blasts. The affinity of steroids for the SBP was directly related to their known killing potency. For example, steroids without glucocorticoid effect such as androstenedione, etiocholanolone, and tetrahydrocortisol were unable to displace radiolabeled dexamethasone from the SBP in the binding reaction. The dose-response curve for in vitro inhibition of [(3)H]thymidine uptake in leukemic blasts correlated closely with the binding affinity of glucocorticoids to the SBP, providing additional support for an essential physiologic role for SBP in steroid action. SBP activity was either greatly diminished or absent in glucocorticoid-resistant cells. Six patients who intially had SBP in their blasts and were responsive to combinations of drugs including glucocorticoids no longer had SBP activity detectable at a time when they no longer responded to combinations of drugs including glucocorticoids. In vitro [(3)H]thymidine uptake was not inhibited by steroids in leukemic blast cells lacking SBP activity. Other patients who had received some antileukemic therapy including glucocorticoids and who still had SBP in their leukemic blasts, were still responsive to drug combinations that included glucocorticoids. This appears to be the first study demonstrating glucocorticoid receptors in a human tissue.

The time for reflection: a luxury of the past

We have examined the in vitro effect of glucocorticoid and nonglucocorticoid steroids on the transport of [3-(14)C]alpha aminoisobutyric acid (AIB) in lymphocytes from patients with chronic lymphocytic leukemia (CLL), and myeloblasts from patients with acute granulocytic leukemia (AGL). AIB uptake by CLL lymphocytes was markedly inhibited at 1.0 muM (52+/-2.1%) and slightly inhibited at 0.1 muM (17+/-3.0%) cortisol. A similar degree of inhibition developed at 50-fold lower concentrations of dexamethasone, indicating that the effect of these steroids on AIB accumulation parallels their glucocorticoid activity in vivo. In contrast, minimal or no inhibition was observed with steroids devoid of glucocorticoid activity (progesterone, testosterone, cortisone). 11-deoxycortisol, a nonglucocorticoid known to impede the binding of cortisol to cellular receptors in animal lymphocytes, failed to inhibit AIB uptake by CLL lymphocytes appreciably, but reduced the effect of cortisol to a statistically significant degree. Hence, cortisol-induced inhibition of AIB transport in CLL lymphocytes is related to its glucocorticoid activity and appears to require initial interaction with glucocorticoid-specific cellular receptors. In contrast, 1.0 muM cortisol enhanced the accumulation of AIB in AGL myeloblasts from each of five patients studied (mean = 19%, range 7-43%). Neither cortisone nor 11-deoxycortisol stimulated AIB uptake, and cortisol-mediated stimulation was not seen during simultaneous treatment with 11-deoxycortisol, suggesting that this effect of cortisol also represents a specific glucocorticoid effect. The divergent effects of cortisol on amino acid transport in CLL lymphocytes and AGL myeloblasts may explain, in part, the contrasting clinical effects of glucocorticoids administered to patients with these lymphoid and granulocytic hematopoietic malignancies.

Induction of cytolysis of cultured lymphoma cells by adenosine 3':5'-cyclic monophosphate and the isolation of resistant variants

Cultured mouse lymphosarcoma cells are killed on exposure to 0.1 mM N(6),O(2')-dibutyryl-adenosine 3':5'-cyclic monophosphate. A population of cells resistant to the killing effect of dibutyryl cyclic AMP at concentrations as high as 1 mM was selected. The growth characteristics of the resistant cells were similar to those of the sensitive parental line. However, the resistant cells contain less cytoplasmic cyclic AMP-binding proteins and decreased cyclic AMP-stimulated protein kinase activity. It is proposed that transition from sensitivity to resistance to dibutyryl cyclic AMP in lymphoma cells is connected with a modification of the cyclic AMP-binding protein, which appears to be the regulatory subunit of the cyclic AMP-activated protein kinase.

Glucocorticoid action on hybrid clones derived from cultured myeloma and lymphoma cell lines

Cells of a cloned myeloma line from a Balb/c mouse contain specific cytoplasmic glucocorticoid receptors and are killed by dexamethasone. Cells of a lymphoma line (from mouse strain C57BL) also contain specific glucocorticoid receptors but are resistant to the steroid. Cells of two hybrid clones with widely differing chromosome numbers, derived by fusion between the resistant lymphoma and the sensitive myeloma, contain specific glucocorticoid receptors with similar binding properties as the parental receptors and are killed by dexamethasone. Since the lethal effect of the steroid is expressed in the hybrid cells, failure of the parent lymphoma line to be affected by dexamethasone is probably not due to an inhibitor of the lethal reaction.

Alpha-aminoisobutyric acid transport in human leukemic lymphocytes: in vitro characteristics and inhibition by cortisol and cycloheximide

We have studied the transport of alpha-aminoisobutyric acid (AIB)-3-(14)C and its response to cortisol and cycloheximide in vitro in blood lymphocytes from untreated patients with chronic lymphocytic leukemia. The accumulation of AIB-3-(14)C increased in a linear fashion for 60 min, and reached an apparent steady state in 120 min. The initial rate of AIB accumulation (V(o)) varied from 1.1 to 10.2 mumoles/kg cell H(2)O per min in cells from 16 different patients; however, V(o) was reproducible in cells from five of six patients which were studied repeatedly over 1-9 months, and correlated positively with the lymphocyte count (r = 0.51, P = < 0.01). Virtually total inhibition of protein synthesis with cycloheximide was found to decrease the accumulation of AIB in cells from four patients which had high rates of AIB transport, but had no effect on transport in cells from four patients which accumulated AIB more slowly. These results indicate that active transport depends, in part, upon the presence of labile protein with a turnover rate which varies among different cell populations. Treatment with 10 muM cortisol for 240 min in vitro reduced the initial rate of AIB-3-(14)C accumulation (V(o)) by 43.4+/-4.1% (SE) (range, 9-66%) in cells from 16 patients. The degree of inhibition did not vary appreciably over a 9 month period in four of five patients. The effect of cortisol was proportional to its starting concentration, and developed at low concentrations (0.1-1.0 muM). Cortisol appears to decrease AIB accumulation by inhibiting active uptake, since it neither enhanced the exodus of AIB, nor inhibited apparently nonsaturable transport. Inhibition was noncompetitive in type, suggesting that cortisol decreases the total capacity of the active transport mechanism.Cortisol inhibited AIB transport indirectly by a process which involved de novo protein synthesis, since inhibition (a) appeared only after 60 min of treatment, (b) was present in treated cells which were subsequently incubated for 60 min in cortisol-free medium, and (c) failed to develop during simultaneous blockade of protein synthesis with cycloheximide, even when cycloheximide itself did not decrease AIB transport.