The composition of adrenal chromaffin granules: an assessment of controversial results

Regulatory mechanism of calcium efflux from cultured bovine adrenal chromaffin cells induced by extracellular ATP

The effect of adenosine-5'-triphosphate (ATP) on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. ATP stimulated the efflux of 45Ca2+ from the cells in a concentration-dependent manner (0.01-1 mM). The 45Ca2+ efflux from the cells was also stimulated by adenosine-5'-O-(3-thiotriphosphate) (ATP-gamma s), alpha beta-methylene-ATP and adenosine-5'-diphosphate (ADP), but was not by adenosine-5'-monophosphate (AMP) and adenosine. The ATP-stimulated 45Ca2+ efflux was not affected by deprivation of the extracellular Ca2+ and Mg2+, but was dependent on the extracellular Na+ concentrations. ATP increased the influx of 22Na+ into the cells. These results indicate that ATP stimulates extracellular Na(+)-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably through its stimulatory effect on membrane Na+/Ca2+ exchange.

Processing of chromogranin B in bovine adrenal medulla. Identification of secretolytin, the endogenous C-terminal fragment of residues 614-626 with antibacterial activity

Chromogranins constitute a family of acidic soluble proteins widely distributed in endocrine cells and neurons. Chromogranin A, the major soluble component in bovine adrenal medullary secretory granules in chromaffin cells, has been shown to be actively processed to peptide fragments [Metz-Boutigue, M. H., Garcia-Sablone, P., Hogue-Angeletti, R. & Aunis, D. (1993) Eur. J. Biochem. 217, 247-257]. In the present paper, the structural features of the proteolytic degradation mechanism of chromogranin B/secretogranin I have been characterized with regard to the possible function of this protein as a precursor of biologically active peptides. Chromogranin-B-derived fragments present in bovine chromaffin granules were identified by microsequencing after separation by two-dimensional gel electrophoresis or high-performance liquid chromatography. A similar approach was performed to characterize chromogranin-B-derived fragments released into the extracellular space from depolarized bovine cultured chromaffin cells. In chromogranin B, 18 cleavage sites were identified along the protein chain and chromogranin B/secretogranin I fragments were generated by proteolytic attack at both the N-terminus and C-terminus. A major fragment corresponding to residues 614-626 of the C-terminal sequence, was identified in the extracellular space; this peptide was found to share sequence and structural similarities with the lytic domain of cecropins and, as expected from this similarity, to display potent antibacterial properties. Endogenous and synthetic peptides were active on Micrococus luteus, killing bacteria in the micromolar concentration range. The synthetic peptide slows the growth of Bacillus megaterium and was inactive towards Escherichia coli. In addition, the synthetic peptide was unable to induce hemolytic activity. This antibacterial function might be of biological significance in the neuroendocrine system of living organisms. We propose to name this peptide secretolytin.

Thyroid hormones modulate both adenosine transport and adenosine A1 receptors in rat brain

Adenosine transport and adenosine A1 receptors in rat brain are subjected to regulation by thyroid hormone levels. The studies were carried out with brain stem synaptosomal preparations from rat brain in euthyroid and various hypothyroid situations. The maximum velocity of the nitrobenzylthioinosine (NBTI)-sensitive adenosine transport was 3.3 +/- 0.3 pmol.mg protein-1.s-1 in euthyroid rats. The transport in 1-wk thyroidectomized rats was decreased by 45.8% with respect to controls. No changes were found in the affinity of euthyroid and hypothyroid rats, with the Michaelis-Menten constant values equal to 1.9 +/- 0.9 and 2.0 +/- 0.5 microM, respectively. The transporter number measured by NBTI binding also decreased; the maximum binding capacity (Bmax) was 112.9 +/- 21.9 and 31.3 +/- 4.1 fmol/mg protein for euthyroid and hypothyroid rats, respectively. The adenosine A1 receptors were measured in synaptosomal membrane preparations in the presence of 100 microM guanosine-5'-O-3-thiotriphosphate for cylopenthyl-1,3-dipropylxanthine 8-[dipropyl 2,3-3H(N)] ([3H]DPCPX) binding. In euthyroid rats, the Bmax value was 227.6 +/- 27.6 fmol/mg protein, a significant decrease of 23% was obtained in 1-wk hypothyroid rats. In all other thyroid situations studied, adenosine transport capacity, adenosine transporter number, and adenosine A1 receptor number were restored to control levels.

Ganglioside GM1 reduces ethanol induced phospholipase A2 activity in synaptosomal preparations from mice

The adaptation (tolerance) to chronic EtOH exposure was explained by the development of resistance to the disordering of the membrane phospholipids (PL). This phenomenon may be associated with changes in enzymes such as phospholipase A2 (PLA2) that govern PL metabolism. The data presented here, using the mouse inhalation model, supports and confirms previously reported findings that chronic exposure to EtOH substantially increased PLA2 activity in synaptosomal preparations from rat brain. We have previously reported that pretreatment with ganglioside GM1 reduced the intoxicating effect of EtOH in mice. The present study indicates that GM1 pretreatment both in vivo and in vitro reduced the EtOH-induced activation of PLA2 in synaptosomal preparations. Thus GM1 may exert its neuroprotective effects by influencing deacylation/reacylation of membrane phospholipids.

