Interaction of glucocorticoid receptors from lymphoid cell lines with their nuclear acceptor sites

Selection of a highly tumorigenic breast cancer cell line sensitive to estradiol to evidence in vivo the tumor-inhibitory effect of butyrate derivative Monobut-3

To increase butyric acid mean residence time in vivo, we have produced a stable butyric acid derivative. Monobut-3. Recently, we have described that Monobut-3 is able to induce phenotypic changes in human mammary tumor cells in vitro. In this study, we explore the in vivo effect of Monobut-3. Human breast tumor cell-lines did not easily produce in vivo xenografts, thus, MCF-7 cells required exogenous 17 beta-estradiol to grow and to form in vivo xenografts. To evaluate in vivo and anti-tumor effects of monobut-3 without exogenous 17 beta-estradiol addition, we have established MCF-7 variant cells, highly tumorigenic MCF-7vht, in which transfection of ras oncogene induced a bypass of estrogen requirement but did not delete the presence of functional estrogen receptor (ER). Monobut-3 inhibited growth of this variant by about 90% at 4 mM and reduced 17 beta-estradiol cell growth stimulation. In vivo, in absence of 17 beta-estradiol, 2 mg per mouse monobut-3 decreased tumor take by about 25% and tumor growth by about 50% in nude mice. This is the first experimental demonstration of an in vivo antitumoral effect of a butyric acid derivative alone on a solid human tumor. These data suggest that this compound does not only act by reducing of 17 beta-estradiol stimulation but it also has an 17 beta-estradiol-independent effect. Absence of toxicity and its antiproliferative effects could suggest its use in clinical treatment of well differentiated carcinoma.

New stable butyrate derivatives alter proliferation and differentiation in human mammary cells

Two new butyric esters which were devised to extend the half-life of n-butyric acid in vivo, were used to study their effects on a number of phenotypic characteristics including cell morphology, cell proliferation, colony formation, cell-surface antigen and estrogen receptor expression in 3 normal immortalized cell lines and 2 carcinoma cell lines derived from the human mammary gland. When treated with butyric esters, human mammary cells acquired numerous cytoplasmic granules and vacuoles, reminiscent of secretory functions, and increased in volume. Modulation of the expression of membrane-associated antigens recognized by the monoclonal antibodies (MAbs) 115D8, 140C1 and 125B5 was also observed. Furthermore, butyrate derivatives inhibited the proliferation of all the cell lines tested and the colony-forming capacity of those that grew in soft agar. The inhibitory effects were, however, reversible upon removal of butyric esters from the culture medium. In the human breast carcinoma cell line, MCF-7, in which the cytostatic effects of butyric esters were the most pronounced, cells accumulated in the G0/G1 phase of the cell cycle. This cell line was the only one to contain estrogen receptors which decreased in number when treated with butyric esters without any modification in their binding affinity. Moreover, the stimulatory effects of estrogen on MCF-7 cell proliferation were antagonized by butyric esters. Our results demonstrate that many of the proliferative and differentiation changes previously reported for n-butyrates in tumor cells are similarly produced by the new stable butyrate derivatives in normal and malignant human mammary cell lines.

Estrogen-inducible progesterone receptor in primary cultures of rat glial cells

The presence of an estrogen-inducible progesterone receptor was demonstrated in primary cultures of newborn rat glial cells by biochemical and immunohistochemical techniques. The progesterone receptor (PR) was measured 3-4 weeks after primary culture in estradiol-containing or control medium. Cells were labeled with the synthetic progestin [3H]R5020 followed by ultracentrifugation analysis of the cellular extracts. A "9 S" PR was observed in the cytosol and a "4-5 S" PR was found in the nuclear high salt, tungstate ions containing extract of estradiol-treated cells. When the antiprogestin [3H]RU486 was used instead of [3H]R5020 as a ligand, a 9 S PR was also found in the cytosol, but a nonactivated "8.5 S" receptor complex was identified in the high salt nuclear fraction in presence of tungstate ions. The levels of PR, as measured by whole cell assay, were significantly increased when glial cells were cultured in the presence of 50 nM estradiol, as compared to nonestradiol-treated controls. The estrogen induction of PR was suppressed by the antiestrogen tamoxifen, but tamoxifen by itself had no effect on PR concentration. When the glucocorticosteroid receptor and PR were measured in parallel after estradiol treatment of the same primary culture, only the levels of PR were increased. The PR was visualized inside glial cells by immunohistochemical studies with a monoclonal antibody specific for the B-form of PR (KC 146), which was recognized by fluorescein-linked or biotinylated secondary antibodies. Strong staining was observed in estradiol-treated cultures, when compared to a weaker staining in control cultures. This is the first demonstration of PR in rat glial cells, and we present evidence of its induction by estradiol in primary cultures.

