Sequential gene regulatory events leading to glucocorticoid-evoked apoptosis of CEM human leukemic cells:interactions of MAPK, MYC and glucocorticoid pathways

Gene expression responses to glucocorticoid (GC) in the hours preceding onset of apoptosis were compared in three clones of human acute lymphoblastic leukemia CEM cells. Between 2 and 20h, all three clones showed increasing numbers of responding genes. Each clone had many unique responses, but the two responsive clones showed a group of responding genes in common, different from the resistant clone. MYC levels and the balance of activities between the three major groups of MAPKs are known important regulators of glucocorticoid-driven apoptosis in several lymphoid cell systems. Common to the two sensitive clones were changed transcript levels from genes that decrease amounts or activity of anti-apoptotic ERK/MAPK1 and JNK2/MAPK9, or of genes that increase activity of pro-apoptotic p38/MAPK14. Down-regulation of MYC and several MYC-regulated genes relevant to MAPKs also occurred in both sensitive clones. Transcriptomine comparisons revealed probable NOTCH-GC crosstalk in these cells.

Inequalities in outcomes of acute kidney injury in England

BACKGROUND

Renal replacement is managed by renal specialists and is well documented in national registries. In contrast, nation-wide data on acute kidney injury (AKI) are difficult to capture as it presents in many different ways to all acute hospitals. This paucity impacts on the coordination of appropriate services.

AIMS

We have set out to use all the information submitted by all hospitals in England to identify emergency patients in whom AKI was a major contributor to their hospital stay. We then examined workload in relation to specialist provision and outcomes of care.

DESIGN AND METHODS

All English hospitals submit a sequential list of International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD 10) codes to describe the diagnosis of each admission. An algorithm was applied to all emergency admissions over a 2-year period to identify AKI. The level of renal specialist care available within each hospital trust was compared with patient outcomes, including 30-day mortality.

RESULTS

The incidence of AKI was 1.34% of all emergency admissions. The numbers and types of AKI cases were similar in all trusts, regardless of the service available. Thirty-day mortality was 30.0%. More than half the acute hospitals did not have on-site renal specialists and their AKI mortality rates were significantly higher (P < 0.001). These differences persisted despite adjusting for multiple variables.

CONCLUSION

The country has created specialist renal units in 45% of hospital trusts, but AKI presents as emergencies to all hospitals and there is an increased risk of mortality in the 55% of trusts without renal specialists.

Folding of the glucocorticoid receptor N-terminal transactivation function: dynamics and regulation

The glucocorticoid receptor (GR) mediates biological effects of glucocorticoids at the level of gene regulation, and plays important roles in many aspects of physiology. In recent years, it has become quite evident that GR behaves very dynamically, controlled by its reversible interactions with a variety of coregulatory proteins at various DNA and non-DNA sites. The N-terminal activation function domain (AF1) of the GR exists in an intrinsically disordered (ID) state, which promotes molecular recognition by providing surfaces capable of binding specific target molecules. Several studies suggest that when in action, the GR AF1 gains structure. Thus, it is hypothesized that the GR AF1 domain may be structured in vivo, at least when directly involved in transcriptional activation. Our recent work supports this conclusion. We propose that by allowing AF1 to rapidly and reversibly adopt various configurations through structural arrangements, AF1 can create protein surfaces that are readily available for selective binding to coregulatory proteins, resulting in GR-mediated transcriptional regulation of target genes.

Effects of different osmolytes on the induced folding of the N-terminal activation domain (AF1) of the glucocorticoid receptor

In order to understand gene regulation by glucocorticoids, it is pivotal to know how the major transactivation domain AF1 of the glucocorticoid receptor (GR) functions. Located in the N-terminal region of the GR, AF1 is quantitatively important for transcriptional regulation, but only in recent years have we begun to understand how AF1 works. This is in part due to the fact that the recombinant AF1 (rAF1) peptide exists as a random ensemble of conformers. Algorithms that predict structure support the view that AF1 is also not well ordered in the holo-GR, and the properties of the amino acids in AF1 suggest that it is intrinsically disordered. However, it is generally believed that intrinsically disordered sequences of the GR AF1 must achieve one or more ordered conformation(s) to carry out transactivation activity. Based on our previous published work and available literature, we hypothesize that a confluence of effects that operate under physiological conditions cause functionally active conformation(s) to form in AF1. We have shown that when rAF1 is incubated in increasing concentrations of a naturally occurring osmolyte trimethylamine-N-oxide (TMAO), the peptide folds into functionally active conformation(s) that selectively binds several critical coregulatory proteins. Because cells contain various organic osmolytes whose effects may be cumulative, and in light of cell-specific effects of GR AF1 action, we tested whether it can be folded by other natural organic osmolytes representative of three classes: certain amino acids (proline), methylamines (sarcosine), and polyols (sorbitol). The osmolyte-induced folding of rAF1 shows greatly increased affinity for specific binding proteins, including TATA box-binding protein (TBP), CREB-binding protein (CBP), and steroid receptor coactivator-1 (SRC-1). Consistent with theory and published data with other proteins, our results show that different osmolytes have differential effects on rAF1 folding. The cell-specific functions of the GR AF1--and by extension the AF1s of other nuclear hormone receptors--may in part be affected by the presence and concentrations of particular osmolytes within a particular cellular environment.

Identification of genes leading to glucocorticoid-induced leukemic cell death

Glucocorticoidal steroids (GC) are capable of causing apoptotic death of many varieties of lymphoid cells; consequently, GC are used in therapy for many lymphoid malignancies. Gene transcription in the GC-treated cells is required for subsequent apoptosis, but only a few of the actual genes involved have been identified. We employed gene microarray analysis to find the network of genes involved in GC-evoked cell death, using three clones derived from the CEM lymphoid leukemia cell line. Clone C1-15 was resistant to GC-evoked apoptosis, although not necessarily to GC-induced gene transcription; the other two underwent apoptosis in the presence of GC. Clone C7-14 was subcloned from the apoptosis-sensitive parental C7 clone to establish karyotypic uniformity. The second sensitive clone, C1-6, was a spontaneous revertant from parental resistant clone C1. A period of > or = 24 h in the constant presence of receptor-occupying concentrations of synthetic GC dexamethasone (Dex) was necessary for apoptosis to begin. To identify the steps leading to this dramatic event, we identified the changes in gene expression in the 20-h period preceding the onset of overt apoptosis. Cells in the log phase of growth were treated with 10(-6) M Dex, and 2-20 h later, mRNA was prepared and analyzed using the Affymetrix HG_U95Av2 chip, containing probes for about 12,600 genes. Of these, approximately 6,000 were expressed above background. Comparisons of the basal and expressed genes in the three clones led to several conclusions: The Dex-sensitive clones shared the regulation of a limited set of genes. The apoptosis-resistant clone C1-15 showed Dex effects on a largely different set of genes. Promoter analysis of the regulated genes suggested that primary gene targets for GC often lack a classic GC response element.

