Microcalcifications in breast cancer: novel insights into the molecular mechanism and functional consequence of mammary mineralisation

BACKGROUND

Mammographic microcalcifications represent one of the most reliable features of nonpalpable breast cancer yet remain largely unexplored and poorly understood.

METHODS

We report a novel model to investigate the in vitro mineralisation potential of a panel of mammary cell lines. Primary mammary tumours were produced by implanting tumourigenic cells into the mammary fat pads of female BALB/c mice.

RESULTS

Hydroxyapatite (HA) was deposited only by the tumourigenic cell lines, indicating mineralisation potential may be associated with cell phenotype in this in vitro model. We propose a mechanism for mammary mineralisation, which suggests that the balance between enhancers and inhibitors of physiological mineralisation are disrupted. Inhibition of alkaline phosphatase and phosphate transport prevented mineralisation, demonstrating that mineralisation is an active cell-mediated process. Hydroxyapatite was found to enhance in vitro tumour cell migration, while calcium oxalate had no effect, highlighting potential consequences of calcium deposition. In addition, HA was also deposited in primary mammary tumours produced by implanting the tumourigenic cells into the mammary fat pads of female BALB/c mice.

CONCLUSION

This work indicates that formation of mammary HA is a cell-specific regulated process, which creates an osteomimetic niche potentially enhancing breast tumour progression. Our findings point to the cells mineralisation potential and the microenvironment regulating it, as a significant feature of breast tumour development.

The effects of benzodiazepines on human opioid receptor binding and function

We performed in vitro studies to investigate the potential interaction of benzodiazepines with cloned human opioid receptor subtypes. Midazolam, chlordiazepoxide, and diazepam directly displaced [(3)H]-diprenorphine binding from kappa and delta receptors, but not mu receptors, whereas flumazenil was inactive. These benzodiazepines also stimulated (35)S-GTPgammaS binding in membranes containing human kappa receptors, and the effect of midazolam was prevented by a selective kappa antagonist. Midazolam was also weakly active at delta-receptor activation, whereas all three were inactive at mu receptors. The results suggest that the analgesic efficacy reported for intrathecal benzodiazepines may be attributed, in part, to direct interaction with kappa-opioid receptors.

IMPLICATIONS

Several human and animal studies have shown analgesic effects of benzodiazepines after spinal injection. Our results show that large concentrations of midazolam, chlordiazepoxide, and diazepam displace the binding of [(3)H]-diprenorphine-an opiate radioligand from kappa receptors. In an in vitro functional assay, midazolam is a weak agonist at the delta-opioid receptor, whereas all three benzodiazepines are kappa-opioid agonists. These findings may partially explain the mechanism of benzodiazepine-induced spinal analgesia.

Preclinical neurochemical and electrophysiological profile of 1192U90, a potential antipsychotic

11192U90 was submitted to receptor binding and monoamine uptake assays. It bound potently at serotonin 5-HT2, dopaminergic D2, serotonin 5-HT1A, and adrenergic alpha 1 and alpha 2 receptors. It also bound to dopaminergic D1, serotonin 5-HT3, serotonin 5-HT4, and sigma sites, albeit with lower affinity. It was essentially inactive at 22 other sites, including those for cholinergic M1 and M2. It weakly inhibited uptake of 3H-norepinephrine, 3H-serotonin and 3H-dopamine. Acute doses of 1192U90 (5 and 20 mg/kg P.O.) increased whole-brain levels of dopamine metabolites but did not affect levels of norepinephrine, dopamine, and serotonin. Subcutaneous injection of 1192U90 (0.8 mg/kg/day) and clozapine (20 mg/kg/day) for 28 days preferentially decreased the number of spontaneously active dopamine cells in the ventral tegmental area (VTA) but not the substantia nigra (SN) of rats, as measured by population sampling. This outcome is characteristics of atypical antipsychotics like clozapine. Acute injections of 1192U90 reversed the rate-inhibiting effects of microiontophoretically applied dopamine and intravenously injected apomorphine and d-amphetamine on dopamine cell firing. Intravenous injection or iontophoretic application of 1192U90 or the 5-HT1A agonist (+/-)8-OH-DPAT inhibited the firing rates of dorsal raphe nucleus (DRN) neurons in rats, and the effects of both compounds were blocked by iontophoretically applied S(-) propranolol, a 5-HT1A antagonist. The results suggest that 1192U90 is a preferential dopamine D2 antagonist as well as a 5-HT1A agonist that may prove to be an atypical antipsychotic.

