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PubMed1995

Processing of secretogranin II by prohormone convertases: importance of PC1 in generation of secretoneurin.

Secretoneurin is a recently characterized neuropeptide present in the primary amino acid sequence of secretogranin II. We investigated the proteolytic processing of secretogranin II by prohormone convertases in vivo in a cellular system using the vaccinia virus system. Both PC1 and PC2 can cleave the secretogranin II precursor at sites of pairs of basic amino acids to yield intermediate-sized fragments. Other convertases like PACE4, PC5 and furin were not active. For the formation of the free neuropeptide secretoneurin a different pattern was found. Only PC1 but none of the other convertases tested including PC2 were capable of generating secretoneurin. Our results demonstrate that the prohormone convertases PC1 and PC2 are involved in proteolytic processing of secretogranin II. The neuropeptide secretoneurin can only be generated by PC1 suggesting tissue-specific processing of secretogranin II in neurons expressing different subsets of the prohormone convertases.

Adrenal Medulla↗
PubMed2005

Expression of proopiomelanocortin and its cleavage enzyme genes in Rana esculenta and Xenopus laevis gonads.

Proopiomelanocortin (POMC) is the precursor protein of different hormones and neuropeptides, and the POMC-derived peptides are produced through proteolytic cleavage. Prohormone convertase PC1 and PC2 are enzymes responsible for the cleavage of the POMC prohormone. The coexpression of POMC, PC1, and PC2 genes was previously described in the brain and the pituitary gland of Rana esculenta and Xenopus laevis, but no data are available for the gonad. The present work demonstrates a gonadal POMC convertase gene expression in Rana esculenta and Xenopus laevis.

Animals↗
PubMed1996

Identification and expression of prohormone-converting enzymes in the rat stomach.

The conversion of regulatory peptide precursors to their active forms usually involves limited proteolysis that may be mediated by subtilisin-like prohormone convertases (PC). We have examined the representation of this enzyme family in rat gastric mucosa. With the use of polymerase chain reaction, employing primers to conserved sequences, we identified from rat antrum clones corresponding to PC1/3, PC2, PC5, and furin. Northern blots indicated that the mRNAs for PC1/3 and PC2 were substantially more abundant in mucosa compared with muscle, and that there were differences in expression in antrum and corpus. In the antrum a PC1/3 probe identified hands of 3 and 4.5 kb that were of equal intensity and were both increased in fasted rats; in corpus, the latter mRNA species predominated and did not change with fasting. In rats treated with omeprazole, there was a preferential increase in the antral 3-kb band. In both antrum and corpus, a PC2 probe hybridized with a band of 2.8 kb that increased in omeprazole-treated rats. The data suggest that 1) PC1/3 and PC2 are expressed in antral mucosa and so are candidates for gastric regulatory peptide processing, 2) there is selective processing of the mRNAs encoding prohormone convertases in different gastric cell populations, and 3) the expression of these enzymes is physiologically regulated.

Amino Acid Sequence↗
PubMed1991

Mammalian neural and endocrine pro-protein and pro-hormone convertases belonging to the subtilisin family of serine proteinases.

Conversion of pro-hormones and precursor proteins into biologically active peptides and proteins involves the concerted action of a number of convertases and post-translation modification enzymes. The identification of the yeast convertase kexin as a prototype processing enzyme led to the discovery of the mammalian convertase designated furin, PC1 and PC2. Whereas furin is ubiquitously expressed, PC1 and PC2 are found only in endocrine and neural tissues and cell lines. In man and mouse, the genes coding for furin, PC1 and PC2 reside on three different chromosomes. The analysis of the intracellular processing of PC1 and PC2 and the removal of their pro-segment is presented, together with a summary of the cleavage specificity of these enzymes for precursors such as pro-opiomelanocortin (POMC) and human pro-renin. The distinct tissue distribution of PC1 and PC2 and their coregulation with POMC in the pituitary neurointermediate lobe adds credence to their physiological role as convertases involved in the tissue-specific processing of precursor proteins.

Amino Acid Sequence↗
PubMed1995

Heterologous processing of rat prosomatostatin to somatostatin-14 by PC2: requirement for secretory cell but not the secretion granule.