Large dense-core vesicles in rat adrenal after reserpine: levels of mRNAs of soluble and membrane-bound constituents in chromaffin and ganglion cells indicate a biosynthesis of vesicles with higher secretory quanta

Rats were injected with a large dose of reserpine known to stimulate the adrenal medulla. Various times after drug treatment the mRNA levels of several constituents of large dense-core vesicles were determined by northern blot analysis and in situ hybridization. The latter method allowed detection of changes in mRNA levels not only in chromaffin cells, but also in the ganglion cells found in adrenal medulla. Levels of the mRNAs of secretory components of large dense-core vesicles (chromogranins A and B, secretogranin II, VGF, and neuropeptide Y) increased in chromaffin cells by 215-857% after 1-3 days of drug treatment. For partly membrane-bound components (dopamine beta-hydroxylase, prohormone convertase 2, carboxypeptidase H, and peptidylglycine alpha-amidating monooxygenase) the changes ranged from 182 to 315%, whereas for glycoprotein III and for intrinsic membrane proteins (cytochrome b561 and vesicle monoamine transporter 2) no change occurred. In ganglion cells the mRNAs that could be detected for VGF, neuropeptide Y, secretogranin II, carboxypeptidase H, and vesicle monoamine transporter 1 showed an analogous pattern of change, with significant increases for the secretory proteins and no change for the membrane components. From these and previous results we suggest the following concept: Long-lasting stimulation of chromaffin cells or neurons does not induce the biosynthesis of a larger number of vesicles but rather leads to the formation of vesicles containing higher secretory quanta of chromogranins and neuropeptides.

Bovine chromaffin cells: studies on the biosynthesis of phospholipids in chromaffin granules

We have studied the biosynthesis of chromaffin granules by labelling primary cultures of bovine chromaffin cells with either [35S]methionine or various precursors for lipids. After labelling the cells were subjected to subcellular fractionation including density gradient centrifugation. After [35S]methionine significant label (mainly represented by labelled chromogranin A) was found in the soluble proteins of chromaffin granules, whereas the membranes were relatively little labelled. However incorporation into membrane bound dopamine beta-hydroxylase and cytochrome b-561 could be demonstrated. Neither of the used lipid precursors ([3H]glycerol, [3H]choline, [3H]palmitic acid or [3H]arachidonic acid) was incorporated to any significant extent into the soluble components of chromaffin granules. Thus there is no evidence that this secretory compartment contains any lipids or acylated proteins. Incorporation of lipid precursors into the membranes of chromaffin granules was apparently low. After short chases labelled lysolecithin was not present in these organelles. However with prolonged chase times labelled lysolecithin, apparently appeared in chromaffin granules irrespective of whether the cells were stimulated or not. We can conclude that the reusable membranes of chromaffin granules have a very low lipid turnover. Lysolecithin is not transferred into these organelles during biosynthesis but is formed in them during their long life span. This formation of lysolecithin is independent of stimulation of these cells and therefore unlikely to be involved in exocytosis.

Biosynthesis of proteins of large dense-core vesicles in rat PC12 cells: regulation by forskolin and phorbol ester

We have investigated the influence of various second messengers on the biosynthesis of large dense-core vesicle constituents in rat PC12 cells. After treatment with forskolin, phorbol ester or a combination of both substances for up to six days, the messenger RNA levels of several vesicle components were determined by northern blotting. Forskolin increased the expression of messenger RNA encoding the soluble proteins chromogranin B, neuropeptide Y and VGF. Addition of phorbol ester markedly enhanced the effects of forskolin. On the other hand, the expression of two further soluble proteins, chromogranin A and secretogranin II, remained fairly unchanged with all treatments tested. Amongst partly membrane-bound vesicle components, the biosynthesis of glycoprotein III and peptidylglycine alpha-amidating mono-oxygenase was significantly up-regulated by combined treatment with forskolin plus phorbol ester. The carboxypeptidase H messenger RNA increased due to phorbol ester and after long-term application of both drugs. In contrast, phorbol ester alone or plus forskolin down-regulated the expression of dopamine beta-hydroxylase. Essentially the same applies to the intrinsic membrane protein cytochrome b-561, whose messenger RNA level declined in all treatment groups. In conclusion, our results show that forskolin and phorbol ester can regulate the composition of large dense-core vesicles in quite distinct patterns.

Diadenosine 5',5"-P1,P4-tetraphosphate (Ap4A), ATP and catecholamine content in bovine adrenal medulla, chromaffin granules and chromaffin cells

The level of diadenosine 5',5"-P1-P4-tetraphosphate (diadenosine tetraphosphate or Ap4A), catecholamines, ATP and other nucleotides has been investigated in perchloric acid extracts of bovine adrenal medulla, chromaffin granules and cultured chromaffin cells. As a control, the amount of Ap4A and ATP has also been measured in human blood platelets. The following values (nmol/mg protein) were found in adrenal medulla: Ap4A, 0.019 +/- 0.004; ATP, 109 +/- 11; ADP, 23.8 +/- 5.8; AMP, 11.3 +/- 1.5; p4A, 0.18 +/- 0.08; catecholamines, 460 +/- 57. The level of Ap4A, catecholamines and ATP (nmol/mg protein) found in chromaffin granules and in chromaffin cells were, respectively: (0.15 +/- 0.07; 2175 +/- 99; 531 +/- 66) and (0.22 +/- 0.14; 1143 +/- 277; 222 +/- 53). In all the cases investigated, the ratio catecholamines/ATP and catecholamines/Ap4A were around 5 and in the order of 10(3), respectively. The amount of Ap4A found here, in bovine adrenal medulla, chromaffin granules and chromaffin cells, is two orders of magnitude lower than previously reported.

Chromogranin A applied to the nucleus accumbens decreases locomotor activity induced by activation of the mesolimbic dopaminergic system in the rat

The aim of the study was to obtain supporting evidence, using a behavioral paradigm, of the hypothesis that chromogranin A attenuates transmitter release in the CNS. We studied the effects of chromogranin A injected into the nucleus accumbens on locomotor activity triggered by application of picrotoxin into the ventral tegmental area of rats. Injection of picrotoxin into the ventral tegmental area, which is known to disinhibit dopaminergic mesolimbic neurons, caused a significant increase in horizontal activity. Distance covered during locomotion and movement time increased more than twofold, whereas stereotypy time and number, indices of nonlocomotor behavior, were not significantly affected by picrotoxin. Pressure injection of chromogranin A into the nucleus accumbens prior to injection of picrotoxin into the ventral tegmental area prevented these locomotor effects and had little or no effect on nonlocomotor behavior. Similarly, the picrotoxin-induced activity was prevented by injecting cobalt chloride into the nucleus accumbens. The results show that chromogranin A has an attenuating effect, either directly or indirectly, on dopaminergic neurotransmission in the nucleus accumbens that can be exemplified by inhibiting picrotoxin-induced locomotor activity. Further studies are needed to determine the mechanism of chromogranin A action in the nucleus accumbens.