The effects of an inhibitor of tryptophan 2,3-dioxygenase and a combined inhibitor of tryptophan 2,3-dioxygenase and 5-HT reuptake in the rat

The effects of a novel inhibitor 680C91 ((E)-6-fluoro-3-[2-(3-pyridyl)vinyl]-1H-indole) of the key enzyme of tryptophan catabolism tryptophan 2,3-dioxygenase (TDO), and a novel inhibitor 709W92 ((E)-6-fluoro-3-[2-(4-pyridyl)vinyl]-1H-indole), of both TDO and 5-hydroxytryptamine (5-HT) reuptake, were examined on tryptophan catabolism, cerebrospinal fluid (CSF) concentrations of tryptophan and 5-HT and serotonergic-mediated physiology and behaviour in the rat. The catabolism of L-[ring-2-14C]tryptophan in vivo was completely inhibited by prior administration of 709W92. 709W92, but not 680C91, potentiated head-twitch produced by 5-hydroxytryptophan, prevented head-twitch and whole brain 5-HT depletion produced by p-chloroamphetamine and rapidly decreased dorsal raphe firing. Both 709W92 and 680C91 elevated CSF tryptophan by up to 260% of basal concentration. A maximally effective dose of 680C91 elevated a global measure of brain extracellular 5-HT (CSF 5-HT) to concentrations similar to those seen maximally after exogenous tryptophan administration (approx 170% of basal). Maximally effective doses of 709W92 increased CSF 5-HT to concentrations comparable to those seen after tryptophan and 5-HT reuptake inhibitor coadministration (approx 900% of basal) and to concentrations greater than those achieved maximally with serotonergically active antidepressant monotherapy (approx 500% of basal). 709W92 did not elevate CSF 5-HT to concentrations associated with the serotonin syndrome (approx 3000% of basal). The combined TDO inhibitor/5-HT reuptake inhibitor, 709W92, showed anxiolytic activity in the rat-pup vocalization model of anxiety. These results show that 709W92 (a novel inhibitor of both TDO and 5-HT reuptake), can produce an elevation of CSF 5-HT similar to that achieved with a serotonin reuptake inhibitor/tryptophan combination therapy but with a more sustained timecourse; such compounds may therefore have superior antidepressant efficacy in the clinic.

The putative dopamine D3 receptor agonist 7-OH-DPAT: lack of mesolimbic selectivity

7-Hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT), an agonist with relative selectivity for the dopamine D3 receptor, was examined in several electrophysiological assays to determine whether it exhibits preferential effects in the mesolimbic versus nigrostriatal dopamine systems. Extracellular single unit activities of substantia nigra pars compacta (A9) and ventral tegmental area (A10) dopamine neurons, and caudate-putamen and nucleus accumbens neurons, were recorded in male rats anesthetized with chloral hydrate. Intravenous (+/-)-7-OH-DPAT potently and completely inhibited the firing of both A9 and A10 dopamine neurons (ED50's: 3.5 +/- 0.7 micrograms/kg and 3.9 +/- 0.9 micrograms/kg, respectively). The active enantiomer, (+)-7-OH-DPAT, was 2 to 3 times more potent than the racemic drug (ED50's: 1.2 +/- 0.3 micrograms/kg and 1.7 +/- 0.4 micrograms/kg for A9 and A10 cells, respectively). There were no significant differences in potency for either form in inhibiting A9 and A10 dopamine neurons. In other studies, iontophoretically applied (+)-7-OH-DPAT caused current-dependent inhibitions of spontaneously active or glutamate-driven caudate-putamen and nucleus accumbens neurons (I50 values, 6.5 and 7.9 nA, respectively). Again, no difference in potency between cell populations was noted. Finally, in cell-attached patch-clamp recordings from freshly dissociated rat caudate-putamen neurons, an 85 pS K+ channel known to be activated by dopamine and the "D2-like" agonist quinpirole was also observed with (+/-)-7-OH-DPAT (0.2-1 microM) applied in the patch pipette.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that the acute behavioral and electrophysiological effects of bupropion (Wellbutrin) are mediated by a noradrenergic mechanism

