Genetics of glucocorticoid receptors

Human prostate cancer: a direct role for oestrogens

We have studied the response to oestrogen and expression of oestrogen receptors in responsive LNCaP and androgen non-responsive PC3 human prostate cancer cell lines. Growth of LNCaP cells is significantly stimulated by physiological concentrations of oestradiol; this growth increase appears to be comparable to that induced by either testosterone or dihydrotestosterone. In contrast, oestradiol significantly inhibits the proliferation of PC3 cells. We also present novel evidence for functional oestrogen binding in LNCaP cells. This evidence was first obtained by means of radioligand binding assays and was further corroborated using: (a) immunocytochemical analysis of oestrogen and progesterone receptors; (b) reverse transcriptase polymerase chain reaction of oestrogen receptor mRNAs; and (c) immunofluorescence of the 27 kDa heat shock protein (Hsp27), which has been reported to be a marker of functional oestrogen receptors. There appeared to be significantly and consistently lower levels of oestrogen receptor expressed in PC3 cells than in LNCaP cells. The observation that oestradiol-induced growth of LNCaP cells is completely reversed by the pure anti-oestrogen ICI 182,780 clearly implies that the biological response of these cells to oestradiol is mediated mainly via its own receptor. On the other hand, use of a neutralizing antibody against transforming growth factor (TGF)-beta 1 results in a remarkable increase in the growth of PC3 cells; this effect is almost completely abolished after the addition of oestradiol. This suggests that the oestradiol-induced growth inhibition may be mediated by TGF-beta 1. These results suggest that the current model for hormone-dependence of human prostatic carcinoma should be revised. This is of special concern, because recent data indicate that prostate cancer has become the most prevalent cancer and the second principal cause of cancer death in western countries.

Benefit of high-dose methylprednisolone in comparison with conventional-dose prednisolone during remission induction therapy in childhood acute lymphoblastic leukemia for long-term follow-up

Eight-year event-free survival (EFS) was evaluated in 205 patients with acute lymphoblastic leukemia (ALL), to consider the efficacy of high-dose methylprednisolone (HDMP) given during remission induction chemotherapy between 1 and 29 days. The St Jude Total XI Study protocol was used after some minor modifications in this trial. Patients were randomized into two groups. Group A (n = 108) received conventional dose (60 mg/m(2)/day orally) prednisolone and group B (n = 97) received HDMP (Prednol-L, 900-600 mg/m(2) orally) during remission induction chemotherapy. Complete remission was obtained in 95% of the 205 patients who were followed-up for 11 years; median follow-up was 72 months (range 60-129) and 8-year EFS rate was 60% overall (53% in group A, 66% in group B). The EFS rate of group B was significantly higher than of group A (P = 0.05). The 8-year EFS rate of groups A and B in the high-risk groups was 39% vs 63% (P = 0.002). When we compared 8-year EFS rate in groups A and B in the high-risk subgroup for both ages together </=2 or >/=10 years, it was 44% vs 74%, respectively. Among patients in the high-risk subgroup with a WBC count >/=50 x 10(9)/l, the 8-year EFS was 38% in group A vs58% in group B. During the 11-year follow-up period, a total of 64 relapses occurred in 205 patients. In group A relapses were higher (39%) than in group B (23%) (P = 0.05). These results suggest that HDMP during remission-induction chemotherapy improves the EFS rate significantly for high-risk patients in terms of the chances of cure.

Cytokine networks and corticosteroid receptors

The role of the inflammatory cytokines on glucocorticosteroid binding (GCSB) and glucocorticosteroid receptor (GR) level was studied. We incubated a B cell line--CESS--, a promonocytic cell line--U937--and a hepatoma cell line--HepG2--in the presence of varying concentrations of IL-1 beta, IL-6 and TNF-alpha for 24 hours. Glucocorticosteroid binding was determined by the method of "whole cell uptake," and characterized by Scatchard analysis. A considerable increase in the glucocorticosteroid binding was induced by all the three cytokines. Northern analysis of the glucocorticoid receptor expression demonstrates that the action of the cytokines is likely not pretranslational. Present data suggest that local imbalance in the ratio of these three cytokines in different pathological cases might influence the glucocorticosteroid sensitivity of the lymphocytes, monocytes and hepatocytes as target cells.