A model of antiglucocorticoid action for designing a potent glucocorticoid antagonist

We have previously shown that the biological efficacy of an antiglucocorticoid is directly related to its affinity for the glucocorticoid receptor in whole cells at 37 degrees C. We have also shown that RU 486-receptor complexes differ from other antiglucocorticoid-receptor complexes in so far as their affinity is as high at 37 degrees C in whole cells as at 0 degree C in a cell-free system, whereas a decrease by a factor of 5-10 is observed with the other antagonists. The aim of the present paper was to evaluate the contributions of temperature and cellular integrity (or the biological events linked to temperature and cellular integrity) to the affinity of a steroid for its receptor for the purpose of determining the parameters favorable to high affinity, which is the prerequisite of a potent antagonist. We provide evidence showing that: (1) an increase in temperature has an unfavorable effect on the affinity of a glucocorticoid for its receptor (4-6-fold decrease between 0 and 37 degrees C), (2) RU 486, like an agonist, forms a complex with the cytosolic glucocorticoid receptor, which satisfies the criteria for an "activated" complex under "in vitro activating treatment", (3) these biological post-binding events (either agonistic or otherwise nature), which change the nature of the complexes, contribute to compensating for the negative effect of rising temperatures on their apparent dissociation constant. We conclude that potent antiglucocorticoids must have a chemical structure allowing them to induce biological post-binding events, such as receptor activation, but in an abortive form which thus effectively "traps" the receptor in a non-functional state.

The mouse glucocorticoid receptor: mapping of functional domains by cloning, sequencing and expression of wild-type and mutant receptor proteins

We have isolated mouse glucocorticoid receptor (GR) cDNAs which, when expressed in transfected mammalian cells, produce a fully functional GR protein. Sequence analysis reveals an open reading frame of 2349 bp which could encode a protein of approximately 86,000 daltons. We have also isolated two receptor cDNAs from mouse S49 nuclear transfer-deficient (nt-) cells which encode mutant forms of the receptor protein. One cDNA encodes a protein that is unable to bind hormone and represents the endogenous hormone binding deficient receptor recently discovered in S49 cells. The lesion in this receptor is due to a single amino acid substitution (Glu-546 to Gly). The second cDNA from nt- cells produces a receptor protein that is able to bind hormone but has reduced nuclear binding. This cDNA, therefore, encodes for the S49 nt- receptor which has been shown to have reduced affinity for DNA. The lesion maps to a single amino acid substitution (Arg-484 to His) located in a highly Cys, Lys, Arg-rich region of the protein previously implicated in DNA binding. Our studies provide unambiguous identification of receptor domains and specific amino acids critical for the hormone and DNA binding properties of this transcriptional regulatory protein. Contained within the first 106 amino acids of the mouse GR is a stretch of nine glutamines with two prolines which are related to the family of transcribed repetitive elements, opa, found in Drosophila melanogaster. A truncated receptor lacking these 106 amino acids is functionally indistinguishable from the wild-type receptor.

Isolation of new types of dexamethasone-resistant variants from a cAMP-resistant lymphoma

We have developed a sequential selection procedure for the isolation of novel steroid-resistant variants of the murine thymoma WEHI-7. The first step involves the isolation of cell lines with an altered cAMP-dependent protein kinase (cAPK) activity by selection for resistance to dibutyryl cAMP (dbcAMP). The second step involves the selection for resistance to dexamethasone (dex) which results in the isolation of variants with decreased receptor function and a cAMPrdexr phenotype. The initial selection, to cAMPr, serves as a permissive step since isolation of spontaneous glucocorticoid resistance from wild-type WEHI-7 does not occur at a measurable frequency. The results demonstrate a potential role for cAPK in regulating the functional levels of glucocorticoid receptor and suggest that mutations in other cellular functions that affect receptor activity could lead to steroid resistance in lymphoid cells.