Bupropion (BW 323U66) has been considered a dopaminergic antidepressant based on its ability to inhibit the uptake of dopamine (DA) somewhat more selectively than it inhibits uptake of norepinephrine (NE) or serotonin (5-HT). This report describes new evidence that bupropion selectively inhibits firing rates of NE cells in the locus coeruleus (LC) at doses significantly lower than those that inhibit activity of midbrain DA cells or dorsal raphe 5-HT cells. The IC50 dose (13 mg/kg i.p.) for inhibition of LC firing produced plasma concentrations that were not significantly different from those generated by the ED50 in the Porsolt test (10 mg/kg i.p.). The fourfold higher dose needed to inhibit DA cell firing (IC50 = 42 mg/kg i.p.) was similar to the dose associated with locomotor stimulation in freely moving rats. Bupropion did not change the firing rates of 5-HT cells in the dorsal raphe nucleus at any dose. In both in vitro and in vivo tests, the metabolite 306U73 (hydroxybupropion), a weak inhibitor of NE uptake, was approximately equipotent to bupropion with regard to inhibition of LC cells. Another metabolite, 494U73, had no effect on LC firing rates over a wide range of doses. Because of species variation in metabolism, 306U73 was not detected in plasma of rats after i.v. doses of bupropion that inhibited LC firing. Only trace amounts of 306U73 were detected after bupropion dosing for the Porsolt test. Pretreatment with reserpine markedly depleted catecholamines and reduced (by 30-fold) the potency of bupropion to inhibit LC firing.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological evidence for a large receptor reserve for inhibition of dorsal raphe neuronal firing by 5-HT1A agonists

Previous studies [Meller et al. (1990) Mol. Pharmacol., 37:231-237] have shown that a large receptor reserve exists for the inhibition of serotonin synthesis in rat cortex and hippocampus by the 5-HT1A agonist 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), whereas little or no reserve exists for the lower efficacy agonists ipsapirone and BMY 7378. The current studies were undertaken to determine if the above drugs exhibit similar relative efficacies and receptor reserves in an electrophysiological model of 5-HT1A receptor activation, i.e., the inhibition of dorsal raphe cell firing. Intravenous dose-response curves were constructed in untreated control rats, or in rats which received an injection of the irreversible receptor inactivator N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ, 6 mg/kg, s.c.) 24 hours before recording. All three drugs fully inhibited dorsal raphe cell firing in control rats (ED50's: 1.5 micrograms/kg, 8-OH-DPAT; 30.0 micrograms/kg, ipsapirone; 17.5 micrograms/kg, BMY 7378). However, unlike effects on serotonin synthesis, EEDQ treatments caused no depression of the maximal inhibitory response for any of the agonists, although all dose-response curves were shifted to the right (ED50's: 10.1 micrograms/kg, 6.7-fold shift, 8-OH-DPAT; 139.9 micrograms/kg, 4.7-fold shift, ipsapirone; 53.8 micrograms/kg, 3.1-fold shift, BMY 7378). Although the order of agonist efficacies was similar for both inhibition of serotonin synthesis and dorsal raphe cell firing (8-OH-DPAT > ipsapirone > BMY 7378), a large (> 50%) receptor reserve was estimated for all three drugs in this electrophysiological system.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of substantia nigra dopamine cell firing by R(-)-N-n-propylnorapomorphine: electrophysiological and autoradiographic studies after regional inactivation of dopamine receptors by microinjection of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline

The irreversible receptor inactivator, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), was injected into rat striatum or substantia nigra to study potential contributions of dopamine receptors in each area to the inhibition of substantia nigra (A9) dopamine cell firing by i.v. R(-)-N-n-propylnorapomorphine (NPA), a dopamine agonist. Extracellular, single unit recording studies showed that the numbers of active dopamine cells, basal firing rates and responses to i.v. R(-)-NPA were unchanged a day after striatal EEDQ injections, despite significant losses of striatal D1 and D2 receptors (confirmed by autoradiography). These results indicate that striatal receptors do not control the basal activity of A9 neurons, nor do they mediate inhibitions of firing by R(-)-NPA. Microinjections of EEDQ into substantia nigra, however, inactivated 75-78% of nigral D1 and D2 receptors and reduced the number of active dopamine cells and slightly increased firing rates. Moreover, dose-response curves to R(-)-NPA were shifted 10-fold to the right and the maximum inhibitory response was depressed. Furchgott analysis of the dose-response curves yielded a steep occupancy-response curve with maximum (> 95%) inhibition of firing at only 24% receptor occupation (i.e., 76% reserve). Thus, the substantial (approximately 70%) receptor reserve previously shown to exist for inhibition of dopamine cell firing by i.v. R(-)-NPA20,21 appears to be intrinsic to the nigra. To assess contributions of nigral D1 and D2 receptors to this response, selective inactivation of each receptor subtype was achieved (confirmed autoradiographically) by treating rats with SCH 23390 (4 mg/kg) or S(-)eticlopride (2 mg/kg), respectively, 30 min before intranigral EEDQ. Selective D2, but not D1, receptor inactivation produced rightward shifts and depressed the maximum of the R(-)-NPA dose-response curve in a manner like that observed after non-selective inactivation of nigral dopamine receptors. Unexpectedly, pretreatment with SCH 23390 (to protect D1 receptors) also produced a modest rightward shift in the R(-)-NPA dose-response curve, suggesting a slight role for D1 receptors in this response. These results indicate that inhibition of A9 dopamine cell firing by i.v. R(-)-NPA is mediated by dopamine receptors located in substantia nigra, but not striatum and confirm the predominant role of nigral D2 receptors.

Autoradiography of dopamine D2 receptors using [3H]YM-09151-2

Rat brain dopamine D2 receptors were labeled autoradiographically using the potent and selective benzamide, [3H]YM-09151-2. Saturation binding data, quantified from autoradiograms, showed specific binding of [3H]YM-09151-2 to striatal D2 receptors with a KD of 82 pM and Bmax of 0.696 pmol/mg protein. Binding equilibrium occurred within 3 h, and a dissociation constant of 15 pM was obtained in kinetic studies. Antagonist competition curves were monophasic and displayed an order of potency expected for D2 receptors: (+)-butaclamol greater than (-)-sulpiride greater than SCH 23390 greater than mianserin. Competition by dopamine resulted in a shallow, biphasic displacement curve. The distribution of [3H]YM-09151-2 binding sites matched the known pattern for D2 receptors, with dense labeling in striatum, olfactory tubercles and nucleus accumbens, and moderate levels in substantia nigra pars compacta and mamillary nuclei. Much lower levels of non-specific binding were observed than are typically obtained when using [3H]spiperone as the ligand. The coincident high affinity and selectivity of [3H]YM-09151-2 for D2 sites should make this compound a preferred choice for tritium-based D2 autoradiography.

Behavioural, biochemical and electrophysiological studies on the motor depressant and stimulant effects of bromocriptine

Bromocriptine (BRC) produced a biphasic behavioural effect in mice; an early depressant phase which lasted for about 1 h and a later stimulant phase which lasted from about 1 to 5 h. The stimulation was blocked with SCH23390. Both phases of activity were accompanied by marked striatal DA autoreceptor effects as indicated by reductions in dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels and by a reduction in the accumulation of DOPA (after inhibition of nigrostriatal DA nerve firing and DOPA decarboxylase). However, while the autoreceptor effects were still evident during the behavioural stimulant phase, there was a gradual rise in DOPAC and HVA from 1 to 4 h after injection, indicating a gradually increasing DA turnover. We were unable, using a variety of behavioural and biochemical paradigms, to demonstrate any change in DA autoreceptor sensitivity after one dose of BRC. In electrophysiological studies, however, it was found that prior exposure of rats to one dose of BRC rendered them subsensitive to the rate-inhibiting effects of a second dose of BRC, as measured in anaesthetized animals using extracellular single cell recordings of identified DA neurons in the substantia nigra pars compacta. It is concluded firstly, that the stimulant phase of BRC in mice occurs despite continued occupation of the DA autoreceptors by BRC because adequate endogenous DA is available to provide the required D1 receptor stimulation and secondly, that the terminal autoreceptors in the striatum (as assessed in mice using biochemical techniques) may be regulated differently to the somatodendritic autoreceptors (as assessed electrophysiologically in rats).