The role of PC2 in prosomatostatin (PSS) processing was investigated in GH3/GH4C1 pituitary cells. These cells are sparsely granulated, express different amounts of PC2 and no PC1. We described heterologous processing of rat PSS (rPSS) co-expressed with PC2 in stably transfected cells, correlate PC2 protein levels under different conditions of transfection with efficiency of PSS processing to somatostatin-14 (SS-14), determine the effect of modulating cell granularity on enzyme expression and PSS processing, and compare the relative potency of PC2 with that of PC1, PSS and cleavage products were monitored by HPLC and radioimmunoassay of SS-like immunoreactivity (SSLI). Radioimmunoassay analysis of N-terminal PC2-like immunoreactivity (PC2 LI) in GH4C1:rPSS, GH4C1:rPSS + PC2 and GH3:rPSS transfectants showed a gradient of PC2 protein of 1:2.6:3.4 in cell extracts and 1:4.7:9 in secretion media from these cells respectively. The concentration of PC2 protein correlated with SS-14 conversion efficiency was 36 +/- 3% in GH4C1:rPSS cells, 56 +/- 7% in GH4C1:rPSS-PC2 cells and 100% in GH3:rPSS cells. Treatment of GH4C1:rPSS + PC2 cells with epidermal growth factor, insulin, and beta-estradiol to induce granules, significantly increased basal and forskolin-stimulated co-release of SS LI and PC2 LI, but had no influence on SS-14 processing efficiency. Hormone treatment led to a small increase in the ratio of mature PC2 (68 kDa) to proPC2 (75 kDa) forms. PC1 stably transfected in GH4C1 cells produced significantly greater SS-14 conversion (62% in cells, 66% in media) compared with PC2 transfectants (53% in cells, 47% in media) These results provide the first proof that PC2 can effect dibasic processing of mammalian PSS, and, along with PC1, qualifies as an authentic SS-14 convertase. The activity of PC2 requires the milieu of the secretory cell but not the secretory granule.

Animals↗
PubMed2003

Comparative aspects of intracellular proteolytic processing of peptide hormone precursors: studies of proopiomelanocortin processing.

In this review, the mechanisms underlying the intracellular processing of peptide hormone precursors, with a focus on proopiomelanocortin (POMC), were discussed on the basis of recent information. POMC as well as other prohormones is processed to active peptides through proteolytic cleavage by prohormone convertases PC1 and/or PC2. However, the cleavage-specificity of PC1 and PC2 in mammals is somewhat different from that in amphibians. From the comparative endocrinological point of view, expression and tissue distribution of PC1 and PC2 were discussed here. In mammals, proteolytic processing of POMC occurs coordinately with the maturation of secretory granules. Studies using immunoelectron microscopy with DAMP (3-[2,4-dinitroanilino]-3'-amino-N-methyldipropylamine) as a pH probe revealed that the acidic pH in the secretory granules, generated by vacular type-H+-ATPase, provides a favorable environment for activating PC1 in AtT-20 cells, a mouse corticotrope tumor cell line. Recent data indicate that the 7B2 protein serves as a chaperone in the regulation of PC2 activation and to control the timing for activating the convertase. Together, secretory granules in endocrine and neuroendocrine cells provide proper sites for biosynthesizing hormones in addition to serving as storage sites and vehicles for the transport of peptide hormones.

Amino Acid Sequence↗
PubMed1995

Differential processing of proglucagon by the subtilisin-like prohormone convertases PC2 and PC3 to generate either glucagon or glucagon-like peptide.

Proglucagon is processed differently in the islet alpha cells and the intestinal endocrine L cells to release either glucagon or glucagon-like peptide 1-(7-37) (GLP1-(7-37)), peptide hormones with opposing actions in vivo. In previous studies with a transformed alpha cell line (alpha TC1-6) we demonstrated that the kexin/subtilisin-like prohormone convertase, PC2 (SPC2), is responsible for generating the typical alpha cell pattern of proglucagon processing, giving rise to glucagon and leaving unprocessed the entire C-terminal half-molecule known as major proglucagon fragment or MPGF (Rouillé, Y., Westermark, G., Martin, S. K., Steiner. D. F. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 3242-3246). Here we present evidence, using mouse pituitary AtT-20 cells infected with a vaccinia viral vector encoding proglucagon, that PC3 (SPC3), the major neuroendocrine prohormone convertase in these cells, reproduces the intestinal L cell processing phenotype, in which MPGF is processed to release two glucagon-related peptides, GLP1 and GLP2, while the glucagon-containing N-terminal half-molecule (glicentin) is only partially processed to oxyntomodulin and small amounts of glucagon. Moreover, in AtT-20 cells stably transfected with PC2 (AtT-20/PC2 cells), glicentin was efficiently processed to glucagon, providing further support for the conclusion that PC2 is the enzyme responsible for the alpha cell processing phenotype. In other cell lines expressing both PC2 and PC3 (STC-1 and beta TC-3), proglucagon was also processed extensively to both glucagon and GLP1-(7-37), although STC-1 cells express lower levels of PC2 and processed the N-terminal domain to glucagon less efficiently. In contrast, GH4C1 and COS 7 cells, which express very little or no PC2 or PC3, failed to process proglucagon, aside from a low level of interdomain cleavage which occurred only in the GH4C1 cells. In vitro PC3 did not cleave at the single Arg residue in GLP1 to generate GLP1-(7-37), its truncated biologically active form, indicating the likelihood that another convertase is required for this cleavage.

