Serum-Soluble E-Cadherin Fragments in Lung Cancer

Aims and background

E-cadherin, also known as uvomorulin or cell-CAM 120/80, is one of the subclasses of cadherins, CA2+-dependent cell adhesion molecules. Several recent studies have suggested that loss of E-cadherin may be associated with tumor progression, such as in lung, gastric, hepatocellular, breast and prostatic carcinoma. Assessment of E-cadherin serum levels in lung cancer showed a relation to histologic type.

Methods and study design

Using an enzyme immunoassay, we determined E-cadherin serum levels in 79 patients affected with lung cancer (stage l–IV), 9 patients with breast cancer, 23 patients with different benign diseases, and 20 healthy patients.

Results

At a specificity level of 90%, E-cadherin diagnostic sensitivity was 66.6%, 47.6% and 43.7% in patients affected with squamous cell carcinoma, small cell carcinoma and adenocarcinoma, respectively.

Conclusions

Preliminary results suggest the use of serum E-cadherin as a prospective tumor marker.

Estrogen and Progesterone Binding Proteins in Human Colorectal Cancer. A Preliminary Characterization of Estradiol Receptor

Estradiol receptor (ER) and progesterone receptor (PgR) were assayed in tumors from 20 patients with primary colorectal cancer. Ten of 20 tumors contained high affinity sites for 17β-estradiol and progesterone. The highest concentration of ER was 56 fmol/mg of protein. The ER dissociation constant ranged from 1.6 × 10−10 M to 8 × 10−10 M (mean 4.6 ± 2.6). The highest concentration of PgR was 42 fmol/mg of protein. The PgR dissociation constant ranged from 3 × 10−9 to 9 × 10−9 M (mean 5.65 ± 2.1). Four out of 20 specimens analyzed were from male patients and all resulted negative for both receptors. Sixty per cent of ER positive tumors were also PgR positive, whereas only 20 % of ER negative were PgR positive. Sucrose gradient centrifugation showed that cytoplasmic ER of colorectal cancer sedimented at 3 S in the absence of protease inhibitors and at 4.5 S in the presence of 1 mM phenylmethylsulphonyl fluoride (PMSF) both in low and in high ionic strength. When chromatographed on Sephadex G-200 almost all ER was quantitatively recovered in the included fractions. Molecular weights of ER eluted from Sephadex G-200 ranged from 90,000 to 50,000 daltons. Elution profile and molecular weight heterogeneity suggest that, in spite of the presence of PMSF, there is a limited proteolysis of ER. Partially purified colorectal cancer ER did not bind to sepharose-heparin. The isoelectric point of ER was 6.4–6.5.

Serum concentration of free T3, free T4 and TSH in healthy children

OBJECTIVE

It is rare that manufacturers report age-related FT3, FT4 and TSH normal ranges in healthy children.

STUDY DESIGN

Using a solid phase time-resolved fluoroimmunometric method, we determined serum FT3, FT4 and TSH in 3,360 healthy children, age 2-16 years, that we grouped into two age ranges (2-7 yr and 9-16 yr).

RESULTS

Boys' and girls' mean serum thyroid hormone values substantially overlap in all age groups. In the age range 2-7 yr, FT3, FT4 and TSH values were 0.10-0.67 ng/dl (mean 0.37 ng/dl), range 0.45-2.29 ng/dl (mean 1.18 ng/dl) and 0.10-5.9 microU/ml (mean 2.2 microU/ml), respectively. In the age range 9-16 yr, FT3, FT4 and TSH values were 0.11-0.53 ng/dl (mean 0.35 ng/dl), 0.69-1.69 ng/dl (mean 1.07 ng/dl) and 0.20-6.1 microU/ml (mean 2.3 pU/ml), respectively.

CONCLUSION

Our results represent a useful set of reference values in children and can help physicians in the management of thyroid diseases.

Serum anti-p53 antibodies in lung cancer: comparison with established tumor markers

As reported earlier, p53 antibodies are detected in the sera of patients with different types of cancer, including lung cancer. In contrast, in the serum of healthy subjects the presence of anti-p53 antibodies is extremely rare. We collected the venous blood samples of 109 patients affected with lung cancer (LC): 57 patients (46 M, 11 F) with non-small-cell carcinoma (NSCLC), 52 others (40 M, 12 F) with small-cell carcinoma (SCLC). Serum p53 antibodies were assayed using ELISA method and all positive sera were confirmed by Western-blot method. In addition, using IRMA methods we assayed serum CEA, TPA, CYFRA21-1 and NSE. Serum p53Ab are detectable (p53Ab-positive) in 35/109 (32.1%) patients with lung cancer. About 17/57 (29.8%) patients affected with NSCLC and 18/52 (34.6%) with SCLC were p53Ab-positive. CEA, TPA, CYFRA21-1 and NSE sensitivity in LC patients (NSCLC+SCLC) is 50.5%, 58.7%, 42.2%, 35.8%, respectively. The lower sensitivity (32.1%) of serum p53Ab is connected with the higher specificity and diagnostic accuracy (100% and 69%, respectively). Out of 35 patients p53Ab-positive, five (14.3%) exhibit only serum p53Ab, while serum values of the established tumor markers were lower than cut-off. Serum p53Ab assessment is a simple and a low-cost assay with a good specificity and diagnostic accuracy that in LC patients can be used at least in association with established tumor markers.

Differentiation of myeloid cell lines correlates with a selective expression of RIZ protein

BACKGROUND

The retinoblastoma-interacting zinc-finger gene RIZ is expressed in two forms (RIZ1 and RIZ2) that differ for the presence near the N-terminus of RIZ1 of a conserved domain, defined PR (PRDI-BF1-RIZ homology), homologous to a similar domain present in other proteins recognized as tumor suppressor gene products. The RIZ1 form is usually absent or expressed at low levels in tumor cells, whereas RIZ2 is frequently expressed. We investigated a possible involvement of RIZ1 in differentiation control using a myeloid cell maturation model that is easily modulated by retinoids and other agents.