Glucocorticoid resistance is a dominant trait in hybrids between cytolytic T-lymphocyte lines and AKR thymomas

By screening several cytolytic T-lymphocyte lines, AKR thymomas, and CTL X AKR thymoma hybrids from two different crosses for their sensitivity to the glucocorticoid (GC) analog dexamethasone (dex), we have found that CTL lines and cytolytically active, IL-2-dependent (CTL-like) hybrids are resistant to the cytostatic or cytolytic effects of dex; AKR thymomas and thymoma-like hybrids (cytolytically inactive, IL-2-independent), however, are sensitive to these effects of the drug. The GC resistance behaves like a dominant trait in these crosses. Although they are resistant to GC, the CTL lines and the CTL-like hybrids do contain functional hormone receptors and macrophage-activating factor (MAF) release by the CTL lines and CTL-like hybrids is inhibited by dex.

Isolation and characterization of lymphosarcoma P1798 variants selected for resistance to the cytolytic effects of glucocorticoids in vivo and in culture

Clonal subpopulations of lymphosarcoma P1798 have been subjected to glucocorticoid selection in vivo and in culture and the glucocorticoid binding and responsiveness of the resistant variants have been compared with those of the parental lines. Cell populations that are resistant to the cytolytic effects of glucocorticoids in vivo exhibit a slightly reduced level of glucocorticoid binding, although nuclear translocation of the hormone-receptor complex is not reduced. Sensitive and resistant tumors exhibit similar kinetics of hormone uptake and dissociation following a single injection of dexamethasone. Selection for glucocorticoid resistance in vivo does not result in an increase in the modal number of chromosomes. Cells that are resistant to the cytolytic effects of glucocorticoids in vivo are completely sensitive to the antiproliferative effects of glucocorticoids in culture. Moreover, dexamethasone increases the expression of mouse mammary tumor provirus in cytolysis-resistant and sensitive cells both in vivo and in culture. Selection for glucocorticoid resistance in culture yields variants with decreased glucocorticoid binding and/or nuclear translocation of the hormone-receptor complex. These cells appear to express classical receptor-defective phenotypes. Nevertheless, cells that are resistant to glucocorticoids in culture undergo cytolysis when treated with glucocorticoids in vivo. These data indicate that, under certain circumstances, different mechanisms may be involved in loss of glucocorticoid responsiveness in vivo and in culture.

Immunochemical characterization of wild-type and variant glucocorticoid receptors by monoclonal antibodies

Monoclonal antibodies raised against the rat liver glucocorticoid receptor were used to investigate receptors of wild-type and glucocorticoid-resistant variants of mouse lymphoma cells. Two of the variant types contained receptors of 'nuclear transfer deficient' (nt-) and 'increased nuclear transfer' (nti) phenotypes, respectively, while the third was of the 'receptorless' (r-) phenotype with negligible hormone binding activity. Three monoclonal antibodies of the IgM class and one of the IgG class reacted with both wild-type and nt- receptors but not with the steroid binding form of nti receptors. Some of the antibodies bound the wild-type and nt- receptors more efficiently after activation at 20 degrees C. By use of an immuno-competition assay we were able to detect cross-reacting material in considerable amounts in extracts of nti and r- cell variants. This material was further characterized by gel filtration and immunoblotting. The immunoreactive material of wild-type, nti and r- cells gave a major band of mol. wt. 94 000 upon SDS-gel electrophoresis while the steroid-binding polypeptides of wild-type and nti receptors have mol. wts. of 94 000 and 40 000, respectively. The data show that in S49.1 mouse lymphoma cells the products of two receptor alleles can be distinguished.