Amino Acid Sequence↗
PubMed1994

Developmental expression of the prohormone convertases PC1 and PC2 in mouse pancreatic islets.

The immunocytochemical distribution and messenger RNA expression of the prohormone convertases PC1 and PC2 involved in the posttranslational processing of precursor proteins were analyzed in mouse and rat pancreatic islets. Immunocytochemical colocalization studies demonstrated a close association of insulin with both PC1 and PC2 in the adult mouse and rat pancreas. The coexpression of insulin with the prohormone convertases was further examined in rat pancreatic tumors induced by streptozotocin-nicotinamide treatment. These insulin-synthesizing tumors expressed PC1 and PC2, whereas insulin-silent adenomas did not. Colocalization studies demonstrated that only PC2, not PC1, colocalizes with glucagon, pancreatic polypeptide, and somatostatin. The highest levels of PC2-like immunoreactivity were observed in the glucagon-containing alpha-cells. Ontogeny studies carried out by in situ hybridization in mice showed the first detectable expression of the prohormone convertases in the pancreatic primordium at midgestation, starting for PC1 on embryonic day 11 and for PC2 on embryonic day 10. Enzyme expression was further confirmed by immunocytochemistry, which detected the presence of immunoreactive PC1- and PC2-like proteins on embryonic days 14 and 17, respectively. Taken together, our data suggest that both PC1 and PC2 play a role in proinsulin processing in vivo, whereas PC2 is a likely candidate convertase participating in the processing of proglucagon, propancreatic polypeptide, and prosomatostatin in pancreatic islets.

Adenoma↗
PubMed1993

GAP-releasing enzyme is a member of the pro-hormone convertase family of precursor protein processing enzymes.

The recent discovery of mammalian endoproteinases which show extensive sequence homology with the yeast Kex 2 gene product (kexin) has lead to the hypothesis that processing enzymes of pro-hormone precursor proteins belong to a family of calcium dependent, subtilisin-like serine proteinases. We previously showed that hypothalamic GAP-releasing enzyme shares these characteristics and possesses the requisite specificity to be considered as a processing enzyme of progonadotropin releasing hormone (pro-GnRH) precursor protein. Thus, GAP-releasing enzyme (and other non-related proteins) were tested for their immunological reactivity with antisera raised against pituitary pro-hormone convertase 1/3 (PC1/3) and insulinoma PC2. On the basis of indirect enzyme-linked immunosorbent (ELISA) and Western blot assays, GAP-releasing enzyme is now shown to be immunologically related to PC1/3. We can conclude that GAP-releasing enzyme is also likely to be a member of the pro-hormone convertase family and should be considered the physiologically relevant processing enzyme of pro-GnRH. It is possible that GAP-releasing enzyme represents bovine hypothalamic PC1/3.

Amino Acid Sequence↗
PubMed2000

Regional and cellular localization of the neuroendocrine prohormone convertases PC1 and PC2 in the rat central nervous system.

PC1 and PC2 are two major enzymes involved in the processing of protein precursors directed to the regulated secretory pathway. Whereas transcripts encoding both enzymes are widely distributed in the central nervous system, information regarding the localization of proteins themselves is still lacking. In an attempt to gain insight into the neurobiologic roles of PC1 and PC2, both enzymes were immunolocalized in the rat brain by using C-terminally directed antibodies, which respectively recognize the 87-kDa PC1 and the 75 and 68-kDa PC2 forms. Adjacent sections immunoreacted with PC1 or PC2 antibodies exhibited selective patterns of immunostaining in regions well characterized with respect to their biosynthesis of multiple neuropeptides such as the cerebral cortex, hippocampus, and hypothalamus. PC1 signal intensity was generally weaker than that of PC2, although both enzymes displayed extensive overlapping patterns of expression. As assessed by double-labeling experiments at the cellular level, PC1 and PC2 immunoreactive signals were localized within the trans-Golgi network and nerve terminals, in keeping with the biosynthetic pathways of neuropeptides. Immunoreactive fibers were detected in many areas throughout the brain but were particularly densely distributed in the hypothalamus and the brainstem. Both enzymes were also localized within dendrites of numerous neurons, supporting the hypothesis that dendritic neuropeptide maturation and release may occur in a large number of brain regions. Taken together, our results provide new evidence that both convertases are efficiently targeted to the neuronal regulated secretory pathway and are well poised to process protein precursors in biologically active end-products within the mammalian brain.