Cellular lipid peroxidation end-products induce apoptosis in human lens epithelial cells

Hydrogen peroxide (H(2)O(2)), an oxidant present in high concentrations in the aqueous humor of the elderly eyes, is known to impart toxicity to the lens---apoptosis being one of the toxic events. Since H(2)O(2) causes lipid peroxidation leading to the formation of reactive end-products, it is important to investigate whether the end-products of lipid peroxidation are involved in the oxidation-induced apoptosis in the lens. 4-Hydroxynonenal (HNE), a major cytotoxic end product of lipid peroxidation, has been shown to mediate oxidative stress-induced cell death in many cell types. It has been shown that HNE is cataractogenic in micromolar concentrations in vitro, however, the underlying mechanism is not yet clearly understood. In the present study we have demonstrated that H(2)O(2) and the lipid derived aldehydes, HNE and 4-hydroxyhexenal (HHE), can induce dose- and time-dependent loss of cell viability and a simultaneous increase in apoptosis involving activation of caspases such as caspase-1, -2, -3, and -8 in the cultured human lens epithelial cells. Interestingly, we observed that Z-VAD, a broad range inhibitor of caspases, conferred protection against H(2)O(2)- and HNE-induced apoptosis, suggesting the involvement of caspases in this apoptotic system. Using the cationic dye JC-1, early apoptotic changes were assessed following 5 h of HNE and H(2)O(2) insult. Though HNE exposure resulted in approximately 50% cells to undergo early apoptotic changes, no such changes were observed in H(2)O(2) treated cells during this period. Furthermore, apoptosis, as determined by quantifying the DNA fragmentation, was apparent at a much earlier time period by HNE as opposed to H(2)O(2). Taken together, the results demonstrate the apoptotic potential of the lipid peroxidation end-products and suggest that H(2)O(2)-induced apoptosis may be mediated by these end-products in the lens epithelium.

The pathway of leukemic cell death caused by glucocorticoid receptor fragment 465*

The truncated glucocorticoid receptor mutant gene 465* codes for a protein that is interrupted by a frame-shift mutation in the second zinc finger of the natural DNA binding domain. Thus, 465* represents the natural amino acid sequence 1-465 followed by 21 novel amino acids starting at position 466. The entire ligand binding domain is missing. Prior studies have shown that transient transfection of the glucocorticoid-resistant leukemic T-cell clone ICR-27 with a plasmid expressing 465* rapidly reduces the number of viable cells. This response does not require activation by a steroid, and a hybrid protein consisting of green fluorescent protein fused to 465* is found primarily in the cytoplasm. In the present study, we present evidence that the decrease in cell number is due to a form of cell death that bears many of the classic characteristics of apoptosis. Expression of the 465* protein can be detected a few hours after electroporation and is followed by activation of caspase-3 as well as reduction of the mitochondrial inner transmembrane potential. The caspase-3 inhibitor ZVAD-fmk blocks 465*-dependent cell death when added acutely after electroporation, but fails to do so later. We conclude that the novel 465* gene causes cell death by apoptosis.

The conformation of the glucocorticoid receptor af1/tau1 domain induced by osmolyte binds co-regulatory proteins

The activation domains of many transcription factors appear to exist naturally in an unfolded or only partially folded state. This seems to be the case for AF1/tau1, the major transactivation domain of the human glucocorticoid receptor. We show here that in buffers containing the natural osmolyte trimethylamine N-oxide (TMAO), recombinant AF1 folds into more a compact structure, as evidenced by altered fluorescence emission, circular dichroism spectra, and ultracentrifugal analysis. This conformational transition is cooperative, a characteristic of proteins folding to natural structures. The structure resulting from incubation in TMAO causes the peptide to resist proteolysis by trypsin, chymotrypsin, endoproteinase Arg-C and endoproteinase Gluc-C. Ultracentrifugation studies indicate that AF1/tau1 exists as a monomer in aqueous solution and that the presence of TMAO does not lead to oligomerization or aggregation. It has been suggested that recombinant AF1 binds both the ubiquitous coactivator CBP and the TATA box-binding protein, TBP. Interactions with both of these are greatly enhanced in the presence of TMAO. Co-immunoadsorption experiments indicate that in TMAO each of these and the coactivator SRC-1 are found complexed with AF1. These data indicate that TMAO induces a conformation in AF1/tau1 that is important for its interaction with certain co-regulatory proteins.

Involvement of caspases in 4-hydroxy-alkenal-induced apoptosis in human leukemic cells

4-Hydroxynonenal (HNE), a reactive and cytotoxic end-product of lipid peroxidation, has been suggested to be a key mediator of oxidative stress-induced cell death and in various cell types has been shown to induce apoptosis. We have demonstrated that HNE, at micromolar concentrations, induces dose- and time-dependent apoptosis in a leukemic cell line (CEM-C7). Interestingly, much higher concentrations of HNE (> 15-fold) were required to induce apoptosis in leukocytes obtained from normal individuals. We also demonstrate that HNE causes a decrease in clonogenicity of CEM-C7 cells. Furthermore, our data characterize the caspase cascade involved in HNE-induced apoptosis in CEM-C7 cells. Using specific fluorogenic substrates and irreversible peptide inhibitors, we demonstrate that caspase 2, caspase 3, and caspase 8 are involved in HNE-induced apoptosis, and that caspase 2 is the first initiator caspase that activates the executioner caspase 3, either directly or via activation of caspase 8. Our studies also suggest the involvement of another executioner caspase, which appears to be similar to caspase 8 but not caspases 2 and 3, in its specificity. The demonstration of decreased clonogenicity by HNE in the leukemic cells, and their higher susceptibility to HNE-induced apoptosis as compared to the normal cells, suggests that such compounds may have potential for leukemia chemotherapy.

Improved response with higher corticosteroid dose in children with acute lymphoblastic leukemia

PURPOSE

We investigated whether there was a dose-response relationship for the use of corticosteroids in childhood acute lymphoblastic leukemia (ALL).

PATIENTS AND METHODS

Three hundred sixty-nine patients, ages 1 to 18 years with ALL, were randomly assigned to receive one of four different doses of corticosteroid (prednisolone 40 mg/m(2)/d or dexamethasone 6, 18, or 150 mg/m(2)/d) administered as a 3-day, single-drug window before initiation of standard, multidrug induction chemotherapy. Corticosteroid drug response was measured by reduction in bone marrow blast counts and absolute peripheral blast counts after 3 days. Glucocorticoid receptor (GCR) number and the effective concentration of dexamethasone resulting in a 50% reduction of leukemic cell viability in vitro (EC-50) were evaluated at days 0 and 3.