Glucocorticosteroid resistance in humans. Elucidation of the molecular mechanisms and implications for pathophysiology

Familial glucocorticoid resistance (FGR) is a rare hereditary disorder characterized by hypercortisolism and the absence of stigmata of Cushing's syndrome. The inability of glucocorticoids to exert their effects on target tissues is compensated for by increases in circulating corticotropin (ACTH) and cortisol, the former causing excess secretion of both adrenal androgens and adrenal steroid-biosynthesis intermediates with salt-retaining activity. There is considerable variability in the clinical presentations of FGR ranging from asymptomatic, to isolated chronic fatigue and to hypertension with or without hypokalemic alkalosis or to hyperandrogenism, or both. In women, hyperandrogenism can result in acne, hirsutism, menstrual irregularities, oligoanovulation, and infertility; in men it may lead to infertility and in children to precocious puberty. The reported molecular defects in FGR, such as point mutations and a microdeletion of the glucocorticoid receptor (GR) gene, cause partial resistance by, respectively, compromising the function of the GR or decreasing its intracellular concentration in glucocorticoid target tissues. Complete glucocorticoid resistance is believed to be incompatible with life in humans. Hence, the glucocorticoid resistance cases reported have been partial and of variable degree. The extreme variability in the clinical manifestations of the disorder can, additionally, be explained by differing sensitivity of target tissues to mineralocorticoids or androgens or both, and perhaps by different biochemical defects of the glucocorticoid receptor, causing selective resistance of certain glucocorticoid responses in specific tissues. Isolated tissue-resistance from a somatic mutation of the GR in a corticotropinoma from a patient with Nelson's syndrome was also found, suggesting that this may be a mechanism of tumorigenesis. There is additional evidence that defects of GR function can appear surreptitiously in a variety of clinical conditions, suggesting that glucocorticoid resistance in humans may be involved in the pathogenesis and/or clinical picture of a plethora of disease states, of which FGR is the archetype.

Glucocorticoid receptors and resistance to glucocorticoids in hematologic malignancies

Glucocorticoids are highly effective in inducing the cytolysis of cells of lymphocytic origin. This property has resulted in their incorporation into chemotherapy regimens used in the treatment of hematologic malignancies. Studies at the molecular and cellular levels have demonstrated that the hormone-induced cytolytic response is mediated through a highly specific cytoplasmic glucocorticoid receptor (GR). The GR has been cloned and sequenced and found to be organized into a discrete series of domains which mediate the receptor functions of hormone binding, nuclear translocation, DNA binding and transcriptional modulation. Thus, the binding of glucocorticoids by the GR induces a series of cellular events which result in the activation or repression of a network of glucocorticoid responsive genes and produces a specific cellular response. Prolonged exposure to glucocorticoids ultimately causes resistance to develop; thereby limiting the usefulness of this class of drugs. Studies addressing the mechanism of resistance have shown that the GR is the primary target of genetic alterations that lead to resistance to cytolysis. Using mouse and human cell lines as model systems, it has been shown that the vast majority of glucocorticoid resistant mutants express low levels or altered forms of the GR. Similarly, in vivo studies on patients have suggested that low GR levels are associated with a poor response to glucocorticoid based therapies. Recently, aberrant GR isolated from a patient with multiple myeloma resistant to glucocorticoids were found to harbor deletions in their hormone binding domains. Sequencing of the receptors suggested that each arose as a result of alternate splicing events. In both cases, the latter event produces a receptor unable to bind hormone leading to the speculation that alternate splicing may serve as a mechanism by which a cell evades the effects of glucocorticoids. The therapeutic implications for patients expressing aberrant receptors is discussed.