Animals↗
PubMed2004

The melanocortin receptor subtypes in chicken have high preference to ACTH-derived peptides.

1 Melanocortin (MC) receptors are widely distributed throughout the body of chicken, like in mammals, and participate in a wide range of physiological functions. 2 To clarify the pharmacological impact of ligands acting in the MC system, we expressed the chicken MC1, MC2, MC3, MC4 and MC5 (cMC1-5) receptors in eukaryotic cells and performed comprehensive pharmacological characterization of the potency of endogenous and synthetic melanocortin peptides. 3 Remarkably, the cMC receptors displayed high affinity for ACTH-derived peptides and in general low affinity for alpha-MSH. It is evident that not only the cMC2 receptor but also the other cMC receptors interact with ACTH-derived peptide through an epitope beyond the sequence of alpha-MSH. 4 The synthetic ligand MTII was found to be a potent agonist whereas HS024 was a potent antagonist at the cMC4 receptor, indicating that these ligands are suitable for physiological studies in chicken. 5 We also show the presence of prohormone convertase 1 (PC1) and PC2 genes in chicken, and that these peptides are coexpressed with proopiomelanocortin (POMC) in various tissues.

Adrenocorticotropic Hormone↗
PubMed2003

Cleavage of recombinant proenkephalin and blockade mutants by prohormone convertases 1 and 2: an in vitro specificity study.

Proenkephalin (PE) derived-peptides are thought to be generated predominantly through endoproteolytic cleavage by prohormone convertases 1 and 2 (PC1 and PC2). In order to compare cleavage site preferences of these convertases, we studied the processing of recombinant wild-type rat PE and of two mutant PEs by recombinant purified mouse PC1 and PC2. Western blot analyses of timed digestions showed that both mouse PC1 and PC2 were able to produce a variety of large and intermediate sized-peptides from wild-type PE as well as from the precursors mutated at initial blockade sites. PC2 exhibited a broader specificity against PE than PC1, generating a much greater number of peptide products. Mass spectrometric identification of cleavage products showed that PC2 appeared to be the principal enzyme involved in the generation of smaller active opioids. Both enzymes were able to cleave various KR- and KK-containing sites, but PC2 was also able to cleave efficiently at an RR-V site and a KK-M site not cleaved by PC1, suggesting the exclusion of large aliphatic residues at the P1' position in PC1 cleavage. Alternative cleavage sites were readily chosen by convertases in blockade mutants, confirming in vivo results that cleavages do not follow an obligatory order. Furthermore, glycosylated PE was less efficiently processed by PC2, indicating that glycosylation may serve as a mechanism to hinder processing.

Amino Acid Sequence↗
PubMed1993

Processing of two homologous precursors, pro-neuropeptide Y and pro-pancreatic polypeptide, in transfected cell lines expressing different precursor convertases.

The processing of two homologous precursors, pro-neuropeptide Y (pro-NPY) and pro-pancreatic poly-peptide (pro-PP), was studied in four neuroendocrine cell lines after transfection: CA-77 medullary thyroid carcinoma cells, AtT-20 corticotrope pituitary cells, RIN2A-19 pancreatic endocrine cells, and NB1 neuroblastoma cells. Northern blot analysis indicated that the AtT-20 cells only expressed precursor convertase 3; in contrast, NB1 cells only expressed precursor convertase 2, whereas the RIN2A-19 and CA-77 cells expressed both enzymes. Despite these differences in expression pattern of precursor convertases the four cell lines were, surprisingly, indistinguishable in respect to their processing of pro-PP and pro-NPY. In all four cell lines, pro-NPY was almost completely converted to NPY, and, in all four cell lines, only around 50% of the PP precursor was converted to PP. The relatively poor processing efficiency of pro-PP was rather similar to the processing efficiency of the endogenously produced precursors in the respective cell lines, pro-calcitonin (CA-77), proopiomelanocortin (AtT-20), proinsulin (RIN2A-19), and pro-vasoactive intestinal polypeptide (NB1). At least in the CA-77 cells, NPY and PP were apparently sorted to the regulated secretory pathway, as upon stimulation with secretagogue the release of the transfected peptides increased in parallel with the endogenously expressed peptide, calcitonin gene-related peptide. Mutagenesis studies showed that on the N-terminal side of the di-basic processing site, the otherwise important difference in structure between PP and NPY, a proline for glutamine in position 34, was not responsible for the difference in processing efficiency. On the C-terminal side of the processing site, the efficient processing of pro-NPY could not be transferred to pro-PP by exchanging the whole C-terminal domains of the precursors. It is concluded that pro-NPY is processed more efficiently than pro-PP in all neuroendocrine cell lines tested independent on their expression of the two main precursor convertases and that mutagenesis data indicate that the structural element responsible for the efficient processing of pro-NPY is not located on the N-terminal side of the dibasic processing site.