MATERIALS AND METHODS

HL60 or NB4 cell lines or patients' leukemic promyelocytes were treated with all- trans -retinoic acid or other agents to induce differentiation. RIZ gene expression was determined with reverse transcriptase polymerase chain reaction (RT-PCR) and RNase protection assay. Immunocytochemistry was performed to assess variation of the intracellular distribution of RIZ protein on all- trans-retinoic acid treatment. Forced expression of RIZ1 protein was obtained with a recombinant adenovirus containing RIZ1 cDNA.

RESULTS

Treatment with retinoic acid induced a selective expression of RIZ1 in HL60 cell line. Retinoic acid effect was maximal at 7 days and correlated to the granulocytic differentiation of cells. A similar effect was obtained in retinoic acid-sensitive NB4 cell line or in patients' leukemic promyelocytes, but not in the retinoic acid-resistant cell line NB4.007/6 or in the U937 cell line. Selective expression of RIZ1 was also induced by 12-O-tetradecanoyl-phorbol-13-acetate in the U937 and HL60 cell lines and by 1,25-dihydroxyvitamin D(3) only in HL60 cells. In HL60 cells, RIZ1 was also induced by activation of a retinoid alpha receptor-independent maturation pathway based on retinoid X receptor agonist and protein kinase A synergism. In addition, retinoic acid produced a redistribution of the antigen within the nucleus in these cells. Forced expression of RIZ1 protein induced growth arrest and death of HL60 cells.

CONCLUSIONS

The correlation between the selective expression of RIZ1 induced by retinoic acid, 12-O-tetradecanoyl-phorbol-13-acetate, or 1,25-dihydroxyvitamin D(3) and differentiation suggested that RIZ protein was involved in myeloid cell differentiation induced by these agents.

Loss of estrogen receptor beta expression in malignant human prostate cells in primary cultures and in prostate cancer tissues

The aim of this study was to investigate the expression of estrogen receptor (ER) beta and alpha genes in normal (N) and malignant (C) primary cultures of human prostate epithelial cells (PEC) and fibroblasts (PFC) and in the prostate tissue donors. Both ERbeta and ERalpha messenger ribonucleic acids were found by RT-PCR analysis in six NPECs and normal prostate tissues and in only one of six CPECs and in the respective cancer tissue donor. The other five CPECs and related cancer tissue donors and all normal and cancer PFCs expressed ERalpha messenger ribonucleic acid alone. Immunoblot analysis, using a polyclonal anti-ERbeta (C-terminal) antibody, demonstrated ERbeta protein in all NPEC lysates and in one of the six CPECS: ERalpha protein was expressed in both NPECs and CPECs when a polyclonal antibody directed against the ERalpha N-terminal domain was used. In contrast, ERalpha protein was not detected in two of the six CPEC lysates when ERalpha C-terminal monoclonal antibodies were used. Using a set of primers designed to amplify the region from exons 6-8, RT-PCR analysis demonstrated the absence of the expected transcript in these cells. The present study shows that the ERbeta gene is expressed together with ERalpha in normal prostates and NPECs, whereas it is barely detectable in prostate cancer and CPECS: Moreover, in some CPECs, the ERalpha gene may be transcribed in a changed protein, resulting from the expression of a deletion variant. Together, these data suggest that prostate malignancy is associated with a potential disorder of ER-mediated pathways.

Gamma1- and gamma2-syntrophins, two novel dystrophin-binding proteins localized in neuronal cells

Dystrophin is the scaffold of a protein complex, disrupted in inherited muscular dystrophies. At the last 3' terminus of the gene, a protein domain is encoded, where syntrophins are tightly bound. These are a family of cytoplasmic peripheral membrane proteins. Three genes have been described encoding one acidic (alpha1) and two basic (beta1 and beta2) proteins of approximately 57-60 kDa. Here, we describe the characterization of two novel putative members of the syntrophin family, named gamma1- and gamma2-syntrophins. The human gamma1-syntrophin gene is composed of 19 exons and encodes a brain-specific protein of 517 amino acids. The human gamma2-syntrophin gene is composed of at least 17 exons, and its transcript is expressed in brain and, to a lesser degree, in other tissues. We mapped the gamma1-syntrophin gene to human chromosome 8q11 and the gamma2-syntrophin gene to chromosome 2p25. Yeast two-hybrid experiments and pull-down studies showed that both proteins can bind the C-terminal region of dystrophin and related proteins. We raised antibodies against these proteins and recognized expression in both rat and human central neurons, coincident with RNA in situ hybridization of adjacent sections. Our present findings suggest a differentiated role of a modified dystrophin-associated complex in the central nervous system.

Estradiol induces functional inactivation of p53 by intracellular redistribution

Estrogen treatment of MCF-7 cells grown in serum-free medium induced a modification of the intracellular distribution of p53 protein. Western blot analysis and immunofluorescence staining showed that p53 was localized in the nucleus of untreated cell and that after 48 h of hormone treatment, it was mostly localized in the cytoplasm. This effect was blocked by the antiestrogen ICI182,780. Intracellular redistribution of p53 was correlated to a reduced expression of the WAF1/CIP1 gene product and to the presence of degradation fragments of p53 in the cytosol. Estradiol treatment prevented the growth inhibition induced by oligonucleotide transfection, simulating DNA damage. This observation indicated that the wild-type p53 gene product present in the MCF-7 cell could be inactivated by estradiol through nuclear exclusion to permit the cyclin-dependent phosphorylation events leading to the G1-S transition. In addition, the estradiol-induced inactivation of p53 could be involved in the tumorigenesis of estrogen-dependent neoplasm.

