Decreased peripheral brain-derived neurotrophic factor levels in Alzheimer's disease: a meta-analysis study (N=7277)

Studies suggest that dysfunction of brain-derived neurotrophic factor (BDNF) is a possible contributor to the pathology and symptoms of Alzheimer's disease (AD). Several studies report reduced peripheral blood levels of BDNF in AD, but findings are inconsistent. This study sought to quantitatively summarize the clinical BDNF data in patients with AD and mild cognitive impairment (MCI, a prodromal stage of AD) with a meta-analytical technique. A systematic search of Pubmed, PsycINFO and the Cochrane Library identified 29 articles for inclusion in the meta-analysis. Random-effects meta-analysis showed that patients with AD had significantly decreased baseline peripheral blood levels of BDNF compared with healthy control (HC) subjects (24 studies, Hedges' g=-0.339, 95% confidence interval (CI)=-0.572 to -0.106, P=0.004). MCI subjects showed a trend for decreased BDNF levels compared with HC subjects (14 studies, Hedges' g=-0.201, 95% CI=-0.413 to 0.010, P=0.062). No differences were found between AD and MCI subjects in BDNF levels (11 studies, Hedges' g=0.058, 95% CI=-0.120 to 0.236, P=0.522). Interestingly, the effective sizes and statistical significance improved after excluding studies with reported medication in patients (between AD and HC: 18 studies, Hedges' g=-0.492, P<0.001; between MCI and HC: 11 studies, Hedges' g=-0.339, P=0.003). These results strengthen the clinical evidence that AD or MCI is accompanied by reduced peripheral blood BDNF levels, supporting an association between the decreasing levels of BDNF and the progression of AD.

The Chromogranin A-derived sympathomimetic serpinin depresses myocardial performance in teleost and amphibian hearts

Chromogranin A (CgA) is an acidic protein co-stored with catecholamines, hormones and neuropeptides in the secretory granules of endocrine, neuronal and other cell types (including cardiomyocytes). Proteolytic cleavage in the C terminus of CgA generates a 2.9kDa peptide named serpinin (Serp; Ala26Leu) that can be modified at its N terminus to form a pyroglutamate residue (pGlu-Serp). In the rat heart, both peptides increase contractility and relaxation through a β-adrenergic-like action mechanism. Accordingly, Serp and pGlu-Serp were proposed as novel myocardial sympatho-adrenergic modulators in mammals. On a comparative basis, here we report the actions of Serp and pGlu-Serp on myocardial contractility in three poikilotherm vertebrate species: the eel (Anguilla anguilla), the goldfish (Carassius auratus) and the frog (Rana esculenta). Using isolated working heart preparations, we show that pGlu-Serp reduces stroke volume in all species tested, while Serp reduces contractility in the frog heart, but is uneffective in eel and goldfish hearts. In the goldfish and frog hearts, pGlu-Serp activates the Nitric Oxide/cGMP pathway involving Endothelin-1 B receptors (frog) and β₃ adrenergic receptors (goldfish). pGlu-Serp-treated hearts from goldfish and frog show increased cGMP content. Moreover, the exposure of the frog heart to pGlu-Serp is accompanied by an increased expression of activated eNOS and Akt. In conclusion, this first report showing that pGlu-Serp inhibits mechanical cardiac performance in teleost and amphibians supports an evolutionary role of the CgA system, and particularly its serpinin component, in the sympatho-adrenergic control of the vertebrate heart.

Carboxypeptidase E protects hippocampal neurons during stress in male mice by up-regulating prosurvival BCL2 protein expression

Prolonged chronic stress causing elevated plasma glucocorticoids leads to neurodegeneration. Adaptation to stress (allostasis) through neuroprotective mechanisms can delay this process. Studies on hippocampal neurons have identified carboxypeptidase E (CPE) as a novel neuroprotective protein that acts extracellularly, independent of its enzymatic activity, although the mechanism of action is unclear. Here, we aim to determine if CPE plays a neuroprotective role in allostasis in mouse hippocampus during chronic restraint stress (CRS), and the molecular mechanisms involved. Quantitative RT-PCR/in situ hybridization and Western blots were used to assay for mRNA and protein. After mild CRS (1 h/d for 7 d), CPE protein and mRNA were significantly elevated in the hippocampal CA3 region, compared to naïve littermates. In addition, luciferase reporter assays identified a functional glucocorticoid regulatory element within the cpe promoter that mediated the up-regulation of CPE expression in primary hippocampal neurons following dexamethasone treatment, suggesting that circulating plasma glucocorticoids could evoke a similar effect on CPE in the hippocampus in vivo. Overexpression of CPE in hippocampal neurons, or CRS in mice, resulted in elevated prosurvival BCL2 protein/mRNA and p-AKT levels in the hippocampus; however, CPE(-/-) mice showed a decrease. Thus, during mild CRS, CPE expression is up-regulated, possibly contributed by glucocorticoids, to mediate neuroprotection of the hippocampus by enhancing BCL2 expression through AKT signaling, and thereby maintaining allostasis.

Serpinins: role in granule biogenesis, inhibition of cell death and cardiac function

Serpinins are a family of peptides derived from proteolytic cleavage of the penultimate and the last pair of basic residues at the C-terminus of Chromogranin A. Three forms of naturally occurring serpinin have been found in AtT-20 pituitary cells and rat heart. They are serpinin, pyrogutaminated (pGlu) -serpinin and a C-terminally extended form, serpinin-RRG. In addition pGlu-serpinin has been found in brain, primarily in neurites and nerve terminals and shown to have protective effects against oxidative stress on neurons and pituitary cells. Serpinin has also been demonstrated to regulate granule biogenesis in endocrine cells by up-regulating the protease inhibitor, protease nexin-1 transcription via a cAMP-PKA-sp1 pathway. This leads to inhibition of granule protein degradation in the Golgi complex which in turn promotes granule formation. More recently, pGlu-serpinin has been demonstrated to enhance both myocardial contractility (inotropy) and relaxation (lusitropy). In the Langendorff perfused rat heart, pGlu-serpinin showed a concentration-dependent positive inotropic effect exerted through a cAMP-PKA dependent pathway. In conclusion, the serpinin peptides have profound effects at many levels that affect the endocrine and nervous systems and cardiac function.

Processing, turnover and release of corticotropins, endorphins and melanotropin in the toad pituitary intermediate lobe

The significance of glycosylation of the ACTH/alpha-MSH-endorphin precursor in the biosynthesis, processing and secretion of its peptide products was examined in the toad neurointermediate (intermediate - posterior) lobe, with the aid of a specific inhibitor of glycosylation, tunicamycin. Tunicamycin did not affect the synthesis of the precursor but prevented its glycosylation. In the presence of tunicamycin the precursor underwent rapid intracellular degradation. Precursor molecules that escaped complete degradation were processed to an ACTH molecule with approximately 19 000 molecular weight and to other atypical peptides, which were released. In vitro studies showed that trypsinization of the non-glycosylated precursor resulted in its random proteolysis while large forms of ACTH were cleaved from the glycosylated precursor. The results indicate that glycosylation of the ACTH/alpha-MSH-endorphin precursor may confer specific conformational properties upon the molecule, thus regulating its limited proteolysis. Turnover and release studies revealed two different pools of ACTH, beta-LPH and alpha-MSH-related peptides in the toad intermediate lobe. One pool contained ACTH, beta-LPH, alpha-MSH and beta-endorphin, which were rapidly synthesized and released, or degraded within 6 h of synthesis if their release was inhibited. The other pool was stored and was stable for at least 10 h, if prevented from being released. Peptides in this stored pool primarily included ACTH, alpha-MSH and beta-LPH; beta-endorphin was a minor component of this pool. The release from both pools of peptides was inhibited by dopamine, while the stored pool was selectively inhibited from release by L-isoprenaline (L-isoproterenol).

