Specific Cytoplasmic Receptors Research Articles

Cellular retinol binding protein 1 transfection reduces proliferation and AKT-related gene expression in H460 non-small lung cancer cells

In recent years, new treatments with novel action mechanisms have been explored for advanced non-small cell lung cancer (NSCLC). Retinoids promote cancer cell differentiation and death and their trafficking and action is mediated from specific cytoplasmic and nuclear receptors, respectively. The purpose of this study was to investigate the effect of Cellular retinol binding protein-1 (CRBP-1) transfection in H460 human NSCLC cell line, normally not expressing CRBP-1. H460 cells were transfected by using a vector pTargeT Mammalian expression system carrying the whole sequence of CRBP-1 gene. For proliferation and apoptosis studies, cells were treated with different concentrations of all-trans Retinoic Acid (atRA) and retinol. AKT-related gene expression was analyzed by using western blot and Signosis array and results analysed by one-way analysis of variance (ANOVA) or by t-student test. CRBP-1+ showed reduced proliferation and viability in basal condition and after atRA treatment when compared to empty-transfected H460 cells. Reduced proliferation in CRBP-1+ H460 cells associated to the down-regulation of pAKT/pERK/pEGFR-related genes. In particular, gene array documented the down-regulation of AKT and Stat-3-related genes, including M-Tor, Akt1, Akt2, Akt3, Foxo1, p27, Jun. Restoration of CRBP-1 expression in H460 cells reduced proliferation and viability in both basal condition and after atRA treatment, likely by down-regulating AKT-related gene level. Further studies are needed to better clarify how those CRBP-1-related intracellular pathways contribute to counteract NSCLC progression in order to suggest a potential tool to improve efficacy of retinoid anti lung cancer adjuvant therapy.

Transcriptional signatures of steroid hormones in the striatal neurons and astrocytes

BackgroundThe mechanisms of steroids actions in the brain mainly involve the binding and nuclear translocation of specific cytoplasmic receptors. These receptors can act as transcription factors and regulate gene expression. However, steroid-dependent transcriptional regulation in different types of neural cells is not yet fully understood. The aim of this study was to evaluate and compare transcriptional alterations induced by various steroid receptor agonists in primary cultures of astrocytes and neurons from mouse brain.ResultsWe utilized whole-genome microarrays (Illumina Mouse WG-6) and quantitative PCR analyses to measure mRNA abundance levels. To stimulate gene expression we treated neuronal and astroglial cultures with dexamethasone (100 nM), aldosterone (200 nM), progesterone (200 nM), 5α-dihydrotestosterone (200 nM) and β-Estradiol (200 nM) for 4 h. Neurons were found to exhibit higher levels of expression of mineralocorticoid receptor, progesterone receptor and estrogen receptor 2 than astrocytes. However, higher mRNA level of glucocorticoid receptor mRNA was observed in astrocytes. We identified 956 genes regulated by steroids. In astrocytes we found 381 genes altered by dexamethasone and 19 altered by aldosterone. Functional classification of the regulated genes indicated their putative involvement in multiple aspects of cell metabolism (up-regulated Slc2a1, Pdk4 and Slc45a3) and the inflammatory response (down-regulated Ccl3, Il1b and Tnf). Progesterone, dihydrotestosterone and estradiol did not change gene expression in astrocytes. We found no significant changes in gene expression in neurons.ConclusionsThe obtained results indicate that glial cells might be the primary targets of transcriptional action of steroids in the central nervous system. Substantial changes in gene expression driven by the glucocorticoid receptor imply an important role for the hypothalamic–pituitary–adrenal axis in the hormone-dependent regulation of brain physiology. This is an in vitro study. Hence, the model may not accurately reflect all the effects of steroids on gene expression in neurons in vivo.