Down-regulation of glucocorticoid receptors in mouse lymphoma cell variants

The mouse thymoma-derived cell line W7 is sensitive to the cytolytic action of glucocorticoids. We have isolated a novel class of cell variant that apparently overcomes its inherent sensitivity to glucocorticoids by reversibly down-regulating the level of glucocorticoid receptors. This phenotype is stable during subcloning in the presence and in the absence of glucocorticoids and is dominant in somatic cell hybrids with wild-type cells. Fusion of this variant with wild-type cells produces hybrids that down-regulate and are less sensitive to glucocorticoids than hybrids of receptor-negative and wild-type cells. This is the first demonstration of a phenotypic change which correlates with down-regulation of the glucocorticoid receptor.

Down-regulation of glucocorticoid receptors in mouse lymphoma cell variants

The mouse thymoma-derived cell line W7 is sensitive to the cytolytic action of glucocorticoids. We have isolated a novel class of cell variant that apparently overcomes its inherent sensitivity to glucocorticoids by reversibly down-regulating the level of glucocorticoid receptors. This phenotype is stable during subcloning in the presence and in the absence of glucocorticoids and is dominant in somatic cell hybrids with wild-type cells. Fusion of this variant with wild-type cells produces hybrids that down-regulate and are less sensitive to glucocorticoids than hybrids of receptor-negative and wild-type cells. This is the first demonstration of a phenotypic change which correlates with down-regulation of the glucocorticoid receptor.

DNA binding properties of glucocorticosteroid receptors bound to the steroid antagonist RU-486

RU-486 is an anti-fertility steroid which also has anti-glucocorticosteroid effects. RU-486 is shown to be a strong antagonist of the glucocorticosteroid-induced cytolytic response of the murine thymoma lines W7TB and T1M1b , and of the induction of mouse mammary tumor virus (MMTV) mRNA in T1M1b cells. The glucocorticosteroid receptor of W7 cells has high affinity for RU-486 (Kd = 3 X 10(-9) M) but the complex formed has low nuclear transfer capacity. Binding of RU-486, as compared with the glucocorticosteroid agonist triamcinolone acetonide, to mouse receptor results in a decreased affinity for DNA in general and a reduced specific recognition of a site in the promoter region of MMTV proviral DNA. The RU-486 complex formed with rat liver receptor exhibits the same behavior; in addition, it is shown that only a fraction of these complexes are activated by temperature and these form highly salt-sensitive interactions with DNA. These results indicate that the binding of RU-486 to glucocorticosteroid receptors mimics pharmacologically the properties of a class of receptor variants (nt-) which are non-functional and have reduced nuclear transfer and altered DNA binding capacity. These results substantiate the importance of DNA binding in receptor function.

Binding of dexamethasone to rat liver nuclei in vivo and in vitro: evidence for two distinct binding sites

The binding of [3H]dexamethasone (DEX) to rat liver nuclei in vitro and in vivo have been compared. In vitro, purified nuclei displayed a single class of specific glucocorticoid binding sites with a dissociation constant (Kd) of approximately 10(-7) M for [3H]DEX at 4 degrees C. The glucocorticoid agonists prednisolone, cortisol, and corticosterone and the antagonists progesterone and cortexolone competed avidly for this site, but the potent glucocorticoid triamcinolone acetonide (TA) competed poorly in vitro. Nuclei isolated from the livers of intact rats contained 1-2 X 10(4) [3H]DEX binding sites/nucleus. Up to 85% of the binding sites were recovered in the nuclear envelope (NE) fraction when NE were prepared either before or after labeling with [3H]DEX in vitro. After adrenalectomy, the specific [3H]DEX binding capacity of both nuclei and NE decreased to 15-20% of control values, indicating sensitivity of the binding sites to hormonal status of the animals. Efforts to restore the binding capacity by administration of exogenous glucocorticoids, however, were unsuccessful. After labeling of rat liver nuclei in vivo by intraperitoneal injection of [3H]DEX or [3H]TA into living animals, the steroid specificity and subnuclear localization of radiolabel were different. Both [3H]TA (which did not bind in vitro) and [3H]DEX became localized to nuclei in a saturable fashion in vivo. With either of these ligands, approximately 20% of the total nuclear radiolabel was recovered in the NE fraction. These results suggest the presence of two separate and distinct binding sites in rat liver nuclei, one which is localized to the NE and binds [3H]DEX (but not [3H]TA) in vitro, and another which is not localized to the NE but binds [3H]DEX and [3H]TA in vivo.