Chromogranin A, an "on/off" switch controlling dense-core secretory granule biogenesis

We present evidence that regulation of dense-core secretory granule biogenesis and hormone secretion in endocrine cells is dependent on chromogranin A (CGA). Downregulation of CGA expression in a neuroendocrine cell line, PC12, by antisense RNAs led to profound loss of dense-core secretory granules, impairment of regulated secretion of a transfected prohormone, and reduction of secretory granule proteins. Transfection of bovine CGA into a CGA-deficient PC12 clone rescued the regulated secretory phenotype. Stable transfection of CGA into a CGA-deficient pituitary cell line, 6T3, lacking a regulated secretory pathway, restored regulated secretion. Overexpression of CGA induced dense-core granules, immunoreactive for CGA, in nonendocrine fibroblast CV-1 cells. We conclude that CGA is an "on/off" switch that alone is sufficient to drive dense-core secretory granule biogenesis and hormone sequestration in endocrine cells.

Lipid raft association of carboxypeptidase E is necessary for its function as a regulated secretory pathway sorting receptor

Membrane carboxypeptidase E (CPE) is a sorting receptor for targeting prohormones, such as pro-opiomelanocortin, to the regulated secretory pathway in endocrine cells. Its membrane association is necessary for it to bind a prohormone sorting signal at the trans-Golgi network (TGN) to facilitate targeting. In this study, we examined the lipid interaction of CPE in bovine pituitary secretory granule membranes, which are derived from the TGN. We show that CPE is associated with detergent-resistant lipid domains, or rafts, within secretory granule membranes. Lipid analysis revealed that these rafts are enriched in glycosphingolipids and cholesterol. Pulse-chase and subcellular fractionation experiments in AtT-20 cells show that the association of CPE with membrane rafts occurred only after it reached the Golgi. Cholesterol depletion resulted in dissociation of CPE from secretory granule membranes and decreased the binding of prohormones to membranes. In vivo cholesterol depletion using lovastatin resulted in the lack of sorting of CPE and its cargo to the regulated secretory pathway. We propose that the sorting receptor function of CPE necessitates its interaction with glycosphingolipid-cholesterol rafts at the TGN, thereby anchoring it in position to bind to its prohormone cargo.

Oligomerization of pro-opiomelanocortin is independent of pH, calcium and the sorting signal for the regulated secretory pathway

Studies indicate that pro-opiomelanocortin (POMC) is sorted to the regulated secretory pathway by binding to a sorting receptor identified as membrane-bound carboxypeptidase E (CPE) [Cool et al. (1997) Cell 88, 73-83]. The efficiency of this sorting mechanism could be enhanced if POMC molecules were to self-associate to form oligomers, prior or subsequent to binding to CPE. Using cross-linking and gel filtration techniques, we demonstrated that POMC forms oligomers at both neutral and acidic pHs and calcium was not necessary. delta N-POMC, which lacks the N-terminal sorting signal for the regulated secretory pathway, also formed similar oligomers, indicating that the sorting and oligomerization domains are different.

In vivo processing of nonanchored Yapsin 1 (Yap3p)

A C-terminally truncated form of yapsin 1 (yeast aspartic protease 3) was overexpressed in yeast and its processing through the secretory pathway was followed by pulse-labeling and immunoprecipitation studies. In the soluble cell extract, three forms of yapsin 1-87, 74, and 18 kDa-were found. Identification of these forms of yapsin 1 using different antisera suggests that the 87-kDa form is pro-yapsin 1, which is processed into two subunits, alpha (18 kDa) and beta (74 kDa), by cleavage at a loop region not found in traditional aspartic proteases. By use of a temperature-sensitive mutant strain, sec18, the generation of the two subunits was found to occur in the endoplasmic reticulum. An active site-mutated yapsin 1 was not processed into the two subunits, suggesting that this process occurs in an autocatalytic manner.

Altered biosynthesis and secretion of pro-opiomelanocortin in the intermediate and anterior pituitary of carboxypeptidase E-deficient, Cpe(fat)/ Cpe(fat)mice

The biosynthesis and secretion of pro-opiomelanocortin (POMC) was examined in the pituitary of Cpe(fat)/ Cpe(fat)mice, which are deficient in carboxypeptidase E, a sorting receptor for the regulated secretory pathway (Cool D R, Normant E, Shen F S, et al. Cell 1997; 83: 73-83). Dopamine inhibited forskolin-stimulated accumulation of cAMP in the intermediate lobe of Cpe(fat)/ Cpe(fat)mice, showing that their dopamine receptors were fully functional. This result indicates that the elevated, dopamine-insensitive POMC secretion previously observed in the intermediate pituitary of Cpe(fat)/ Cpe(fat)mice was constitutive, rather than due to defective dopamine receptors. Concomitant with the increase in POMC secretion was a twofold increase in POMC mRNA levels and [(35)S]-methionine incorporation into POMC. In the anterior pituitary of Cpe(fat)/ Cpe(fat)mice, a 1.6-fold increase in basal release of POMC was accompanied by a similar increase in [(35)S]-methionine incorporation into POMC, although POMC mRNA levels were unchanged. Thus, the intermediate and anterior pituitary of Cpe(fat)/ Cpe(fat)mice compensate for the constitutive secretion of POMC by upregulating biosynthesis.

Identification and characterization of Saccharomyces cerevisiae yapsin 3, a new member of the yapsin family of aspartic proteases encoded by the YPS3 gene

A new aspartic protease from Saccharomyces cerevisiae, with a high degree of similarity with yapsin 1 and yapsin 2 and a specificity for basic residue cleavage sites of prohormones, has been cloned. This enzyme was named yapsin 3. Expression of a C-terminally truncated non-membrane anchored yapsin 3 in yeast yielded a heterogeneous protein between 135-200 kDa which, upon treatment with endoglycosidase H, migrated as a 60 kDa form. Amino-acid analysis of the N-terminus of expressed yapsin 3 revealed two different N-terminal residues, serine-48 and phenylalanine-54, which followed a dibasic and a monobasic residue respectively. Cleavage of several prohormones by non-anchored yapsin 3 revealed a specificity distinct from that of yapsin 1.

Identification of a novel prohormone sorting signal-binding site on carboxypeptidase E, a regulated secretory pathway-sorting receptor

Sorting of the prohormone POMC to the regulated secretory pathway necessitates the binding of a sorting signal to a sorting receptor, identified as membrane carboxypeptidase E (CPE). The sorting signal, located at the N terminus of POMC consists of two acidic (Asp10, Glu14) and two hydrophobic (Leu11, Leu18) residues exposed on the surface of an amphipathic loop. In this study, molecular modeling of CPE predicted that the acidic residues in the POMC-sorting signal bind specifically to two basic residues, Arg255 and Lys260, present in a loop unique to CPE, compared with other carboxypeptidases. To test the model, these two residues on CPE were mutated to Ser or Ala, followed by baculovirus expression of the mutant CPEs in Sf9 cells. Sf9 cell membranes containing CPE mutants with either Arg255 or Lys260, or both residues substituted, showed no binding of [125I]N-POMC1-26 (which contains the POMC-sorting signal motif), proinsulin, or proenkephalin. In contrast, substitution of an Arg147 to Ala147 at a substrate-binding site, Arg259 to Ala259 and Ser202 to Pro202, in CPE did not affect the level of [125I]N-POMC1-26 binding when compared with-wild type CPE. Furthermore, mutation of the POMC-sorting signal motif (Asp10, Leu11, Glu14, Leu18) eliminated binding to wild-type CPE. These results indicate that the sorting signal of POMC, proinsulin, and proenkephalin specifically interacts with Arg255 and Lys260 at a novel binding site, independent of the active site on CPE.