Characterization of selective glucocorticoid-dependent responses in a glucocorticoid-resistant smooth muscle tumor cell line

The DDT1 MF2 smooth muscle cell line was derived from an estrogen/androgen-induced leiomyosarcoma arising in the hamster ductus deferens. Growth of this cell line is arrested in G0/G1 by treatment with glucocorticoids. To facilitate the study of the mechanism of glucocorticoid-induced cell growth arrest, a glucocorticoid-resistant variant cell line, DDT1 MF2 GR1 (GR1), was developed by genetic selection. Growth of this mutant cell line is completely resistant to the inhibitory action of glucocorticoids. However, we now demonstrate that both primary and secondary glucocorticoid-induced events still exist in the GR1 cell line. By analyzing the expression and genetic pattern of glucocorticoid receptor, no detectable rearrangement of the glucocorticoid receptor gene was found although the expression of both mRNA and protein levels of the receptor were lower in the variant compared to wild-type cells. In addition, we found that the expression of two growth-associated genes, Ha-ras and transforming growth factor beta 1 (TGF-beta 1) are down-regulated by glucocorticoids in wild-type DDT1 MF2 cells but not in GR1 cells. These results indicated that the function or activity of glucocorticoid receptor in the GR1 cells is not qualitatively altered. Our data suggest that a lower glucocorticoid receptor level is not the real cause or at least not the single cause for the GR1 cell's loss of sensitivity to the inhibitory action of glucocorticoid. Instead, we postulate the existence of a defect downstream of the primary site of action of glucocorticoid receptor complexes in GR1 cells.

Modulation of glucocorticosteroid binding in human lymphoid, monocytoid and hepatoma cell lines by inflammatory cytokines interleukin (IL)-1 beta, IL-6 and tumour necrosis factor (TNF)-alpha

In order to elucidate the role of the inflammatory cytokines in regulating glucocorticosteroid binding (GCSB) and glucocorticosteroid receptor (GR) level we incubated a B-cell line (CESS), a promonocytic cell line (U937) and a hepatoma cell line (HepG2) in the presence of varying concentrations of IL-1 beta, IL-6 and TNF-alpha for 24 h. Glucocorticosteroid binding was determined by the method of 'whole cell uptake', and the cellular appearance of the glucocorticosteroid receptor was detected by immunocytochemistry. A rise in the glucocorticosteroid binding was induced by all three cytokines. The increase in level of glucocorticosteroid receptors in the cells shown by immunocytochemistry was much more pronounced. However, antagonistic effects were demonstrated by both methods between IL-6 and TNF-alpha, and between IL-1 beta and TNF-alpha when they were applied simultaneously, in U937. Present data suggest that local imbalance in the ratio of these three cytokines in different pathological cases might influence the glucocorticosteroid sensitivity of the lymphocytes, monocytes and hepatocytes as target cells.

Anti-estrogen antibodies in systemic lupus erythematosus: a quantitative evaluation of serum levels

We measured the beta-estradiol binding capacity of serum gamma-globulins in four subject groups; 1) normal men, 2) normal women who had never taken oral contraceptives, 3) normal women who had a history of oral contraceptive use and, 4) patients with systemic lupus erythematosus (SLE). We used dextran-coated charcoal to strip endogenous estradiol from serum proteins, added 3H-estradiol, and measured its association with proteins in various electrophoretic fractions following zone separation on agarose gels. Most of the bound radioactivity was present in the albumin, beta and gamma-globulin fractions. Binding to gamma-globulins was elevated in SLE patients, and normal controls who had taken oral contraceptives, as opposed to other controls (p less than 0.005). Gamma-region radioactivity could be removed by protein-G adsorption prior to zone electrophoresis. Isoelectric focusing revealed a pattern of tritiated-E2 binding consistent with polyclonal B-cell activation in all groups. There was no correlation between the extent of gamma-region binding and the total serum immunoglobulin level for any of the groups studied, nor was there a correlation between E2 binding and anti-DNA titers in the SLE group. The average anti-estradiol antibody concentrations in SLE sera (assuming equimolar binding) was 105 ng/ml (95% CL = 92-118), whereas their average anti-DNA antibody concentration was in the microgram/ml range. Thus, quantitatively, the level of anti-estradiol antibodies is at least an order of magnitude lower than the anti-DNA antibodies characteristic of this disease.