Efficacy and potency comparisons among aporphine enantiomers: effects on dopamine neurons in substantia nigra of rat

Extracellular single unit recording studies were carried out on male rats to determine the responses of dopamine neurons of the substantia nigra to intravenous administration of the enantiomers of the aporphine congeners, apomorphine (APO), N-n-propylnorapomorphine (NPA) and 11-hydroxy-N-n-propylnorapomorphine (11-OH-NPa). The R-(-)-configuration was found to be the most critical determinant of the efficacy and potency of the agonists. All R-(-)-aporphines were full agonists, able to inhibit completely firing of dopamine cells. The order of potencies, defined by the ID50s, was: (-)NPA, 2.0 +/- 0.4 nmol/kg greater than (-)11-OH-NPa, 4.7 +/- 0.7 nmol/kg greater than (-)APO, 18.0 +/- 4.0 nmol/kg. Thus, potency was increased about 9-fold by replacing the 6N methyl of APO with an n-propyl (NPA). Conversely, the 10-hydroxy was not essential for agonist activity (11-OH-NPa) but could increase potency. In the S-(+)-series responses varied. (+)N-n-Propylnorapomorphine exhibited agonist properties and could fully inhibit dopamine cells, but its potency was low (ID50 1550 nmol/kg); (+)APO produced only slight but significant decreases in firing at large (8434 nmol/kg) doses and (+)11-OH-NPa was devoid of efficacy in that it caused no significant changes in firing. Despite their loss of efficacy and potency, the (+)-enantiomers apparently did retain affinity for DA receptors, since they could act as antagonists if given before (-)APO or NPA. These findings suggest that stereochemical conformation and key structural elements of the aporphines are interactive in determining agonist efficacy and potency within this physiological test system.

Differences in dopamine receptor reserve for N-n-propylnorapomorphine enantiomers: single unit recording studies after partial inactivation of receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline

Previous studies with (S)-(+)-N-n-propylnorapomorphine (NPA), an enantiomer of the potent dopaminergic agonist (R)-(-)-NPA, showed that this compound had a complex pharmacological profile. For example, (S)-(+)NPA had weak dopaminergic agonist potency, in that it could slow and ultimately stop firing of substantia nigra and ventral tegmental area dopamine neurons. However, antagonist properties were also evident inasmuch as immediate pretreatment with a low dose of (S)-(+)-NPA caused a significant rightward shift of the (R)-(-)-NPA dose-response curve. This dual agonist-antagonist nature of (S)-(+)-NPA suggested a low intrinsic efficacy for (S)-(+)-NPA. To test this hypothesis, we conducted dose-response studies for the inhibition of rat substantia nigra dopamine cell firing by (R)-(-)- and (S)-(+)-NPA 1 day after partial irreversible dopamine receptor inactivation with 6 mg/kg N-ethoxycarbonyl-2-ethoxy-1-2-dihydroquinoline (EEDQ) in an ethanol vehicle. This degree of inactivation resulted in a significant, parallel, rightward shift of the (R)-(-)-NPA dose-response curve relative to ethanol-treated control rats, with no loss of maximal response. After pretreatment with the same dose of EEDQ, however, the maximal response to (S)-(+)-NPA was reduced by 22% with no shift on the dose axis. The dose-response curves for control and EEDQ-treated groups were subjected to Furchgott analysis to determine per cent response versus fractional occupancy relationships for each drug. A steep hyperbolic relationship was revealed for (R)-(-)-NPA. Fifty per cent and maximal (greater than 95%) inhibitions of cell firing occurred at 3.5% and approximately 32% receptor occupancies, respectively. Hence, for (R)-(-)-NPA there is about a 68% receptor reserve in this model. The same analysis for (S)-(+)-NPA yielded an occupancy versus response plot that was more shallow and linear. Half-maximal effects occurred at 66% occupancy and the maximal response (96% inhibition) required 94% occupancy, indicating few spare receptors for (S)-(+)-NPA. Because the ratio of fractional occupancies at a given level of response is a measure of relative efficacy, we calculated a relative efficacy of (S)-(+)- to (R)-(-)-NPA of 0.05 (at the 50% response level). This confirms that (S)-(+)-NPA indeed has a much lower intrinsic efficacy than the (R)-(-)-antipode and may account for the previously reported antagonist property of the (+)-form under certain treatment conditions.