Vasopressin gene expression in rat choroid plexus

Vasopressin (VP) levels in cerebrospinal fluid (CSF) change in response to physiological stimuli and under various pathological conditions. The sources of CSF VP have yet to be clarified, however. In the present study, we provide evidence indicating that VP is synthesized in the choroid plexus, the primary site of CSF formation. All experiments were performed on adult male Sprague-Dawley rats. The presence of VP mRNA in choroid plexus epithelium was demonstrated by in situ hybridization histochemistry using the 35S-labeled riboprobe that was complementary to cDNA fragment of rat VP encoding the C-terminus part of proVP. In situ hybridization findings were confirmed by reverse transcriptase-polymerase chain reaction analysis. Immunohistochemistry for VP-associated neurophysin (VP-NP), a polypeptide component of proVP, revealed subapical accumulation of VP-NP-immunopositive product in choroidal epithelial cells. Immunoprecipitation and immunoblotting of choroidal protein extracts with anti-VP-NP antibody demonstrated the presence of a approximately 10-kD polypeptide that was also detected in hypothalamus. We hypothesize that the choroid plexus-derived VP exerts autocrine and/or paracrine effects on tissues near the CSF system.

Carboxypeptidase E is a sorting receptor for prohormones: binding and kinetic studies

The binding of pro-opiomelanocortin,(POMC), pro-insulin, pro-enkephalin and chromogranin A (CGA) to the regulated secretory pathway sorting receptor, carboxypeptidase E (CPE), in bovine pituitary secretory granule (SG) membranes was investigated. N-POMC1-26, which contains the POMC sorting signal, bound to CPE in the SG membranes with low affinity and the binding was ion independent. Pro-insulin bound CPE with similar kinetics. Pro-enkephalin, but not CGA bound to CPE with similar IC50 as pro-insulin and N-POMC1-26. Crosslinking studies showed that pro-insulin and pro-enkephalin bound specifically to SG membrane CPE, similar to N-POMC1-26 reported previously. CPE was extracted from the SG membranes with NaHCO3 or KSCN, but not Triton X-100/1 M NaCl. The results show that CPE is tightly associated with SG membranes and binds several prohormones, but not CGA, with similar kinetics, providing further evidence that membrane CPE has the characteristics to function as a common sorting receptor for targeting prohormones to the regulated secretory pathway.

Depletion of carboxypeptidase E, a regulated secretory pathway sorting receptor, causes misrouting and constitutive secretion of proinsulin and proenkephalin, but not chromogranin A

Previous studies have shown that the prohormone POMC is sorted to the regulated secretory pathway (RSP), at the trans-Golgi network, by binding of a conformation-dependent sorting signal to a sorting receptor, identified as membrane-bound carboxypeptidase E (CPE) (Cool et al., 1997, Cell, 88:73-83). In this study, the role of CPE as a sorting receptor for other RSP proteins that contain sorting signals (proinsulin, proenkephalin, and chromogranin A) was investigated in neuroendocrine cells (Neuro-2a) stably expressing CPE antisense RNA. Whereas these cells were depleted of CPE by greater than 85%, electron microscopy showed that they contain dense core secretory granules identical to wild-type Neuro-2a cells, indicating that CPE is not essential for granulogenesis. Secretion and immunocytochemical studies showed that, in wild-type Neuro-2a cells, endogenous proenkephalin and transfected proinsulin/insulin were localized to punctate secretory granules and were released via the RSP. However, in CPE-depleted cells, these two prohormones were released constitutively and had a Golgi-like distribution but were not localized to punctate secretory granules. In contrast, chromogranin A was present in punctate secretory granules and released via the RSP, in wild-type and CPE-depleted Neuro-2a cells. Thus, the sorting of proinsulin and proenkephalin to the RSP, like POMC, necessitates binding to CPE, and hence, CPE acts as a common sorting receptor for targeting these prohormones to the RSP. In contrast, the sorting signal of chromogranin A does not use CPE as a sorting receptor, suggesting the existence of other sorting receptors for the RSP.

Cleavage efficiency of the novel aspartic protease yapsin 1 (Yap3p) enhanced for substrates with arginine residues flanking the P1 site: correlation with electronegative active-site pockets predicted by molecular modeling

Yapsin 1, a novel aspartic protease with unique specificity for basic residues, was shown to cleave CCK13-33 at Lys23. Molecular modeling of yapsin 1 identified the active-site cleft to have negative residues close to or within the S6, S3, S2, S1, S1', S2', and S3' pockets and is more electronegative than rhizopuspepsin or endothiapepsin. In particular, the S2' subsite has three negative charges in and close to this pocket that can provide strong electrostatic interactions with a basic residue. The model, therefore, predicts that substrates with a basic residue in the P1 position would be favored with additional basic residues binding to the other electronegative pockets. A deletion of six residues close to the S1 pocket in yapsin 1, relative to rhizopuspepsin and other aspartic proteases of known 3D structure, is likely to affect its specificity. The model was tested using CCK13-33 analogues. We report that yapsin 1 preferentially cleaves a CCK13-33 substrate with a basic residue in the P1 position since the substrates with Ala in P1 were not cleaved. Furthermore, the cleavage efficiency of yapsin 1 was enhanced for CCK13-33 analogues with arginine residues flanking the P1 position. An alanine residue, substituting for the arginine residue in the P6 position in CCK13-33, resulted in a 50% reduction in the cleavage efficiency. Substitution with arginine residues downstream of the cleavage site at the P2', P3', or P6' position increased the cleavage efficiency by 21-, 3- and 7-fold, respectively. Substitution of Lys23 in CCK13-33 with arginine resulted not only in cleavage after the substituted arginine residue, but also forced a cleavage after Met25, suggesting that an arginine residue in the S2' pocket is so favorable that it can affect the primary specificity of yapsin 1. These results are consistent with the predictions from the molecular model of yapsin 1.

Enhanced brain opioid receptor activity precedes blood-brain barrier disruption

We studied the effects of transient postischemic increased opioid receptors (OPR) binding (mu, delta, kappa) on blood-brain barrier (BBB), brain water content and brain mitochondrial oxidative enzymes system. Cats were exposed to temporary middle cerebral artery occlusion (MCAO). The significant increased OPR bindings observed 10 min after the release of MCAO (ischemic rCBF = 7 +/- 1 to 11 +/- 2 ml/100 g/min) preceded the early and late BBB disruptions, brain edema and postischemic impaired mitochondrial oxidative enzymes functions. Further, the study suggests indirectly that the latter process was irreversible and hence associated with subsequent ischemic cerebral infarction. In addition, the results revealed a possible viable therapeutic window in the early postischemic recirculation period, before the onset of impaired mitochondrial oxidative function.

Activation and processing of non-anchored yapsin 1 (Yap3p)

A C-terminally truncated form of yapsin 1 (yeast aspartic protease 3), the first member of the novel sub-class of aspartic proteases with specificity for basic residues (designated the Yapsins), was overexpressed and purified to apparent homogeneity, yielding approximately 1 microg of yapsin 1/g of wet yeast. N-terminal amino acid analysis of the purified protein confirmed that the propeptide was absent and that the mature enzyme began at Ala68. The mature enzyme was shown to be composed of approximately equimolar amounts of two subunits, designated alpha and beta, that were associated to each other by a disulfide bond. C-terminally truncated proyapsin 1 was also expressed in the baculovirus/Sf9 insect cell expression system and secreted as a zymogen that could be activated upon incubation at an acidic pH with an optimum at approximately 4.0. When expressed without its pro-region, it was localized intracellularly and lacked activity, indicating that the pro-region was required for the correct folding of the enzyme. The activation of proyapsin 1 in vitro exhibited linear kinetics and generated an intermediate form of yapsin 1 or pseudo-yapsin 1.

