Formation of inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate from inositol 1,3,4,5-tetrakisphosphate and their pathways of degradation in RBL-2H3 cells

Previous studies with antigen-stimulated rat basophilic leukemia (RBL-2H3) cells indicated the formation of multiple isomers of each of the various categories of inositol phosphates. The identities of the different isomers have been elucidated by selective labeling of [3H]inositol 1,3,4,5-tetrakisphosphate with [32P]phosphate in the 3'-or 4',5'-positions and by following the metabolism of different radiolabeled inositol phosphates in extracts of RBL-2H3 cells. We report here that inositol 1,3,4,5-tetrakisphosphate, when incubated with the membrane fraction of extracts of RBL-2H3 cells, was converted to inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate. Further dephosphorylation of the inositol polyphosphates proceeded rapidly in whole extracts of cells, although the process was significantly retarded when ATP (2 mM) levels were maintained by an ATP-regenerating system. The degradation of inositol 1,4,5-trisphosphate proceeded with the sequential formation of inositol 1,4-bisphosphate, the inositol 4-monophosphate (with smaller amounts of the 1-monophosphate), and finally inositol. Inositol 1,3,4-trisphosphate, on the other hand, was converted to inositol 1,3-bisphosphate and inositol 3,4-bisphosphate and subsequently to inositol 4-monophosphate and inositol 1-monophosphate (stereoisomeric forms were undetermined). The possible implications of the apparent interconversion between inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in regulating histamine secretion in the RBL-2H3 cells are discussed.

Synthesis, receptor binding, and tissue distribution of (17 alpha,20E)- and (17 alpha,20Z)-21-[125I]iodo-19-norpregna-1,3,5(10), 20-tetraene-3,17-diol

The isomeric (17 alpha,20E)- and (17 alpha,20Z)-(iodovinyl)estradiol derivatives 3 and 6, and their no-carrier-added (nca) [125I]iodovinyl analogues, were tested for their relative target tissue retention and binding affinity for the estrogen receptor. The (iodovinyl)estradiols 3 and 6 were prepared via destannylation of the (17 alpha,20E)- and (17 alpha,20Z)-tributylstannyl precursors 2 and 4 with retention of configuration. Selective formation of the E or Z isomers 2 and 4 during the reaction of 17 alpha-ethynylestradiol 1a with tri-n-butyltin hydride was controlled by the presence or absence of the catalyst, the polarity of the solvent, and the reaction temperature. The nca [125I]iodovinyl analogues [125I]-3a and [125I]-6a were obtained in good radiochemical yield and high purity by treatment of 2a and 4a with [125I]NaI in the presence of H2O2 and chloroamine-T, respectively. Of the two isomeric iodovinyl derivatives 3 and 6, the 20Z isomer 6a exhibited the highest receptor binding affinity and the [125I]-6a gave the highest in vivo receptor-mediated target tissue uptake.

Assessment of IgE-receptor function through measurement of hydrolysis of membrane inositol phospholipids. New insights on the phenomena of biphasic antigen concentration-response curves and desensitization

Previous studies have shown that hydrolysis of membrane inositol phospholipids in rat basophilic leukemia (RBL-2H3) cells depended on the rate and extent of the aggregation of receptors of IgE. This response was used as an experimental probe to study the role of IgE receptors in initiating stimulatory and inhibitory processes within the cell. The response was amplified markedly by increasing the concentration of external Ca2+ from 0 to 1 mM, but the concentration required to support half-maximal response varied from less than 0.1 mM for the most potent cross-linking reagent, DNP24BSA (24 molecules of DNP attached to 1 molecule of BSA) to 0.5 mM for the least potent reagent, aggregated OVA. The dependency of phosphoinositide hydrolysis on external Ca2+ was reduced to zero once hydrolysis of inositol phospholipids was underway but secretion of histamine remained totally dependent on the presence of 0.5 to 1 mM external Ca2+. The stimulatory response persisted as long as receptors remained aggregated but it was modulated by a biochemical process, possibly the activation of protein kinase C, that targeted specifically aggregated receptors, or an associated protein. For example, when cells had become desensitized to high concentrations of one Ag, a normal response could be evoked with a second Ag. Also cells that had become desensitized could be reactivated by permeabilizing the cells. Interestingly, bell-shaped Ag dose-response curves, which were characteristic for both the phosphoinositide and secretory responses, were transformed to sigmoid-shaped curves once cells were permeabilized and dialyzed.