Amino Acid Sequence↗
PubMed2006

PC1/3 and PC2 gene expression and post-translational endoproteolytic pro-opiomelanocortin processing is regulated by photoperiod in the seasonal Siberian hamster (Phodopus sungorus).

A remarkable feature of the seasonal adaptation displayed by the Siberian hamster (Phodopus sungorus) is the ability to decrease food intake and body weight (by up to 40%) in response to shortening photoperiod. The regulating neuroendocrine systems involved in this adaptation and their neuroanatomical and molecular bases are poorly understood. We investigated the effect of photoperiod on the expression of prohormone convertases 1 (PC1/3) and 2 (PC2) and the endoproteolytic processing of the neuropeptide precursor pro-opiomelanocortin (POMC) within key energy balance regulating centres of the hypothalamus. We compared mRNA levels and protein distribution of PC1/3, PC2, POMC, adrenocorticotrophic hormone (ACTH), alpha-melanocyte-stimulating hormone (MSH), beta-endorphin and orexin-A in selected hypothalamic areas of long day (LD, 16:8 h light:dark), short day (SD, 8:16 h light:dark) and natural-day (ND, photoperiod depending on time of the year) acclimated Siberian hamsters. The gene expression of PC2 was significantly higher within the arcuate nucleus (ARC, P < 0.01) in SD and in ND (versus LD), and is reflected in the day length profile between October and April in the latter. PC1/3 gene expression in the ARC and lateral hypothalamus was higher in ND but not in SD compared to the respective LD controls. The immunoreactivity of PC1/3 cleaved neuropeptide ACTH in the ARC and PC1/3-colocalised orexin-A in the lateral hypothalamus were not affected by photoperiod changes. However, increased levels of PC2 mRNA and protein were associated with higher abundance of the mature neuropeptides alpha-MSH and beta-endorphin (P < 0.01) in SD. This study provides a possible explanation for previous paradoxical findings showing lower food intake in SD associated with decreased POMC mRNA levels. Our results suggest that a major part of neuroendocrine body weight control in seasonal adaptation may be effected by post-translational processing mediated by the prohormone convertases PC1/3 and PC2, in addition to regulation of gene expression of neuropeptide precursors.

Adaptation, Physiological↗
PubMed2003

Deletion of the Nhlh2 transcription factor decreases the levels of the anorexigenic peptides alpha melanocyte-stimulating hormone and thyrotropin-releasing hormone and implicates prohormone convertases I and II in obesity.

Body weight is controlled by the activation of signal transduction pathways in both the brain and peripheral tissues. Interestingly, although many hypothalamic neuropeptides and receptors have been implicated in the regulation of body weight, the transcriptional and posttranscriptional mechanisms through which these genes are expressed in response to changes in energy balance remain unclear. Our laboratory studies a mouse in which targeted deletion of the neuronal basic helix-loop-helix (bHLH) transcription factor, nescient helix-loop-helix 2 protein (Nhlh2), results in adult-onset obesity. The aim of this work was to use the phenotype of the Nhlh2 knockout mouse and the expression pattern of Nhlh2 to identify genes that are regulated by this transcription factor. In this article, we show that Nhlh2 is expressed throughout the adult hypothalamus. Using dual-label in situ hybridization, we demonstrate that, in the arcuate nucleus of the adult hypothalamus (ARC), Nhlh2 expression can be found in rostral proopiomelanocortin (POMC) neurons, whereas in the paraventricular nucleus (PVN), Nhlh2 is expressed in TRH neurons. In addition, we find that hypothalamic POMC-derived alphaMSH in the ARC and TRH in the PVN are regulated posttranscriptionally via Nhlh2-mediated control of prohormone convertase I and II mRNA levels. This is the first report in which regulation of body weight is linked to the action of a neuronal bHLH transcription factor on prohormone convertase mRNA levels. Furthermore, this work supports a direct role for transcriptional control of neuropeptide processing enzymes in the etiology of adult-onset obesity.