High-performance liquid chromatographic-colorimetric assay for glycine carboxypeptidase activity

A rapid and sensitive assay method for the determination of glycine carboxypeptidase activity has been reported. This method is based on the monitoring of the absorption at 460 nm of 4-dimethylaminoazobenzene-4'-sulfonyl-Gly-L-Phe, enzymatically formed from the substrate 4-dimethylaminoazobenzene-4'-sulfonyl-Gly-L-Phe-Gly, after separation by high-performance liquid chromatography (HPLC) using a TSK gel ODS-80TM reversed-phase column by isocratic elution. This method is sensitive enough to measure 4-dimethylaminoazobenzene-4'-sulfonyl-Gly-L-Phe at concentrations as low as 1 pmol and yield highly reproducible results and requires less than 7.5 min per sample for separation and quantitation. The pH optimum for glycine carboxypeptidase activity was 4.8 to 5.4. The Km and Vmax values were respectively 21.1 micromol and 3.73 pmol/microg/h with the use of enzyme extract obtained from bovine pituitary. Glycine carboxypeptidase activity was strongly inhibited by Ag+, Cu2+ and p-chloromercuriphenylsulfonic acid. Among the organs examined in a mouse, the highest specific activity of the enzyme was found in testis. The sensitivity and selectivity of this method will aid in efforts to examine the physiological role of this peptidase.

The presence of arginine vasopressin and its mRNA in rat choroid plexus epithelium

Arginine vasopressin (AVP) plays an important role in the regulation of secretory function and hemodynamics of choroid plexus, the primary site of cerebrospinal fluid (CSF) production. In the present study, localization of AVP and its transcripts in choroid plexus of adult male Sprague-Dawley rats was studied by immunohistochemistry and in situ hybridization histochemistry, respectively. For immunohistochemical analysis, AVP-specific polyclonal rabbit antibody was employed. Plasmid, pGrVP, containing a 232-bp fragment of rat AVP cDNA encoding the C-terminus of proAVP, was used as a probe to detect AVP mRNA. AVP-immunoreactive product was predominantly localized close to the apical (CSF-facing) membrane of choroidal epithelium while AVP transcripts were distributed throughout the cytoplasm of the cells. Our findings indicate that AVP is synthesized in choroid plexus epithelium, which suggests autocrine and/or paracrine actions of this peptide in choroidal tissue.

Intracellular misrouting and abnormal secretion of adrenocorticotropin and growth hormone in cpefat mice associated with a carboxypeptidase E mutation

Cpefat mice carry a mutation in the carboxypeptidase E/H gene which encodes an exopeptidase that removes C-terminal basic residues from endoproteolytically cleaved hormone intermediates. These mice have endocrine disorders including obesity, infertility, and hyperproinsulinemia-diabetes syndrome, but the etiology remains an enigma. Because studies have identified membrane carboxypeptidase E as a sorting receptor for targeting prohormones to the regulated secretory pathway for processing and secretion, the intracellular routing and secretion of pro-opiomelanocortin/adrenocorticotropin and growth hormone from anterior pituitary cells were investigated in Cpefat mice. In Cpefat mice, pro-opiomelanocortin was accumulated 24-fold above normal animals in the pituitary and it was poorly processed to adrenocorticotropin. Furthermore, pro-opiomelanocortin was secreted constitutively at high levels, showing no response to stimulation by corticotropin-releasing hormone. Similarly, growth hormone release was constitutive and did not respond to high K+ stimulation. Both pro-opiomelanocortin and growth hormone levels were elevated in the circulation of Cpefat mice versus normal mice. These data provide evidence that the lack of carboxypeptidase E, the sorting receptor, results in the intracellular misrouting and secretion of pro-opiomelanocortin and growth hormone via the constitutive pathway in the pituitary of Cpefat mice.

Receptor-mediated targeting of hormones to secretory granules: role of carboxypeptidase E

Peptide hormones, neuropeptides, and other molecules such as the granins are specifically packaged into granules of the regulated secretory pathway and released in a calcium-dependent manner upon stimulation. Many of these molecules are synthesized as larger precursors (prohormones) that are processed to biologically active products within the granules. It has now become apparent that prohormones, proneuropeptides, and the granins contain conformation-dependent sorting signal motifs that facilitate their specific sorting and packaging into regulated secretory granules. Recently, a receptor to which these sorting signals bind has been identified as the membrane form of carboxypeptidase E (CPE) and localized to the Golgi apparatus, where sorting occurs, specifically at the trans-Golgi network. In this article, we review the evidence for a sorting signal-receptor-mediated mechanism for routing peptide hormones and prohormones to the regulated secretory granules. We also describe a mouse model, Cpe(fat), which has the CPE gene naturally mutated. Pituitary hormones were misrouted and secreted in an unregulated manner via the constitutive pathway in these Cpe(fat) mice, leading to endocrine disorders.

The structure of synenkephalin (pro-enkephalin 1-73) is dictated by three disulfide bridges

Mass spectrometry of fragments produced by limited proteolytic digestion of pro-enkephalin was used to locate the disulfide bridges in synenkephalin (pro-enkephalin 1-73), a domain which contains sorting information for targeting the pro-neuropeptide to the granules of the regulated secretory pathway in neuroendocrine cells. Mass spectrometric analysis was optimized by using chemicals that gave low interference with the ionization and desorption processes, and computer software which simplified the identification of all possible disulfide-linked peptide fragments. Three disulfide bridges between Cys2-Cys24, Cys6-Cys28, and Cys9-Cys41 were identified. Protein conformational prediction of synenkephalin1-42 shows beta-turns which facilitate the formation of these disulfide bonds.

Carboxypeptidase E is a regulated secretory pathway sorting receptor: genetic obliteration leads to endocrine disorders in Cpe(fat) mice

A proposed mechanism for sorting secretory proteins into granules for release via the regulated secretory pathway in endocrine-neuroendocrine cells involves binding the proteins to a sorting receptor at the trans-Golgi network, followed by budding and granule formation. We have identified such a sorting receptor as membrane-associated carboxypeptidase E (CPE) in pituitary Golgi-enriched and secretory granule membranes. CPE specifically bound regulated secretory pathway proteins, including prohormones, but not constitutively secreted proteins. We show that in the Cpe(fat) mutant mouse lacking CPE, the pituitary prohormone, pro-opiomelanocortin, was missorted to the constitutive pathway and secreted in an unregulated manner. Thus, obliteration of CPE, the sorting receptor, leads to multiple endocrine disorders in these genetically defective mice, including hyperproinsulinemia and infertility.

Yeast aspartic protease 3 is sorted to secretory granules and activated to process proopiomelanocortin in PC12 cells

The subcellular localization and functionality of transfected yeast aspartic protease 3 (YAP3p) in a mammalian cell line were investigated. The complementary DNAs encoding the prohormone-processing enzyme (YAP3p) and a prohormone, bovine POMC, were cotransfected into PC12 (rat pheochromocytoma) cells. Immunocytochemical analysis of the cells using a YAP3p antibody showed a perinuclear punctate distribution of YAP3p in the cell body as well as immunostaining in the tips of the neurites. This pattern of immunostaining indicates localization of YAP3p in secretory granules. Analysis of the processing of POMC showed that in cells transfected with the POMC complementary DNA alone, only POMC was found, indicating a lack of processing of the prohormone. However, in cells coexpressing YAP3p, the POMC was completely processed to yield ACTH-(1-39) and ACTH-(1-14), consistent with the specificity of YAP3p found in vitro. Pulse-chase studies showed that POMC was processed after 20 min of chase, suggesting that processing occurred in the late Golgi network and continued in the secretory granules. Western blot analysis determined that YAP3p was secreted from the cells in a regulated manner. This study provides the first demonstration that a yeast prohormone-processing enzyme (YAP3p) of the aspartic protease class can be sorted correctly to secretory granules and activated to process a prohormone (POMC) in a highly efficient manner in mammalian cells.

