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Biomedical subjects

M Chretien

Publications and source records attributed to M Chretien.

At least 19 recordsLinked to original sources
PubMed1999

Distribution and regulation of proconvertases PC1 and PC2 in human pituitary adenomas.

Pituitary adenomas are members of the family of neuroendocrine cells and tumors which have secretory granules containing chromogranins/secretogranins and other proteins. Pituitary adenomas express the neuroendocrine specific proconvertases PC1 (also known as PC3) and PC2, which are important for the proteolytic processing of chromogranins/secretogranins molecules. We examined the distribution of PC1 and PC2 in primary cultures of 20 pituitary adenomas and analyzed the regulation of the proconvertase mRNAs and proteins by various secretagogues including hypothalamic hormones and phorbol ester to determine the role of PC1 and PC2 in CgA processing in pituitary adenomas. Although PC2 was present in all adenomas, there was a differential distribution of PC1 with PRL adenomas expressing lower levels of PC1 compared to other adenoma types by RT-PCR analysis, in situ hybridization and immunostaining. Treatment of primary cultures of pituitary adenomas with phorbol 12-myristrate 13-acetate (PMA) resulted in an increase in pancreastatin (PST) secretion in most pituitary adenomas and increased PC1 mRNA and protein expression in gonadotroph adenomas, but not in other types of adenomas. Analysis of a human pituitary adenoma cell line, immortalized by recombinant defective adenovirus (HP75), which expressed chromogranin A, FSH, PC1 and PC2 showed that PST was secreted by these immortalized cells. Treatment with TGF beta 1 resulted in an increase in PST secretion and in PC1 mRNA and protein. These results indicate that a) there is a differential distribution of PC1 in human pituitary adenomas with PRL adenomas expressing very little PC1 mRNA and protein and b) that PC1 expression in gonadotropin hormone-producing adenomas is regulated by PMA and TGF beta 1. These findings support the observation that chromogranin A is a substrate for the endoproteinase PC1 in human pituitary adenoma cells.

Adenoma↗
PubMed1996

Characterization of structural determinants and molecular mechanisms involved in pro-stromelysin-3 activation by 4-aminophenylmercuric acetate and furin-type convertases.

Stromelysin-3 (ST3) is a matrix metalloproteinase (MMP) which has been implicated in cancer progression and in a number of conditions involving tissue remodelling. In contrast to other MMPs which are secreted as zymogens requiring extracellular activation, ST3 is found in the extracellular space as a potentially active mature form, suggesting that the activation of the ST3 proform differs from that of other MMPs. We show in the present study that the ST3 proform is not autocatalytically processed in the presence of 4-aminophenylmercuric acetate (APMA). By using ST3/ST2 chimeras, we demonstrate that resistance to APMA is due to properties associated with both the ST3 pro- and catalytic domains. In agreement with the observation made by Pei and Weiss [Pei and Weiss (1995) Nature (London) 375, 244-247], we find that the requirement for activation of the ST3 proform by the furin convertase is entirely contained within a stretch of 10 amino acids located at the junction between the ST3 pro- and catalytic domains. Furin cleaves human and mouse ST3 equally well. However, PACE-4, a furin-like convertase, is much more efficient on the mouse enzyme, suggesting that ST3 protein determinants other than the conserved Ala-Arg-Asn-Arg-Gln-Lys-Arg sequence preceding the furin cleavage site are implicated in PACE-4 action. Finally, we show that processing of the ST3 proform is inhibited by a furin inhibitor in human MCF7 breast cancer cells stably transfected to constitutively express a full-length human ST3 cDNA. Using brefeldin A, we demonstrate that, in these MCF7 cells, the 56 kDa precursor form of ST3 is post-translationally modified in the cis- or media-Golgi into a 62 kDa proform. Thereafter, its processing into the 47 kDa mature form occurs in the trans-Golgi network and is followed by secretion into the extracellular space.

Amino Acid Sequence↗
PubMed1996

cDNA structure, tissue distribution, and chromosomal localization of rat PC7, a novel mammalian proprotein convertase closest to yeast kexin-like proteinases.