Intracellular and extracellular processing of chromogranin A. Determination of cleavage sites

Chromogranins are a family of acidic soluble proteins which exhibit widespread distribution in endocrine cells and neurons. Chromogranin A (CGA), the major soluble component of the secretory granules in chromaffin cells of the adrenal medulla, is a single polypeptide chain of 431 residues with an apparent molecular mass of 70-75 kDa and a pI of 4.5-5. In mature bovine chromaffin granules about 50% of the CGA has been processed. In the present paper, the structural features of the proteolytic degradation mechanism have been characterized with regard to the possible function of CGA as a prohormone, as suggested by recent studies. CGA-derived components present in chromaffin granules were subjected to either two-dimensional gel electrophoresis or HPLC and the N-terminal of each fragment was sequenced. Immunoblotting with antisera to specific sequences within the CGA molecule were used to characterize these fragments further at their C-terminal. In addition, a similar approach was performed to characterize CGA-derived fragments released into the extracellular space from directly depolarized bovine cultured chromaffin cells. Our results identified several proteolytic cleavage sites involved in CGA degradation. Intragranular processing occurs at 12 cleavage sites along the peptide chain located in both N- and C-terminal moieties of the protein; a preferential proteolytic attack in the C-terminal part was noted. We found that CGA processing also occurs in the extracellular space after release, generating new shorter fragments. The proteolytic cleavage sites identified in this study were compared with the cleavage points which are thought to be involved in generating CGA fragments with specific biological activity: pancreastatin, chromostatin and N-terminal vasostatin fragments. In addition, a new 12-amino-acid CGA-derived peptide corresponding to the sequence 65-76 was identified in the soluble core of purified chromaffin granules. This short peptide was released, together with catecholamines, after stimulation of cultured chromaffin cells suggesting its presence within the storage complex of chromaffin granules. The specific biological activity of this CGA-derived fragment remains to be determined.

Secretory protein traffic. Chromogranin A contains a dominant targeting signal for the regulated pathway

Secretory proteins are targeted into either constitutive (secreted upon synthesis) or regulated (stored in vesicles and released in response to a secretagogue) pathways. To investigate mechanisms of protein targeting into catecholamine storage vesicles (CSV), we stably expressed human chromogranin A (CgA), the major soluble protein in human CSV, in the rat pheochromocytoma PC-12 cell line. Chromaffin cell secretagogues (0.1 mM nicotinic cholinergic agonist, 55 mM K+, or 2 mM Ba++) caused cosecretion of human CgA and catecholamines from human CgA-expressing cells. Sucrose gradients colocalized human CgA and catecholamines to subcellular particles of the same buoyant density. Chimeric proteins, in which human CgA (either full-length [457 amino acids] or truncated [amino-terminal 226 amino acids]) was fused in-frame to the ordinarily nonsecreted protein chloramphenicol acetyltransferase (CAT), were expressed transiently in PC-12 cells. Both constructs directed CAT activity into regulated secretory vesicles, as judged by secretagogue-stimulated release. These data demonstrate that human CgA expressed in PC-12 cells is targeted to regulated secretory vesicles. In addition, human CgA can divert an ordinarily non-secreted protein into the regulated secretory pathway, consistent with the operation of a dominant targeting signal for the regulated pathway within the peptide sequence of CgA.

Posttranslational processing of proenkephalins and chromogranins/secretogranins

Posttranslational processing of peptide-precursors is nowadays believed to play an important role in the functioning of neurons and endocrine cells. Both proenkephalins and chromogranins/secretogranins are considered as precursor molecules in these tissues, resulting in posttranslationally formed degradation products with potential biological activities. Among the proteins and peptides of neuronal and endocrine secretory granules, the enkephalins and enkephalin-containing peptides have been most extensively studied. The characterization of the post-translationally formed degradation products of the proenkephalins have enabled the understanding of their processing pathway. Chromogranins/secretogranins represent a group of acidic glycoproteins, contained within hormone storage granules. The biochemistry, biogenesis and molecular properties of these proteins have already been studied for 25 years. The chromogranins/secretogranins have a widespread distribution throughout the neuroendocrine system, the adrenal medullary chromaffin granules being the major source of these storage components. Recent data provide evidence for a precursor role for all members of the chromogranins/secretogranins family although also several other functions have been proposed. In this review, some of the methods applied to study proteolytic processing are described. In addition, the posttranslational processing of chromogranins/secretogranins and proenkephalins, especially the biochemical aspects, will be discussed and compared. Recent exciting developments on the generation and identification of potential physiologically active fragments will be covered.

Effect of P2Y agonists on adenosine transport in cultured chromaffin cells

Adenosine transport in cultured chromaffin cells was inhibited by purinergic P2y-receptor agonists without significant changes in the affinity constant, the values being between 1 +/- 0.4 and 1.6 +/- 0.6 microM. The Vmax parameter was modified significantly, being 40 +/- 1.0, 26 +/- 5.0, 32 +/- 3.0, and 22 +/- 4.7 pmol/10(6) cells/min for control, adenosine-5'-O-(2-thiodiphosphate), 5'-adenylylimidodiphosphate, and P1,P4-di(adenosine-5'-) tetraphosphate (Ap4A) (100 microM for every effector), respectively. Ap4A, a physiological ligand for P2y receptors in chromaffin cells, showed the highest inhibitory effect (45%). This transport inhibition is explained by an increase in the cytosolic Ca2+ concentration ([Ca2+]i) and the activation of protein kinase C (PKC). Experiments of [Ca2+]i measurement with the fura-2 technique showed that P2y agonists, as well as bradykinin, were able to increase [Ca2+]i, this effect being independent of the presence of extracellular Ca2+. The peptide bradykinin, determined to be coupled to phosphatidylinositol hydrolysis and internal Ca2+ mobilization in chromaffin cells, exhibited a behavior similar to that of P2y agonists in adenosine transport inhibition (39%). P2y agonists and bradykinin increased PKC activity associated with the membrane fraction (about 50% increase in particulate PKC activity with respect to controls). The present studies suggest that adenosine transport is regulated by P2y-purinergic receptors mediated via Ca2+ mobilization and PKC activation.