Immunological identification and localization of yeast aspartic protease 3-like prohormone-processing enzymes in mammalian brain and pituitary

The novel aspartic proteases, yeast aspartic protease 3 and the mammalian POMC-converting enzyme (PCE), can process prohormones at specific basic residue cleavage sites. We show that an antibody against yeast aspartic protease 3 (YAP3p) cross-reacted with purified bovine PCE on Western blot, indicating structural homology between these two enzymes, but not with other aspartic proteases, such as renin or cathepsin D. A PCE-sized anti-YAP3p-immunoreactive band was detected on Western blots of bovine intermediate lobe where PCE activity has been found. YAP3p antiserum also cross-reacted with a protein of approximately 90 kDa from mouse hypothalamus and anterior pituitary, and bovine anterior pituitary secretory granules. Distribution studies showed the presence of anti-YAP3p-immunopositive cells in bovine pituitary and peptide-rich brain regions, including the mouse arcuate nucleus and hippocampus and the rat supraoptic nucleus, paraventricular nucleus, cortex, striatum, and reticular nucleus. In the bovine intermediate pituitary, a subpopulation of cells was intensely stained with the YAP3p antiserum, and in combination with in situ hybridization, these cells were shown to contain POMC messenger RNA (mRNA). Only a subpopulation of cells was immunopositive for anti-YAP3p in bovine anterior pituitary, and most of these cells were identified by double immunostaining with ACTH antiserum as corticotrophs. In situ hybridization in combination with immunocytochemistry provided evidence for the localization of arginine vasopressin mRNA in YAP3p-immunopositive neurons in the rat supraoptic nucleus, whereas cholecystokinin mRNA was detected in YAP3p-immunopositive cells in the rat cortex and hippocampus. These results support the hypothesis that YAP3p-like aspartic proteases, including PCE, play a role in prohormone processing in endocrine/neuroendocrine cells in vivo.

Etiology of the differences in corticotropin-releasing hormone-induced adrenocorticotropin secretion of black and white women

After i.v. oCRH, plasma immunoreactive ACTH (ACTH-IR) is significantly greater in blacks than in whites; however, there is no corresponding increase in cortisol secretion. To test the hypothesis that there are black-white differences in adrenal responsiveness to ACTH that underlie this phenomenon, weight-, age-, and education-matched black (n = 10) and white (n = 10) women were i.v. infused with 5 differing doses of ACTH1-24 (0, 0.003, 0.01, 0.1, and 1 microgram/kg) with measured plasma cortisol and DHEA. To test the alternative hypothesis that greater post-CRH plasma ACTH-IR in blacks is caused by qualitative differences in circulating ACTH-immunoreactive peptides, we collected pre- and post-CRH plasma from 5 black and 5 white women and measured ACTH-IR after sample fractionation, using high-pressure liquid chromatography. There were no racial differences in adrenal responsiveness to differing doses of ACTH1-24 and no differences in the distribution of the forms of ACTH-IR before CRH. After CRH, whites had predominant ACTH-IR peaks at the retention times of ACTH1-39 and ACTH1-39-sulfoxide, whereas blacks had prominent peaks at several additional retention times. The post-CRH ratio of intact to total ACTH was significantly lower in blacks than in whites (0.27 +/- 0.17 vs. 0.71 +/- 0.17, P < 0.003). We conclude that there are qualitative differences in post-CRH circulating ACTH-IR in blacks and whites, leading to a greater immunoreactive to bioactive ACTH ratio in blacks. Such differences in the circulating forms of ACTH can account for greater CRH-stimulated ACTH-IR in blacks.

Differential coexpression of genes encoding prothyrotropin-releasing hormone (pro-TRH) and prohormone convertases (PC1 and PC2) in rat brain neurons: implications for differential processing of pro-TRH

Pro-TRH is cleaved at paired basic residues to yield five copies of TRH and cryptic peptides. Recent studies have shown that the prohormone convertases, PC1 and PC2, can process pro-TRH correctly. To determine whether these two enzymes could play a role in pro-TRH processing in vivo, the regional and cellular colocalization of pro-TRH messenger RNA (mRNA) with the mRNAs encoding the prohormone convertases PC1 and PC2 was examined in rat brain, using in situ hybridization histochemistry. Differential regional distribution of pro-TRH mRNA with PC1 and/or PC2 mRNA was found in several brain regions. For example, in the olfactory regions, there was coexpression of pro-TRH mRNA in the glomerular layer with PC2 mRNA, but not PC1 mRNA, whereas in the tenia tecta, coexpression of pro-TRH and PC1 mRNAs was evident, but PC2 mRNA was absent. Pro-TRH mRNA in the paraventricular nucleus was coexpressed with both PC1 and PC2 mRNAs, whereas the basal lateral hypothalamus showed coexistence of pro-TRH mRNA with PC2 mRNA, but not PC1 mRNA. Interestingly, pro-TRH was expressed in the thalamic reticular nucleus, but neither PC1 nor PC2 was detectable in this region. Cellular colocalization studies using double in situ hybridization histochemistry showed the presence of PC2 mRNA in the pro-TRH neurons of the olfactory glomerular layer and basal lateral hypothalamus, and PC1 mRNA in the pro-TRH neurons in the paraventricular nucleus. These results suggest that PC1 and PC2 are enzyme candidates for the processing of pro-TRH in vivo. Moreover, the differential distribution of PC1 and PC2 mRNAs with pro-TRH mRNA may be responsible for the differential processing of this prohormone in the central nervous system. The absence of PC1 and PC2 mRNAs in certain TRH neurons raises the possibility that prohormone convertases other than PC1 and PC2 may be involved in the processing of brain pro-TRH.

Yeast aspartic protease 3 (Yap3) prefers substrates with basic residues in the P2, P1 and P2' positions

The yeast aspartic protease Yap3 is localised to the secretory pathway and correctly cleaves pro-alpha-mating factor at its dibasic sites. We determined the specificity of Yap3 for mono-, di-, and multi-basic cleavage sites in the context of 15 residue synthetic proalbumin peptides. Yap3 cleaved after dibasic ArgArg and LysArg sites but not after monobasic Arg sites even when there was an additional arginine at -6 and/or -4. Yap3 did not cleave a tetra-arginine site and tri-basic sites (RRR and RRK) were poor substrates. Cleavage always occurred C-terminal to the last arginine in the di- or tri-basic sequence. The optimal cleavage site sequence was RR DR and this substrate was cleaved 8-9-fold faster than the normal RR DA sequence. In contrast to Kex2, Yap3 did not remove the propeptide from normal proalbumin or a range of natural or recombinant proalbumin variants. However at pH 4.0 Yap3 slowly cleaved proalbumin and albumin between domains 2 and 3.

Specificity and kinetic studies on the cleavage of various prohormone mono- and paired-basic residue sites by yeast aspartic protease 3

The specificity and relative efficiency of cleavage of mono- and paired-basic residue processing sites by YAP3p was determined in vitro for a number of prohormone substrates: human ACTH1 39, bovine proinsulin, porcine cholecystokinin 33, cholecystokinin (CCK) 13-33, dynorphin A(1-11), dynorphin B(1-13), and amidorphin. YAP3p generated ACTH1-15 from ACTH1-39. It cleaved proinsulin at the paired-basic residue sites of the B-C junction as well as the C-A junction. Leu-enkephalin-Arg and Leu-enkephalin-Arg-Arg were generated from dynorphin A and dynorphin B, respectively. YAP3p generated Met-enkephalin-Lys-Lys from amidorphin showing that cleavage by this enzyme can occur at a lone pair of Lys residues. CCK33 was cleaved at Lys23 and Arg9, each containing an upstream Arg residue at the P6 and P5 position, respectively. Km values were between 10(-4) and 10(-5) M for the various substrates, with the highest affinity exhibited for the tetrabasic site of ACTH1-39 (1.8 x 10(-5) M). The tetrabasic residue site of ACTH1-39 was cleaved with the highest relative efficiency (kcat/Km = 3.1 x 10(6) m-1 s-1), while that of the monobasic site of CCK13-33 and the paired-basic site of proinsulin B-C junction, were cleaved less efficiently at 4.2 x 10(4) m-1 s-1 and 1.6 x 10(4) m-1 s-1, respectively.