The retinoblastoma-interacting zinc-finger protein RIZ is a downstream effector of estrogen action

Co-immunoprecipitation experiments in cell extract from cultured cells or target tissues indicated that estrogen receptor was complexed with the retinoblastoma binding protein RIZ in a ligand-dependent manner. Mapping of interaction sites indicated that in both proteins the same regions and motifs responsible for the interaction of transcriptional co-activator and nuclear receptors were involved. In cultured cells, estradiol induced a redistribution of RIZ protein within the nucleus and in the cytoplasm. A similar effect was produced in vivo, in prepuberal rat endometrium, by administration of a physiological dose of estradiol. Therefore, RIZ protein could be a specific effector of estrogen action downstream of the hormone-receptor interaction, presumably involved in proliferation control.

Identification of a DNA binding protein cooperating with estrogen receptor as RIZ (retinoblastoma interacting zinc finger protein)

Double-stranded DNA fragments were selected from a random pool by repeated cycles of estrogen receptor-specific immunoprecipitation in the presence of a nuclear extract and PCR amplification (cyclic amplification and selection of target, CAST, for multiple elements). Fragments were cloned and sequence analysis indicated the 5-nucleotide word TTGGC was the most recurrent sequence unrelated to the known estrogen responsive element. Screening a HeLa cell expression library with a probe designed with multiple repeats of this sequence resulted in the identification of a 1700-aa protein showing a complete homology with the product of the human retinoblastoma-interacting zinc-finger gene RIZ. In transfection experiments, RIZ protein was able to bestow estrogen inducibility to a promoter containing an incomplete estrogen responsive element and a TTGGC motif. RIZ protein present in MCF-7 cell nuclear extract retarded the TTGGC-containing probe in an EMSA. Estrogen receptor was co-immunoprecipitated from MCF-7 cell extract by antibodies to RIZ protein and vice versa, thus indicating an existing interaction between these two proteins.

Interaction of vault particles with estrogen receptor in the MCF-7 breast cancer cell

A 104-kD protein was coimmunoprecipitated with the estrogen receptor from the flowtrough of a phosphocellulose chromatography of MCF-7 cell nuclear extract. mAbs to this protein identified several cDNA clones coding for the human 104-kD major vault protein. Vaults are large ribonucleoprotein particles of unknown function present in all eukaryotic cells. They have a complex morphology, including several small molecules of RNA, but a single protein species, the major vault protein, accounts for >70% of their mass. Their shape is reminiscent of the nucleopore central plug, but no proteins of known function have been described to interact with them. Western blot analysis of vaults purified on sucrose gradient showed the presence of estrogen receptor co-migrating with the vault peak. The AER317 antibody to estrogen receptor coimmunoprecipitated the major vault protein and the vault RNA also in the 20,000 g supernatant fraction. Reconstitution experiments of estrogen receptor fragments with the major vault protein mapped the site of the interaction between amino acids 241 and 280 of human estrogen receptor, where the nuclear localization signal sequences are located. Estradiol treatment of cells increased the amount of major vault protein present in the nuclear extract and coimmunoprecipitated with estrogen receptor, whereas the anti-estrogen ICI182,780 had no effect. The hormone-dependent interaction of vaults with estrogen receptor was reproducible in vitro and was prevented by sodium molybdate. Antibodies to progesterone and glucocorticoid receptors were able to coimmunoprecipitate the major vault protein. The association of nuclear receptors with vaults could be related to their intracellular traffic.

Identification of the Syrian hamster cardiomyopathy gene

The BIO14.6 hamster is a widely used model for autosomal recessive cardiomyopathy. These animals die prematurely from progressive myocardial necrosis and heart failure. The primary genetic defect leading to the cardiomyopathy is still unknown. Recently, a genetic linkage map localized the cardiomyopathy locus on hamster chromosome 9qa2.1-b1, excluding several candidate genes. We now demonstrate that the cardiomyopathy results from a mutation in the delta-sarcoglycan gene that maps to the disease locus. This mutation was completely coincident with the disease in backcross and F2 pedigrees. This constitutes the first animal model identified for human sarcoglycan disorders.

Prostaglandin E2 induction of binding activity to CRE and AP-2 elements in human T lymphocytes

Prostaglandins of the E series are immunomodulatory agents which exert inhibitory as well as stimulatory effects on a variety of immune responses. Since it is known that PGE2 is able to increase cAMP levels, we investigated whether it can affect gene expression through the activation of the transcription factors which bind enhancer elements in the promoter regions of cAMP-regulated genes. Using electrophoretic mobility shift assay, we demonstrated that a short treatment of human T lymphocytes with PGE2 induces specific binding activity to CRE and AP-2, but not AP-1, DNA elements. Since the okadaic acid, a potent protein phosphatase inhibitor, prolongs the induction of the binding activity, phosphorylation events are likely to occur. This activity seems to be due to increased cAMP levels because forskolin and IBMX mimic the effects of PGE2. More interestingly, transfection experiments with CRE-CAT plasmide show that PGE2 activates the transcription of a CRE-containing promoter. These data support the positive role for PGE2 on some immune functions.