RESULTS

Increasing dexamethasone doses resulted in greater marrow blast response (P =.007), with a similar trend in peripheral-blood blast response. High-dose corticosteroid regimens (dexamethasone 18 or 150 mg/m(2)/d) elicited better responses than standard doses of dexamethasone or prednisone (bone marrow, P =.002; peripheral blasts, P =.05). Among patients treated with standard-dose corticosteroids, 38% with resistant (EC-50 > 10(-7)) peripheral blasts had a good response compared with 92% with sensitive (EC-50 < 10(-7)) peripheral blasts (P =.01). In contrast, there was no differential response according to EC-50 group after high-dose corticosteroids. Similarly, an association between response and GCR on peripheral-blood blasts was noted after standard-dose corticosteroid regimens but not after high-dose corticosteroid regimens.

CONCLUSION

Response of ALL to glucocorticoid therapy increased with dose. Higher-dose corticosteroid treatment abrogated the effect of relative drug insensitivity and of low GCR on peripheral blasts.

Hormonal regulation of physiological cell turnover and apoptosis

Physiological cell turnover plays an important role in maintaining normal tissue function and architecture. This is achieved by the dynamic balance of cellular regeneration and elimination, occurring periodically in tissues such as the uterus and mammary gland, or at constant rates in tissues such as the gastrointestinal tract and adipose tissue. Apoptosis has been identified as the prevalent mode of physiological cell loss in most tissues. Cell turnover is precisely regulated by the interplay of various endocrine and paracrine factors, which modulate tissue and cell-specific responses on proliferation and apoptosis, either directly, or by altering expression and function of key cell proliferative and/or death genes. Although recent studies have provided significant information on specific tissue systems, a clearly defined pathway that mediates cell turnover has not yet emerged for any tissue. Several similarities exist among the various tissues with regard to the intermediates that regulate tissue homeostatis, enabling a better understanding of the general mechanisms involved in the process. Here we review the mechanisms by which hormonal and cytokine factors mediate cell turnover in various tissues, emphasizing common themes and tissue-specific differences.

Structure-apoptotic potency evaluations of novel sterols using human leukemic cells

Three oxidized analogs of cholesterol have been characterized for their ability to cause apoptotic cell death in CEM-C7-14 human leukemic cells. In addition to testing 15-ketocholestenol (K15), 15-ketocholestenol hydroxyethyl ether (CK15), and 7-ketocholesterol hydroxyethyl ether (CK7), an oxysterol of known apoptotic response, 25-hydroxycholesterol (25OHC), served as a standard for comparison. Growth studies based on dye exclusion by viable cells while using a sublethal concentration of oxysterols ranked their potency for cell kill as 25OHC > K15 > CK15 > CK7. Both the TUNEL assay (terminal deoxynucleotidyl transferase-mediated dUTP-X nick end labeling), which quantifies the amount of DNA nicks caused by a toxic agent, and the MTT assay, which measures cell metabolism and thus reflects cell viability, substantiated the same rank order. An ELISA assay for evaluating release of DNA fragments into the cytosol after treatment gave a similar potency order. The oncogene c-myc mRNA was suppressed by all three oxysterols, with 25OHC and K15 being the most potent suppressors. Hoechst and Annexin V staining documented that these oxysterols kill cells by an apoptotic pathway as evidenced by condensation of nuclear chromatin and plasma membrane inversion, respectively. From these in vitro studies, we believe that 25OHC, K15, and possibly CK15 have the potential to be chemotherapeutic agents.

Normocortisolemic Cushing's syndrome initially presenting with increased glucocorticoid receptor numbers

A girl who developed Cushingoid features in peripuberty, but was eucortisolemic, was previously reported to have markedly elevated lymphocyte glucocorticoid receptor sites per cell with normal binding affinity as a potential cause of her phenotype. Her circadian rhythm of cortisol and pituitary-adrenal axis were initially intact, but later proved to be dysregulated. The patient presented at age 10.8 yr with centripetal obesity, moon facies, buffalo hump, and purple striae, but no statural stunting, which is a cardinal sign of Cushing's syndrome. At 11.5 yr she suffered a compression fracture of the L1 vertebra. That prompted treatment with the antiprogestin drug mifepristone (RU486), which was administered at high dose to achieve an antiglucocorticoid effect. From ages 13.75 yr through 15.5 yr, RU486 was administered in various intervals to suppress her Cushingoid features. Once RU486 was introduced, however, a consistent correlation over time between the Cushingoid features and glucocorticoid receptor sites per cell was no longer observed. However, the number of glucocorticoid receptor sites per cell tended to decrease in response to administering RU486. Ultimately, her Cushingoid phenotype proved to be transient.

HIV-1 reverse transcriptase is phosphorylated in vitro and in a cellular system

Phosphorylation modulates the activity of many proteins that interact with nucleic acids including DNA and RNA polymerases. The HIV-1 reverse transcriptase (RT) is essential during the replicative cycle of the HIV-1 virus. HIV-1 RT has several potential sites for phosphorylation that could regulate its activities. In this work, the phosphorylation of HIV-1 RT is examined in vitro and in vivo, to evaluate any role for this modification in regulating RT metabolism. Recombinant unphosphorylated HIV-1 RT heterodimer expressed in bacteria can be phosphorylated in vitro by several purified mammalian protein kinases. Seven kinases were tested, and five of these enzymes phosphorylated HIV-1 RT. Using an insect baculovirus expression system, the 66 kDa HIV-1 RT was also phosphorylated in vivo. However, HIV-1 RT immunoprecipitated from H9-lymphoma cells infected with HIV-1 showed negligible phosphorylation. Our results indicate that purified HIV-1 RT can be phosphorylated by several mammalian protein kinases in vitro and during expression in baculovirus infected insect cells.

Interdomain signaling in a two-domain fragment of the human glucocorticoid receptor

Studies of individual domains or subdomains of the proteins making up the nuclear receptor family have stressed their modular nature. Nevertheless, these receptors function as complete proteins. Studies of specific mutations suggest that in the holoreceptors, intramolecular domain-domain interactions are important for complete function, but there is little knowledge concerning these interactions. The important transcriptional transactivation function in the N-terminal part of the glucocorticoid receptor (GR) appears to have little inherent structure. To study its interactions with the DNA binding domain (DBD) of the GR, we have expressed the complete sequence from the N-terminal through the DBD of the human GR. Circular dichroism analyses of this highly purified, multidomain protein show that it has a considerable helical content. We hypothesized that binding of its DBD to the cognate glucocorticoid response element would confer additional structure upon the N-terminal domain. Circular dichroism and fluorescence emission studies suggest that additional helicity as well as tertiary structure occur in the two-domain protein upon DNA binding. In sum, our data suggest that interdomain interactions consequent to DNA binding imparts structure to the portion of the GR that contains a major transactivation domain.