Processing of pro-opiomelanocortin in GH3 cells: inhibition by prohormone convertase 2 (PC2) antisense mRNA

The processing of pro-opiomelanocortin (POMC) was examined in GH3 cells, a rat sommatomammotrope cell line, by transiently-transfecting the cells with mouse POMC cDNA. The peptide products were extracted, chromatographed on HPLC and identified by specific radioimmunoassay. POMC was processed to generate ACTH-related peptides, beta-endorphin and Lys-gamma 3- MSH, with complete disappearance of the POMC precursor. The ACTH-related molecules were identified as ACTH1-14, ACTH1-15, ACTH1-17, as well as ACTH1-39. GH3 cells which were not transfected with POMC cDNA did not contain endogenous POMC-related peptides. RT-PCR demonstrated that GH3 cells contain prohormone convertase 2 (PC2) mRNA but no PC1 mRNA. To determine if PC2 was the enzyme responsible for POMC processing in this cell line, GH3 cells were stably-transfected with PC2 antisense cDNA. A cell line was obtained which showed an absence of PC2 protein compared to control untransfected GH3 cells, indicating successful hybridization of PC2 antisense mRNA to the endogenous PC2 mRNA. When this cell line was then transiently-transfected with POMC cDNA, POMC was not processed. The results from these experiments suggest that PC2 alone can correctly process POMC to biologically active smaller peptides in vivo. Additionally, the GH3 cell line with and without incorporation of PC2 antisense cDNA can be used as a model system to study the role of PC2 in the post-translational processing of other prohormones and proproteins in vivo.

Pro-thyrotropin-releasing hormone processing by recombinant PC1

Pro-thyrotropin-releasing hormone (proTRH) is the precursor to thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH2), the hypothalamic releasing factor that stimulates synthesis and release of thyrotropin from the pituitary gland. Five copies of the TRH progenitor sequence (Gln-His-Pro-Gly) and seven cryptic peptides are formed following posttranslational proteolytic cleavage of the 26-kDa rat proTRH precursor. The endopeptidase(s) responsible for the physiological conversion of proTRH to the TRH progenitor form is currently unknown. We examined the in vitro processing of [3H]leucine-labeled or unlabeled proTRH by partially purified recombinant PC1. Recombinant PC1 processed the 26-kDa TRH precursor by initially cleaving the prohormone after the basic amino acid at either position 153 or 159. Based on the use of our well-established antibodies, we propose that the initial cleavage gave rise to the formation of a 15-kDa N-terminal peptide (preproTRH25-152 or pre-proTRH25-158) and a 10-kDa C-terminal peptide (pre-proTRH154-255 or preproTRH160-255). Some initial cleavage occurred after amino acid 108 to generate a 16.5-kDa C-terminal peptide. The 15-kDa N-terminal intermediate was further processed to a 6-kDa peptide (prepro-TRH25-76 or preproTRH25-82) and a 3.8-kDa peptide (preproTRH83-108), whereas the 10-kDa C-terminal intermediate was processed to a 5.4-kDa peptide (prepro-TRH206-255). The optimal pH for these cleavages was 5.5. ZnCl2, EDTA, EGTA, and the omission of Ca2+ inhibited the formation of pYE27 (preproTRH25-50), one of the proTRH N-terminal products, by 48, 82, 72, and 45%, respectively. This study provides evidence, for the first time, that recombinant PC 1 enzyme can process proTRH to its predicted peptide intermediates.

Localization of vasopressin mRNA and immunoreactivity in pituicytes of pituitary stalk-transected rats after osmotic stimulation

The presence of [arginine] vasopressin (AVP) mRNA and AVP immunoreactivity in pituicytes of the neural lobe (NL) of intact and pituitary stalk-transected rats, with and without osmotic stimulation, was examined. AVP mRNA was analyzed by Northern blotting, as well as by in situ hybridization in combination with immunocytochemistry using anti-glial fibrillary acidic protein (GFAP) as a marker for pituicytes. In intact rats, a poly(A) tail-truncated 0.62-kb AVP mRNA was detected in the NL and was found to increase 10-fold with 7 days of continuous salt loading. Morphological analysis of the NL of 7-day salt-loaded rats revealed the presence of AVP mRNA in a significant number of GFAP-positive pituicytes in the NL and in areas most probably containing nerve fibers. Eight days after pituitary stalk transection the NL AVP mRNA diminished in animals given water to drink, whereas in those given 2% saline for 18 h followed by 6 h of water, a treatment repeated on 6 successive days beginning 2 days after surgery, the 0.62-kb AVP mRNA was present. The AVP mRNA in the pituitary stalk-transected, salt-loaded rats showed an exclusive cellular distribution in the NL, indicative of localization in pituicytes. Immunoelectron microscopy showed the presence of AVP immunoreactivity in a subpopulation of pituicytes 7 and 10 days after pituitary stalk transection in salt-loaded animals, when almost all AVP fibers had disappeared from the NL. These data show that a subset of pituicytes in the NL is activated to synthesize AVP mRNA and AVP in response to osmotic stimulation.

Comparison of the molecular forms of the Kex2/subtilisin-like serine proteases SPC2, SPC3, and furin in neuroendocrine secretory vesicles reveals differences in carboxyl-terminus truncation and membrane association

The molecular forms and membrane association of SPC2, SPC3, and furin were investigated in neuroendocrine secretory vesicles from the anterior, intermediate, and neural lobes of bovine pituitary and bovine adrenal medulla. The major immunoreactive form of SPC2 was the full-length enzyme with a molecular mass of 64 kDa. The major immunoreactive form of SPC3 was truncated at the carboxyl terminus and had a molecular mass of 64 kDa. Full-length 86-kDa SPC3 with an intact carboxyl terminus was found only in bovine chromaffin granules. Immunoreactive furin was also detected in secretory vesicles. The molecular masses of 80 and 76 kDa were consistent with carboxyl-terminal truncation of furin to remove the transmembrane domain. All three enzymes were distributed between the soluble and membrane fractions of secretory vesicles although the degree of membrane association was tissue specific and, in the case of SPC3, dependent on the molecular form of the enzyme. Significant amounts of membrane-associated and soluble forms of SPC2, SPC3, and furin were found in pituitary secretory vesicles, whereas the majority of the immunoreactivity in chromaffin granules was membrane associated. More detailed analyses of chromaffin granule membranes revealed that 86-kDa SPC3 was more tightly associated with the membrane fraction than the carboxyl terminus-truncated 64-kDa form.

Processing of prothyrotropin-releasing hormone (Pro-TRH) by bovine intermediate lobe secretory vesicle membrane PC1 and PC2 enzymes