Identification of a novel sarcoglycan gene at 5q33 encoding a sarcolemmal 35 kDa glycoprotein

Mutations in any of the genes encoding the alpha, beta or gamma-sarcoglycan components of dystrophin-associated glycoproteins result in both sporadic and familial cases of either limb-girdle muscular dystrophy or severe childhood autosomal recessive muscular dystrophy. The collective name 'sarcoglycanopathies' has been proposed for these forms. We report the identification of a fourth member of the human sarcoglycan family. We named this novel cDNA delta-sarcoglycan. Its mRNA expression is abundant in striated and smooth muscles, with a main 8 kb transcript, encoding a predicted basic transmembrane glycoprotein of 290 amino acids. Antibodies specifically raised against this protein recognized a single band at 35 kDa on western blots of human and mouse muscle. Immunohistochemical staining revealed a unique sarcolemmal localization. FISH, radiation hybrid and YAC mapping concordantly linked the delta-sarcoglycan gene to 5q33, close to D5S487 and D5S1439. The gene spans at least 100 kb and is composed of eight exons. The identification of a novel sarcoglycan component modifies the current model of the dystrophin-glycoprotein complex.

A novel p53 mutant in human breast cancer revealed by multiple SSCP analysis

DNA from tumor tissue and peripheral blood lymphocytes of primary breast cancer patients was screened for the presence of p53 mutations. In DNA from one tumor we found that the histidine codon 193 (CAT) was somatically converted to arginine (CGT). This amino acid residue is highly conserved in many species, thus suggesting that such mutation plays an important role in the loss of wt-p53 function.

Characterization and epitope mapping of a new panel of monoclonal antibodies to estradiol receptor

A new panel of monoclonal antibodies to the calf uterus estrogen receptor was prepared. Thirteen antibodies were characterized for their isotype and for the affinity for the antigen. These antibodies recognize the human receptor and can be used in Western blot analysis. The location of the epitopes was mapped on the antigen structure using synthetic fragments of estrogen receptor, and it was possible to group the antibodies in five groups. Many antibodies were useful for the purification of estrogen receptor from tissue extracts by immunoaffinity chromatography. The reciprocal inhibition of the antibodies for the antigen binding was measured with an immunoadsorption assay. This was maximal and symmetrical for antibody pairs within the same group, but was incomplete and, in some instances, asymmetrical between pairs of antibodies from different groups. One antibody was able to inhibit the estrogen receptor-DNA interaction, whereas two others were unable to recognize the receptor-DNA complexes. This new panel of antibodies is a useful addition to the existing tools for studying structure and function of the estrogen receptor.

Detection of a nonsense mutation in the dystrophin gene by multiple SSCP

A combination of multiplex PCR with the single strand conformation polymorphism (SSCP) technique was employed to screen for point mutations in the human dystrophin gene. Co-amplification of 11 exons from genomic DNA of Duchenne and Becker muscular dystrophy (DMD/BMD) patients with no deletion or duplication was performed and the samples subjected to multiple SSCP analysis. We report the case of a nonsense mutation in a Duchenne patient identified by this approach. The mutation introduces a termination codon within exon 8 of the dystrophin gene. It is predicted to cause a very premature translational termination accounting for the severe phenotype observed. The patient inherited this mutation from his mother. In addition the analysis revealed 5 polymorphisms useful for internal control.

Purified estrogen receptor enhances in vitro transcription

An in vitro transcription system was developed to investigate the mechanisms of gene regulation by the estrogen receptor (ER). ER purified from calf uterus was highly active in enhancing RNA transcription from a template DNA containing estrogen response elements (EREs) upstream from a minimal promoter. Under the conditions employed, no addition of tissue specific factors was required and both estrogen or antiestrogens were ineffective. The stimulation of transcription correlated with the copy number of EREs in the template. The addition of competitor ERE oligonucleotides specifically inhibited the ER-induced transcription. We suggest that the ER may be involved in the formation of the stable initiation complex.

Proteolytic activity of the purified hormone-binding subunit in the estrogen receptor

The hormone-binding subunit of the calf uterus estradiol receptor was purified as a hormone-free molecule. Immunoaffinity chromatography with a specific monoclonal antibody was used as the final step. The purified subunit was specifically labeled by radioactive diisopropyl fluorophosphate. The diisopropyl fluorophosphate-labeled amino acid was serine. The purified receptor was able to release the fluorogenic or chromogenic group from synthetic peptides containing phenylalanine at the carboxyl terminus. This occurred only in the presence of estradiol and was hampered by aprotinin and diisopropyl fluorophosphate. Estradiol-dependent hydrolytic activity was also found in the eluate from gel slices after SDS/PAGE of purified receptor. This activity comigrated with the renaturable estradiol-binding activity. The estradiol antagonists 4-hydroxytamoxifen and ICI 164,384 as well as other steroid hormones were unable to activate this hydrolytic activity.

In vitro binding of the purified hormone-binding subunit of the estrogen receptor to oligonucleotides containing natural or modified sequences of an estrogen-responsive element

Estrogen receptor (ER) was purified from calf uterus by immunoaffinity chromatography in the absence of the ligand. The purified ER consists of a mixture of monomer and homodimer forms of 67-kDa hormone-binding subunit (no 90-kDa heat shock protein is present). The purified ER was incubated with a 32P-labeled 61-basepair oligonucleotide containing the sequence of the estrogen response element (ERE) of the Xenopus laevis A2 vitellogenin gene. DNA mobility shift assays showed formation of specific complexes of the ERE containing oligonucleotide with ER, formation which did not require and was not affected by estradiol or antiestrogenic molecules. Both the monomer and the dimer were equally able to interact with the ERE-containing oligonucleotide. Sucrose gradient experiments showed that only the ER monomer is able to interact with an oligonucleotide in which a single mutation destroyed the dyad symmetry of ERE. Multiple symmetric mutations which did not alter the dyad symmetry of ERE nevertheless totally destroyed the ability of the oligonucleotide to form complexes with either the monomeric or dimeric form of ER. These results suggest that ER is able to bind to ERE independently of the presence of estradiol or other proteins and, therefore, that estradiol does not act by modulating the ability of ER to bind to ERE on DNA.