The structure of the nuclear hormone receptors

The functions of the group of proteins known as nuclear receptors will be understood fully only when their working three-dimensional structures are known. These ligand-activated transcription factors belong to the steroid-thyroid-retinoid receptor superfamily, which include the receptors for steroids, thyroid hormone, vitamins A- and D-derived hormones, and certain fatty acids. The majority of family members are homologous proteins for which no ligand has been identified (the orphan receptors). Molecular cloning and structure/function analyses have revealed that the members of the superfamily have a common functional domain structure. This includes a variable N-terminal domain, often important for transactivation of transcription; a well conserved DNA-binding domain, crucial for recognition of specific DNA sequences and protein:protein interactions; and at the C-terminal end, a ligand-binding domain, important for hormone binding, protein: protein interactions, and additional transactivation activity. Although the structure of some independently expressed single domains of a few of these receptors have been solved, no holoreceptor structure or structure of any two domains together is yet available. Thus, the three-dimensional structure of the DNA-binding domains of the glucocorticoid, estrogen, retinoic acid-beta, and retinoid X receptors, and of the ligand-binding domains of the thyroid, retinoic acid-gamma, retinoid X, estrogen, progesterone, and peroxisome proliferator activated-gamma receptors have been solved. The secondary structure of the glucocorticoid receptor N-terminal domain, in particular the taul transcription activation region, has also been studied. The structural studies available not only provide a beginning stereochemical knowledge of these receptors, but also a basis for understanding some of the topological details of the interaction of the receptor complexes with coactivators, corepressors, and other components of the transcriptional machinery. In this review, we summarize and discuss the current information on structures of the steroid-thyroid-retinoid receptors.

Trimethylamine N-oxide-induced cooperative folding of an intrinsically unfolded transcription-activating fragment of human glucocorticoid receptor

A number of biologically important proteins or protein domains identified recently are fully or partially unstructured (unfolded). Methods that allow studies of the propensity of such proteins to fold naturally are valuable. The traditional biophysical approaches using alcohols to drive alpha-helix formation raise serious questions of the relevance of alcohol-induced structure to the biologically important conformations. Recently we illustrated the extraordinary capability of the naturally occurring solute, trimethylamine N-oxide (TMAO), to force two unfolded proteins to fold to native-like species with significant functional activity. In the present work we apply this technique to recombinant human glucocorticoid receptor fragments consisting of residues 1-500 and residues 77-262. CD and fluorescence spectroscopy showed that both were largely disordered in aqueous solution. TMAO induced a condensed structure in the large fragment, indicated by the substantial enhancement in intrinsic fluorescence and blue shift of fluorescent maxima. CD spectroscopy demonstrated that the TMAO-induced structure is different from the alpha-helix-rich conformation driven by trifluoroethanol (TFE). In contrast to TFE, the conformational transition of the 1-500 fragment induced by TMAO is cooperative, a condition characteristic of proteins with unique structures.

Glucocorticoids, oxysterols, and cAMP with glucocorticoids each cause apoptosis of CEM cells and suppress c-myc

In clones of the CEM human acute lymphoblastic leukemic cell line, glucocorticoids, oxysterols and activators of the cAMP pathway acting synergistically with glucocorticoids, each can cause apoptotic cell death. Morphologically and kinetically, these deaths resemble one another. The kinetics are striking: in each case, after addition of the lethal compound(s), an interval of approximately 24 h follows, during which cell growth continues unabated. During this "prodromal" period, removal of the apoptotic agent leaves the cells fully viable. We hypothesize that a sequence of biochemical events occurs during the prodrome which eventually results in the triggering of the full apoptotic response as evidenced by the activation of caspases and DNA fragmentation. At some point, the process is irreversible and proceeds relatively rapidly to cell death. Suppression of c-Myc seems a universal early event evoked by each of these lethal compounds or combinations, and we conclude that the negative regulation of this proto-oncogene is an important aspect of the critical pre-apoptotic events in these cells.

Activation of human O6-methylguanine-DNA methyltransferase gene by glucocorticoid hormone

O6-methylguanine-DNA methyltransferase (MGMT), a ubiquitous DNA repair protein, removes the mutagenic DNA adduct O6-alkylguanine, which is synthesized both endogenously and after exposure to alkylnitrosamines and alkylating antitumor drugs such as 2-chloroethyl-N-nitrosourea (CNU). The MGMT gene is highly regulated in mammalian cells and its overexpression, observed in many types of tumor cells, is often associated with cellular resistance to CNU. Dexamethasone, a synthetic glucocorticoid hormone, was found to increase MGMT expression in HeLa S3 cells, concomitant with their increased resistance to CNU. Two putative glucocorticoid responsive elements (GREs) were identified in the human MGMT (hMGMT) promoter. Transient expression of the luciferase reporter gene driven by an hMGMT promoter fragment containing these GREs was activated by dexamethasone. DNase I footprinting assays demonstrated the binding of glucocorticoid receptor to these sequences. In vitro transcription experiment showed that these DNA sequences are functional in glucocorticoid receptor signal-mediated activation of transcription. These results suggest glucocorticoid-mediated induction of the MGMT gene contributes to high level expression of MGMT.

Apoptosis induced by oxysterol in CEM cells is associated with negative regulation of c-myc

Previously we have demonstrated that treatment of the human lymphoblastic leukemic CEM cells with 25-hydroxycholesterol (25OHC) induces apoptosis. In the present study, we show that both c-myc mRNA and c-Myc protein levels are reduced only in oxysterol-sensitive and not in oxysterol-resistant cells after treatment with concentrations of 25OHC that kill the sensitive CEM cells. The repression of c-Myc protein precedes c-myc mRNA reduction, and both events occur before the onset of cell death. Our data suggest that 25OHC-induced suppression of c-myc gene expression in CEM cells results from posttranscriptional regulation. These results demonstrate the regulation by an oxysterol of a gene/gene product important for cell growth and viability and an association between oxysterol-induced apoptosis of CEM cells and the negative regulation of c-myc.

Estrogen-induced microsatellite DNA alterations are associated with Syrian hamster kidney tumorigenesis

Exposure to estrogens is associated with an increase in cancers, including malignancies of the breast and uterus in humans, and of the kidney in hamsters. DNA damage induced by metabolic activation of estrogen has been postulated to result in gene mutations critical for the development of estrogen-induced kidney tumors in hamsters. As part of our examination of the genetic consequences of estrogen-induced DNA damage, we searched for estrogen-induced alterations in microsatellite DNA, a frequent site of mutation in tumors. Genomic DNA isolated from kidney of hamsters treated with estradiol, from estrogen-induced kidney tumors and from untreated age-matched controls, was examined by Southern blot analysis with three multi-locus oligonucleotide probes: (GACA)4, (CAC)6 and (CAG)6. Alterations in DNA fragments containing GACA and CAC tandem repeats were detected in kidney DNA of hamsters treated with hormone for 3 and 4 months, whereas no such effects were seen in control animals. In estrogen-induced tumors, microsatellite alterations were observed in fragments that contain these same two repeat sequences and also CAG repeat sequences. The induction of microsatellite alterations by estradiol in kidney DNA preceding estrogen-induced renal malignancy may play a role in hormone-induced tumorigenesis.