By using reverse transcription-coupled PCR on rat anterior pituitary RNA, we isolated a 285-bp cDNA coding for a novel subtilisin/kexin-like protein convertase (PC), called rat (r) PC7. By screening rat spleen and PC12 cell lambda gt11 cDNA libraries, we obtained a composite 3.5-kb full-length cDNA sequence of rPC7. The open reading frame codes for a prepro-PC with a 36-amino acid signal peptide, a 104-amino acid prosegment ending with a cleavable RAKR sequence, and a 747-amino acid type I membrane-bound glycoprotein, representing the mature form of this serine proteinase. Phylogenetic analysis suggests that PC7 represents the most divergent enzyme of the mammalian convertase family and that it is the closest member to the yeast convertases krp and kexin. Northern blot analyses demonstrated a widespread expression with the richest source of rPC7 mRNA being the colon and lymphoid-associated tissues. In situ hybridization revealed a distinctive tissue distribution that sometimes overlaps with that of furin, suggesting that PC7 has widespread proteolytic functions. The gene for PC7 (Pcsk7) was mapped to mouse chromosome 9 by linkage analysis of an interspecific backcross DNA panel.

Amino Acid Sequence↗
PubMed1994

Structure of the gene for the testis-specific proprotein convertase 4 and of its alternate messenger RNA isoforms.

Proprotein convertase 4 (PC4) is a mammalian secretory serine endoproteinase similar to the yeast KEX2 gene product and specifically expressed in testicular germs cells. PC4 mRNA isoforms that vary in size and 3' coding sequence have been reported (N. G. Seitah, R. Day, J. Hamelin, A. Gaspar, M. W. Collard, and M. Chrétien, 1992, Mol. Endocrinol. 6: 1559-1570). To determine the origin of these various forms, the mouse PC4 gene was cloned and its organization determined. The structural gene is approximately 9.5 kb long. It contains 15 exons and 14 introns. The exon-intron organization is very similar to that of the genes for the related convertases furin, PC1, and PC2. The upstream region carries several GGGCGG and three CCAAT but no TATAA motifs. Analysis of the 5' end of PC4 mRNA in the testis has led to the identification of two novel 5' splice variants that might encode a nonsecretory enzyme. The multiple forms of PC4 mRNA can all be explained by alternate splicing of primary transcripts of a single gene.

Alternative Splicing↗
PubMed1993

From proopiomelanocortin to cancer. Possible role of convertases in neoplasia.

Melanophore-stimulating hormones (MSHs) are produced from a common precursor called proopiomelanocortin (POMC). These peptides have been at the center of studies on the prohormone theory since 1967. The recent discovery of endoproteases which can convert POMC to MSHs is having more biological implications than previously imagined, most particularly for proliferative diseases like cancer.

Amino Acid Sequence↗
PubMed1992

Expression of the neuroendocrine cell marker 7B2 in human ACTH secreting tumours.

OBJECTIVE AND DESIGN: Pro-opiomelanocortin gene expression is a ubiquitous phenomenon which takes place not only in the pituitary but also in many normal and tumoral non-pituitary tissues. However, the clinical features of the ectopic ACTH syndrome are rarely encountered. To further investigate this problem we examined series of normal human pituitaries and endocrine tumours evaluating the tissue content of pro-opiomelanocortin peptides, and the state of neuroendocrine differentiation as indicated by the biochemical marker 7B2. PATIENTS AND MEASUREMENTS: Tissue concentration of 7B2, pro-opiomelanocortin products (joining peptide and beta-endorphin) were measured in 13 pituitary corticotrophic adenomas and 13 non-pituitary tumours associated with the ectopic ACTH syndrome (five out of 20 bronchial carcinoid tumours, two out of 19 phaeochromocytomas, one out of 11 medullary thyroid carcinomas, three pancreatic and two thymic carcinoid tumours). Molecular weight forms of immunoreactive 7B2 and 7B2 RNA messenger were determined using Western and Northern blot analysis respectively. RESULTS: In all tissues examined, concentrations of immunoreactive beta-endorphin (fmol/mg tissue wet weight) showed widely distributed values from less than 0.7 to 1,340,000, which were correlated (r = 0.975, P less than 0.01) with that of immunoreactive joining peptide, another pro-opiomelanocortin fragment. In the 13 non-pituitary tumours associated with the ectopic ACTH syndrome, immunoreactive beta-endorphin concentrations ranged from 8.6 to 548,000, whereas in normal and tumoral pituitaries they varied from 16,600 to 364,800, and 5000 to 1,340,000, respectively. Immunoreactive 7B2 was detected in 67 of 68 neuroendocrine tumours. Tissue concentrations (fmol/mg tissue wet weight) of immunoreactive 7B2 varied from 135 to 1787 in pituitary tumours; from less than 0.5 to 555 in bronchial carcinoids; from 21.7 to 793 in phaeochromocytomas; from less than 1.6 to 948 in medullary thyroid carcinomas. Western blot analysis showed a predominant molecular weight form of immunoreactive 7B2 at 22 kDa. Northern blot analysis of RNA extracted from ACTH secreting pituitary and non-pituitary tumours showed a predominant signal hybridizing at 1.5 kb with a 7B2 probe. CONCLUSION: These results show that all ACTH secreting tumours have biochemical markers for neuroendocrine differentiation. Tissue concentrations of pro-opiomelanocortin peptides are variable, being extremely high in the most benign tumours and low in those with an aggressive growing pattern, and are not correlated with the biochemical neuroendocrine markers.