An aprotinin binding site localized in the hormone binding domain of the estrogen receptor from calf uterus

It has been proposed that the estrogen receptor bears proteolytic activity responsible for its own transformation. This activity was inhibited by aprotinin. Incubation of transformed ER with aprotinin modified the proteolytic digestion of the hormone binding subunit by proteinase K. The smallest hormone-binding fragment of the ER, obtained by tryptic digestion, was still able to bind to aprotinin. These results suggest that aprotinin interacts with ER and the hormone-binding domain of ER is endowed with a specific aprotinin-binding site.

Aprotinin inhibits the hormone binding of the estrogen receptor from calf uterus

Micromolar concentrations of the proteinase inhibitor, aprotinin, produced a dose-dependent inhibition in the binding capacity of the estrogen receptor from calf uterus. Aprotinin inhibition was greater at 28 degrees C than at 4 degrees C and only occurred when conditions allowed the receptor transformation. When aprotinin was tested in the presence of transformation inhibitors, its effect was no longer seen. The binding capacity of the highly purified estrogen-binding subunit was similarly inhibited.

Metal binding sites of the estradiol receptor from calf uterus and their possible role in the regulation of receptor function

The existence of putative metal binding sites on the estradiol receptor (ER) molecule from calf uterus was evaluated by immobilizing various divalent metals to iminodiacetate-Sepharose. ER from both crude and highly purified preparations binds to metal-containing adsorbents complexed with Zn(II), Ni(II), Co(II), and Cu(II), but not to those complexed with Fe(II) and Cd(II). Elution of ER was obtained by chelating agents or by imidazole, thus indicating that histidine residues on the ER molecule are involved in the interaction with the metal. Analysis of affinity-labeled ER by [3H]tamoxifen aziridine after elution from a column of Zn(II)-charged iminodiacetate-Sepharose showed that ER fragments obtained by extensive trypsinization were also bound. Zn(II) and the same other metals able to bind ER, when immobilized on resins, inhibit the binding of estradiol to the receptor at micromolar concentrations. This inhibition is noncompetitive and can be reversed by EDTA. The inhibition of the hormone binding was still present after trypsin treatment of the cytosol, and it was abolished by preincubation with the hormone. Micromolar concentrations of these metals were able to block those chemical-physical changes occurring during the process of ER transformation in vitro. Furthermore, if added to pretransformed ER-hormone complex, they strongly inhibited the binding of the complex to isolated nuclei. The presence of metal binding sites that modulate the ER activity in the hormone binding domain of ER is therefore speculated. Since progesterone receptor showed the same pattern of binding and elution from metal-containing adsorbents, the presence of metal binding regulatory sites could be a property of all steroid receptors.

Estradiol receptor has proteolytic activity that is responsible for its own transformation

We have investigated the effect of various protease inhibitors and substrates on the hormone- and temperature-dependent binding of partially purified estradiol-receptor complex to isolated nuclei. Only serine protease substrates and inhibitors significantly depressed estradiol receptor transformation. At 20 degrees C, we observed 50% inhibition with about 3 microM aprotinin or with 1.4 mM diisopropyl fluorophosphate. Aprotinin also blocked those size and charge modifications of receptor that are characteristic of the transformation process. The estradiol receptor was able to bind to aprotinin-agarose only under transforming conditions; i.e., the interaction was hormone- and temperature-dependent and inhibited by molybdate. Diisopropyl fluorophosphate, a covalent reagent for serine esterases, competitively inhibited the binding and specifically eluted the estradiol-receptor complex that had been bound to aprotinin-agarose. These results indicate that estradiol receptor transformation is due to the effect of a serine protease and that the receptor itself is endowed with this catalytic activity, which is triggered by the steroid.

Interaction between estrogen receptor and subcellular structures of target cells: nuclear localization of unoccupied receptor and its modification induced by estradiol

Experimental conditions affecting the partitioning of the estrogen receptor were studied. Homogenization of rat uteri at 25 degrees C resulted in a particulate partitioning of the estrogen receptor. The use of frozen tissue (-70 degrees C) or pre-exposure of the tissue to 0 degrees C prior to 25 degrees C homogenization, homogenization at 0 degrees C and tissue dilution all induced soluble partitioning of the receptor. The estrogen receptor found in the particulate fraction was mostly associated with the nuclei, even in the absence of hormone. The interaction between estradiol and the estrogen receptor induced modification in the receptor's charge and size that promoted its cold-insensitive association with the nuclei of target cells. These modifications were studied in a cell-free in vitro system and were reversibly blocked by molybdate. Similar changes occurred in vivo when estradiol interacted with the receptor in the nuclei of target cells.

Particulate nature of the unoccupied uterine estrogen receptor

Homogenization of rat uteri at 25 degrees C resulted in a particulate partitioning of the estrogen receptor. Homogenization at 0 degrees C, the use of frozen tissue, or the pre-exposure of the tissue to 0 degrees C prior to 25 degrees C homogenization induced soluble partitioning of the estrogen receptor. Binding of a radiolabeled monoclonal antibody indicated that, in absence of estradiol, the estrogen receptor is particulate and is associated with the nuclei-enriched fraction of the target cell. The presence of receptor in the soluble fraction thus appears to be an artifact of homogenization. The unoccupied receptor, loosely associated with the particulate fraction (cold-sensitive) represents the "native" form of receptor which, upon arrival of the hormone, becomes tightly associated (cold-insensitive). The transition from the cold-sensitive to the cold-insensitive status is accompanied by a modification of the electrical charge of the receptor.