Cyclosporine (CsA) in lupus nephritis: assessing the evidence

After more than 40 years since the first demonstration that high-dose corticosteroids can modify the relentless outcome of lupus nephritis [1], the ideal treatment of lupus nephritis is still far from being established. There is some agreement that the initial treatment should be aggressive, particularly in proliferative forms (so-called induction therapy) and should be followed by a maintenance regimen aimed at preventing flares of activity while minimizing the side effects of treatment. However, there are differing views on how to use the available immunomodulating drugs in the various phases of the disease. In particular, there is still much controversy about the current therapies for maintenance [2]. Notwithstanding the different approaches used, it should be noted that the treatment of systemic lupus erythematosus (SLE) nephritis relies on three main categories of drugs, i.e. corticosteroids, alkylating agents and inhibitors of purine synthesis. However, all these drugs have a narrow therapeutic index, and their prolonged administration can cause severe iatrogenic toxicity. In this review, we will try to assess whether cyclosporine (CsA), a drug that interferes with the immune response at levels different from those of corticosteroids and immunosuppressive drugs, may have a role to play in the therapeutic armamentarium of lupus nephritis. CsA is a pro-drug that gains pharmacological activity after binding to its specific cytoplasmic receptor cyclophylin. The complex CsA–cyclophylin interferes with a complex of phosphatases called calcineurin that has a key role in the immune response. Contact with the antigen-presenting cell generates a strong influx of calcium ions into the lympho-

High levels of cellular retinol binding protein-1 expression in leiomyosarcoma: possible implications for diagnostic evaluation

Retinoid bioavailability is regulated by the activity of specific cytoplasmic receptors. High levels of cellular retinol binding protein-1 (CRBP-1) have been documented during experimental arterial and wound-healing processes, but data concerning neoplastic smooth muscle tissues are scarce and/or controversial. This study reports that the expression of CRBP-1 is markedly higher in uterine and gastrointestinal leiomyosarcomas than in leiomyomas and normal myometrium; CRBP-1 was practically absent in normal gastrointestinal smooth muscle tissue. CRBP-1 positivity was particularly elevated in the epithelioid variant of leiomyosarcoma; it was associated with increased proliferative and apoptotic rates and inversely related to smooth muscle differentiation evaluated by alpha- and gamma-smooth muscle actin and desmin expression. Western blotting and reverse-transcription polymerase chain reaction confirmed the observations concerning CRBP-1 and actin isoform expression and revealed higher NF-kappa-Bp65 and RAR alpha and lower Bax protein levels in leiomyosarcoma than in the other conditions. These findings document that a high CRBP-1 expression is associated with smooth muscle malignancy and suggest that CRBP-1 expression represents a new useful marker for the classification of unusual variants of smooth muscle tumors.

Sex differences in response to steroids in preterm sheep lungs are not explained by glucocorticoid receptor number or binding affinity.

We recently reported that prenatal glucocorticoid therapy is less effective at promoting an improvement in lung function in male than in female sheep. This observation, and the higher incidence of respiratory distress syndrome in human males, suggests that the male fetal lung may be less responsive to glucocorticoids than is the female fetal lung. Since glucocorticoids are known to exert their effects via specific cytoplasmic glucocorticoid receptors (GR), we hypothesized that there may be sexual dimorphism in either the number or binding affinity of lung GR. To test the hypothesis, binding of dexamethasone (a synthetic glucocorticoid, 0.5-40 nM) by cytosolic fractions of male (n = 16) and female (n = 16) fetal sheep lung was measured at 125 days gestation (term = 148 days). Scatchard analysis of dexamethasone binding showed that the total number of GR (Bmax) did not significantly differ between male (346 +/- 42 fmol/mg protein) and female (277 +/- 23 fmol/mg protein) fetuses. The measured binding affinity (Kd) in male fetal lungs (6.85 +/- 0.43 nM) was not significantly different from that in females (8.46 +/- 1.02 nM). In conclusion, this study suggests that sex differences in fetal sheep lung responses to glucocorticoid therapy are not due to differences in the number or binding affinity of lung GR.

Topical corticosteroids in nasal polyposis.

Nasal polyps are the common end-point of a number of conditions characterised by inflammation and are rarely 'curable' in its true sense. After consideration of the underlying aetiology and confirmation of the diagnosis, they are normally managed by a combination of medical and surgical interventions. Of these, topical corticosteroids have proved to be the medical treatment of choice. The objectives of the medical management are to eliminate or reduce the size of polyps, re-establish nasal airway and nasal breathing, improve or restore the sense of smell, and prevent recurrence of nasal polyps. The mechanism of action of corticosteroids may be by a multifactorial effect on various aspects of the inflammatory reaction, the effect being initiated by their binding to a specific cytoplasmic glucocorticoid receptor. At a cellular level, there is a reduction in the number of antigen-presenting cells, in the number and activation of T cells, in the number of mast cells, and in the number and activation of eosinophils. When polyps are large (grade 3) topical medication is difficult to instil in a very blocked nose and surgery or short term systemic corticosteroids may be required. Topical corticosteroids are of use in the primary treatment of nasal polyps when they are of a small or medium size (grades 1 and 2) and in the maintenance of any therapeutic improvement. The efficacy of topical corticosteroids such as betamethasone sodium phosphate nose drops, beclomethasone dipropionate, fluticasone propionate and budesonide nasal sprays in reducing polyp size and rhinitis symptoms has been demonstrated in several randomised, placebo-controlled trials. Beclomethasone dipropionate, flunisolide and budesonide sprays have also been shown to delay the recurrence of polyps after surgery. Placebo-controlled studies of agents that have shown a significant clinical effect in the management of nasal polyposis are reviewed.