Use of the uranaffin reaction in the identification of neuroendocrine granules

This overview emphasizes the utility of the uranaffin reaction in the diagnosis of tumors derived from neuroendocrine cells. The history, cell organelle specificity, tissue specificity, pH requirements, and detailed procedure of the uranaffin reaction is provided. Uranaffin-positive granules are also identified within the NS granules of the stem cell paraneuron (archiparaneuron) of coelenterates, and a hypothetical evolutionary scheme depicting the possible origins of the key biochemical features of the advanced mammalian NS granule is included. The role of nucleotides, a major component of true NS granules, is discussed. A possible intragranular function of ATP as a regulator of osmotic pressure and the extracellular physiologic effects of secreted intragranular nucleotides are discussed in some detail.

Chromogranin A and pancreastatin-like immunoreactivity in serum of gastrinoma patients

Gastrin and pancreastatin-like immunoreactivity were determined by radioimmunoassay methods and chromogranin A was determined by enzyme-linked immunoassay in sera from 18 patients with gastrinomas (Zollinger-Ellison syndrome) and in 20 age and sex matched controls. Gastrin serum levels in the gastrinoma patients were in the range 26-80,000 pmol/l, and in the controls 5-31 pmol/l. Chromogranin A serum levels in the gastrinoma group were in the range 6-2,700 ng/ml (mean +/- SEM: 400 +/- 147 ng/ml). The mean value of chromogranin A was significantly higher than in the control group (8 +/- 2 ng/ml, p = 0.008). The serum levels of pancreastatin-like immunoreactivity in the gastrinoma patients were in the range 23-1,994 pg/ml (597 +/- 123 pg/ml). The mean value of pancreastatin-like immunoreactivity in the gastrinoma group was significantly higher than in the control group (104 +/- 25 pg/ml, p = 0.0002). The levels of chromogranin A and pancreastatin-like immunoreactivity were significantly higher in patients with verified metastatic disease (p = 0.04, p = 0.01 respectively). There was a significantly positive correlation between levels of gastrin and pancreastatin-like immunoreactivity (r = 0.7, p = 0.002), while no correlation was found between gastrin and chromogranin A levels or between levels of chromogranin A and pancreastatin-like immunoreactivity. The study demonstrates an elevation of both chromogranin A and pancreastatin-like immunoreactivity in serum of gastrinoma patients. The lack of correlation between gastrin and chromogranin A, however, gives an indication that the gastrinoma cells are not the main source of serum chromogranin A elevation.

Immunocytochemistry of paraneurons in the female urethra of the horse, cattle, sheep, and pig

The aim of this study is to describe the presence of neuroendocrine (NE) cells (paraneurons), producing biogenic amines and/or peptidergic hormones, in the female urethra of cattle, sheep, pigs, and horses, by means of histochemical and double labeling immunofluorescent techniques. 5-Hydroxy-tryptamine-, chromogranin A-, cholecystokinin- and somatostatin-containing NE cells are present in the urethral epithelium of all the species studied, with the unique exception of the lack of somatostatin cells in the horse. Paraneurons containing 5-hydroxytryptamine colocalized with chromogranin A or cholecystokinin were also found in all subjects. Such active substances are hypothesized to play a role in the contraction of the urethral musculature, emission of urogenital fluids, and inhibition of endocrine and exocrine secretions.

The presence of phospholipase A2 in bovine adrenal medulla: arguments for more than one type of phospholipase A2

Since phospholipase A2 (PLA2) is expected to play a role in the mechanism of exocytosis, the presence and subcellular localization of PLA2 in bovine adrenal medulla have been studied. The results of this study reveal that, although a large part of the PLA2 activity in chromaffin cells is due to a lysosomal PLA2, a cytoplasmic PLA2 is also present. This finding is supported by experiments in which the influence of pH, CaCl2 and NaCl on cytoplasmic PLA2 as well as the binding capacity to concanavalin A are investigated. According to these results the properties of a cytoplasmic PLA2 are clearly different from those reported by other authors for the lysosomal PLA2. For this reason, in chromaffin cells a PLA2 could be present which remains in the cytosol when the cell is in rest. Future experiments will have to prove whether this PLA2 becomes associated with the plasma membrane upon stimulation of the cell, thus mediating exocytosis.

Bovine chromaffin granule membranes undergo Ca(2+)-regulated exocytosis in frog oocytes

We have devised a new method that permits the investigation of exogenous secretory vesicle function using frog oocytes and bovine chromaffin granules, the secretory vesicles from adrenal chromaffin cells. Highly purified chromaffin granule membranes were injected into Xenopus laevis oocytes. Exocytosis was detected by the appearance of dopamine-beta-hydroxylase of the chromaffin granule membrane in the oocyte plasma membrane. The appearance of dopamine-beta-hydroxylase on the oocyte surface was strongly Ca(2+)-dependent and was stimulated by coinjection of the chromaffin granule membranes with InsP3 or Ca2+/EGTA buffer (18 microM free Ca2+) or by incubation of the injected oocytes in medium containing the Ca2+ ionophore ionomycin. Similar experiments were performed with a subcellular fraction from cultured chromaffin cells enriched with [3H]norepinephrine-containing chromaffin granules. Because the release of [3H]norepinephrine was strongly correlated with the appearance of dopamine-beta-hydroxylase on the oocyte surface, it is likely that intact chromaffin granules and chromaffin granule membranes undergo exocytosis in the oocyte. Thus, the secretory vesicle membrane without normal vesicle contents is competent to undergo the sequence of events leading to exocytosis. Furthermore, the interchangeability of mammalian and amphibian components suggests substantial biochemical conservation of the regulated exocytotic pathway during the evolutionary progression from amphibians to mammals.