Interaction of rat liver glucocorticoid receptor with heparin

When rat liver cytosol containing [3H]dexamethasone-glucocorticoid receptor complex is exposed to immobilized heparin (Sepharose-heparin; Seph-hep) the steroid receptor complex binds to the substituted Sepharose avidly [Kd = 3.5 (+/- 1.7) X 10(-10) M], and 80-90% of the receptor present is adsorbed to the solid phase after 40 min at 0 degree C. The binding is enhanced by Mn2+ (10 mM) and Mg2+, whereas Ca2+ and Sr2+ are ineffective. Sodium molybdate (10 mM) does not influence the reaction but enhances receptor stability. Moreover, binding of the receptor to Seph-hep is dependent on the ionic strength of the medium, because binding is totally reversed by 300 mM KCl. The bound [3H]dexamethasone-receptor complex can be recovered from Seph-hep with solutions (4 mg/mL) of heparin (95% release), dextran sulfate (88%), and chondroitin sulfate (63%); total calf liver RNA is less effective (9%), whereas dextran, D-glucosamine, N-acetyl-D-glucosamine, D-glucuronic acid, and sheared calf thymus DNA are totally ineffective (less than 3%). Both "native" and temperature "transformed" forms of the glucocorticoid receptor interact with immobilized heparin. These results strongly suggest that the receptor site that binds heparin is distinct from that binding DNA. An immediate application of this newly found ability of the glucocorticoid receptor to interact with heparin is the use of Seph-hep for affinity chromatography purification of the glucocorticoid receptor. A purification of 10-fold, with a recovery of 55-65%, can be achieved by using either 4 mg/mL heparin or 300 mM KCl to elute [3H]dexamethasone-receptor bound to the resin.

Estradiol and progesterone receptors in malignant gastrointestinal tumors

Estradiol and progesterone receptors were assayed in tumors from 79 patients with primary colorectal and 56 patients with stomach adenocarcinomas. Eighteen of 79 colorectal cancers contained estradiol receptor, while 34 specimens were positive for progesterone receptor. In stomach cancer, the positive samples were 8 for estradiol and 14 for progesterone receptors. In both types of tumors, the Kd was in the range of 10(-10) M for estradiol and 10(-9) M for progesterone receptor, respectively. In colorectal adenocarcinomas, the presence of progesterone receptor seems to be partially correlated to the presence of estradiol receptor while, in stomach tumors, this correlation is lost. The positivity of at least one receptor in colorectal cancers is higher in the female sex. The contrary occurs for stomach cancer. Sucrose gradient centrifugation showed that cytoplasmic estradiol receptor of stomach cancer sedimented at 8S or 4 to 5S at low ionic strength. The isoelectric point of stomach cancer estradiol receptor is 6.5.

Effect of sodium molybdate on cytosolic estrogen receptor

Estrogen binding activity of crude calf uterus cytosol is rapidly destroyed in heating. The time course of inactivation at 37 degrees C shows a biphasic pattern; sodium molybdate (5-10 mM) completely blocks one of the components in the estradiol-free cytosol, while it has little effect on cytosolic receptor complexed with estradiol. Partially purified native 8S receptor loses its heat sensitivity, and, as a consequence, the molybdate effect disappears. By sucrose gradient analysis of crude cytosol it is evident that molybdate does not affect the sedimentation properties of the estradiol receptor at low temperature. However, at increasing temperatures, molybdate prevents the disappearance of the receptor peak in the crude cytosol or the formation of large, KCl-resistant, aggregates in the presence of estradiol. The partially purified native 8S receptor does not aggregate on heating; addition to it of receptor-depleted cytosol results in the recovery of heat inactivation and aggregate formation, and this is prevented by molybdate. Molybdate has no protective effect on any other inactivating agent which does not act through aggregation of receptors. A crude cytosolic preparation of the receptor which is unable to form heat-dependent aggregates does not display the fast heat inactivating component.

Assay of total estradiol receptor in tissue homogenate and tissue fractions by exchange with sodium thiocyanate at low temperature

After injection of radioactive estradiol to ovariectomized rats, the [3H]estradiol--receptor complex transferred to the nuclei can be solubilized by low concentrations of NaSCN. The extraction by NaSCN is significantly more efficient than that obtained by KCl and is, in fact, complete; i.e., no radioactivity can be found in the nuclei after extraction. Since NaSCN also induces the exchange of receptor-bound estradiol with free hormone [Sica, V., Puca, G. A., Molinari, A. M., Buonaguro, F. M., & Bresciani, F. (1980) Biochemistry 19, 83], a simple assay method has been set up which measures receptor in tissue and tissue fractions, including nuclei and whole homogenate, at 0--4 degrees C, irrespective of whether the receptor is or is not interacting with endogenous hormone. The procedure consists of a simple incubation step at 0--4 degrees C overnight (16 h) of the nuclear fraction, cytosol, and a total homogenate in the presence of excess radioactive estradiol and 0.5 M NaSCN. This method is very easy to carry out, accurate, and precise and avoids the loss of binding sites which results from the heating procedures utilized in other methods. The ability to measure the binding in both the soluble and the particulate fractions of rat uterus permits the determination of the rate of the cytoplasmic to nuclear transfer of estrogen after injection of various hormone concentrations. No nuclear transfer was observed after administration of other nonestrogen hormones such as progesterone, testosterone, or hydrocortisone while a nonsteroid antiestrogen, tamoxifen, was able to translocate the receptor. It was found that 2 h after injection of estradiol into ovariectomized rats total receptor content of uterus shows a decrease which is proportional to the amount of hormone injected. After injection of a hyperphysiological dose of 17 beta-estradiol, a certain amount of the receptor--hormone complex remains in the cytosol for at least 4 h. The nuclear turnover of estradiol receptor related to the progesterone receptor induction has been studied. Actinomycin D and cycloheximide prevent nuclear processing.