Age of Onset↗
PubMed1999

The subtilisin/kexin family of precursor convertases. Emphasis on PC1, PC2/7B2, POMC and the novel enzyme SKI-1.

Proopiomelanocortin (POMC) is a precursor to various, bioactive peptides including ACTH, beta LPH, alpha MSH, and beta endorphin (beta END). Processing of POMC at dibasic residues is tissue-specific and is performed by either PC1 alone (resulting in ACTH and beta LPH, anterior pituitary corticotrophes) or by a combination of PC1 and PC2 (yielding alpha MSH and beta END, pituitary neurointermediate lobe and hypothalamus). The PC2-specific binding protein 7B2 is intimately involved in the zymogen activation of proPC2 into PC2. Structure-function studies of these enzymes demonstrated the presence of N- and C-terminal domains, as well as specific amino acids within the catalytic segment that influence the degree of activity of each enzyme and the interaction of PC2 with 7B2. The tissue distribution, plasticity of expression, and the multiple precursors that are differentially cleaved by PC1 and/or PC2, predict a wide array of combinatorial activities of these convertases within the endocrine and neuroendocrine system. The phenotypic consequences of the absence of genetic expression of either PC1 or PC2 are now explored using knockout mice and in human patients suffering from obesity and diabetes.

Animals↗
PubMed2004

Improved PC1/3 production through recombinant expression in insect cells and larvae.

Protein convertase 1/3 is a serine endoproteinase present in the regulated secretory pathway of endocrine and neuroendocrine cells. It is responsible for the processing of numerous prohormones and proneuropeptides into their biologically active moieties, often following cleavage at pairs of basic residues. The determination of its three-dimensional structure, as well as the understanding of its enzymatic properties, would greatly benefit from the production and availability of large amounts of recombinant enzyme. We report herein improvements in the production of PC1/3 by expressing recombinant mutated forms in both insect cells (Spodoptera frugiperda, Sf9 cells) and larvae (Trichoplusia ni commonly referred to as cabbage looper). On one hand, we deleted the last 135 COOH-terminal residues of mPC1/3 and, on the other hand, we replaced the signal peptide of mPC1/3 by the viral glycoprotein gp67 signal peptide. These modifications were shown to improve markedly (up to 125%) the secretion into the Sf9 cells medium and the amount of enzymatic activity recovered when compared to the original vector. Moreover, intracoelemic injection of the vectors into insect larvae led to the production and purification of enzymatically active enzyme at a level of 30 microg/larva in the case of mPC1/3 and to the production of a high amount of another enzymatically active convertase, PC7. The optimal viral titer for infection of larvae was determined to be 10(6)pfu/ml. Taking into account the purification protocol combined with the ease and efficiency of using larvae, it should now be possible to meet the needs for biochemical and structural studies.

Animals↗
PubMed2000

Endocrine disruptive effects of polychlorinated aromatic hydrocarbons on intestinal cholecystokinin in rats.

The ubiquitous and persistent nature of polychlorinated aromatic hydrocarbons (PCAHs) in our environment and the risk of exposure to PCAHs have provoked concern over their potential toxicity. In humans, exposure to PCAHs is aimed chiefly at epithelial cells residing in the intestinal mucosa, because oral intake of contaminated food is a major source of PCAHs. The purpose of this study, therefore, was to examine the effects of chronic exposure to various PCAHs [i.e. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB-126), and 2,2'4,4'5,5'-hexachlorobiphenyl (PCB-153)], given alone or as mixtures, on intestinal cholecystokinin (CCK) peptide and messenger RNA levels. We show that chronic PCAH treatment significantly lowers intestinal levels of stored CCK peptide. Intestinal CCK messenger RNA levels are not affected. In addition, 3,3',4,4',5-pentachlorobiphenyl treatment increased intestinal insulin-like growth factor-binding protein-3 levels in a dose-related manner. Acute 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment of intestinal CCK cells lowered levels of CCK-processing enzymes (i.e. prohormone convertase-1 and -2). Together, these data indicate that PCAHs may decrease intestinal levels of stored CCK peptide by affecting the intestinal insulin-like growth factor system and CCK processing.

Animals↗