Macromolecular exchanges between the nucleus and cytoplasm.

The control of transcription and translation is of fundamental importance in cell biology. In this regard, the nuclear envelope is in a unique position to contribute to the regulation of these events, by directing macromolecular exchanges between the nucleus and cytoplasm. Such exchanges occur through the nuclear pore complexes, mainly by signal-mediated processes. Different signals are required for import and export. Specific cytoplasmic or nuclear receptors initially bind the signal-containing substrate, and the complex subsequently interacts with the pores. Additional factors then assist in translocation across the envelope. Current research is focused mainly on further characterization of transport receptors, translocation factors, as well as components of the nuclear pore complex, i.e., the nucleoporins. The ultimate goal is to understand the molecular interactions that occur among the different components of the transport apparatus, the energy sources for transport, and how variations in transport capacity are generated. J. Cell. Biochem. Suppls. 30/31:214-219, 1998. © 1998 Wiley-Liss, Inc.

Regulation of glucocorticoid receptor function and angiotensin-converting enzyme activity

The central link in the mechanism of action of glucocorticoids is specific cytoplasmic glucocorticoid receptors (GH). Their synthesis is programmed by 1 gene of chromosome 5 [44]. The direct biosynthesis of GR occurs in the endoplasmic reticulum of the cytoplasm [12]. In the cytoplasm, GRs bind to heat shock proteins (HSP, chaperone proteins) mol. mass of 50, 70, 90 kD [20, 59]. Like the mass of the GR – HSP complex is 300 kD [14]. In the absence of glucocorticoids, GRs are localized mainly in the cytoplasm [30, 63]. In 1 cell contains from 5000 to 100 000 specific GH. GRs have been found in many mammalian tissues [13], however, certain tissues do not contain GRs: the intermediate pituitary, Kupffer and endothelial cells of the liver, renal glomeruli, and proximal convoluted tubules [12, 31].

Effects of corticosteroid therapy in non-allergic rhinosinusitis.

Corticosteroids have a multifactorial effect initiated by their binding to a specific cytoplasmic glucocorticoid receptor. At the cellular level there is a reduction in the number of antigen-presenting cells, in the number and activation and T cells, in the number of epithelial mast cells, and in the number and activation of eosinophils. Steroids have a proven effect on symptoms and signs in non-allergic rhinosinusitis with eosinophilia and in nasal polyposis. Topically applied drugs, studied in many controlled trials, reduce rhinitis symptoms, improved nasal breathing, reduce the size of polyps and their recurrence, but have a poor effect on the sense of smell and no direct effect on sinus pathology. Systemic steroids, less well studied, appear to have an effect on all types of symptoms and pathology, the sense of smell included. A short course of systemic steroids is as effective as polypectomy with a snare. Individualized management of nasal polyposis and non-allergic rhinosinusitis with eosinophilia may consist of long-term topical steroids, short-term systemic steroids, or surgery, in various combinations.

Novel Steroid Derivative Modulates Gene Expression of Cytokines and Growth Regulators

Topical steroid treatment is a common therapy for psoriasis. Steroids are known to bind to specific cytoplasmic receptors and to influence gene expression. We investigated the effects of the novel steroid derivative mometasone furoate on the expression of putative target genes in normal human epidermal cells (KC). Gene expression was measured by semiquantitative mRNA-PCR. In addition, cytokine receptor characteristics were assessed by ligand binding studies. We found a dose-dependent downregulation of proinflammatory mediators (IL-8, TNF alpha). Genes involved in growth regulation (HER-2, p53) were also modulated. IL-8 binding to KC was inhibited. We conclude that modulation of the expression of cytokine, cytokine receptor and growth factor genes may contribute to the antipsoriatic action of steroids.

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.

Dominant missense mutations in a novel yeast protein related to mammalian phosphatidylinositol 3-kinase and VPS34 abrogate rapamycin cytotoxicity.