Galanin and neuropeptide Y in chromaffin granules from the guinea-pig

We have examined the subcellular distribution of galanin-like immunoreactivity, neuropeptide Y-like immunoreactivity and the catecholamines noradrenaline and adrenaline in the adrenal medulla from guinea-pigs. By differential centrifugation of the adrenal medulla homogenate the neuropeptides as well as the catecholamines sedimented in a 10,000 g pellet. This pellet was resuspended and further examined in discontinuous and continuous density gradients. In the discontinuous gradient the catecholamines peaked in the heavy bottom fraction, assumed to contain chromaffin granules. Galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity were also enriched in this fraction. However, both neuropeptides showed high levels of sedimentable material also in a fraction of intermediate density. In the continuous density gradient, the sum of sedimentable and soluble catecholamines showed peak values in two fractions corresponding to 1.07 and 1.47 M sucrose, respectively. The NA peak in the denser fraction was more pronounced than the corresponding A peak. Galanin-like immunoreactivity showed only one peak, in the fraction corresponding to 1.07 M sucrose. The data suggest that galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity are partly stored with catecholamines in chromaffin granules. However, galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity was also found in fractions lighter than those containing the bulk of the catecholamines.

Stimulation of rat adrenal medulla can induce differential changes in the peptide and mRNA levels of chromogranins, neuropeptides and other constituents of chromaffin granules

The levels of various components of chromaffin granules were determined in rat adrenals after treatment with several stimulants. After reserpine the levels of calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and chromogranin B but not those of chromogranin A and secretogranin II were elevated. On the other hand, the mRNA of chromogranins A, B and secretogranin II were significantly increased. Treatment with oxotremorine or nicotine (multiple injections for 2 or 3 days) induced analogous changes for peptide and mRNA levels, however, the increases were smaller and for the mRNA less consistent. A single injection of oxotremorine or nicotine raised only the levels of CGRP and NPY and of the NPY mRNA whereas those of the chromogranins and their respective mRNAs remained unaltered. Amongst the membrane proteins only the levels of dopamine beta-hydroxylase are increased after prolonged stimulation, whereas those of cytochrome b-561, carboxypeptidase H and synaptin/synaptophysin (SYN) remain unaltered. Thus, the biosynthesis of chromaffin granules can be regulated in quite sophisticated patterns.

Extracellular ATP as a trigger for apoptosis or programmed cell death

Extracellular ATP is shown here to induce programmed cell death (or apoptosis) in thymocytes and certain tumor cell lines. EM studies indicate that the ATP-induced death of thymocytes and susceptible tumor cells follows morphological changes usually associated with glucocorticoid-induced apoptosis of thymocytes. These changes include condensation of chromatin, blebbing of the cell surface, and breakdown of the nucleus. Cytotoxicity assays using double-labeled cells show that ATP-mediated cell lysis is accompanied by fragmentation of the target cell DNA. DNA fragmentation can be set off by ATP but not the nonhydrolysable analogue ATP gamma S nor other nucleoside-5'-triphosphates. ATP-induced DNA fragmentation but not ATP-induced 51Cr release can be blocked in cells pretreated with inhibitors of protein or RNA synthesis or the endonuclease inhibitor, zinc; whereas pretreatment with calmidazolium, a potent calmodulin antagonist, blocks both DNA fragmentation and 51Cr release. The biochemical and morphological changes caused by ATP are preceded by a rapid increase in the cytoplasmic calcium of the susceptible cell. Calcium fluxes by themselves, however, are not sufficient to cause apoptosis, as the pore-forming protein, perforin, causes cell lysis without DNA fragmentation or the morphological changes associated with apoptosis. Taken together, these results indicate that ATP can cause cell death through two independent mechanisms, one of which, requiring an active participation on the part of the cell, takes place through apoptosis.

Calmodulin-binding proteins in granule and plasma membranes from bovine chromaffin cells

Calmodulin-binding proteins in chromaffin granule membrane and chromaffin cell plasma membranes have been investigated and compared. Chromaffin granules were purified by centrifugation over a 1.7 M sucrose layer. Plasma membranes were obtained in a highly purified form by differential and isopycnic centrifugation. Enzymatic determinations of 5'-nucleotidase, a generally accepted plasma membrane marker, showed a 40-50-fold enrichment as compared to the cell homogenate. Marker enzyme studies demonstrated only minimal contamination by other subcellular organelles. After solubilization with Triton X-100, calmodulin-binding proteins were isolated from chromaffin granule membranes and plasma membranes by affinity chromatography on a calmodulin/Sepharose 4B column. On two-dimensional polyacrylamide gelelectrophoresis a prominent protein (Mr = 65,000, pI ranging from 5.1 to 6) consisting of multiple spots, was present in the calmodulin-binding fraction from chromaffin granule membranes as well as from plasma membranes. Besides this 65 kDa protein both fractions had at least four groups of proteins in common. Also, proteins typical for either preparation were observed. In the calmodulin-binding protein preparations from chromaffin granule membranes a prominent spot with Mr = 80,000 and a pH ranging from 5.0 to 5.7 was present. This protein was enzymatically and immunologically identified as dopamine-beta-monooxygenase.

Glycoprotein II from adrenal chromaffin granules is also present in kidney lysosomes

Glycoprotein II (GP II) is a protein found in the membranes of chromaffin granules from adrenal medulla. Immunoblotting (one- and two-dimensional) revealed that this antigen is also present in liver and in kidney. Subcellular fractionation of the latter organ indicated that GP II was present in lysosomes. This was confirmed by immunoelectron microscopy. The antiserum against GP II immunolabelled the membranes of organelles which could be identified as lysosomes by the labelling of their contents with an antiserum against cathepsin D. Thus GP II is an antigen common to secretory vesicles and lysosomes.