Effect of chemical perturbation with NaSCN on receptor-estradiol interaction. A new exchange assay at low temperature

When 0.5 M sodium thiocyanate is added to uterine cytosol previously labeled with excess [3H]-17 beta-estradiol, no change can be detected in the steady-state cytosol concentration of [3H]estradiol-receptor complex for at least 20 h at 4 degrees C. However, the rate of exchange of bound estradiol in the presence of NaSCN was found to be substantially higher than that in the absence of the chaotropic salt. In the presence of NaSCN, the dissociation rate of the complex increases about 10-fold (K-1 SCN = 1.10 x 10(-2) min-1 vs. K-1 = 1.07 X 10 (-3)min-1) while the rate of association increases about 2-fold (K1 SCN = 1.2 X 10(7) min-1M-1 vs.K1= 7.4 X 10(6) min-1 M-1). The Kd changes 6.4-fold (Kd SCN = 9 X 10(-10) M vs. Kd = 1.4 x 10(-10 M) with no decrease in the number of binding sites as shown by Scatchard plots of saturation experiments. This effect of NaSCN can be exploited to assay preformed estrogen-receptor complex by exchange with [3H]estradiol at low temperature. When the sample containing preformed complex is incubated overnight (16 h) at 4 degrees C with excess [3H]estradiol in the presence of 0.5 M NaSCN, there is a quantitative exchange of nonlabeled for estradiol without loss of binding sites. Hormonal steroids other than estrogens do not interfere, and the exchange estradiol is bound with high affinity. Precision, accuracy, and linearity of the method are highly satisfactory.

Estradiol receptor of calf uterus: interactions with heparin-agarose and purification

Heparin attached covalently to agarose beads binds the "native" form of the estradiol receptor with very high affinity. Chondroitin sulfate does not bind to the receptor. When the receptor is complexed with hormone, the affinity is at least 10 times higher. Only the "native" and not the "nuclear" or the "derived" (i.e., after activation by a calcium-dependent enzyme) forms of the estradiol receptor interact with heparin. The "native" estradiol-receptor complex is purified to homogeneity after chromatography on columns of heparin-agarose, Sephadex G-200, and DEAE-cellulose, followed by two more Sephadex G-200 columns. The purified molecule is a single polypeptide of molecular weight 69,000 by polyacrylamide gel electrophoresis in sodium dodecyl sulphate. The sedimentation coefficient on sucrose gradients is 4.3 S, the Stokes radius from gel filtration is 36.5 A, and the isoelectric point is 6.4. The purified [3H]estradiol-receptor complex exchanges the radioactive hormone with estradiol or other estrogenic steroids, but not with testosterone, 5alpha-dihydrotestosterone, or progesterone.

Estrogen binding proteins of calf uterus. Molecular and functional characterization of the receptor transforming factor: A Ca2+-activated protease

It was previously shown that calf uterus cytosol contains a Ca2+-activated receptor transforming factor (RTF) which irreversibly converts the larger molecular states of estrogen receptor (5.3 to 8.6 S, depending on ionic strength) into a smaller, salt-stable form (4.5 S, independent of ionic strength). We now describe a method for rapid and reliable separation of precursor and RTF-transformed receptor forms, which takes advantage of a difference in isoelectric point between the two: the more acidic precursor (isoelectric point, 6.2) is still retained by DEAE-cellulose under conditions (0.12 M KCl, pH 8.3) which produce release from cellulose of the less acidic transformed form (isoelectric point, 6.6 to 6.8). Based on this method of separation, RTF activity can be assayed easily and we could thus progress in the purification and physical and functional characterization of this factor, RTF has been purified about 100-fold. Molecular properties, as assayed by methods suited to partially purified preparations, are as follows: sedimentation coefficient, 6.4 S; Stokes radius, 45 A; molecular weight, 115,000; isoelectric point, 4.9. The Michaelis constant, expressed as moles/liter of estradiol binding sites, is 1.25 X 10(8), at pH 7.5 and 4 degrees, pH 8.5 is optimum for activity. RTF attacks native casein (Km, 1.25 X 10(-5) mol/liter at pH 7.5 and 22 degrees) but not hemoglobin, ovalbumin, or albumin. N-Benzoylarginine methyl ester is a competitive inhibitor of RTF-induced receptor transformation, while L-leucylglycylglycine and N-benzoyltyrosinamide are not. RTF activity is protected by -SH compounds. RTF activity is Ca2+-dependent. Ca2+ starts an activation-inactivation cycle of RTF, with permanent loss of transforming activity which proceeds at a particularly fast rate in the absence of substrate. Mg2+ is inactive, while Sr2+ and Mn2+ may in part substitute for Ca2+. RTF is present in both endometrium and myometrium. RTF is not a lysosomal hydrolase, as shown by its alkaline pH optimum (8.5) and exclusive location in cytosol, nor is it trypsin or a protease of the trypsin group. Also, it is distinct from known proteases of human uterus. The functional significance of this Ca2+-activated protease of cytosol with alkaline pH optimum and high affinity for the larger native form of receptor is still unknown.

Guanylate cyclase. Existence of different forms and their regulation by nucleotides in calf uterus

The activity of calf uterus guanylate cyclase (EC 4.6.1.2) exists in at least two and most probably three distinct forms. The cytosolic enzyme exhibits hyperbolic substrate curves with respect to GTP and Mn2+, while the particulate cyclases (nuclear and microsomal)display sigmoidal (GTP) and hyperbolic (Mn2+) relationships. The Hill coefficient for the GTP dependence is 0.9 for the cytosolic, 1.5 for the nuclear, and 1.4 for the microsomal enzyme. The cytosolic enzyme has a Km for GTP of 70 muM while half maximal velocity occurs at 90 and 100 muM GTP for the nuclear and microsomal enzymes, respectively. The Ka for Mn2+ is 0.57, 0.71 or 0.75 mM for the cytosolic, nuclear, or microsomal enzyme, respectively.