Assessment of IgE-receptor function through measurement of hydrolysis of membrane inositol phospholipids. New insights on the phenomena of biphasic antigen concentration-response curves and desensitization

Previous studies have shown that hydrolysis of membrane inositol phospholipids in rat basophilic leukemia (RBL-2H3) cells depended on the rate and extent of the aggregation of receptors of IgE. This response was used as an experimental probe to study the role of IgE receptors in initiating stimulatory and inhibitory processes within the cell. The response was amplified markedly by increasing the concentration of external Ca2+ from 0 to 1 mM, but the concentration required to support half-maximal response varied from less than 0.1 mM for the most potent cross-linking reagent, DNP24BSA (24 molecules of DNP attached to 1 molecule of BSA) to 0.5 mM for the least potent reagent, aggregated OVA. The dependency of phosphoinositide hydrolysis on external Ca2+ was reduced to zero once hydrolysis of inositol phospholipids was underway but secretion of histamine remained totally dependent on the presence of 0.5 to 1 mM external Ca2+. The stimulatory response persisted as long as receptors remained aggregated but it was modulated by a biochemical process, possibly the activation of protein kinase C, that targeted specifically aggregated receptors, or an associated protein. For example, when cells had become desensitized to high concentrations of one Ag, a normal response could be evoked with a second Ag. Also cells that had become desensitized could be reactivated by permeabilizing the cells. Interestingly, bell-shaped Ag dose-response curves, which were characteristic for both the phosphoinositide and secretory responses, were transformed to sigmoid-shaped curves once cells were permeabilized and dialyzed.

The inhibition of a tumour cell surface protease in vivo and its re-activation by oxidation

Colonic tumour cells possess a cell surface protease capable of binding 9-aminoacridine to its active centre, thus locating cells when viewed under a fluorescence microscope. In vivo and in frozen sections, the enzyme is masked by a protein inhibitor. This inhibitor can be displaced by formaldehyde fixation of the tissue and then replaced by adding a fresh extract of colon or lung tissue. The inhibitor is modified by oxidation; provided by air, oxidized glutathione or potassium permanganate, resulting in a change in conformation in the inhibitor and this then results in the enzyme binding the fluorescent probe. The effect of oxidation can be reversed by dithiothreitol. It is proposed that these changes are brought about by a disulphide exchange acting on the inhibitor which indirectly controls the activity of the cell surface enzyme in vivo. The steps described above can be conveniently followed on sections of tissue mounted on a microscope slide; this has the advantage that the same cells can be monitored during a sequence of reactions. It is believed that these techniques could well be applied to other enzyme systems than the tumour protease described in this study.

Identification of variants of the basophilic leukemia (RBL-2H3) cells that have defective phosphoinositide responses to antigen and stimulants of guanosine 5'-triphosphate-regulatory proteins

Antigen immunoglobulin E-mediated secretion of histamine from RBL-2H3 cells is associated with substantial hydrolysis of membrane inositol phospholipids and a rise in the concentration of cytosol Ca2+ (calcium signal). Such responses differed among cloned variant lines of the RBL-2H3 cell line from undetectable (1A3 bromodeoxyuridine-resistant (BUDRR), 2B1 BUDRR, and 1B3 BUDRR lines) to about 80% of those in the parent RBL-2H3 cells. In all but one line (1B3 thioguanine-resistant (TgR)), the intensities of the phosphoinositide response and of the calcium signal were correlated with the secretory response. The 1B3 TgR line had no detectable calcium signal (as measured by quin 2 fluorescence or uptake of 45Ca2+) but paradoxically showed modest rates of hydrolysis of inositol phospholipids and of secretion. The responses of the 1B3 TgR line were, however, dependent on the presence of external Ca2+ ions. The induction of secretion with antigen, therefore, was invariably associated with the hydrolysis of inositol phospholipids, but it was not necessarily associated with a change in concentration of cytosol Ca2+. All antigen unresponsive clones could secrete when synergistic signals were induced by exposure to the Ca2+ -ionophore, A23187 and the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate. These lines, otherwise, had immunoglobulin E receptors and had no obvious defect in their capacity to synthesize the inositol phospholipids or in their phenotypic expression of phospholipase C as measured in cell extracts. One finding of possible relevance to the role of guanosine 5'-triphosphate-regulatory proteins in the activation of phospholipase C was the inability of one antigen-nonresponsive line to respond to NaF (in intact cells) or to guanosine 5'-(3-O-thio)triphosphate (in electrically permeabilized cells).

Identification of variants of the basophilic leukemia (RBL-2H3) cells that have defective phosphoinositide responses to antigen and stimulants of guanosine 5'-triphosphate-regulatory proteins

Antigen immunoglobulin E-mediated secretion of histamine from RBL-2H3 cells is associated with substantial hydrolysis of membrane inositol phospholipids and a rise in the concentration of cytosol Ca2+ (calcium signal). Such responses differed among cloned variant lines of the RBL-2H3 cell line from undetectable (1A3 bromodeoxyuridine-resistant (BUDRR), 2B1 BUDRR, and 1B3 BUDRR lines) to about 80% of those in the parent RBL-2H3 cells. In all but one line (1B3 thioguanine-resistant (TgR)), the intensities of the phosphoinositide response and of the calcium signal were correlated with the secretory response. The 1B3 TgR line had no detectable calcium signal (as measured by quin 2 fluorescence or uptake of 45Ca2+) but paradoxically showed modest rates of hydrolysis of inositol phospholipids and of secretion. The responses of the 1B3 TgR line were, however, dependent on the presence of external Ca2+ ions. The induction of secretion with antigen, therefore, was invariably associated with the hydrolysis of inositol phospholipids, but it was not necessarily associated with a change in concentration of cytosol Ca2+. All antigen unresponsive clones could secrete when synergistic signals were induced by exposure to the Ca2+ -ionophore, A23187 and the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate. These lines, otherwise, had immunoglobulin E receptors and had no obvious defect in their capacity to synthesize the inositol phospholipids or in their phenotypic expression of phospholipase C as measured in cell extracts. One finding of possible relevance to the role of guanosine 5'-triphosphate-regulatory proteins in the activation of phospholipase C was the inability of one antigen-nonresponsive line to respond to NaF (in intact cells) or to guanosine 5'-(3-O-thio)triphosphate (in electrically permeabilized cells).