Rapamycin is a macrolide antifungal agent that exhibits potent immunosuppressive properties. In Saccharomyces cerevisiae, rapamycin sensitivity is mediated by a specific cytoplasmic receptor which is a homolog of human FKBP12 (hFKBP12). Deletion of the gene for yeast FKBP12 (RBP1) results in recessive drug resistance, and expression of hFKBP12 restores rapamycin sensitivity. These data support the idea that FKBP12 and rapamycin form a toxic complex that corrupts the function of other cellular proteins. To identify such proteins, we isolated dominant rapamycin-resistant mutants both in wild-type haploid and diploid cells and in haploid rbp1::URA3 cells engineered to express hFKBP12. Genetic analysis indicated that the dominant mutations are nonallelic to mutations in RBP1 and define two genes, designated DRR1 and DRR2 (for dominant rapamycin resistance). Mutant copies of DRR1 and DRR2 were cloned from genomic YCp50 libraries by their ability to confer drug resistance in wild-type cells. DNA sequence analysis of a mutant drr1 allele revealed a long open reading frame predicting a novel 2470-amino-acid protein with several motifs suggesting an involvement in intracellular signal transduction, including a leucine zipper near the N terminus, two putative DNA-binding sequences, and a domain that exhibits significant sequence similarity to the 110-kDa catalytic subunit of both yeast (VPS34) and bovine phosphatidylinositol 3-kinases. Genomic disruption of DRR1 in a mutant haploid strain restored drug sensitivity and demonstrated that the gene encodes a nonessential function. DNA sequence comparison of seven independent drr1dom alleles identified single base pair substitutions in the same codon within the phosphatidylinositol 3-kinase domain, resulting in a change of Ser-1972 to Arg or Asn. We conclude either that DRR1 (alone or in combination with DRR2) acts as a target of FKBP12-rapamycin complexes or that a missense mutation in DRR1 allows it to compensate for the function of the normal drug target.

Dominant missense mutations in a novel yeast protein related to mammalian phosphatidylinositol 3-kinase and VPS34 abrogate rapamycin cytotoxicity.

Rapamycin is a macrolide antifungal agent that exhibits potent immunosuppressive properties. In Saccharomyces cerevisiae, rapamycin sensitivity is mediated by a specific cytoplasmic receptor which is a homolog of human FKBP12 (hFKBP12). Deletion of the gene for yeast FKBP12 (RBP1) results in recessive drug resistance, and expression of hFKBP12 restores rapamycin sensitivity. These data support the idea that FKBP12 and rapamycin form a toxic complex that corrupts the function of other cellular proteins. To identify such proteins, we isolated dominant rapamycin-resistant mutants both in wild-type haploid and diploid cells and in haploid rbp1::URA3 cells engineered to express hFKBP12. Genetic analysis indicated that the dominant mutations are nonallelic to mutations in RBP1 and define two genes, designated DRR1 and DRR2 (for dominant rapamycin resistance). Mutant copies of DRR1 and DRR2 were cloned from genomic YCp50 libraries by their ability to confer drug resistance in wild-type cells. DNA sequence analysis of a mutant drr1 allele revealed a long open reading frame predicting a novel 2470-amino-acid protein with several motifs suggesting an involvement in intracellular signal transduction, including a leucine zipper near the N terminus, two putative DNA-binding sequences, and a domain that exhibits significant sequence similarity to the 110-kDa catalytic subunit of both yeast (VPS34) and bovine phosphatidylinositol 3-kinases. Genomic disruption of DRR1 in a mutant haploid strain restored drug sensitivity and demonstrated that the gene encodes a nonessential function. DNA sequence comparison of seven independent drr1dom alleles identified single base pair substitutions in the same codon within the phosphatidylinositol 3-kinase domain, resulting in a change of Ser-1972 to Arg or Asn. We conclude either that DRR1 (alone or in combination with DRR2) acts as a target of FKBP12-rapamycin complexes or that a missense mutation in DRR1 allows it to compensate for the function of the normal drug target.