TRH is synthesized from a larger 26-kilodalton (kDa) prohormone (pro-TRH). Rat pro-TRH contains five copies of the TRH progenitor sequence (Gln-His-Pro-Gly) and seven other cryptic peptides. Each of the five TRH progenitor sequences is flanked by pairs of basic amino acids. We used a bovine intermediate lobe secretory vesicle membrane preparation, which contains the prohormone convertases (PCs) PC1 and PC2, to study the in vitro processing of pro-TRH. Pro-TRH was radiolabeled using [3H]Leu in AtT20 cells transfected with prepro-TRH complementary DNA, and the labeled 26-kDa pro-TRH was isolated from the cell extract by preparative sodium dodecyl sulfate-gel electrophoresis. Incubation of [3H]pro-TRH with the intermediate lobe secretory vesicle membrane preparation was followed by immunoprecipitation with antibodies specific for various regions of the pro-TRH sequence, and the immunoprecipitates were analyzed by sodium dodecyl sulfate-gel electrophoresis. Immunoprecipitation of the reaction mixture with anti-pCC10 antibody (an antibody that recognizes the intact precursor and amino-terminal intermediate products of processing) showed a time-dependent appearance of a 15-kDa and a 6-kDa peptide and, at times, a 3.8-kDa peptide with diminution of the 26-kDa substrate. Immunoprecipitation of the incubate with the C-terminal-directed antibody, pYE17 (an antibody that recognizes the intact precursor and C-terminal intermediate products of processing), showed the generation of 16.5-, 10-, and 5.4-kDa products in a time-dependent manner, with disappearance of the substrate. Western blot analysis demonstrated that the secretory vesicle membrane preparation contains PC1 and PC2. Immunodepletion studies with antiserum specific for PC1 or PC2 demonstrated that PC1 and PC2 can process pro-TRH to these intermediate products. An initial site of cleavage appeared to be either at the 152-153 or the 158-159 pair of basic residues to yield a 15-kDa N-terminal fragment that was then processed to the 6-kDa [TRH-(25-74)] and 3.8-kDa [TRH-(83-112)] forms. The 10-kDa C-terminal peptide generated by this cleavage was then processed to a 5.4-kDa peptide [TRH-(208-255)]. Alternatively, an initial cleavage at the 107-108 or the 112-113 bonds was also observed, yielding a 16.5-kDa C-terminal product that was further processed to the 5.4-kDa peptide. The pH profile for the appearance of both C- and N-terminal products showed a bimodal distribution, with optima at both 5.5 and 7.5. The cleavage of pro-TRH was enhanced by Ca2+ and partially inhibited by Zn2+.(ABSTRACT TRUNCATED AT 400 WORDS)

The Neuro-2a neuroblastoma cell line expresses [Met]-enkephalin and vasopressin mRNA and peptide

Mouse neuroblastoma Neuro-2a cells were examined for the expression of pro-enkephalin mRNA, protein, and Met-enkephalin ([Met]-Enk) peptide. Reverse transcriptase/polymerase chain reaction (RT/PCR) and in situ hybridization demonstrated the presence of pro-enkephalin mRNA in these cells. Immunocytochemistry using an antibody which recognizes pro-enkephalin and high pressure liquid chromatography (HPLC) followed by radioimmunoassay indicated that pro-enkephalin was synthesized in these cells and processed to yield the bioactive pentapeptide, [Met]-Enk. Furthermore, release studies showed that the [Met]-Enk was secreted from these cells with high K+ stimulation. Using double labeling, in situ hybridization combined with immunocytochemistry, we demonstrated that prohormone convertase 2 (PC2) mRNA is colocalized with pro-enkephalin in the same Neuro-2a cells, suggesting that this enzyme may be responsible for processing this precursor. we also showed the presence of vasopressin mRNA and arginine-vasopressin peptide in these cells using in situ hybridization and immunocytochemistry, respectively. Thus, the Neuro-2a cells are a multiple neuropeptide-producing cell line and an excellent model for studying the mechanisms involved in the synthesis, intracellular targeting and processing of endogenous pro-enkephalin and pro-vasopressin, as well as other transfected neuropeptide precursors.

Expression of pit-1 messenger ribonucleic acid and protein in the human placenta

It is well established that the human placenta produces a wide range of hormones similar to those secreted by the pituitary and hypothalamus. However, the physiological role and regulation of placental hormone synthesis and release are still largely unknown. GH (GH-N) is expressed in the pituitary, where it requires the tissue-specific transcription factor Pit-1. Chorionic somatomammotropin A (CS-A) and CS-B as well as the placental GH variant (GH-V), which also belong to the GH gene family and are located in the same chromosomal cluster, are expressed in the placental syncytiotrophoblast. The presence of Pit-1-binding sites in the CS-A and GH-V promoter regions predicts that Pit-1 may be expressed in the placenta. However, this has not yet been demonstrated. To examine possible similarities in the regulation of these genes in the pituitary and placenta, we studied the expression of pit-1 messenger ribonucleic acid (mRNA) in the human placenta, transformed human placental cells, and the JEG-3 choriocarcinoma cell line. Polymerase chain reaction (PCR) products of the expected size were amplified from first and third trimester placentas, transformed placental cells, and JEG-3 complementary DNA by reverse transcription-PCR. The pit-1-specific sequence was confirmed by restriction endonuclease digestion, Southern hybridization, and DNA sequencing. Human pituitary tissue was used as a positive control; no PCR product was obtained from hippocampus (negative control). In situ hybridization of placental tissue sections revealed the presence of pit-1 mRNA in first and third trimester syncytiotrophoblast. Pit-1 protein was localized by immunohistochemistry with the same tissue distribution and a nuclear localization pattern. These data demonstrate expression of pit-1 mRNA and Pit-1 protein in the human placenta, thus questioning its role as a pituitary-specific regulator of GH-N gene transcription. The expression of Pit-1 in the placenta, together with its previously demonstrated capability to bind to and activate the CS-A and the GH-V promoters, suggests that it may play a role in the regulation of hormones belonging to the GH gene family in both pituitary and placenta.

Secretion of yeast aspartic protease 3 is regulated by its carboxy-terminal tail: characterization of secreted YAP3p

Yeast aspartic protease 3 (YAP3p), a basic-residue specific proprotein processing enzyme, was shown to be a membrane-associated protease. The membrane association of YAP3p was demonstrated to be through a glycophosphatidylinositol anchor situated in the carboxy terminus of the enzyme. Carboxy-terminal truncation of YAP3p by 37 amino acids resulted in secretion of YAP3p into the growth medium. Western blot analysis after sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed two secreted forms of YAP3p with apparent molecular masses of approximately 180 and approximately 90 kDa. YAP3p has an isoelectric point of approximately 4.5 as determined by isoelectric focusing gel electrophoresis. Treatment of YAP3p with endoglycosidase H reduced the size of both forms of the protein to approximately 65 kDa, consistent with the presence of 10 potential N-linked glycosylation sites in the deduced amino acid sequence of this protein. Removal of the N-linked sugars did not affect the enzymatic activity of YAP3p. Analysis of the effect of temperature on the stability and the rate of enzymatic activity of YAP3p showed that the enzyme retained 100% of its activity when incubated for 1 h at 37 degrees C, while incubation at 50 degrees C for 1 h resulted in approximately 80% loss of activity. The dependence of activity on temperature demonstrated a calculated Q10 of 1.95.

Identification of the sorting signal motif within pro-opiomelanocortin for the regulated secretory pathway

The NH2-terminal region of pro-opiomelanocortin (POMC) is highly conserved across species, having two disulfide bridges that cause the formation of an amphipathic hairpin loop structure between the 2nd and 3rd cysteine residues (Cys8 to Cys20). The role that the NH2-terminal region of pro-opiomelanocortin plays in acting as a molecular sorting signal for the regulated secretory pathway was investigated by using site-directed mutagenesis either to disrupt one or more of the disulfide bridges or to delete the amphipathic loop entirely. When POMC was expressed in Neuro-2a cells, ACTH immunoreactive material was localized in punctate secretory granules in the cell body and along the neurites, with heavy labeling at the tips. ACTH was secreted from these POMC-transfected cells in a regulated manner. Disruption of both disulfide bridges or the second disulfide bridge or removal of the amphipathic hairpin loop resulted in constitutive secretion of the mutant POMC from the cells and a lack of punctate secretory granule immunostaining within the cells. We have modeled the NH2-terminal POMC Cys8 to Cys20 domain and have identified it as an amphipathic loop containing four highly conserved hydrophobic and acidic amino acid residues (Asp10-Leu11-Glu14-Leu1). Thus the sorting signal for POMC to the regulated secretory pathway appears to be encoded by a specific conformational motif comprised of a 13-amino acid amphipathic loop structure stabilized by a disulfide bridge, located at the NH2 terminus of the molecule.