Resistance of human leukemic CEM-C1 cells is overcome by synergism between glucocorticoid and protein kinase A pathways: correlation with c-Myc suppression

Glucocorticoids (GCs) induce apoptosis in lymphoid cells that contain functional GC receptors (GRs). However, GC resistance often is seen in cells with demonstrable GRs; one such line is CEM-C1. We have tested the hypothesis that positive interactions between GC and cyclic AMP (cAMP) regulate GC actions in CEM clones. Treatment of both GC-resistant CEM-C1 [resistant to 1 microM dexamethasone (Dex)] and the sensitive sister clone, CEM-C7 (approximately 65% cell death with 20 nM Dex, approximately 99% death with 1 microM Dex), with a < or = 20 microM concentration of the protein kinase A activator, forskolin, had no significant effect on cell viability. Cotreatment with Dex and forskolin resulted in a strong synergistic death response, with only approximately 10% CEM-C1 cells surviving treatment with 1 microM Dex and 20 microM forskolin. This death was blocked by the GR antagonist RU 38486. However, the extent of apoptosis did not correlate with the amount of GR protein or binding activity in either C7 or C1 cells. As reported previously, Dex-evoked cell death was associated with suppression of c-Myc in C7 cells. In CEM-C1 cells, Dex alone did not affect c-Myc; however, Dex plus forskolin suppressed c-Myc levels. To evaluate mechanisms of Dex-forskolin synergism, fresh subclones of CEM-C7 (clone 14) and CEM-C1 (clone 15) were isolated, to ensure purity of phenotype. In these, forskolin (with or without Dex) caused a similar increase in cAMP (approximately 300-fold) and phospho-cAMP-responsive element binding protein (approximately 4-5-fold) levels, whereas total cAMP-responsive element binding protein expression was not affected. GR transcription function, as tested from a GR-responsive 330-bp mouse mammary tumor virus promoter-luciferase reporter construct, was induced 8- and 4-fold by 1 microM Dex treatment of CEM-C7-14 and CEM-C1-15 cells, respectively. Forskolin (10 microM) significantly potentiated Dex response in CEM-C1-15 cells (13.5-fold) but had only a modest effect (1.5-fold) in CEM-C7-14 cells. These studies suggest that sensitization of CEM-C1 cells by cross-talk between GR and protein kinase A pathways may occur via cooperative effects on GR-mediated gene transcription.

The many roles of c-Myc in apoptosis

The proto-oncogene c-myc encodes a transcription factor c-Myc, which is of great importance in controlling cell growth and vitality. The quantity of c-Myc is carefully controlled by many mechanisms, and its actions to induce and repress genes are modulated by interactions with other regulatory proteins. Understanding the kinetic and quantitative relationships that determine how and what genes c-Myc regulates is essential to understanding how Myc is involved in apoptosis. Reduction of c-myc expression and its inappropriate expression can be associated with cellular apoptosis. This review outlines the nature and regulation of the c-myc gene and of c-Myc and presents the systems and conditions in which Myc-related apoptotic events occur. Hypotheses of the mechanisms by which expression and repression of c-myc lead to apoptosis are discussed.

Protein-protein interactions are implied in glucocorticoid receptor mutant 465*-mediated cell death

Previously we have shown that ICR-27, a clone of glucocorticoid-resistant human leukemic T cells, showed rapid cell loss upon transient transfection with plasmids expressing certain fragments of the human glucocorticoid receptor lacking the ligand binding domain. An extreme example was the frameshift GR mutant 465*, mutated after amino acid 465. This generated a novel 21-amino acid "tail," beginning within the second zinc finger of the human glucocorticoid receptor DNA binding domain, a region required for ICR-27 cell death caused by hologlucocorticoid receptor plus hormone. The cell loss mediated by 465* was faster but quantitatively equivalent to that caused by hologlucocorticoid receptor plus hormone. We are therefore investigating the mechanism of action of 465*. We overexpressed 465* with or without a glutathione S-transferase tag fused to its N terminus and tested its ability to affect glucocorticoid response element (GRE)-driven reactions in vitro. Partially purified 465* showed little binding to a consensus GRE, caused virtually no stimulation of transcription from a GRE, and failed to inhibit GR-driven transcription. However, GST-465* "trapped" several proteins from ICR-27 cell extracts, including c-Jun; recombinant c-Jun also was bound in vitro. In co-transfection assays of CV-1 cells, 465* expression reduced phorbol ester (12-O-tetradecanoylphorbol-13-acetate) transcriptional activation from a promoter containing multiple AP-1 sites. Further studies proved the repressive activity of 465* was c-Jun-specific and not due to squelching artifacts. The data suggest that interaction of 465* with other proteins, such as c-Jun, might be responsible for its cell killing function.

Relationship between biochemical, virological, and histological response during interferon treatment of chronic hepatitis C

The present study was conducted to evaluate the relationship between biochemical, virological, and histological response during the course of interferon therapy. Ninety consecutive patients with well-documented chronic hepatitis C virus (HCV) were treated with 5 MU of interferon alfa-2b three times weekly for 6 months. Liver biopsy was performed, and serum HCV RNA titer was measured before and at the completion of interferon treatment. Normalization of serum alanine transaminase (ALT) concentration (biochemical response) was observed in 50% of patients. In these patients, Knodell score declined significantly from 9.6 +/- 0.5 to 5.0 +/- 0.5 (P < .01), and 75% became HCV RNA negative. The remaining patients (50%) were biochemical nonresponders; mean Knodell score declined from 9.6 +/- 0.5 to 7.7 +/- 0.5 (P < .01), and 11% became HCV RNA negative. For both biochemical responders and nonresponders, the decline in Knodell score was confined to the components of hepatic inflammation (piecemeal necrosis + lobular + portal inflammation); no change in fibrosis was observed. Hepatic inflammation declined by 5 points or more in 69% of biochemical responders and 48% of biochemical nonresponders, and by at least 50% from pretreatment values in 74% and 38% of biochemical responders and biochemical nonresponders, respectively. For all patients (both biochemical responders and nonresponders) who remained viremic at the conclusion of interferon therapy, the reduction in hepatic inflammation was a linear function of the decline in HCV RNA titer. We conclude that more than one third of patients who had no biochemical response after 6 months of interferon therapy achieved a similar improvement in hepatic histology as was observed in patients with biochemical response. This improvement in hepatic histology appeared to correlate with a reduction in HCV RNA titer, especially in patients who remained viremic.