Inhibition of glucocorticosteroid action in cultured L-929 mouse fibroblasts by RU 486, a new anti-glucocorticosteroid of high affinity for the glucocorticosteroid receptor

The rate of growth of L-929 mouse fibroblasts in vitro is decreased by the glucocorticosteroid dexamethasone (dex) in vitro, as well as cell adhesiveness. These effects were abolished by RU 486, a new synthetic anti-hormone steroid, in both serum-containing medium and serum-free, chemically defined culture medium. RU 486 did not display any glucocorticosteroid-like activity. 3H-RU 486 binds with high affinity (KDeq approximately 0.4 nM) to the same high affinity receptor-binding sites as dex (KD approximately 0.5 nM) in the cell cytosol, as indicated by Scatchard plot, gradient-ultracentrifugation and competition studies. After incubation of whole cells with 3H-RU 486 at 37 degrees C, a radioactive antihormone-receptor complex was found in the nucleus. However, quantitative studies vs 3H-dex indicated that the antagonist provokes less nuclear receptor complex than the agonist.

Regulation of fibronectin biosynthesis by glucocorticoids in human fibrosarcoma cells and normal fibroblasts

When treated with the synthetic glucocorticoid dexamethasone, HT1080 human fibrosarcoma cells show changes in morphology, adhesion, and the extracellular matrix. Dexamethasone treatment results in a tenfold increase in the rate of fibronectin biosynthesis in HT1080 cells and a twofold increase in untransformed, normal human fibroblasts. Maximal induction levels are attained within one cell generation, while decay of the response requires several cell cycles. Pulse-chase studies showed that most of the newly synthesized fibronectin is secreted into the medium. The glucocorticoid antagonist, RU-486, blocks the dexamethasone-induced changes but does not alter the basal rate of fibronectin production. Therefore, fibronectin biosynthesis appears to be controlled by two distinct mechanisms--one, regulating basal rates of fibronectin production, which is transformation-sensitive and glucocorticoid-independent; and another, which is mediated by the glucocorticoid receptor, resulting in elevated rates of fibronectin biosynthesis upon dexamethasone treatment both in normal fibroblasts and in HT1080 cells.

A new determinant of glucocorticoid sensitivity in lymphoid cell lines

The SAK cell line, derived from a spontaneous thymic lymphoma in an AKR mouse, is resistant to lysis by glucocorticoids in spite of the presence of functional glucocorticoid receptor. Receptor function was determined by hormone binding analyses, as well as characterization of hormonal effects on cell growth and on the accumulation of murine leukemia virus and metallothionein mRNAs. SAK cells were fused with a receptor-defective (and therefore resistant) variant of a well-characterized murine thymoma line, W7. The resulting hybrids are glucocorticoid sensitive, demonstrating complementation of the receptor defect in W7 cells by the functional glucocorticoid receptor of SAK. This fusion shows that SAK cells are resistant to the hormone due to the absence of another function designated "I" for lysis. SAK cells were also fused with glucocorticoid-sensitive W7 cells (containing wild-type receptor), generating glucocorticoid-sensitive hybrids, which demonstrate that the dexamethasone-resistant phenotype of the SAK cells is recessive. Resistant derivatives of this hybrid were found which still contain the full amount of receptor. Chromosome analysis revealed that, on the average, the resistant derivatives had lost two chromosomes, suggesting segregation of chromosomes carrying genetic material necessary for the "lysis" function. The drug 5-azacytidine (a known inhibitor of DNA methylation) has been shown to cause heritable changes in gene expression. Treatment of SAK cells with 5-azacytidine generated glucocorticoid-sensitive clones at high frequency, suggesting that the gene(s) involved in the "lysis" function are intact and have been inactivated through a process such as differentiation.