Biomembrane-modulated, lysosomal phospholipase A2 contamination of chromaffin granule ghosts

It was reported that subcellular fractionation of bovine adrenal medulla results in the separation of distinct, non-calcium-dependent phospholipases A2--one associated with chromaffin granule ghosts, another with lysosomes. The basis of this distinction is pH optimum: in routine assays utilizing neat liposomal substrates, the chromaffin granule ghost-associated enzyme is alkaline-active whereas the lysosomal enzyme is acid-active (Husebye, E.S. and Flatmark, T. (1987) Biochim. Biophys. Acta 920, 120-130). We now report that biomembranes after liposomal substrates and/or lysosomal phospholipase A2 such that the enzyme now hydrolyzes them (at low cation concentration) with an alkaline pH optimum. In a lysosomal membrane fraction, phospholipase A2 activity at pH 7.5 relative to activity at pH 5.0 increases as increasing amounts of lysosomal membranes are assayed. The pH optimum of chromaffin granule ghost-associated phospholipase A2 toward liposomal substrates is likewise biomembrane-dependent and, when assayed carefully, is indistinguishable on the basis of optimal pH from the lysosomal enzyme. Although chromaffin granule ghost-associated phospholipase A2 is most likely a lysosomal contaminant, its broad, biomembrane-modulated pH range may still allow it to participate in catecholamine secretion. More importantly, however, sensitivity of adrenal medullary lysosomal phospholipase A2 to biomembranes broadens its potential physiologic pH range and may also play a role in the regulation of this potentially deleterious activity.

Small cell lung carcinoma: clinicopathological, immunohistochemical, and ultrastructural study

Sixty-seven cases of small cell lung carcinoma (SCLA) in Tri-Service General Hospital (TSGH) during the past 16 years were studied. For patients with extensive stage of disease, the mean survival time and 2-year survival rate were 7.2 months and 3.1% versus 13.4 months and 16.7% for patients with limited stage. A better prognosis was obtained by treatment with a combination of intensive chemotherapy and radiotherapy. Immunohistochemical studies were performed by the peroxidase-antiperoxidase method. The positive rates in descending order were bombesin (80%), synaptophysin (74.3%), neurofilament (68.6%), neuron-specific enolase (60%), low molecular weight cytokeratin (54.3%), high molecular weight cytokeratin (25.7%), chromogranin-A (22.9%), adrenocorticotrophic hormone (0). Seven cases were examined and found to be ultrastructure; only 3 cases were found to contain neurosecretory granules. We emphasize that electron microscopy is not necessary as a routine diagnostic procedure, while light microscopy should be employed whenever possible; the immunohistochemical study should be considered within this context.

Synthesis of chromogranin A, dopamine beta-hydroxylase, and chromaffin vesicles

Primary cultures of bovine adrenal medullary cells synthesize chromogranin A (CgA) and dopamine beta-hydroxylase (DBH) and incorporate them into chromaffin vesicles. The incorporation of L-[35S]methionine into CgA, DBH, and total protein was approximately linear for 8 h at methionine concentrations of 12.5, 25, and 50 microM. Newly synthesized CgA and DBH were initially incorporated into vesicles of low buoyant density that matured over 24 h into vesicles having the greater buoyant density of chromaffin vesicles. Approximately 10% of the newly synthesized CgA is released constitutively within 4 h of formation, approximately 30-40% appears to be degraded, and the remainder is incorporated into chromaffin vesicles, which can secrete CgA in response to nicotinic stimulation. Newly synthesized DBH follows a similar course. Once incorporated into chromaffin vesicles, the newly synthesized CgA and DBH appear to be stable for 2-3 days and then decline with a half-time of 3-4 days. Primary cultures of bovine adrenal medullary cells are a good model system for studying factors regulating CgA and DBH synthesis and the formation of chromaffin vesicles.

Ultrastructural identification of human secretin cells by the immunogold technique. Their costorage of chromogranin A and serotonin

We have localized secretin in a morphologically distinctive endocrine cell scattered in the epithelium covering the villi and uppermost crypts of the human duodenum and jejunum. The human secretin cell was characterized by relatively large (mean diameter 299 nm +/- 69 SD), fairly irregular granules, the majority of which showed homogeneous distribution of secretin and chromogranin A immunolabelling in a structurally homogeneous core. Other granules had a targetoid pattern due to an inner, argyrophobe, secretin-immunoreactive body surrounded by an argyrophil, chromogranin A immunoreactive mantle. These targetoid granules represent a distinctive ultrastructural marker of the secretin cell. Secretin cell granules have been shown to react with chromogranin A antibodies and Grimelius' silver, while lacking chromogranin B immunoreactivity. About 1/3 of secretin cells also showed serotonin immunostaining.

Proteolytic processing of chromogranin A in cultured chromaffin cells

The prohormone chromogranin A is the major soluble component of secretory granules in chromaffin cells of adrenal medulla and in many other different endocrine cell types. The proteolytic processing of chromogranin A was studied in cultured bovine chromaffin cells using [35S]methionine to label proteins and a specific antibody to immunoprecipitate the native protein and its breakdown products. In resting cells, it was found that the degradation of chromogranin A is a slow process, since no degradation was observed after a 40 h incubation with radiolabelled methionine. Stimulation of cells with a single pulse or with successive pulses of nicotine did not significantly enhance the degree of proteolytic processing of chromogranin A. As it has recently been shown (Simon, J.P., Bader, M.F. and Aunis, D. Biochem. J. (1989) 260, 915-922) that protein kinase C may be involved in the regulation of chromogranin A synthesis, the possibility that prohormone processing may also be controlled by protein kinase C was examined using the activator of protein kinase C, 12-O-tetradecanoylphorbol 13-acetate (TPA). However, incubation of cells with TPA did not significantly modify chromogranin A processing, indicating that biosynthesis and proteolytic processing of chromogranin A are two distinctly regulated mechanisms. Glucocorticoids are known to exert regulatory control of chromaffin cell metabolism; however, incubation of cells with dexamethasone did not alter slow chromogranin A processing. Stimulation of labelled cells rapidly released newly synthesized chromogranin A into external medium. In addition, released chromogranin A was found to be actively processed into its 60 kDa and 43 kDa breakdown products. This extracellular proteolytic degradation mechanism may be of importance with regard to the function of chromogranin A as a prohormone.