Estrogen binding proteins of calf uterus. Inhibition of aggregation and dissociation of receptor by chemical perturbation with NaSCN

Sodium thiocyanate up to 0.5 M is compatible with a stable estradiol-t-receptor complex during sucrose gradient centrifugation; however, the maximum permissible concentration in 0.1 M during Sephadex G-100 and G-200 chromatography. When NaSCN 0.1 M is added to low-salt cytosol (approximately 7 mg of protein/ml); (1) age-dependent aggregation of receptor is inhibited; (2) peaks of estrogen-binding activity in sucrose gradients and on Sephadex chromatography are sharp; (3) instead of the usual larger molecular states ("8S") found in low salt, most of estrogen receptor is under the following form: 4.1S; Stokes radius, 36 A; mol wt 61 000; flfo, 1.25; homogeneous at electrofocusing, with isoelectric point at 6.0. When cytosol containing NaSCN 0.1 M is diluted down to 2-3 mg of protein/ml or, only for sucrose gradients, NaSCN concentration is increased to 0.4-0.5 M, the 61000 dalton species decreases, being substituted, without loss of bound estradiol-t, by the following estrogen-binding entity: 28S; Stokes radius, 28 A; mol wt 32 000; flfo, 1.44. In the presence of NaSCN, KCl up to 0.4 M does not affect in a significant manner the molecular properties of the above forms. When NaSCN is dialyzed out, most receptor reverts to a 8-9S state. When cytosol is preincubated with Ca2+ (4 mM) and KCl (0.4 M) before addition of NaSCN, the above picture is modified only in the following aspects: (1) Sephadex chromatography peaks are broader and slightly but reproducibly shifted toward higher elution volumes; (2) the electrofocusing pattern consists of a two-peak heterogeneous band shifted toward higher pH (isoelectric points 6.4 and 6.6); (3) upon dialysis of NaSCN there is little or no reversion to faster sedimenting states. These modifications appear to depend on limited proteolytic attack of receptor by Ca2+ -activated receptor transforming factor (RTF), not on binding of Ca2+ to receptor. Present data suggest that the 4.1S entity is a dimer resulting from side-by-side pairing of 2.8S subunits. Molecular dimension of larger receptor forms purified from cytosol are consistent with the hypothesis that under native conditions in vivo dimers are coupled end-by-end into tetrameric structures with two stronger (between subunits) and two weaker (between dimers) bonding regions, and that tetramers may further self-associate. While NaSCN reversibly releases native dimers and subunits by direct impairment of intersubunit bonds, Ca2+ activated RTF irreversibly and specifically releases slightly modified, about 60000 mol wt dimers, by preferential proteolytic attack of the weaker bonding regions and indirect destruction of involved bonds. In vivo, this effect of RTF may be instrumental in mobilization and nuclear penetration of receptor-estradiol complex. Heteroassociation of receptor with other proteins of cytosol is not excluded by the above hypothesis.

Interaction of the estradiol receptor from calf uterus with its nuclear acceptor sites

The specific interaction between 17 beta-estradiol-receptor complex and nuclear acceptors was analyzed by immobilizing various nuclear proteins to CNBr-activated agarose. The specific, high affinity sites identified in a fraction of basic proteins that can be solubilized from purified nuclei of calf uterus (Puca, G.A., Sica, V., and Nola. E (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 979-983) were chromatographed on Sephadex G-100 columns. Elution of the acceptor activity depends on the pH and ionic strength of the buffer used. With 5 mM HCl, however, a peak of acceptor activity with a molecular weight of about 70,000 was partially dissociated from the other basic nuclear proteins. The high affinity binding of the receptor to the acceptor proteins was estradiol-, but not progesterone-, cortisone-, or testosterone-dependent; it was very sensitive to ionic strength and showed a physiological pH optimum. Low affinity binding, such as that seen between receptor and histone, showed no estradiol dependence and little ionic strength and pH sensitivity. Native or heat-denatured DNA strongly modified the receptor-acceptor interaction, reducing the number of binding sites of acceptor for the receptor without changing the high affinity of the interaction. Heating of the acceptor protein before its covalent linkage to agarose considerably increased the affinity of the resulting agarose derivative. Free sulfhydryl groups of the receptor but not of the acceptor molecule play an important role in the acceptor-receptor interaction. When receptor and acceptor preparations were incubated in solution, the resulting complex was included on a Sephadex G-100 column and it eluted from DEAE-cellulose columns at lower ionic strength than the receptor alone. Even though not absolutely specific, these two properties allowed determination of the molecular weight (85,000) of the acceptor protein at neutral pH and more nearly physiological ionic strength. The apparent KD of the acceptor-receptor interaction was determined to be 2 x 10(-10) M at O degrees. Apparently similar, high affinity binding sites for estradiol receptors are also present in nuclei of other tissues.

Identification of a high affinity nuclear acceptor site for estrogen receptor of calf uterus

By means of affinity chromatography, specific nuclear acceptor sites for estradiol receptors are identified in a fraction that can be solubilized from purified nuclei with 2 M NaCl. Interaction between these acceptor sites and crude or partially purified estradiol receptor shows a high association constant (over 10(9) M). Receptor-acceptor interaction is dependent on physiological concentrations of 17beta-estradiol; it is disrupted by high ionic strength. The nuclear acceptor sites appear to be protein in nature and exist in 5- to 10-fold excess over the estrogen binding sites present in the cytosol. Single- or double-stranded DNA does not bind estrogen-receptor complexes. Acceptor sites appear to be associated with basic nuclear proteins as judged by hydroxyapatite chromatography. The nuclear acceptor sites probably represent less than 0.1% of the purified basic proteins from the nucleus.