Effects of N-n-propylnorapomorphine enantiomers on single unit activity of substantia nigra pars compacta and ventral tegmental area dopamine neurons

Prompted by conflicting reports of both agonist and antagonist properties of the S-(+)-enantiomer of the potent dopamine agonist R-(-)-N-n-propylnorapomorphine (NPA), we carried out extracellular, single unit recording studies to compare the effects of both enantiomers on substantia nigra and ventral tegmental area (VTA) dopamine neurons in male rats anesthetized with chloral hydrate. Like the classic dopamine agonist apomorphine, R-(-)-NPA inhibited cell firing in both populations. Mean cumulative doses to inhibit firing by 50% (ID50) were 0.53 micrograms/kg for nigral and 0.50 micrograms/kg for VTA dopamine cells, respectively, reflecting a potency for R-(-)-NPA 10-fold greater than that of apomorphine for inhibition of nigral dopamine cells (ID50 5.3 micrograms/kg). Inhibitions elicited by R-(-)-NPA could be fully reversed by i.v. haloperidol (0.2 mg/kg) but not by S-(+)-NPA in doses up to 0.9 mg/kg. Interestingly, S-(+)-NPA also exhibited agonist activity in both cell groups but with a much lower potency than R-(-)-NPA. In addition, VTA dopamine cells displayed a significantly greater sensitivity to the drug: ID50 values of 149 micrograms/kg vs. 514 micrograms/kg for VTA and substantia nigra neurons, respectively (P less than .01). Prior administration of haloperidol (0.1 mg/kg) consistently and fully prevented the inhibitory effects of S-(+)-NPA on all cells tested, although subsequent administration of haloperidol (up to 1.6 mg/kg) did not reverse completely S-(+)-NPA-induced inhibitions in all cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Managing skin damage induced by doxorubicin hydrochloride and daunorubicin hydrochloride

The pathophysiology and mechanisms of toxicity of anthracycline-induced skin damage are reviewed, and the various available therapeutic interventions are discussed. Skin ulcers caused by the vesicant antineoplastic agents doxorubicin hydrochloride and daunorubicin hydrochloride begin slowly, and the extent of the tissue damage produced is often underestimated. Within a week, untreated infiltrations of these agents can advance to serious indurations and ulcerations, causing extensive damage to underlying structures such as tendons and bones. Two theories have been proposed to explain the mechanism of action of anthrocycline-induced tissue damage; one holds that doxorubicin-DNA complexes form causing cell death, and the other holds that these agents are reduced to free radicals that can cause cell-membrane damage. Nonpharmacologic treatment of extravasation consists of stopping the infusion at the first sign of a problem and attempting to aspirate fluid and drug back through the same needle. The application of ice packs for the next 24-72 hours is recommended. A variety of pharmacologic approaches have been evaluated to ameliorate tissue damage. Corticosteroids, sodium bicarbonate, beta-adrenergic agents, and dimethyl sulfoxide have been used with some success. Patients who do not respond to initial conservative treatments should be referred to a plastic surgeon for skin grafting and reconstruction. The best treatment for anthracycline toxicity is prevention.

Estrogen withdrawal in chick oviduct. Evidence for continued expression of active unique genes using an "expressed" DNA probe

We have analyzed the effect of estrogen on the kinds of unique DNA sequences which are transcriptionally expressed in chick oviduct with an "expressed" DNA probe. Steady-state nRNA in estrogen-stimulated chick oviduct represents about 25% of the complexity of total chick unique DNA. To purify this expressed DNA fraction, chick unique DNA was isolated, nick-translated, and hybridized to chemically mercurated oviduct nRNA (Hg-nRNA); the resulting hybrids were bound to sulfhydryl-Sepharose, and DNA was selectively recovered by thermal elution in formamide buffer. To compare the sequence homology between nRNAs isolated from oviduct before or up to 6 days after estrogen withdrawal, trace amounts of expressed DNA derived from estrogen-stimulated oviduct were hybridized in RNA-excess reactions. All nRNAs hybridized with equal efficiency. Furthermore, hybridization of expressed DNA to nRNA mixtures showed that nRNA from nonwithdrawn and withdrawn oviduct contained a similar set of unique sequences. The data indicate that, at most, only a small percentage (0--5%) of transcriptionally active unique DNA sequences are shut down when estrogen is removed from the circulation.

