Specific binding of 3H-estradiol to the cytosol of rat pancreas and uterus: bound sites in pancreatic extracts do not translocate 3H-estradiol to nuclei suggesting a basic difference in mode of action

Classical oestrogen receptor is not detectable in pancreatic adenocarcinoma

Recent reports have suggested the presence of oestrogen receptors (ER) in pancreatic carcinoma. Therefore the tumour may be sensitive to hormone manipulation therapy. We examined 23 biopsies of human pancreatic carcinoma tissue for the presence of ER. The tissue was assayed by two methods: Iso-electric focusing (IEF) and ER-ICA an immunocytochemical assay. All biopsies were tested with ER-ICA and ten by IEF. Each biopsy was assessed histologically for tumour content and 20 contained adenocarcinoma. None of the samples of pancreatic carcinoma were positive for ER using the ER-ICA, and none demonstrated the binding peak typical of ER in the IEF assay. These results suggest that in pancreatic carcinoma oestrogen receptor is either absent (or at very low levels), or of a different type to that found in breast and uterine tissue. On theoretical grounds at least, this must raise questions as to the oestrogen sensitivity of pancreatic cancer.

Site-specific antibodies to the DNA-binding domain of estrogen receptor distinguish this protein from the 3H-estradiol-binding protein in pancreas

The estradiol-binding protein (EBP) in extracts of rat and rabbit pancreata was characterized by sucrose density gradient analysis, immunoaffinity adsorption and Western blot (immunoblot) analysis using polyclonal antibodies raised against EBP. Rat pancreatic extracts labeled with 3H-estradiol contained a readily resolvable peak of steroid-binding activity that sedimented as a 4S complex on sucrose density gradients in the presence or absence of 0.4 M KCl. Estrogen receptor (ER) from calf uterine cytosols sedimented as a 4S complex on gradients containing 0.4 M KCl and as an 8S entity on gradients without KCl. Incubation of cytosol fractions from rat pancreas and calf uterus with benzoyl-DL-arginyl-p-nitroanilide (BAN) increased specific binding of 3H-estradiol to EBP but not to ER. Furthermore, two distinct site-specific antibodies to the DNA-binding domain of ER caused a marked increase in sedimentation rate of 3H-estradiol-labeled ER while normal rabbit serum and antibodies against EBP were ineffective in this regard. These data suggest that a significant portion, if not all, of the DNA-binding domain of ER is absent from EBP. Examination of the amino acid sequence of the DNA-binding domain of ER revealed a region of 10 amino acids that is significantly homologous to somatostatin, a tetradecapeptide that is a co-ligand in the binding of 3H-estradiol to EBP. Based on this observation, a possible mode of action of EBP in pancreatic acinar cells is proposed.

Specific binding of cholecystokinin, estradiol and somatostatin to human pancreatic cancer xenografts

We recently reported that human pancreatic cancers differentially respond to the growth inhibitory effects of an estradiol (E2) receptor antagonist, tamoxifen, and a long-acting analogue of somatostatin, Sandostatin. In the present study two human pancreatic cancers, established as xenografts in nude mice, were examined as representative of cancers that respond to either tamoxifen (PGER) or Sandostatin (SKI), for the presence of binding sites for various hormones. Male nude mice were inoculated with either SKI or PGER, by passage of tumor chunks (3 mm2) to the interscapular region. Tumors, obtained from mice after approximately 30 days of in vivo growth, were analyzed for binding to cholecystokinin-octapeptide (CCK), somatostatin and E2, by published procedures, using either crude tumor membranes (CCK), cytosol and nuclear fractions (E2), or cryostat sections of whole tumors (somatostatin). SKI was highly positive for high-affinity (Kd = approximately 1 nM) CCK binding sites at the time of resection with a binding capacity of approximately 1000 fmol/mg protein. With increasing passages, the total number of high-affinity binding sites for CCK, were reduced to non-detectable levels in SKI tumors, while non-saturable binding (Kd = greater than 10 nM) became increasingly evident. Early passages of PGER tumors were similarly positive for high-affinity binding sites for CCK, that steeply declined with increasing passages. Specific binding sites for E2, were observed only in the cytosolic fractions of PGER, with a high binding affinity (Kd = approximately 0.05 nM) and a low binding capacity (15 +/- 3 fmol/mg cytosolic proteins), at all passages examined; E2 binding sites were not detected in cytosolic and nuclear fractions of SKI and in the nuclei of PGER, at all passages. SKI and PGER at different passages were examined for somatostatin binding, and both the early and late passages of PGER were devoid of somatostatin binding sites, while SKI tumors were positive for them. Based on the above results, it appears likely that Sandostatin directly inhibited the growth of SKI tumors, since SKI was positive for somatostatin binding sites; it appears less likely that Sandostatin indirectly mediated its inhibition by attenuating possible stimulatory effects of CCK. Growth inhibitory effects of tamoxifen on PGER were apparently via E2 binding sites, since only the tumors positive for E2 binding sites (PGER) responded to tamoxifen; it remains to be determined if tamoxifen can exert additional effects independent of E2 binding sites on pancreatic cancers.(ABSTRACT TRUNCATED AT 400 WORDS)