Temperature-sensitive mutants for steroid-sensitive growth of S115 mouse mammary tumor cells

We have generated temperature-sensitive (ts) mutants for steroid-regulated anchorage-independent cell growth. Androgen-responsive S115+A mouse mammary tumor cells were mutagenized with ethyl methane sulfonate and the variants which were growth-arrested in suspension at the nonpermissive temperature of 41 degrees C were selected by killing dividing wild-type cells with the DNA synthesis inhibitors 5-fluoro-2'-deoxyuridine or cytosine arabinoside. Fifteen clones were isolated and characterized for morphology and growth properties. Three (ts21, ts27, ts33) of the phenotypic variants were ts for androgen-maintained anchorage-independent growth, two of them (ts27 and ts33) also for growth in monolayer. Growth arrest at 41 degrees C was not due to a defect in androgen receptor function in any of the mutant cell lines as shown by steroid binding assays and by the androgen-stimulated expression of both endogenous MMTV RNA and the transiently transfected LTR-CAT gene at the nonpermissive temperature. It remains to be determined for clone ts33 whether the defect is in postreceptor events of steroid action or in genes affecting general mechanisms of cell growth. However, since in clones ts21 and ts27 general cell growth remains functional at 41 degrees C under serum stimulation, defects may be in postreceptor steroid-related pathways. It is hoped that these mutants will provide a useful tool for study of steroid regulation of cell growth and in particular of the property of anchorage-independent growth.

Prognostic significance of glucocorticoid receptor determination in patients with chronic lymphocytic leukemia and immunocytoma--lack of a positive correlation between receptor levels and clinical responsiveness

Glucocorticoid receptors (GR) have been suggested to have prognostic significance in patients with CLL treated with chemotherapy containing glucocorticoid. In this study, the GR levels in 65 patients with advanced CLL and immunocytoma (clinical stages III and IV according to Rai) were determined by means of a whole cell assay. The median GR-level was 1,920 bs/c with a range from 0 to 9591. The patients were subsequently treated according to a prospective, randomized trial with either a combination of chlorambucil and prednisolone, or with prednimustine. No significant difference in receptor levels was found between responders (median = 1940 bs/c; n = 47) and nonresponders (median = 1950 bs/c; n = 14). To assess the influence of receptor content on prognosis we have analyzed the relationship between GR content and survival time and duration of response. There was no significant difference in duration of response and in survival between those patients with high (greater than 1920 bs/c) and those with low GR levels (less than 1920 bs/c) (log-rank test). Our data suggest that determination of GR provides no reliable indicator for clinical response to regimens with glucocorticoid as a component in patients with CLL and immunocytoma.

Isolation and characterization of a mouse L cell variant deficient in glucocorticoid receptors

The growth of mouse L cell fibroblasts is inhibited by glucocorticoids, and we have selected spontaneous glucocorticoid-resistant L cells in culture. One cloned variant exhibits a stable phenotype in the absence of selective conditions. This variant contains no specific glucocorticoid-binding capacity, no immunoreactive glucocorticoid receptor protein, and no detectable glucocorticoid receptor messenger RNA. A glucocorticoid-dependent reporter gene requires exogenous glucocorticoid receptor cDNA and steroid in order to be expressed in this variant. Genomic DNA analysis of the variant cell line indicates that there has been no gross alteration in receptor gene structure. These results suggest that the variant may be deficient in transcription of the glucocorticoid receptor gene.