The tyrosine 89 residue of yeast FKBP12 is required for rapamycin binding

Rapamycin (Rm) is a macrolide antifungal agent related to FK506 that exhibits potent immunosuppressive properties which are mediated through interaction with specific cytoplasmic receptors (FKBPs or RBPs, for FK506- and Rm-binding proteins, respectively). These proteins possess peptidyl-prolyl cis-trans isomerase (PPIase) activity in vitro which is inhibited by the binding of Rm and FK506. In Saccharomyces cerevisiae, Rm sensitivity (Rm s) is mediated by binding of the drug to RBP1, a homolog of the 12-kDa human FK506-binding protein (FKBP12); null mutations in the yeast RBP1 gene result in a recessive drug resistance phenotype. To identify missense mutations that define amino acid (aa) residues in RBP1 involved in drug sensitivity, we selected and genetically characterized over 250 independent Rm r rbp1 mutants and screened them for both RB1-specific mRNA and protein expression. Whereas all rbp1 mutants expressed abundant levels of RBP1 mRNA, stable RBP1 protein production was detected in only one mutant strain. The RBP1 gene was PCR-generated (in triplicate) from several rbp1 mutants and independent clones were sequenced. Most of the immunoblot-negative alleles were found to contain various types of null mutations; however, some alleles contained specific missense mutations that apparently affect protein stability in vivo. The single immunoblot-positive allele was found to contain a mutation altering a specific residue (Tyr 89) which is conserved among the known FKBPs, and which, based on the solution and x-ray structures of human FKBP12, has been proposed to be part of a hydrophobic drug-binding pocket for FK506 and Rm. Analysis of [ 3H]Rm binding in rbp1 mutant vs. wild-type yeast cell extracts indicated that the Tyr 89 → Asp (Y89D) change results in an approx. 95% loss of binding activity. These data confirm the assignment of this Tyr residue as being involved in Rm binding.

Novel aspects of hormone action: Intracellular ligand supply and its control by a series of tissue specific enzymes

On the basis of bioassays four major classes of steroid hormones can be identified in man: glucocorticoids (cortisol) involved in cellular differentiation and metabolism, inflammation and the stress response; mineralocorticoids (aldosterone), involved in the transport of sodium across epithelia; sex steroids (testosterone, oestrogen and progesterone), controlling development of the embryonic, pubertal and adult reproductive phenotype, gametogenesis and behaviour; and vitamin D (1,25_dihydroxyvitamin D,>, involved in differentiation, bone development and calcium homeostasis. Thyroid hormones play a vital role in development and the control of metabolic processes throughout life. It is clear therefore that these hormones have widespread effects in many different tissues, and we are now nearer to understanding their mechanism of action. After entry into the cell from circulating fluids, the hormone or a metabolite binds to a specific cytoplasmic or nuclear receptor. Following conformational changes in the ligand/receptor complex (involving the dissociation of heat shock proteins from the receptor, and possibly phosphorylation of the complex), binding occurs to DNA sequences on target genes (so called hormone response elements, HREs) result-

Characterization of uterine sex steroid receptors in the pig and their variation during the oestrous cycle

The present study establishes and validates an in vitro binding and exchange assay for tissue receptors for oestradiol (E) and progesterone (P) in pig uterus. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptor proteins with high affinity. The relative concentrations of the receptors were measured in dissected samples from endometrium and myometrium obtained at late prooestrus, oestrus, and luteal phases of the oestrous cycle. The Scatchard analysis of the oestradiol and R 5020-receptor complex displayed linearity and indicated a single class of high affinity, low capacity binding sites. Significant variations were seen in the binding of E and P to their cytosolic and nuclear receptors, following the changes in the circulating levels of the hormones in blood plasma during the oestrous cycle. Both tissue components, i.e. endometrium and myometrium followed a similar pattern when related to the stage of the oestrous cycle considered. The ERc increased from prooestrus, reaching a maximum at standing oestrus, thereafter decreasing. The concentrations of ERn increased from prooestrus towards the early luteal phase, with a significant reduction by day 8 of the cycle. The amounts of PRc were maximal at standing oestrus, remaining high during the early luteal phase, while the PRn showed a linear increase from oestrus onwards throughout the luteal phase.

Progesterone and Oestradiol‐17β Receptors in the Porcine Myometrium During the Oestrous Cycle

The concentrations of the tissue receptors for oestradiol (E) and progesterone (P) in the porcine myometrium at different stages of the oestrous cycle have been investigated by in vitro binding and exchange methods. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptors proteins with high affinity. The amount of ERc did not vary significantly throughout the cycle. Significant variations in the amount of myometrial ERn were observed with high concentrations during late pro-oestrus. The amount of PRc reached a top value in early pro-oestrus. A significant increase in PRn levels was observed at early luteal phase, and it remained high during the rest of the luteal phase. The temporal relationships between the variations in levels of oestradiol and progesterone nuclear receptors in myometrial tissue and those of the circulating plasma levels were established. The data obtained in this study suggest a relationship between the changes in levels of oestradiol and progesterone myometrial binding and the uterine motility pattern during the oestrous cycle.