Characterization and partial purification of soluble, lysosomal phospholipase(s) A2 from adrenal medulla

Soluble, cation-dependent, lysosomal phospholipase A2 in bovine adrenal medulla has been biochemically characterized and partially purified, and its unique pH-dependent modulation by cations has been investigated. Chromatographically distinct activities with somewhat broad pI ranges centered at 7.8, 8.1, and 8.4 have been purified 83-, 1900- and 4400-fold, respectively, from the soluble fraction of tissue homogenates. With a specific activity of 4.2 mumol phospholipid hydrolyzed per mg protein per min, the fraction of pI 8.4 is the most highly purified lysosomal phospholipase A2 reported to date; yet silver staining of isoelectric focusing gels indicates that all three species are still only minor components of the protein mixtures with which they co-purify. Lysosomal phospholipase(s) A2 has an apparent molecular weight of 30,600, as determined by gel permeation chromatography; and is probably an oligomannose-containing glycoprotein as indicated by binding to concanavalin A-Sepharose and elution by methyl alpha-D-mannopyranoside. Cation concentrations modulate hydrolysis of biomembranous phospholipid, but not neat liposomal phospholipids, in a complex manner over a broad pH range (pH 4.0-8.0). Triton X-100 stabilizes the enzyme(s) but is inhibitory when present during assay; consequently, detergent-phospholipid mixed micelles are poor substrates. Thus, experimental results are dramatically dependent on the physicochemical nature of the substrate. The role of this phospholipase(s) A2 in the membrane fusion and lysis events of catecholamine secretion, as well as its regulation by cellular proteins, can now be investigated utilizing this partially purified enzyme(s).

Chromogranin A-processing proteinases in purified chromaffin granules: contaminants or endogenous enzymes?

It was the purpose of this study to define the chromogranin A-processing proteinases present in highly purified preparations of bovine chromaffin granules. The most active enzyme had a pH optimum of 5.0 and was inhibited by pepstatin. It could be identified immunologically as a cathepsin D-like enzyme and subcellular fractionation established its lysosomal origin. After removal of this enzyme the remaining activity at pH 5.0 was mainly due to a cathepsin B-like proteinase. The presence of this enzyme could also be attributed to lysosomal contamination. In the presence of calcium, a further proteolytic activity became apparent at pH 5.0. This enzyme which was inhibited by rho-chloromercuriphenylsulfonic acid was localized in chromaffin granules. A trypsin-like peptidase, most active at pH 8.2, was enriched in a membrane wash of chromaffin granules. Subcellular fractionation indicated that this enzyme is preferentially bound to the membranes of very dense particles probably representing a subpopulation of chromaffin granules. This study establishes that the most active chromogranin A-degrading proteinases present in highly purified chromaffin granules are attributable to lysosomal contamination. Two enzymes with low activity (a Ca2+ activated proteinase and a trypsin-like enzyme) are, apparently, true constituents of chromaffin granules.

Sympathetic axons and nerve terminals: the protein composition of small and large dense-core and of a third type of vesicles

Homogenates of bovine splenic nerve and of vas deferens were subjected to differential and density gradient centrifugation to investigate their noradrenaline-storing organelles. The subcellular fractions obtained were analysed by immunoblotting in order to define the presence of various antigens in small dense-core and large dense-core vesicles. In both large granule and microsomal fractions from splenic nerve only one type of noradrenaline-storing vesicle was found, which represents the large dense-core vesicles. These organelles contained chromogranin A, chromogranin B, cytochrome b-561, carboxypeptidase H, glycoprotein II, glycoprotein III, dopamine beta-hydroxylase and the monoamine carrier which are also present in adrenal chromaffin granules. The subcellular distribution of synaptin/synatophysin was more complex since this protein was apparently present in two organelles: in a light vesicle which did not contain significant amounts of antigens found in large dense-core vesicles (dopamine beta-hydroxylase, cytochrome b-561 and the monoamine carrier) and in the dense fractions of the gradient, possibly within large dense-core vesicles. In the microsomal gradient from vas deferens several markers (catecholamines, synaptin/synaptophysin and dopamine beta-hydroxylase) were found in a bimodal distribution, which is consistent with their presence in small and large dense-core vesicles. When the larger granules were removed with higher centrifugation speed a microsomal fraction containing only light vesicles was obtained. After gradient centrifugation of this fraction several components (catecholamines, dopamine beta-hydroxylase, cytochrome b-561, the monoamine carrier and synaptin/synaptophysin) were concentrated in a peak at low density; apparently only small dense-core vesicles were now present.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal chromaffin granules and secretory granules from thyroid parafollicular cells have several common antigens

The presence of various antigens in two types of isolated endocrine vesicles (chromaffin granules and secretory vesicles of thyroid parafollicular cells) was investigated by immunoblotting. The two types of vesicles have three common secretory proteins: chromogranin A, chromogranin B and secretogranin II. Furthermore, six common membrane antigens were found: cytochrome b-561, carboxypeptidase H, glycoprotein II, glycoprotein III, synaptin/synaptophysin and SV 2. These results demonstrate that vesicles obtained from neural crest-derived endocrine cells not only share several common secretory peptides and proteins, but also have common properties as far as their membrane antigens are concerned.