Use of a glucocorticoid-inducible promoter for expression of herpes simplex virus type 1 glycoprotein gC1, a cytotoxic protein in mammalian cells

Abundant expression of herpes simplex virus type 1 glycoprotein gC (gC1) in transfected mammalian cells has not previously been achieved, possibly because gC1 protein is toxic to cells. To approach this problem, the gC1 coding sequence was placed under the control of the weak but inducible glucocorticoid-responsive promoter from the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). As controls to evaluate for gC1 cytotoxicity, the MMTV LTR promoter was used to express glycoprotein gD1, and a strong, constitutive promoter from the Moloney murine sarcoma virus LTR was used to express gC1. L cells were transfected with these constructs, and a clone expressing gC1 from the inducible MMTV LTR promoter was analyzed. In the absence of glucocorticoid (dexamethasone) stimulation, only a low level of gC1 mRNA expression was detected; after overnight stimulation with dexamethasone, transcription increased approximately 200-fold. Abundant gC1 protein that was functionally active in that it bound complement component C3b, was produced. From passages 5 through 26 (70 cell population doublings), the gC1-producing clone became less responsive to overnight dexamethasone stimulation. The block to gC1 expression occurred at the level of transcription and was associated with hypermethylation of the MMTV LTR DNA. Treatment of the clone with 5-aza-2'-deoxycytidine partially reversed the block in gC1 protein production. Late-passage cells assumed a gC1-negative phenotype that appeared to offer a selective growth advantage, which suggested that gC1 was cytotoxic. Several findings support this view: (i) some cells expressing gC1 after overnight stimulation with dexamethasone assumed bizarre, syncytial shapes; (ii) continuous stimulation with dexamethasone for 5 weeks resulted in death of most cells; (iii) cells transfected with gC1 under the control of the strong Moloney murine sarcoma virus promoter assumed bizarre shapes, and stable gC1-expressing clones could not be established; and (iv) cells induced to express gD1 retained a normal appearance after overnight stimulation or 15 weeks of continuous stimulation with dexamethasone. The inducible MMTV LTR promoter is useful for expressing gC1 and may have applications for expressing other cytotoxic proteins.

Use of a glucocorticoid-inducible promoter for expression of herpes simplex virus type 1 glycoprotein gC1, a cytotoxic protein in mammalian cells

Abundant expression of herpes simplex virus type 1 glycoprotein gC (gC1) in transfected mammalian cells has not previously been achieved, possibly because gC1 protein is toxic to cells. To approach this problem, the gC1 coding sequence was placed under the control of the weak but inducible glucocorticoid-responsive promoter from the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). As controls to evaluate for gC1 cytotoxicity, the MMTV LTR promoter was used to express glycoprotein gD1, and a strong, constitutive promoter from the Moloney murine sarcoma virus LTR was used to express gC1. L cells were transfected with these constructs, and a clone expressing gC1 from the inducible MMTV LTR promoter was analyzed. In the absence of glucocorticoid (dexamethasone) stimulation, only a low level of gC1 mRNA expression was detected; after overnight stimulation with dexamethasone, transcription increased approximately 200-fold. Abundant gC1 protein that was functionally active in that it bound complement component C3b, was produced. From passages 5 through 26 (70 cell population doublings), the gC1-producing clone became less responsive to overnight dexamethasone stimulation. The block to gC1 expression occurred at the level of transcription and was associated with hypermethylation of the MMTV LTR DNA. Treatment of the clone with 5-aza-2'-deoxycytidine partially reversed the block in gC1 protein production. Late-passage cells assumed a gC1-negative phenotype that appeared to offer a selective growth advantage, which suggested that gC1 was cytotoxic. Several findings support this view: (i) some cells expressing gC1 after overnight stimulation with dexamethasone assumed bizarre, syncytial shapes; (ii) continuous stimulation with dexamethasone for 5 weeks resulted in death of most cells; (iii) cells transfected with gC1 under the control of the strong Moloney murine sarcoma virus promoter assumed bizarre shapes, and stable gC1-expressing clones could not be established; and (iv) cells induced to express gD1 retained a normal appearance after overnight stimulation or 15 weeks of continuous stimulation with dexamethasone. The inducible MMTV LTR promoter is useful for expressing gC1 and may have applications for expressing other cytotoxic proteins.