The effect of several sex steroid hormones on the growth rate of three Morris hepatoma tumor lines.

Morris hepatoma 44, whose growth is sensitive to thyroid hormones and prolactin, contains specific receptors for these hormones. In the present experiments, male Buffalo rats bearing Morris hepatoma 7787 were studied to determine the effects of several sex steroid hormones. Castration 1 week postimplantation inhibited tumor growth relative to controls (-53%). Replacement with testosterone propionate (1 mg per day s.c. injection) restored tumor growth to control levels, whereas administration of testosterone (2 mg per day s.c. injection) to castrated controls resulted in significant stimulation. Testosterone administered to control animals at a dose of 1 mg per day stimulated tumor growth (62%), whereas 2 mg per day failed to do so. Progesterone (4-pregnon-3,20-dione) at doses of 125 or 250 micrograms per day (Silastic implants) had no effect on tumor growth, whereas 500 micrograms per day stimulated tumor growth relative to controls. Estrogen (17 beta-estradiol) at doses of 6, 12, or 24 micrograms per day (Silastic implants) did not influence tumor growth. Cytoplasmic testosterone receptors have been demonstrated in tumors (2.2 +/- 0.8 fmoles per mg cytoplasm), although specific cytoplasmic estrogen and progesterone receptors could not be identified in this model. In female rats bearing either Morris hepatoma 44, 7787 or 5123-D, testosterone markedly stimulated tumor growth (226, 328 and 58%, respectively, relative to controls). In conclusion, although Morris hepatoma 7787 appears to be androgen (testosterone) dependent and contains cytoplastic androgen receptors, it lacks specific cytoplasmic receptors for estrogen and progesterone and is not influenced by these hormones except at very high doses of progesterone.

Tamoxifen alone or in combination with estradiol-17β inhibits the growth and malignant transformation of hepatic hyperplastic nodules

Hepatic hyperplastic nodules (HHNs) induced by the ‘resistant hepatocyte method’ of Solt et al. were studied as an experimental prototype of oral contraceptive-related tumors. Cytoplasmic estrogen receptors were present in all HHNs harvested and their concentration was always less than that in normal liver. No specific cytoplasmic progestin receptors could be measured in the above tumor or liver specimens. The long-term administration of estradiol-17β ( 4.8–24.0 μg/day) resulted in the death of all but one of 20 animals prior to termination at 10 months. Tamoxifen ( 0.25–2.5 mg biweekly), which did not lead to excess mortality, decreased HHN grade (proportion of liver slice occupied by HHN) and inhibited malignant transformation. Combination therapy with single-dose estradiol-17β ( 4.8 μg/day) and various doses of tamoxifen ( 0.25–2.5 mg biweekly) in most cases reduced mortality, HHN grade and malignant transformation. Cytoplasmic progestin receptors were absent and estrogen receptors were either undetectable or present in low concentrations in hepatic tumors harvested at the time of termination. Our results indicated that HHNs are hormone-dependent and that malignant transformation can be inhibited by tamoxifen alone or in combination with estradiol-17β.

Tamoxifen alone or in combination with estradiol-17β inhibits the growth and malignant transformation of hepatic hyperplastic nodules

Hepatic hyperplastic nodules (HHNs) induced by the ‘resistant hepatocyte method’ of Solt and Farber were studied as an experimental prototype of oral contraceptive-related tumors. Cytoplasmic estrogen receptors were present in all HHNs harvested and their concentration was always less than that in normal liver. No specific cytoplasmic progestin receptors could be measured in the above tumor or liver specimens. The long-term administration of estradiol-17β (4.8–24.0 μg/day) resulted in the death of all but one of 20 animals prior to termination at 10 months. Tamoxifen (0.25–2.5 mg biweekly) which did not lead to excess mortality, decreased HHN grade (proportion of liver slice occupied by HHN) and inhihited malignant transformation. Combination therapy with single-dose estradiol-17β (4.8 μg/day) and various doses of tamoxifen (0.25–2.5 mg biweekly) in most cases reduced mortality, HHN grade and malignant transformation. Cytoplasmic progestin receptors were absent and estrogen receptors were either undetectable or present in low concentration in hepatic tumors harvested at the time of termination. Our results indicate that HHNs are hormone-dependent and that malignant transformation can be inhibited by tamoxifen alone or in combination with estradiol-17β.