Biochemistry of the chromogranin A protein family

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Effect of secretagogues on chromogranin A synthesis in bovine cultured chromaffin cells. Possible regulation by protein kinase C

Chromogranin A is a major component of storage granules in many different secretory cell types. After [35S]methionine labelling of proteins from cultured bovine chromaffin cells, chromogranin A was immunoprecipitated with specific antibodies, and the radioactivity incorporated into chromogranin A was determined and used as an index of its synthesis rate. Depolarization of cells with nicotine or high K+ evoked a Ca2+-dependent increase in chromogranin A synthesis, whereas muscarine, which does not evoke significant Ca2+ influx from bovine chromaffin cells, had no effect on chromogranin A synthesis. Forskolin, an activator of adenylate cyclase, affected neither the basal nor the nicotine-stimulated rate of chromogranin A synthesis. In contrast, 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, significantly enhanced the incorporation of radioactivity into chromogranin A. Sphingosine, an inhibitor of protein kinase C, abolished both nicotine-stimulated and TPA-induced chromogranin A synthesis. In addition, long-term treatment of chromaffin cells with TPA decreased protein kinase C activity and inhibited the nicotine-stimulated chromogranin A synthesis. These results suggest that protein kinase C may play an important role in the control of chromogranin A synthesis.

An increased pool of secretory hormones and peptides in adrenal medulla of stroke-prone spontaneously hypertensive rats

Secretory components of the adrenal medulla were compared in normotensive Wistar-Kyoto (WKY) rats and in stroke-prone spontaneously hypertensive rats (SHRSP) at both 4 and 12 months of age. Noradrenaline, adrenaline, dopamine, neuropeptide Y, and chromogranins A and B were significantly higher in adrenal glands of SHRSP than those of WKY rats at 4 months. At 12 months, the levels of these components in SHRSP had increased even more (about 200% in WKY rats). There was no change in the relative composition of the adrenal "secretory cocktail." Neither the chromogranin A/chromogranin B ratio nor their apparent proteolytic processing in chromaffin granules differed between SHRSP or WKY rats. The lack of a significant change in membrane-bound cytochrome b561 and the small increase in dopamine beta-hydroxylase suggest that the higher levels of secretory components in SHRSP are not simply caused by an increase in the number of chromaffin granules, but possibly by a selective increase in the secretory content of these organelles providing a larger package for quantal release by exocytosis. This may be relevant for the elevation of blood pressure in this strain. The immunological methods described in this paper allow for the first time a determination of the secretory quantal levels in catecholamine storage. This should be useful for further studies in hypertensive models.

Free concentrations of sodium, potassium and calcium in chromaffin granules

We have measured the contents of Na+ and K+ in isolated chromaffin granules. Total contents varied between 227 and 283 nmol/mg of protein, equivalent to matrix concentrations of 53-66 mM. The value found depended on the isolation buffer used, and the ratio of the two ions reflected the composition of the buffer. We then measured the free concentration of each of these ions, and of Ca2+, in the matrix, by using a null-point method with acridine-fluorescence quenching. This monitored H+ fluxes induced by an ionophore in the presence of known concentrations of the ion in the supporting medium. In contrast with organic constituents of the matrix, which have low activity coefficients, Na+ and K+ were found to have activity coefficients around 0.8 Ca2+, however, was strongly bound: its free concentration was only 0.03% of the total.

The dispersed neuroendocrine cells: the structure, function, regulation and effects of xenobiotics on this system

Cells which express morphological and functional markers originally described in neurons and neural crest-derived endocrine cells are now known to originate from both ectodermal and endodermal progenitors. These cells are organized to secrete peptides, amines, and other regulatory products in response to neurogenic or chemical stimulation. Individual products may function in endocrine, paracrine, neurotransmitter, or neuromodulatory roles. Multiple products are often produced by individual cells and stored in the same secretory granules. The hormonal profiles of particular types of neuroendocrine cells can, to varying degrees, be changed by environmental signals during development or in adult life. These changes are caused both by transcriptional and post-transcriptional mechanisms. Hormonal profiles are also altered during the development and progression of neoplasia. Signals which stimulate hormone secretion produce a number of ancillary effects, including activation and induction of enzymes which replenish hormone stores, activation of cellular oncogenes, and stimulation of cell proliferation. The effects of environmental signals on neuroendocrine cells are mediated by intracellular transduction pathways which involve cyclic AMP, phosphatidylinositol, calcium, and receptor protein kinase activity. These effects can be potentiated, inhibited, or qualitatively altered by exogenous agents.

Ontogenesis of chromogranin A and B and catecholamines in rat adrenal medulla

The ontogenesis of chromogranins A and B and catecholamines was investigated for rat adrenal medulla. The chromogranins, the major secretory peptides of chromaffin granules, were characterized by one- and two-dimensional immunoblotting. Chromogranin B appeared identical in fetal and postnatal adrenals. On the other hand a significant portion of chromogranin A immunoreactivity in fetal adrenals was present in a component which was identified as a proteoglycan form of chromogranin A. In adult adrenals this proteoglycan chromogranin A was different and much less prominent. Total chromogranins and catecholamines increased parallely from the 17th prenatal day to the adult stage. However in early periods of development chromaffin granules are likely to contain relatively higher catecholamine levels than adult granules. At the end of the gestational period both the ratio of adrenaline to noradrenaline and of chromogranin A vs B increases sharply. These results establish that from the 17th prenatal day onward fetal adrenal glands contain chromaffin granules which are filled with both the major secretory peptides and catecholamines. The relative composition of the secretory content (adrenaline vs noradrenaline and chromogranin A vs chromogranin B) changes at the end of the gestational period in parallel with the development of the corticosteroid-producing adrenal cortex.

Co-localization of chromogranin A and B, secretogranin II and neuropeptide Y in chromaffin granules of rat adrenal medulla studied by electron microscopic immunocytochemistry

The co-localization of various antigens in rat chromaffin granules was investigated by the immunogold staining procedure. In ultrathin serial sections staining of chromaffin granules was obtained with antisera against chromogranin A, chromogranin B, secretogranin II and neuropeptide Y. These results indicated that these antigens are costored within chromaffin granules. To further corroborate this point a double immunogold staining procedure was used. This method unequivocally established that chromogranin A, chromogranin B, secretogranin II and neuropeptide Y are co-localized in the same chromaffin granules. These results are relevant for studies demonstrating changes in the level of these peptides in adrenal medulla. The co-localization makes it likely that such changes lead to a different relative composition of the secretory quanta of chromaffin granules.