Characteristics of 25-hydroxycholesterol-induced apoptosis in the human leukemic cell line CEM

Cholesterol and related compounds can give rise to oxygenated sterol molecules (oxysterols) which are potent regulators of lymphoid cell growth. Oxysterols added exogenously cause cell death of several lines of cultured cells, and on the basis of limited criteria, it has been suggested that this death is apoptosis. In the present study, we show definitive evidence that 25-hydroxycholesterol (25OHC) kills cells of the clone CEM-C7 by apoptosis and establish the temporal sequence of related cellular and biochemical events. Cell shrinkage was evident as early as 12 h, while cell death was not evident until after 24 h. It mounted rapidly after that, and by 72 h, virtually all cells were dead. Electron microscopic analysis shows that by 24 h after treatment and before the onset of cell death, early ultrastructural features typical of apoptosis were present. DNA breaks were detected by TUNEL assay prior to the onset of cell death. Two types of specific DNA pieces often associated with apoptosis were found as increasing numbers of cells died. DNA fragments of 300 and 50 kbp were not appreciable until 42 h, and internucleosomal cleavage was observed by 48 h after oxysterol addition. None of these effects were seen in an oxysterol-resistant CEM subclone, establishing the specificity for apoptosis of the biochemical and morphological events. z-VAD.FMK, a peptide inhibitor of ICE-related proteases delayed but did not prevent the apoptosis of CEM-C7 cells induced by 25OHC. The addition of mevalonate partially protected CEM-C7 cells from apoptosis but did not restore cell growth.

Elevated expression of Bcl-2 and Bcl-x by intestinal intraepithelial lymphocytes: resistance to apoptosis by glucocorticoids and irradiation

Administration of glucocorticoids or exposure to ionizing radiation in vivo results in a rapid cell death of thymocytes. We report that murine small intestinal intraepithelial lymphocytes (IEL) are resistant to both steroid- and radiation-induced deletion. This is due to resistance to apoptosis, as evidenced by the absence of detectable apoptotic IEL nuclei in situ after in vivo glucocorticoid treatment. IEL express normal levels of glucocorticoid receptors and these receptors bind [3H]dexamethasone to equivalent levels as other lymphocyte populations. Thus, their survival is due to post-receptor signaling mechanisms. Many IEL express high levels of Bcl-2 and that of these Bcl-2high IEL are largely TCR gamma delta +. Those IEL that do express high levels of Bcl-2 are CD8 alpha + beta - CD4-. In addition, IEL express Bcl-x, another protein shown to be involved in the protection of cells from apoptotic signals. IEL represent the first lymphocyte population in vivo shown to have high levels of expression of both molecules, that otherwise occur only in activated lymphocytes in vitro. These data suggest that the Bcl-2+Bcl-x+ IEL are activated cells and not an effete population of cells necessarily destined to die. Also, the high levels of Bcl-2 and Bcl-x in this in vivo activated population supports the in vitro correlate of protection from activation-induced cell death.

Glucocorticoid/oxysterol-induced DNA lysis in human leukemic cells

Both glucocorticoids and oxysterols, steroids with quite different known transduction pathways, cause the death of lymphoid cells. Dual TUNEL/propidium iodide assays on sensitive human leukemic CEM-C7 clones treated with either steroid were clearly positive by 48 h, consistent with apoptosis. Both steroids evoked two distinctive types of DNA lysis: cleavage into large fragments of several different sizes and the classic "ladders", multiples of approximately 200 base pairs. Conventional gel electrophoresis showed that a small proportion of total DNA had undergone laddering 36-48 h after treatment with glucocorticoid or 24 h after oxysterol exposure. On field inversion gel electrophoresis of cellular DNA both steroids caused an increase in an array of large DNA fragments <50 kb in size. A 50 kb fragment appeared 36 h after treatment with either steroid, but only oxysterol treatment caused a significant increase in a 300 kb fragment. Oxysterol treatment did not result in DNA fragmentation in the resistant M10R5 subclone, which retained sensitivity to glucocorticoids. We conclude that glucocorticoids and oxysterols kill these cells with similar, but not identical, patterns of DNA lysis which occur just before or concomitant with the onset of cell death.

Optimal ligand binding by the recombinant human glucocorticoid receptor and assembly of the receptor complex with heat shock protein 90 correlate with high intracellular ATP levels in Spodoptera frugiperda cells

The full-length human glucocorticoid receptor (hGR), overexpressed in Spodoptera frugiperda (Sf9) cells, associates with heat shock protein 90 (hsp90) and hsp70 and binds dexamethasone with high affinity. Baculovirus infection of Sf9 cells grown in TNM-FH medium results in the rapid depletion of glucose from the medium within 24 h. Noting a discrepancy between hGR protein levels and ligand binding capacity in such cultures, we hypothesized that the depletion of glucose from the medium could result in intracellular ATP depletion and consequently affect the ligand binding capacity of the recombinant hGR. Supplementation of the Sf9 culture medium with additional glucose resulted in a three-fold increase in intracellular ATP levels, and a three-fold increase in 3H-dexamethasone binding capacity, without altering the protein levels of hGR, hsp90 or hsp70. However, more hsp90 co-immunoprecipitated with hGR from cells grown in glucose supplemented medium. Our data support the hypothesis that high-affinity ligand binding by hGR requires the ATP-dependent formation of the hGR:hsp90 heterocomplex. Besides having practical consequences for the production of recombinant GR and other related proteins, our findings could ultimately have relevance in diseases such as diabetes mellitus.

Transfected glucocorticoid receptor and certain GR fragments evoke cell death in malignant lymphoid, not myeloid cell lines

Previously we have shown that glucocorticoid sensitivity could be restored to a clone of glucocorticoid-resistant leukemic T cells by transfecting them with an expression vector for the glucocorticoid receptor. Furthermore, transfection with plasmids expressing fragments of the receptor containing the DNA-binding domain resulted in constitutive loss of cells. In this paper, we report the results of transfecting both types of constructs into lines of glucocorticoid-resistant human leukemic cells of T cell, B cell, and myeloid origin. In all the lymphoid lines tested, transfection of the holoreceptor gene resulted in appearance of steroid-dependent cell death. In the same lines, transfection of glucocorticoid receptor fragments expressing amino acids 1-465* (465 residues of the normal sequence plus a novel 21 amino acid C-terminus) or expressing only 398-465* caused cell death without the addition of steroids. The amount of cell loss following transfection of these constitutively lethal fragments was in the same range as that following transfection of the holo glucocorticoid receptor plus administration of glucocorticoid. However, the cell loss due to the constitutively active fragments occurred more rapidly. Neither of the myeloid lines tested were sensitive to any of the transfected constructs, with or without added steroid.