Glucocorticoid and thyroid hormones transcriptionally regulate growth hormone gene expression

In order to define the molecular mechanisms by which glucocorticoids and thyroid hormone act to regulate growth hormone gene expression, the sites at which they exert their effects on growth hormone biosynthesis were examined in vivo and in a pituitary cell line. Glucocorticoids were shown to rapidly increase accumulation of growth hormone mRNA and nuclear RNA precursors. Glucocorticoids and thyroid hormone were shown to rapidly and independently increase growth hormone gene transcription. These events are shown to occur physiologically in animals and further establish the importance of growth hormone gene expression as a model for steroid regulation.

Lymphoma cell variants of decreased glucocorticoid sensitivity

Glucocorticoid-sensitive S49.1 mouse lymphoma cells were mutagenized and cloned in soft agar containing 10 nM dexamethasone. A series of clones were grown and tested for growth inhibition by dexamethasone. While most clones were completely resistant to the steroid, some were sensitive but required significantly higher glucocorticoid concentrations for the same response than wild-type cells. Two of these low-sensitivity clones were used for binding studies; they showed significantly decreased levels of glucocorticoid receptors as compared to wild-type cells. The data support the view that the level of cellular steroid hormone receptors quantitatively controls hormone responsiveness in closely related cells.

Characterization of nuclear ecdysteroid receptor from crayfish integument

The existence of nuclear ecdysteroid receptors in isolated nuclei from crayfish integument was demonstrated. Nuclei were prepared from crayfish hypodermis by use of a modified Chauveau-method and exposed to [3H]-ecdysteroids. The nuclear hormone receptor complex sedimented at about 5 S and the available binding sites had a high affinity to [3H]-ecdysteroids. Treatment of the nuclei with pronase and DNase completed or partially reduced nuclear bound ecdysone, whereas RNase was without any effect. Competition of nuclear bound ecdysone by various steroids confirmed ponasterone A and kaladasterone as the best competitors followed by 20-OH-ecdysone and ecdysone, whereas compounds like poststerone, "triol" or hydrocortisone did not compete. If [3H]-20-OH-ecdysone was used as the radio-ligand, 20-OH-ecdysone was a better competitor than ecdysone indicating that there may be two different binding sites for ecdysone and 20-OH-ecdysone; this was further substantiated by the finding of two different number of binding sites for these steroids.

Selective inhibition by sodium butyrate of glucocorticoid-induced tyrosine aminotransferase synthesis in hepatoma tissue-cultured cells

Sodium butyrate in a 5 mM concentration prevents the induction of tyrosine aminotransferase in hepatoma culture cells, without affecting the basal level of the enzyme. This effect is reversible immediately after the removal of butyrate, or after a lag, if butyrate was present for more than 2 h. Neither the amount of cellular RNA nor the rate of total RNA synthesis were affected by sodium butyrate. Furthermore, butyrate does not inhibit protein synthesis: [35S]methionine incorporation into proteins, measured in a reticulocyte lysate system, shows no significant difference between the translation capacity of the RNAs from butyrate-treated cells and from dexamethasone-induced or uninduced cells. Nevertheless, when tyrosine aminotransferase was isolated from the translation products by its specific antiserum and analyzed by gel electrophoresis, we observed that the amount of the enzyme synthetized in the presence of RNAs from dexamethasone/butyrate-treated cells was strongly diminished relative to that synthesized in the presence of RNA from dexamethasone-induced cells. These experiments indicate that the treatment of the cells with butyrate decreases the activity of the specific messenger RNA for tyrosine aminotransferase to a level close to the basal level.

Glucocorticoid-mediated inhibition of ornithine decarboxylyase activity in S49 lymphoma cells