Estrogen withdrawal in chick oviduct. Characterization of RNA synthesized in isolated nuclei using a mercurated precursor

1. As a prerequisite for analyzing the effect of estrogen on transcription in chick oviduct, we describe suitable methods for the synthesis (under conditions restricting reinitiation), and isolation of RNA transcripts from oviduct nuclei in vitro, utilizing mercurated UTP (Hg-UTP) as an RNA precursor and chromatography on sulphydryl-Sepharose (SH-Sepharose) to recover mercurated RNA (Hg-RNA). The techniques described include treatment of Hg-RNA with p-hydroxymercuribenzoate, to improve the efficiency of binding to SH-Sepharose, and elution of Hg-RNA from SH-Sepharose after treatment with 60% formamide at 90 degrees C, to eliminate contamination by aggregated nucleic acid. 2. RNA synthesized by endogenous form B RNA polymerase (using either UTP or Hg-UTP as precursor) was recovered in nuclear lysates in the form of 30--85-S heterogeneous RNA . protein complexes, and after removal of protein, was 10--12 S in size. 3. The nature of RNA transcripts synthesized in vitro was examined by hybridization. More than 90% of the RNA was complementary to "unique" DNA sequences, and 50--60% of the hybridized RNA could be competed with homologous, steady-state nuclear RNA, indicating a significant degree with homologous, steady-state nuclear RNA, indicating a significant degree of homology between in vitro transcripts and in vivo RNA. The level of homology was similar whether RNA synthesis was performed in low salt, or in high salt in the presence of heparin. Possible reasons for only partial competition in these experiments are discussed. 4. Withdrawal of estrogen from chicks leads to a 50% reduction in endogenous RNA polymerase activities in nuclei within 48 h. Similar levels of competition with Hg-RNA transcripts for "unique" DNA were obtained using oviduct nuclear RNAs isolated before or after estrogen withdrawal, and even with liver nuclear RNA. Thus, in oviduct, those sequences present in primary transcripts, and analyzed under our experimental conditions, are present in different hormonal states and also in other chick tissues.

The concept of mRNA abundance classes: a critical reevaluation

Derivative plots have been constructed for hybridization reactions between polysomal poly(A)-containing RNA and oligo(dT)-primed cDNA. In one method the derivative was calculated directly from the data, and in the other, from a non-linear least squares fit using 9-10 ideal components. In some cases these methods yield very similar results and strongly suggest that the hybridization data support discrete components. Reactions with two and four major components indicate that the often-reported three abundance class model is only one of several possibilities for eukaryotic cells. In other situations neither method strongly suggests the presence of discrete components (in one case even after enrichment of the cDNA population by kinetic fractionation), implying that the components are closely spaced or that the entire mRNA population of those cells may not exist as discrete abundance classes. The universal occurrence of discrete abundance classes should be critically reexamined.

Effects of estrogen and progesterone on transcription, chromatin and ovalbumin gene expression in the chick oviduct

The effects of estrogen, progesterone and estrogen + progesterone combined on nuclear transcriptional processes in oviducts of immature chicks, previously withdrawn from estrogen, are reported. The responses to the steroids of the endogenous nuclear RNA polymerase activities, both nucleolar (I) and nucleoplasmic (II), the chromatin compositions and template capacities, and the appearance of ovalbumin messenger RNA (mRNA) are compared. When immature chicks (previously treated at 14 days with estrogen) are withdrawn from estrogen treatment, there is a gradual reduction in both polymerase activities. Diurnal variations in polymerase II activties in the oviduct of withdrawn chicks required that subsequent experiments include time-matched controls. The hormones alter RNA polymerase II and II activities in vivo as assayed in isolated nuclei. Progesterone represses the polymerase I and II activities, while estrogen alone and estrogen + progesterone enhance both polymerase activities immediately after injection. Diethylstillbestrol, a synthetic estrogen, causes changes similar to those of estrogen. The effects of these steroids on the polymerases are detected within 15 min of hormone injection. Changes in the capacities of chromatins to serve as template for RNA synthesis in general correlated with changes in polymerase II activities. Interestingly, in the case of estrogen treatment, the acidic chromatin protein (but not histone) levels fluctuate positively with the template capacities of the chromatin. An antagonism between estrogen and progesterone is observed in the responses of both RNA polymerases I and II activities as well as in the chromatin template capacity. Levels of messenger RNA coding for ovalbumin, as detected by hybridization with labeled complementary DNA, increase in oviducts of withdrawn chicks within 2--3 of the injection of estrogen, progesterone or estrogen + progesterone. This rapid accumulation of ovalbumin mRNA is not accompanied in each case by a similar increase in polymerase II activity or chromatin template capacity.