Use of hepatic lidocaine metabolism to monitor patients with chronic liver disease

Lidocaine is converted to its primary metabolic product monoethylglycinexylodide (MEGX) via cytochrome P-4503A4 within the liver. A steady-state concentration of MEGX appears in serum within 15 min following the intravenous administration of lidocaine. The present article reviews some of the data suggesting that this MEGX value can be utilized to assess hepatic function. MEGX production declines stepwise with the severity of chronic hepatitis. In patients with cirrhosis, MEGX declines further with worsening Child class. Nearly all persons with MEGX of < 20 ng/ml had cirrhosis confirmed upon histologic evaluation. Severe life-threatening complications of cirrhosis were observed only in patients with MEGX production below 20 ng/ml. One-year survival for patients with an MEGX value of < 10 ng/ml was only 50%. In contrast, 1-year survival for patients with MEGX of > 10 ng/ml was approximately 80%. These data suggest that MEGX could be utilized as an accurate test of hepatic function and to predict morbidity and mortality related to complications of chronic liver disease. However, this test does have several limitations. There is wide interpatient variability between MEGX and hepatic histology, which severely impairs the ability of this test to accurately predict hepatic histology. In addition, MEGX is affected by gender and several medications. However, since MEGX does decline stepwise with advancing histology in any given patient, the available data suggest that serial monitoring of MEGX could be utilized to track hepatic metabolic capacity in patients with chronic hepatitis and cirrhosis.

Lymphoid cell resistance to glucocorticoids in HIV infection

In humans infected with the HIV-1 virus there may be a disproportionate severity of signs and symptoms of illness compared to the fraction of CD4+ infected T-lymphoid cells. In part, this may be due to altered intercellular signalling systems and intracellular signal transduction. Glucocorticoids are well known for their effects on the vitality and function of lymphoid cells. Patients with HIV infections often show elevated circulating levels of cortisol, suggesting some misfunction in the regulatory systems that maintain the levels of this critical hormone. At the cellular level, it is known that both acute HIV infection and glucocorticoids can cause apoptotic cell death in thymic lymphocytes. However, chronically HIV-infected cells appear to be resistant to glucocorticoid-evoked cell death. Glucocorticoid receptor-ligand binding studies on patients' cells have shown reduced affinity between the receptor binding sites and test steroids. In vitro, chronically HIV-infected cells of the lymphoid CEM line displayed resistance to glucocorticoid-induced apoptosis. These cells showed reduced numbers of binding sites with little alteration in apparent affinity between ligand and receptor. Thus it appears that there may often be malfunction of the normal glucocorticoid response in HIV-infected cells probably due to altered interactions between the glucocorticoid receptor and its hormone. Such alterations may have clinical consequences, including the possibility of a relatively longer life span of infected CD4+ T-lymphocytes, as well as systemic effects of chronically elevated cortisol level.

Role of c-jun induction in the glucocorticoid-evoked apoptotic pathway in human leukemic lymphoblasts

Accumulated evidence suggests tI AP-1 family in CEM cell clones exposed to the glucocorticoid dexamethasone (Dex) has been investigated. Dex is known to cause apoptosis of lymphoid cells in general and of sensitive human lymphoid CEM cell clones in particular. This study finds that Dex induces c-jun mRNA and cJun protein in cells of the sensitive clone CEM-C7 and of the lysis-sensitive OEM hybrid clone H10. CEM-O7 cells were screened for several other Jun/Fos family proteins. Both cFos and JunD were expressed but were unaffected by the steroid, and JunB was not detected. In the continual presence of Dex the induction of cJun began about 6 h after addition of Dex, reached a maximum by 24 h, and plateaued for 72 h, while cell death did not begin until 24-48 h. In clone OEM-Cl cells, which contain glucocorticoid receptor (GR) but are resistant to lysis by Dex, the basal, and even the fully induced, cJun levels are below the basal levels in OEM-07 and H10 cells. To test the hypothesis that cJun plays an important role in steroid-evoked apoptosis, stable transfectants expressing Dex-regulable antisense c-jun RNA were established. Mass cultures of these cells showed reduced sensitivity to Dex, and in three of three clones tested, complete resistance to Dex was obtained. This occurred even though endogenous genes (GR, c-jun) normally responsive to Dex were still inducible, indicating that the GR and basic glucocorticoid response apparatus were intact. It is concluded that Dex induces cJun levels in sensitive OEM cells before cell death and that this induction plays a role in the apoptotic process.

Successful in vitro purging of leukemic blasts from marrow by cortivazol, a pyrazolosteroid: a preclinical study for autologous transplantation in acute lymphoblastic leukemia and non-Hodgkin's lymphoma

An important new approach to curative treatment of leukemia is vigorous treatment of autologous marrow to remove residual abnormal cells in vitro prior to reinfusion. This in vitro 'purging' must destroy the malignant cells while preserving sufficient normal precursors to allow re-establishment of normal in vivo function. We have confirmed that cortivazol (CVZ), a glucocorticoid with an unusual structure, can kill dexamethasone (DEX)-resistant leukemic cells and have examined its ability to purge DEX-sensitive (CEM-C7) and -resistant (ICR-27) human leukemic blasts artificially mixed with normal marrow mononuclear cells in vitro. By carefully defining time and dose, we established a 'therapeutic window' that allowed 'cure' of the artificial remission marrow. A sufficient number of viable normal myeloid precursor cells (CFU-GM) remained to suggest that normal marrow precursors adequate for successful marrow transplantation could survive such treatment. CVZ could be a useful drug for in vitro purging of bone marrow for autologous transplantation in patients with acute lymphoblastic leukemia or non-Hodgkin's lymphoma, sensitive or resistant to standard glucocorticoid.

Cloning of a teleost fish glucocorticoid receptor shows that it contains a deoxyribonucleic acid-binding domain different from that of mammals

In the teleost fish, physiological and biochemical studies suggest that glucocorticoids regulate both salt balance and metabolic activities. In mammals, however, these functions are divided between glucocorticoids and mineralocorticoids. In mammals, separate receptors for these two classes of steroid hormone have been cloned and sequenced. To begin to understand the regulation in fish of the vital processes ascribed to glucocorticoids, we have cloned, sequenced, expressed, and studied the steroid-binding and transcriptional activation capabilities of the rainbow trout (Onchorhynchus mykiss) glucocorticoid receptor. Northern blot analysis shows a single rainbow trout GR messenger RNA species of 7.5 kilobases expressed in gill, intestine, skeletal muscle, kidney, and liver. The trout GR 2274-nucleotide coding sequence provides for a protein of 758 amino acids, with appropriate similarities to mammalian GR, with one striking exception. As in other members of the steroid/thyroid/retinoid receptor family, the DNA-binding domain contains two putative zinc fingers. These have high homology with those of other GRs. However, between the zinc fingers in the trout GR are found 9 more amino acids than are seen in mammalian GRs, raising questions as to the functional form of the fish, as opposed to the mammalian, GR. It has been proposed that as fish appear to use glucocorticoids for both metabolic and salt control, presumably through a single GR, GR would prove to be the evolutionary precursor to mammalian GR and mineralocorticoid receptor (MR). Computer analysis of the known sequences of GRs and MRs, however, suggests that the fish GR did not give rise to the MR of higher animals, but that both subfamilies of receptor arose from some earlier gene.

Steroid hormones. Membrane transporters of steroid hormones

The discovery of a plasma membrane ABC protein that exports steroids in yeast highlights the possibility that similar membrane sorting systems in mammalian cells may modulate the access of steroids to their receptors.