Hormonal influences on the middle-affinity estrogen-binding sites in the liver of the newt Pleurodeles waltl

The effects of hormonal changes on the male-specific, middle-affinity, estrogen-binding component (MEBC) were investigated in the Pleurodele. Induction of MEBC was shown to be under androgen control, similar to that observed for the cytoplasmic middle-affinity estrogen-binding sites in rat liver and human hepatoma cells. But, in contrast to the male-specific middle-affinity estrogen-binding sites identified in the rat, the administration of estrogen to male Pleurodeles did not lead to the disappearance of MEBC but raised levels significantly. The MEBC displays the properties of type II middle-affinity estrogen-binding sites, which are characterized by an oestrogen-dependent rise, a sensitivity to reducing agents, a specificity for diethylstilbestrol, and a binding capacity enhanced by increasing dilutions of cytosol. In female Pleurodeles, MEBC can be induced by treatment with androgens. This induction appears to be modulated by the estrogen/androgen ratio. The induction of MEBC and the estrogen-dependent increase in the male were not found to be correlated with hepatocyte proliferation.

The isolation and characterization of estrogen binding proteins in the pancreas of male and female hamsters

Specific estradiol binding proteins (EBP) that have been described in the pancreatic tissues of a number of species are thought to be important in maintaining the structural and functional integrity of the pancreas. However, possible sex-related differences in the presence and characteristics of EBP have not been examined. In the present study, we have analyzed the pancreatic tissues of male and female Syrian golden hamsters for the presence of EBP and progesterone binding protein (PBP), and further characterized these sites. Our results indicate the presence of only one class of EBP with a high capacity (greater than 500 fmol/mg protein) and low affinity (Kd greater than 1.0 nM) in the pancreatic cytosol of female hamsters. On the other hand, there appeared to be two distinct classes of EBP in the male pancreas. One class of EBP in the male pancreas had a high binding affinity (Kd = less than 0.05 nM) and low capacity (less than 10 fmol/mg protein); we have arbitrarily called these Type I EBP. The second class of EBP in the male pancreas which resembled EBP in the female pancreas had a high capacity (greater than 100 fmol/mg protein) and a low binding affinity (Kd = greater than 1.0 nM); we have called these Type II EBP. The sucrose-density gradient profile of EBP for male and female hamster pancreas demonstrated the presence of both an 8S binding protein and a 4S binding protein in the male pancreas; the female pancreas had only a 4S binding protein. PBP were not detected in pancreas of either male or female hamsters. We conclude that significant sex-related differences are present in the EBP populations of the hamster pancreas.

Lack of pancreatic [3H]estradiol-binding activity in cystic fibrosis

A major characteristic of cystic fibrosis (CF) is the progressive degeneration of acinar cells in the pancreas. It is now well established that the normal pancreas contains an abundant amount of an [3H]estradiol-binding protein. Although the physiological function of this protein is unknown, available evidence suggests that it modulates resting secretion from acinar cells. Analysis of pancreatic autopsy samples from 13 patients who had CF demonstrated a high degree of correlation between loss of acinar cells and loss of [3H]estradiol-binding activity. Autopsy samples taken from individuals unaffected by CF contained large amounts of the [3H]estradiol-binding protein that were significantly correlated with the tissue content of amylase. This biological model demonstrates that the [3H]estradiol-binding protein in pancreas is localized primarily within acinar cells. Based on the presumed regulatory role this protein has on pancreatic secretion, an hypothesis is offered to account for acinar cell degeneration in individuals suffering from cystic fibrosis.