Frog prohormone convertase PC2 mRNA has a mammalian-like expression pattern in the central nervous system and is colocalized with a subset of thyrotropin-releasing hormone-expressing neurons

The prohormone convertase (PC2) is expressed in the mammalian central nervous system (CNS) and has been shown to play an important role in the processing of certain neuropeptide precursors and prohormones at paired basic residues. Amphibian PC2 cDNA was recently cloned for the frog Xenopus laevis, and both its sequence and its pituitary expression pattern were shown to be very similar to those of mammalian PC2. To investigate further the function of PC2 in the vertebrate CNS, we used in situ hybridization histochemistry to localize the distribution of cells expressing PC2 mRNA in the frog brain and the spinal cord. The distribution of PC2-expressing cells was also compared with that of cells expressing thyrotropin-releasing hormone (TRH) mRNA or peptide. PC2-expressing cells were detected in specific nuclei that were widely distributed in the frog CNS. In forebrain, telencephalic PC2 mRNA was found in the olfactory bulb, pallium, striatum, amygdala, and septum, and diencephalic PC2 mRNA was seen in the preoptic area, thalamus, and hypothalamus. More posteriorly, PC2 cells were localized to midbrain tegmentum, the torus semicircularis, and the optic tectum, as well as the cerebellum, brainstem, and spinal cord. Despite this wide distribution steady-state levels of PC2 mRNA were clearly different in various brain nuclei. Regions with higher levels showed good correspondence to areas shown by others in frog to contain large numbers of neuropeptide-expressing cells, including TRH cells. On the other hand, not all brain areas with high levels of TRH mRNA had high levels of PC2 mRNA. Localization studies combining in situ hybridization and immunocytochemistry showed that, at least in optic tectum and brainstem, PC2 mRNA and pro-TRH peptide coexist. These findings suggest that pro-TRH is processed by PC2 in some, but possibly not all, brain regions. Thus, different converting enzymes may be involved in pro-TRH processing in different brain regions.

In vitro processing of anthrax toxin protective antigen by recombinant PC1 (SPC3) and bovine intermediate lobe secretory vesicle membranes

Protective antigen (PA), an 83-kDa protein produced by Bacillus anthracis, requires proteolytic activation at a tetrabasic site (RKKR167) before it can combine with either edema factor or lethal factor on the cell surface. The complex is then endocytosed and the target cell intoxicated. Previous work has demonstrated that furin, a ubiquitously distributed, subtilisin-like protease, can perform this cleavage. In this study, another member of the furin family, PC1 (SPC3), was tested as a putative processing enzyme for PA. Recombinant PC1, partially purified from the medium of stably transfected L-cells, cleaved PA to a 63-kDa fragment (PA63) and a 20-kDa fragment (PA20). Amino-terminal sequence analysis of the 63 kDa product demonstrated that cleavage occurred between Arg167 and Ser168. The pH optimum for in vitro PA cleavage was 6.0 and the enzymatic activity was calcium-dependent. Medium from untransfected L-cells did not cleave PA. Site-directed mutagenesis of the tetrabasic cleavage site revealed that PC1 preferred to cleave sequences containing basic residues at positions -1 and -4 relative to the wild-type cleavage site, demonstrating that PC1 can cleave substrates at a monobasic residue site in vitro. Substrates having basic residues at the -1 and -2 positions were cleaved with approximately twofold less efficiency than wild-type PA. Mutants of PA containing basic residues in positions -1 and either -2 or -4 of the cleavage site were predicted to be substrates for PC1 and were more toxic to L-cells expressing PC1 than to untransfected L-cells. These results demonstrate that PA is cleaved by PC1 in vivo. Membranes from bovine intermediate lobe secretory vesicles which contain both prohormone convertases, PC1 and PC2, also cleaved PA to PA63 with a pH optimum of 5.5. Immunodepletion studies using antisera against PC1 and PC2 showed that these are the enzymes primarily responsible for the cleavage of PA in the membrane preparation. Thus, both recombinant PC1 and a membrane preparation containing endogenous PC1 can activate PA.

In vitro processing of proopiomelanocortin by recombinant PC1 (SPC3)

The prohormone convertases, PC1 (SPC3) and PC2, are subtilisin-like serine proteases capable of processing neuropeptide precursors. In cotransfection experiments, other investigators have found that PC1 and PC2 can process POMC to appropriate peptide products. In this study, recombinant rat PC1 was stably expressed in a mouse L-cell line and partially purified. Mouse POMC was cleaved by recombinant PC1 to generate ACTH intermediates, ACTH, ACTH linked to joining peptide, joining peptide, 16-kilodalton N-POMC, N-POMC-(1-74), and beta-lipotropin. Recombinant PC1 was also found to cleave ACTH to ACTH-(1-15) and bovine N-POMC-(1-77) to gamma 3 MSH. The pH optimum of the cleavages was 6.0. We conclude that recombinant PC1 is capable of processing POMC in vitro at all of the paired basic residues, with the exception of Lys-Arg and Lys-Lys in beta-lipotropin and beta-endorphin, respectively. This in vitro study showed a more general specificity of recombinant PC1 for paired and tetrabasic residues of POMC than was previously found in cotransfection experiments. Other cellular regulatory mechanisms probably play a role in limiting the processing of POMC in vivo in the anterior pituitary, where gamma 3 MSH and alpha MSH are not found in significant amounts.

Diurnal rhythm of plasma delta-sleep-inducing peptide in humans: evidence for positive correlation with body temperature and negative correlation with rapid eye movement and slow wave sleep

Since delta-sleep-inducing peptide (DSIP) was isolated in 1977, numerous reports have suggested that this nonapeptide stimulates delta-sleep [slow wave sleep (SWS)]. Although DSIP-like immunoreactivity (DSIP-LI) has been found in the serum of many animals and man, its diurnal rhythm and relation to sleep stages have not been well defined. We hypothesized that circulating levels of this putative sleep hormone would be highest at night and would probably be elevated before or during episodes of SWS. We, therefore, measured plasma DSIP-LI levels every 30 min for 24 h in 12 normal volunteers in whom we obtained simultaneous polygraphic recordings. We found a distinct diurnal rhythm for plasma DSIP-LI levels, with the maximum at 1500 h and the minimum at 0100 h. DSIP-LI levels were substantially lower in rapid eye movement sleep (P < 0.005) and somewhat lower in SWS (P < 0.05) compared to awake values. DSIP-LI levels did not rise before, during, or after a significant percentage of episodes of SWS. We found, however, that the diurnal rhythm of DSIP-LI closely followed that of body temperature with a high degree of correlation (r2 = 0.66; P < 0.0001). We conclude that endogenous elevations of circulating DSIP may be associated with suppression of slow wave and rapid eye movement sleep, and that the circadian rhythm of this peptide is coupled directly or indirectly to that of body temperature.

Developmental changes in Gs and G(olf) proteins and adenylyl cyclases in mouse brain membranes

Guanine nucleotide-binding (G) proteins, Gs and G(olf) mediate the increase in cAMP formation through the activation of adenylyl cyclases. The developmental profiles of Gs, G(olf) and adenylyl were determined in mouse striatum and whole brain using immunobloting with specific antisera. Gs and the 115 kDa and 150 kDa adenylyl cyclases were present at the earliest age tested, embryonic day (E) 14.5 G(olf) and the 160 kDa adenylyl cyclase emerged in parallel, postnatally; during this period the increase in the relative abundance of the 150 kDa was observed. Gpp[NH]p activated Gs/G(olf) in a dose dependent manner, with a smaller response observed in embryos compared to adults. Mn2+ and forskolin activated the adenylyl cyclases and this activation increased during development. At E 14.5, maximal activation with Mn2+ and forskolin elicited a similar increase in cAMP levels, but from postnatal day 1, a nearly two fold higher response was obtained with forskolin compared to Mn2+; at the same time the 160 kDa adenylyl cyclase was detected. These data suggest that the appearance of certain forms of stimulatory G proteins was developmentally correlated with the expression of specific adenylyl cyclases.