Point mutations in the human vitamin D receptor gene associated with hypocalcemic rickets

Hypocalcemic vitamin D-resistant rickets is a human genetic disease resulting from target organ resistance to the action of 1,25-dihydroxyvitamin D3. Two families with affected children homozygous for this autosomal recessive disorder were studied for abnormalities in the intracellular vitamin D receptor (VDR) and its gene. Although the receptor displays normal binding of 1,25-dihydroxyvitamin D3 hormone, VDR from affected family members has a decreased affinity for DNA. Genomic DNA isolated from these families was subjected to oligonucleotide-primed DNA amplification, and each of the nine exons encoding the receptor protein was sequenced for a genetic mutation. In each family, a different single nucleotide mutation was found in the DNA binding domain of the protein; one family near the tip of the first zinc finger (Gly----Asp) and one at the tip of the second zinc finger (Arg----Gly). The mutant residues were created in vitro by oligonucleotide directed point mutagenesis of wild-type VDR complementary DNA and this cDNA was transfected into COS-1 cells. The produced protein is biochemically indistinguishable from the receptor isolated from patients.

Assignment of estradiol receptor gene to mouse chromosome 10

Differences in restriction fragment lengths were detected with murine estrogen receptor cDNA (clone MOR-100) between Chinese hamster and mouse. These were used to determine the chromosomal location of the estrogen receptor in the mouse by Southern blot analysis of DNAs obtained from a panel of mouse-Chinese hamster somatic cell hybrids. The mouse estrogen receptor gene was localized on mouse chromosome 10.

Chemical cross-linking of heteromeric glucocorticoid receptors

Glucocorticoid receptors of wild-type and nti ("increased nuclear transfer") mutant S49.1 mouse lymphoma cells exist in extracts under low-salt conditions predominantly as high molecular weight species (Mr greater than or equal to 300,000). These receptor-hormone complexes are unable to bind to DNA. High salt (300 mM KCl) produces dissociated receptors of Mr 116,000 and 60-A Stokes radius (wild type) and Mr 60,000 and 38-A Stokes radius (nti mutant), both of which bind to DNA. We used reaction with bifunctional N-hydroxysuccinimide esters as well as oxidation with Cu2+/o-phenanthroline to stabilize the high molecular weight structures. These cross-linked complexes do not interact with DNA, but reductive cleavage again produces the dissociable receptor forms and restores their ability to bind to DNA. The protein modifying reagents iodoacetamide and diethyl pyrocarbonate also produce stabilized high molecular weight receptor complexes. Cross-linking of the high molecular weight receptor forms can also be achieved in intact cells. Immunochemical techniques were used to prove that the complexes cross-linked either in vivo or in cell extracts do contain the heat shock protein of Mr 90,000 as a common constituent. The data show that the high molecular weight receptor complexes are preexisting in intact cells and that dissociation generates DNA binding ability.

Steps of glucocorticoid action in normal and diabetic rat placenta

This investigation examined the effects of Streptozotocin diabetes in pregnancy on several parameters of glucocorticoid action in the rat placenta. Pregnant diabetic rats showed reduced body weight, increased adrenal weight and serum corticosterone concentrations. Glucocorticoid receptors in placental cytosol of labyrinthine zone, measured in the absence of MoO4Na2 were similar in control and diabetic rats, but after addition of MoO4Na2 receptor number were moderately, but significantly reduced in diabetic placentas (P less than 0.01). No changes in affinity were detected in saturation analysis. Furthermore, transformation of the receptor assessed by its capacity for binding to DNA-cellulose, was enhanced in diabetic animals, suggesting increased efficiency of the receptor-bound hormone. Since the function of the glucocorticoid receptor of rat placenta may be the inhibition of local progesterone production (Heller and De Nicola, J. steroid Biochem. 19 (1983) 1339-1343), we determined progesterone synthesis in vitro and found that diabetic placentas synthesized significantly less progesterone than control tissue (P less than 0.05). Lastly, we found that the metabolism of corticosterone to 11-dehydrocorticosterone, while declining in control placentas as pregnancy advanced, it was sustained in diabetic pregnancy. It is suggested that diabetic rat placentas showed increased activity towards the glucocorticoid receptor, resulting in reduction in progesterone synthesis and sustained catabolism of corticosterone. The latter may possibly constitute a compensatory mechanism to protect the fetal compartment from high levels of maternal glucocorticoids.