Glucocorticoid antagonist RU 486 reverses agonist-induced apoptosis and c-myc repression in human leukemic CEM-C7 cells

A synthetic glucocorticoid dexamethasone (DEX) inhibits proliferation and induces apoptosis of clone CEM-C7 cells, but not in clone CEM-C1 cells, even though they contain glucocorticoid receptors (GR). We previously showed that suppression of c-myc is a critical step in glucocorticoid-induced cell lysis of C7 cells. It is not reduced in C1 cells. In this study we review the basis for this conclusion and present evidence that the glucocorticoid antagonist RU 486 rescues DEX-treated C7 cells from cell death. An increase in DEX-repressed c-myc mRNA levels precedes the recovery of cell growth. A threshold level of Myc expression appears to be required to maintain growth and viability of C7 cells. Although C1 cells are highly resistant to lysis by glucocorticoids, addition of forskolin, an inducer of protein kinase A, synergizes to evoke complete apoptosis. This synergistic effect is prevented by RU 486, indicating direct involvement of the GR.

Altered endothelin 1 concentration in brain and peripheral regions during thyroid dysfunction

Earlier studies have shown that plasma concentrations of endothelin 1 (ET-1) and the receptors for ET are altered during hyperthyroidism, while they are not affected during hypothyroidism. The present study was undertaken to determine the changes in concentration of endogenous ET-1 in various tissues of hyper- and hypothyroid rats. Hyperthyroidism was induced by daily administration of thyroxine (T4, 0.1 mg/kg, i.p.) for 8 weeks, while hypothyroidism was induced by daily administration of methimazole (10 mg/kg, i.p.) for 8 weeks. The concentration of endogenous ET-1 was determined in the brain regions (hypothalamus, corpus striatum, pituitary, hippocampus and spinal cord), heart, adrenals, kidneys and thoracic aorta using a radioimmunoassay procedure. Blood pressure and heart rate were significantly increased in hyperthyroid rats, while they were not affected in hypothyroid rats when compared with control (euthyroid) rats. Serum T4 and T3 levels were significantly increased in hyperthyroid rats, while they were significantly decreased in hypothyroid rats when compared with euthyroid rats. The concentrations of ET-1 in the hypothalamus, corpus striatum, hippocampus and spinal cord were not altered in hyper- or hypothyroid rats when compared with euthyroid rats. However, the pituitary showed a significant (p < 0.001) increase (104%) in ET-1 concentration in hyperthyroid rats when compared with euthyroid ones, while hypothyroid rats did not show any significant change in ET-1 concentration in the pituitary. In peripheral tissues ET-1 concentrations were not altered in the heart and adrenals of hyper- and hypothyroid rats when compared with euthyroid rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxysterol sensitive and resistant lymphoid cells: correlation with regulation of cellular nucleic acid binding protein mRNA

Oxygenated derivatives of cholesterol inhibit cholesterol synthesis, prevent lymphoid cell growth, and evoke cell death. We have employed a novel selection method to isolate M10 cells, a line of oxysterol-resistant cells, from the sensitive clone CEM C7. Concentrations of the potent sterol 25-hydroxycholesterol that occupy the oxysterol binding protein cause cell death in CEM C7, but not in M10 cells. Both cell lines have similar amounts of the oxysterol binding protein with similar affinities for oxysterol. However, in neither line are the levels of oxysterol binding protein mRNA affected by 1 microM 25-hydroxycholesterol. Furthermore, both cells express the cellular nucleic acid binding protein (CNBP), a 7 zinc finger, DNA-binding protein of unknown function, regulated by oxysterols. The levels of CNBP mRNA are significantly reduced by 25-hydroxycholesterol in the sensitive CEM C7 cells, in which the dose response and time course are consistent with occupancy of the oxysterol binding protein by oxysterol and with subsequent cell kill. However, in the resistant M10 cells, CNBP mRNA levels are unaffected by these concentrations of the 25-hydroxycholesterol. Our results suggest a role for CNBP in oxysterol-induced regulation of cell viability and growth.

Heat shock protein is tightly associated with the recombinant human glucocorticoid receptor:glucocorticoid response element complex

The association of heat shock proteins (hsp) with steroid hormone receptors may have functional significance for steroid receptor action. The association of hsp90 with steroid receptors is thought to maintain the receptors in the nonactivated state until their interaction with the respective ligand. The association of hsp70 with progesterone receptor has been well documented. However, there is evidence both for and against the association of hsp70 with the glucocorticoid receptor (GR). We have examined the interaction between hsp70 and human (h) GR over-expressed in the Baculovirus system. Immunoprecipitation and sucrose gradient centrifugation studies demonstrated the association of hsp70 with both the nonactivated and in vitro activated hGR. We were unable to dissociate hGR and hsp70 by incubation of crude cytosol with 3 mM ATP and 0.5 M NaCl. In vivo activation of hGR did not result in dissociation of hsp70 from hGR. Hsp70 coeluted with hGR from a glucocorticoid response element (GRE)-Sepharose column, suggesting that hsp70 is part of the GRE-hGR complex. Both an anti-hGR antibody and an anti-hsp70 antibody were capable of further retarding the migration of a [32P]GRE-hGR complex in polyacrylamide gels. The in vitro activated hGR has been shown to be highly active in an in vitro transcription system. We speculate that hsp70 may influence the DNA-binding and/or transcriptional activities of hGR.

Renal endothelin mechanism in altered thyroid states

Endothelin (ET) mechanisms were studied in hyper- and hypo-thyroid states in rats. Hyperthyroidism was induced by daily administration of thyroxine (0.1 mg/kg, i.p.) for 8 weeks, while hypothyroidism was induced by daily administration of methimazole (10 mg/kg, i.p.) for 8 weeks. The concentration of endogenous ET-1 was determined in the kidneys using radioimmunoassay. Systemic hemodynamics and renal blood circulation was measured using a radioactive microsphere technique. A significant increase in systolic and diastolic blood pressure, heart rate and cardiac output was observed in hyperthyroid rats as compared to eu- and hypo-thyroid rats. Total peripheral resistance was found to be similar in eu-, hyper- and hypo-thyroid rats. The endogenous concentration of ET-1 in the kidneys was significantly lower in hyper- as compared to eu- and hypo-thyroid rats. The blood flow to the kidneys was significantly increased in hyper- as compared to eu- and hypo-thyroid rats. Infusion of ET-1 (100 ng/kg/min i.v. for 45 min) produced a significant decrease in blood flow to the kidneys of eu-, hyper- and hypo-thyroid rats. The decrease in blood flow was similar in eu-, hyper- and hypo-thyroid rats, indicating that the response of renal blood vessels to exogenous ET-1 is not altered during thyroid dysfunction. Since endogenous ET-1 is involved in the regulation of vascular tone, it may be concluded that in hyper-thyroid rats decrease in concentration of the renal ET-1 could be contributing to an increase in blood flow to the kidney.