Quantitation of elongating form A and B RNA polymerases in chick oviduct nuclei and effects of estradiol

The number of elongating form A and B RNA polymerases in chick oviduct nuclei was estimated by measuring incorportaion of 3H-UTP into 3' termini of nascent RNA chains in the presence of heparin to inhibit initiation, and quantitation labeled uridine released from these termini after alkaline hydrolysis. The method corrects for conversion of UMP to uridine (U) during manipulations and for production of 3' termini by ribonucleases and phosphatases. The results indicate that a large fraction of RNA polymerases elongating in vivo is retained in isolated nuclei: per diploid genome, approximately 1 x104 form B and 2 x103 form A enzymes are present. These levels are sufficient to maintain normal in vivo rates of mRNA and rRNA synthesis, but the average density of packing of polymerases on DNA is considerably less than the maximum density predicted by Miller and Bakken (1972), suggesting that initiation of polymerases of DNA is a limiting factor in the control of transcription. Rates of elongation of polymerases in vitro are severely impaired, indicative of a loss of elongation factors during nuclear isolation. After 6 hr of estradiol treatment in vivo, the level of form A enzymes in ovoduct nuclei increases to 5 x 103; little change in the number of form B enzymes is seen.

The purification and properties of hen oviduct form B DNA-dependent RNA polymerase

Hen oviduct form B DNA-dependent RNA polymerase has been extensively purified and its properties analysed. It seems likely to consist of a mixture of two forms of the type observed in tissues from other species. Furthermore using S1 nuclease to digest single-stranded DNA, we show that although form B can transcribe double-stranded DNA template it has a very strong preference for single-stranded regions. Also the rate of elongation on native DNA in vitro was measured and is an order of magnitude slower than that reported to be operative in vivo.

Effects of progesterone on protein metabolism in chicken oviduct tissue pretreated with oestrogen

1. The effect of simultaneous injections of oestrogen benzoate and progesterone (0.5mg/day each) on immature chicken oviduct tissue pretreated with oestrogen benzoate (0.5mg/day) was studied. 2. After 3 days of treatment with both hormones, the weight of the tissue doubles as compared with tissue treated only with oestradiol benzoate. 3. The progesterone-induced weight increase had no effect on total DNA content of the tissue, but greatly increased the protein/DNA and RNA/DNA ratios. 4. Amino acid incorporation in vivo after progesterone treatment was elevated as measured by using 2h pulses of amino acids; this effect could be accounted for by observed alterations in the concentrations of free amino acids in the tissue. 5. With longer pulses of amino acid the specific radioactivity of total protein remained high in tissue treated with progesterone, at times when specific radioactivity of protein in oestrogen-treated animals was diminishing. 6. From a knowledge of the specific radioactivity of labelled amino acids in the free amino acid pool and in newly synthesized protein, the rate of protein synthesis was estimated in differently treated tissues. 7. The results suggest that progesterone treatment does not cause an increase in protein synthesis. It is concluded that the observed accumulation of oviduct protein is achieved via an effect of progesterone on protein catabolism.

Cytoplasmic effects of cortisol in liver

1. The time-course of the induction by cortisol of tryptophan pyrrolase in mouse liver was established. 2. The kinetics of labelling of mouse liver polyribosomes and the distribution of radioactivity in the various sizes of polyribosomes were investigated. It is concluded that the major part of the messenger RNA is monocistronic. 3. Cortisol administered to adrenalectomized mice stimulates in parallel the ability of ribosomes and polyribosomes, both free and bound, to incorporate amino acids into protein. 4. This stimulation does not appear to affect in a selective manner particular regions of the gradients of polyribosomes. 5. Administration of cortisol enhances the ability of the denser fraction of the rough microsomes to incorporate labelled amino acids. Adrenalectomy has minor effects on the pool sizes and specific radioactivities of liver amino acids which are counteracted by the hormone. However, these appear insufficient to influence the changes observed. 6. Adrenalectomy causes an increase in the percentage of ribosomes existing as polyribosomes and a fall in the proportion bound to the membrane of the endoplasmic reticulum. After treatment of these animals with cortisol there is a marked increase in the proportion of bound ribosomes. 7. The influence of cortisol on the membranous components of liver cytoplasm is discussed.