Yeast alpha-factor and somatostatin enhance binding of [3H]estradiol to proteins in rat pancreas and Saccharomyces cerevisiae

Pancreatic tissue contains an [3H]estradiol-binding protein that requires a coligand in the steroid-binding reaction. The endogenous coligand appears to be the tetradecapeptide somatostatin. Yeast alpha-factor, a tridecapeptide pheromone that induces conjugation between haploid cells of opposite mating type, was found to be as effective as somatostatin in enhancing specific binding of [3H]estradiol to partially purified pancreatic protein. Supernatant fractions from yeast cells also contain an [3H]estradiol-binding protein. alpha-Factor can enhance specific binding of [3H]estradiol to such yeast fractions. Somatostatin, somatostatin analogues, and an analogue of alpha-factor enhanced binding of [3H]estradiol but did not inhibit cell growth or induce morphological changes in S. cerevisiae. Thus, it appears that coligand-requiring [3H]estradiol-binding activity and mating in yeast are not directly related.

Binding of estrogen receptor from N-nitrosomethylurea-induced rat mammary tumors to nuclei

The binding of the cytoplasmic estrogen receptor (ERc) from N-nitrosomethylurea (NMU)-induced rat mammary tumors to the nucleus using a cell-free system is described. All tumors studied were estrogen-receptor-positive and most of them were hormone-dependent. Sixty-two percent of all tumors investigated (n = 134) decreased in size more than 30% 4-5 days after ovariectomy. Brief heating of the cytosol loaded with tritiated estradiol induced activation of the ERc measured by an increase of nuclear binding activity. Temperature-dependent activation was evident in every case. The optimal time and temperature of activation were 15-60 min at 30 degrees C. After denaturation of the ERc by heating for 20 min at 56 degrees C only small parts of free estradiol could be bound to nuclei. Mg2+ ions and EDTA inhibited the nuclear binding of the receptor. The nuclear binding assay was performed for 1 hr at 0-4 degrees C. After this time the activated ERc was bound nearly maximally to nuclei. Under optimized conditions 50-60% of the ERc could be bound to nuclei maximally. Using the same medium for the preparation of crude and purified nuclei the binding of the receptor to both kinds of nuclei was similar. Na2MoO4 prevented the activation of the ERc from NMU-tumors completely but did not influence the binding of the previously activated receptor to nuclei.

The synthetic protease substrate N-benzoyl-L-argininyl-p-nitroanilide activates specific binding of [3H]estradiol to a protein in rat pancreas: relationship of structure to activity

N-benzoyl-L-arginyl-p-nitroanilide (BAN), a synthetic substrate for trypsin-like proteolytic enzymes, is a potent activator of [3H]estradiol-binding to a protein present in rat pancreas. When partially purified, this protein is almost devoid of [3H]estradiol-binding activity in the absence of an endogenous accessory factor. BAN can mimic the natural coligand in this steroid binding reaction. The effect of BAN is specific since a number of derivatives of this substance are inactive or may even inhibit steroid binding. It is unlikely that BAN exerts this stimulatory action indirectly, possibly by preventing proteolytic inactivation of the [3H]estradiol-binding protein, since preincubation of the protein in the absence of BAN resulted neither in reduced rate, nor extent, of steroid binding following BAN addition. Also, a number of protease inhibitors had no effect on the binding reaction. Of those inhibitors tested, only antipain significantly enhanced binding of [3H]estradiol, but only about 20 percent as effectively as BAN.