Regioselective A-ring iodination of estradiol diacetates

Treatment of estrone or estradiol acetate with thallium trifluoroacetate in TFA and subsequent reaction with KI gave the 2-iodoestrogens as the major product. In the case of estradiol diacetate, treatment of the thallation product with [125I]NaI, using the same reaction conditions, gave exclusively the 2-iodo isomer. Thus, regioselectivity combined with rapidity, renders this procedure particularly suitable for A-ring radioiodination of estradiol with short-lived isotopes.

Some studies on the release of histamine from mast cells treated with d-tubocurarine

d-Tubocurarine (dTc) released histamine in non-cytotoxic fashion from peritoneal mast cells of the rat, mouse and hamster. The response was similar to that evoked by other cationic liberators such as compound 48/80 and polylysine in that it was extremely rapid and enhanced by calcium-deprivation at suboptimal concentrations of secretagogue. Tissue mast cells obtained by enzymic dissociation of the heart, lung and mesentery of the rat and guinea pig were unreactive or hyporesponsive to the effect of dTc. The compound liberated only very small amounts of histamine from isolated preparations of perfused guinea pig heart but significantly increased the rate and contractility of the heart. These results are discussed in terms of the general functional heterogeneity of mast cells from different locations.

Comparison of the histamine-releasing action of substance P on mast cells and basophils from different species and tissues

The action of the neuropeptide substance P as a histamine-releasing agent has been compared in histamine-containing cells from a variety of different tissues and species. Peritoneal mast cells from rat, mouse and hamster but not human cells gave a concentration-dependent release of histamine in response to substance P. Release was greater in the absence than in the presence of calcium in the extracellular medium. Mast cells from rat mesentery, lung and heart released histamine in response to substance P, but heart mast cells responded only weakly. All guinea-pig mast cells and histamine-containing cells from human tissues did not give any substantial substance-P-induced release of histamine. The data provides further evidence for the functional heterogeneity of histamine-containing cells.

Definition of essential sequences and functional equivalence of elements downstream of the adenovirus E2A and the early simian virus 40 polyadenylation sites

In addition to the highly conserved AATAAA sequence, there is a requirement for specific sequences downstream of polyadenylic acid [poly(A)] cleavage sites to generate correct mRNA 3' termini. Previous experiments demonstrated that 35 nucleotides downstream of the E2A poly(A) site were sufficient but 20 nucleotides were not. The construction and assay of bidirectional deletion mutants in the adenovirus E2A poly(A) site indicates that there may be redundant multiple sequence elements that affect poly(A) site usage. Sequences between the poly(A) site and 31 nucleotides downstream were not essential for efficient cleavage. Further deletion downstream (3' to +31) abolished efficient cleavage in certain constructions but not all. Between +20 and +38 the sequence T(A/G)TTTTT was duplicated. Function was retained when one copy of the sequence was present, suggesting that this sequence represents an essential element. There may also be additional sequences distal to +43 that can function. To establish common features of poly(A) sites, we also analyzed the early simian virus 40 (SV40) poly(A) site for essential sequences. An SV40 poly(A) site deletion that retained 18 nucleotides downstream of the cleavage site was fully functional while one that retained 5 nucleotides downstream was not, thus defining sequences required for cleavage. Comparison of the SV40 sequences with those from E2A did not reveal significant homologies. Nevertheless, normal cleavage and polyadenylation could be restored at the early SV40 poly(A) site by the addition of downstream sequences from the adenovirus E2A poly(A) site to the SV40 +5 mutant. The same sequences that were required in the E2A site for efficient cleavage also restored activity to the SV40 poly(A) site.

Synthesis, tissue distribution and tumor uptake of 99mTc- and 67Ga-tetrasulfophthalocyanine

Complexes of tetrasulfophthalocyanine with 99mTc, 69Ga and 67Ga were prepared by the condensation of sulfophthalic acid with the appropriate metal-species. The Ga-complex was also obtained by exchange of the central hydrogens of the empty tetrasulfophthalocyanine. The labeled complexes were purified by thin layer chromatography and characterized by their chromatographic properties. Their biodistribution in rabbits and tumor-bearing rats revealed that most of the radioactivity accumulated in the kidneys, liver, ovaries, adrenals and spleen. Comparison of these distribution pattern with those of [99mTc]pertechnetate and 67Ga-citrate confirmed the in vivo stability of the labeled complexes. The 67Ga-complex reached better tumor-to-blood and tumor-to-muscle ratios than 67Ga-citrate.