Modulation of DNA binding of glucocorticoid receptors

Glucocorticoid receptors of several rodent and human cell lines were subjected to mild proteolysis with several proteases. A hormone binding fragment of Mr approximately 40,000 was generated which had increased affinity for DNA as revealed by DNA-cellulose chromatography. It behaved similar to the truncated nti ('increased nuclear transfer') receptor of mutant mouse lymphoma cells. These data led to the view that wild-type receptors of Mr approximately 94,000 contain in addition to the functional domains for hormone binding and interaction with DNA a third domain ('modulation domain') which is essential for biological activity. Monoclonal antibodies against wild-type receptors were used in DNA binding experiments and increased affinity for DNA was observed. The data suggest that reacting the receptor with antibody leads to functional elimination of the modulation domain as if it were cleaved off by mild proteolysis. Antibody treatment neither caused nor inhibited receptor activation to a DNA binding form.

Antiinflammatory and immunoregulatory effects of glucocorticoids: mode of action

In this review emphasis is put on the mechanisms for the antiinflammatory and immunoregulatory role of glucocorticoids in man. Glucocorticoids have numerous effects some of which are permissive; steroids are thus important not only for what they do, but also for what they permit or enable other hormones and signal molecules to do. Some important effects are the result of altered protein synthesis due to steroidreceptor complex formation. One such protein is macrocortin which is induced by glucocorticoids. Macrocortin inhibits the enzyme phospholipase A2, thereby reducing the formation of prostaglandins and leukotriens. Steroids also reduce the release or synthesis of plasminogen activator and certain cytokines such as interleukin 1 and macrophage migration inhibitory factor. Glucocorticoids inhibit the release of histamin and lysosomal constituents of possible importance for the inflammatory response. In addition, steroids have profound effects on the circulation and distribution of white blood cells.

Progression to steroid insensitivity can occur irrespective of the presence of functional steroid receptors

A major problem in treatment of cancers arising in steroid-sensitive cells is their inevitable progression to a steroid-insensitive state; current therapies are based on the assumption that hormone insensitivity is associated with loss of receptor. We demonstrate for the first time that breast tumor cells can progress to steroid insensitivity in spite of functional steroid receptors. Transfection of the steroid-inducible LTR-C3 gene into unresponsive S115 mouse mammary tumor cells results in full inducibility of that gene with both androgen and glucocorticoid. Thus, although all known endogenous inducible parameters are lost, the steroid sensitivity of a transfected exogenous gene demonstrates that the machinery for steroid responsiveness is still fully functional. Furthermore, these transfected genes retain steroid sensitivity only while steroid is present; on prolonged withdrawal of steroid, they lose responsiveness, implying an epigenetic mechanism is involved.

Subunit dissociation and activation of wild-type and mutant glucocorticoid receptors

Apparent molecular weights of wild-type and nti ('increased nuclear transfer') mutant glucocorticoid receptors were obtained from Stokes radii and sedimentation coefficients. At low salt concentrations molecular forms of Mr 328,000 and 298,000 of the wild-type and mutant, respectively, were predominant. Increasing ionic strength resulted in receptor dissociation. Dissociated forms of Mr 130,000 and 63,000 of the wild-type and mutant, respectively, were obtained at 300 mM KCl and above. Some metal oxi-anions prevented dissociation. Receptor activation to allow DNA binding produced the dissociated forms which could be separated from non-activated receptors by filtration through DNA-cellulose or by DEAE-cellulose chromatography. Non-activated wild-type and nti receptors eluted from DEAE-cellulose under identical conditions while activated wild-type and nti receptors eluted differently. Partially proteolyzed wild-type receptors behaved identically to nti receptors. We conclude that the large forms of wild-type and nti receptors are heteromeric and contain only one hormone-building polypeptide per complex.