Evidence that somatostatin (SRIF14) is the primary coligand in pancreas required for specific binding of [3H]estradiol in pancreatic tissue: demonstration that [3H]estradiol and [125I]SRIF14 form complexes of varying size with a specific binding protein

There is present in rat pancreas a protein that requires an accessory factor in order to bind [3H]estradiol. To identify this accessory factor 874g of dog pancreas were acid extracted, and following selective filtration and dialysis, the low molecular weight constituents (less than 10,000) were concentrated by lyophilization. Samples of this lyophilizate were fractionated by high performance liquid chromatography (HPLC) and eluate fractions analyzed for their capacity to enhance binding of [3H]estradiol to a protein fraction from rat pancreas that had been purified relatively free of endogenous accessory factor. Such enhancement of [3H]estradiol-binding activity eluted predominantly in one peak that coincided with the elution profile of pure somatostatin (SRIF14). Analysis of eluate fractions for somatostatin-like immunoreactive material (SLIM) indicated coincidence of SLIM with the factor that enhanced binding of [3H]estradiol. It appears likely that accessory factor in pancreas is primarily somatostatin (SRIF14). Following incubation of [125I]SRIF14 and [3H]estradiol with a partially purified binding-protein fraction from rat pancreas, a complex containing labeled [125I] and [3H] was separated by Sephadex G-200 column chromatography. In the presence of 25 microM SRIF14, which activates [3H]estradiol-binding maximally in the presence of 10 nM steroid, a protein peak containing both radiolabeled ligands eluted in the void volume indicating an apparent molecular size in excess of 200,000 Daltons. At a concentration of 1 microM SRIF14, a complex eluted at a position corresponding to an apparent Mr of 120,000. Evidently, the steroid and polypeptide mutually enhance binding to this pancreatic protein, and depending on their concentrations form structures of widely varying sizes.

An overview of pancreatic exocrine secretion

Genes for all proteins have encoded in their DNA sequences, information that specifies where these proteins will localize within the cell. Nascent translation products of transcripts of these genes, that possess a specific NH2-terminal signal sequence, are able to translocate into a specialized membranous conducting system called the endoplasmic reticulum (ER), or can be incorporated directly into a target organelle (i.e. mitochondrion). Nascent polypeptides lacking this signal sequence remain in the cytosol. Once segregation into the ER has occurred each protein appears to migrate at a characteristic rate to a connecting organelle; the Golgi Complex. Here, enzymatic modifications of these proteins determines the organelle with which each will eventually become associated. In secretory tissues such as the exocrine pancreas, many different proteins are directed into specialized secretory structures called zymogen granules. These granules are maintained in a "ready-to-release" state by steroid hormones. In the absence of estrogens and glucocorticoids the zymogen granules disappear. Physiologically, secretion from the exocrine pancreas is brought about by parasympathetic nerve stimulation, or by the gut hormone cholecystokinin (CCK). Interaction of acetylcholine or CCK with specific receptors on pancreatic acinar cells initiates the process of exocytosis; that is, fusion of the zymogen granule membrane with the plasma membrane resulting in extracellular release of the contents of the secretory granule.

Role of steroids in secretion--modulating effect of triamcinolone and estradiol on protein synthesis and secretion from the rat exocrine pancreas

Following adrenalectomy of male rats, or adrenalectomy and ovariectomy of females, there was marked depletion of zymogen granules in acinar cells of the pancreas. Within 9 h after treatment with either triamcinolone or 17 beta-estradiol, complete restoration of these secretory vesicles was observed. This repletion was not inhibited by actinomycin-D. Supernatant fractions (100,000 g, 60 min) of rat pancreas, from both normal and surgically altered animals, contained proteins that bound [3H]-triamcinolone and [3H]-estradiol, suggesting that the action of these hormones is exerted directly on the pancreas. Binding of both steroid hormones required the presence of an additional coligand referred to as accessory factor. In addition, the binding proteins for [3H]-triamcinolone and [3H]-estradiol eluted in similar positions after Sephadex G-200 and CM Affi-gel Blue chromatography. It is uncertain, however, whether a single protein binds both steroid hormones since they had different binding isotherms. Scatchard analysis of binding of [3H]-estradiol yielded a single straight line of negative slope from which it was calculated that there were about 4.4 pmol of binding sites per mg protein, having an average apparent Kd of about 5 X 10(-8) M. Similar analysis of the data for [3H]-triamcinolone yielded a straight line of zero slope indicating nonsaturable binding of hormone at concentrations as high as 10 microM. Since both [14C]-L-leucine incorporation into protein and amylase secretion were affected markedly by the steroid-hormonal status of the animal, it is presumed that steroid-bound complexes in acinar cells of the pancreas modulate synthesis and secretion of protein.