Incubation of wild-type S49 lymphoma cells with glucocorticoids, such as dexamethasone and hydrocortisone, inhibits the activity of ornithine decarboxylase (L-ornithine carboxylyase, EC 4.1.1.17), the rate-limiting enzyme in the pathway of polyamine biosynthesis. The kinetics of this inhibition are more rapid than the glucocorticoid-mediated growth arrest in the G1 phase of the cell cycle or in glucocorticoid-mediated cytolysis of these cells. The inhibition of ornithine decarboxylase activity by corticosteroids is specific for steroids of the glucocorticoid class. Results obtained with variant S49 cells having lesions in the pathways of glucocorticoid or cyclic AMP action indicate that cytoplasmic glucocorticoid receptors, as well as nuclear transfer of steroid--receptor complexes, are required for the inhibition of ornithine decarboxylase activity but that this inhibition does not require hormonal activation of adenylate cyclase or cyclic AMP-dependent protein kinase. Because glucocorticoid-mediated inhibition of ornithine decarboxylase occurs when cellular protein synthesis has decreased less than 20%, this inhibition may represent a specific glucocorticoid-mediated deinduction of ornithine decarboxylase in S49 cells. Inhibition of ornithine decarboxylase activity may offer a useful marker for suppression of growth and cell cycle progression in these and other lymphoma cells.

Analysis of steroid resistance in lymphoid cell hybrids

In an attempt to obtain a more detailed understanding of the action of the glucocorticoid-receptor complex in mouse lymphoid cell lines, steroid sensitivity has been investigated in hybrids. Hybrids between dexamethasone (dex)-sensitive and dexamethasone-resistant (Dexr) variants, and hybrids between different Dexr variants were investigated. In the case of Dexr x Dexs hybrids, the possibility of negative complementation was tested; in the case of Dexr x Dexr hybrids, positive complementation was investigated. Neither positive nor negative complementation could be detected; dex sensitivity was always dominant over dex resistance. However, hybrids which contain positive receptor allele(s) segregated out Dexr clones at higher frequencies than expected from studies of pseudodiploid cell lines. This study suggests that different mechanisms give rise to the dex-resistant phenotype in pseudodiploid lymphoid cell lines and in pseudotetraploid hybrids of these cell lines.

Glucocorticoid-induced lymphocytolysis: state of the genetic analysis

The glucocorticoid-induced lysis of lymphoid cell lines offers a genetic approach to steroid hormone action because unresponsive variants can easily be selected as resistant to this lytic effect. The present state of analysis of lymphocytolysis in two murine cell lines, the S49 T-lymphoma and the W7 thymoma, is reviewed. All glucocorticoid-resistant variants isolated so far result from various defects in the glucocorticoid receptor. The absence of variants blocked at another step of the lytic mechanism is discussed. The observed hemizygosity of the glucocorticoid receptor locus in the S49 line and the instability of cell hybrids illustrate some of the potential problems encountered in somatic cell genetics.

Steroid hormone toxicity in human fibroblasts does not correlate with high affinity receptor content

Human diploid skin fibroblasts derived from normal individuals and those with the testicular feminization syndrome (TFM) have been shown to be killed to the same degree by dihydrotestosterone in spite of the absence of high affinity cellular androgen receptors in the TFM fibroblasts. Furthermore, several different normal fibroblast strains from various anatomical sites all showed similar amounts of androgen-induced cytotoxicity even though their respective receptor contents differed by as much as ten-fold. These results suggest that steroid-induced cytotoxicity in human fibroblasts is not correlated with receptor content, unlike murine lymphoid cells in which the receptor content has been shown to be closely related to their ability to survive hormone exposure.

General features of steroid resistance on lymphoid cell lines

Some general features of dexamethasone resistance in five murine lymphoid cell lines were investigated. To obtain large numbers of dexamethasone-resistant (Dexr) variants, a technique was developed by which mouse lymphoid cell lines can be grown with high efficiency on the surface of agar plates without a feeder layer. A total of 271 Dexr variants were investigated, and 90% of them turned out to lack detectable steroid receptor whereas 10% have receptor with, in most cases, a normal affinity for the steroid hormone. Most of this latter class of variants, however, have reduced amounts of receptor and the receptor of all of them displayed altered nuclear binding characteristics. None of the five investigated lymphoid cell lines yielded a Dexr variant with a normal receptor. These results confirm the idea that the high incidence of receptor variant may be due, at least in part, to the haploid state of a gene coding for the receptors. In cell fusion experiments it could be shown that Dexs is dominant over Dexr, but that a Dexr a-lele in a tetraploid cell can lead to an increased frequency of steroid resistance.