ACTH Syndrome, Ectopic↗
PubMed1991

7B2, a possible marker for nonfunctioning pancreatic islet cell tumor.

Plasma 7B2 was measured in 13 patients with pancreatic islet cell tumors, 11 with pancreatic adenocarcinoma and 31 normal subjects as a control. The mean (+/- SD) concentrations of plasma 7B2 in the normal subjects and the patients with pancreatic islet cell tumors were 67 +/- 10 and 1041 +/- 1786 pmol/l, respectively, and the value in the patients with pancreatic islet cell tumors was significantly higher than that in the normal subjects (p less than 0.01). Elevation of plasma 7B2 over the normal range, defined as less than the mean + 3SD value of those in the normal subjects, was found in 10 of 13 patients with pancreatic islet cell tumors including 4 with nonfunctioning tumor. Plasma 7B2 dropped into the normal range postoperatively in 3 patients with nonfunctioning tumor. Plasma 7B2 concentrations in the patients with pancreatic adenocarcinoma remained in the normal range. These results raise a possibility that 7B2 is a useful marker for pancreatic islet cell tumors, in particular nonfunctioning tumor.

Adenoma, Islet Cell↗
PubMed1990

Assignment of the gene for neuroendocrine protein 7B2 (SGNE1 locus) to mouse chromosome region 2[E3-F3] and to human chromosome region 15q11-q15.

The gene for 7B2, a protein found in the secretory granules of neural and endocrine cells (gene symbol SGNE1) was localized to the E3-F3 region of mouse chromosome 2 and to the q11-q15 region of human chromosome 15. This was determined by in situ hybridization, using a mouse 7B2 cDNA and an intronic fragment of the corresponding human gene as probes. The respective locations of SGNE1 in the two species correlate with the conservation of loci between these subregions of mouse chromosome 2 and human chromosome 15. Clinically, the human SGNE1 DNA fragment may serve as a molecular probe of this locus in both the Prader-Willi and the Angelman syndromes, which are often accompanied by submicroscopic chromosomal deletions in the 15q11-15q13 region.

Animals↗
PubMed1989

Aldosterone secretion inhibitory factor: a novel neuropeptide in bovine chromaffin cells.

We report the identification and the primary structure of a novel neuroendocrine peptide which inhibits aldosterone secretion. The peptide was isolated from 1.5 x 10(10) cultured bovine chromaffin cells by reversed phase and ion exchange HPLC. It is chromatographically and structurally distinct from atrial natriuretic factor (ANF), which we formely identified in chromaffin tissue. This new Aldosterone Secretion Inhibitory Factor (ASIF) is predominant in cultured chromaffin cells and cross-reacts with ANF receptor sites involved in the inhibition of aldosterone production in zona glomerulosa cells. The sequence of this 35-amino acid peptide includes the shorter fragment isolated from porcine brain confirming its neuropeptide character. ASIF might be involved in concert with ANF in the paracrine regulation of aldosterone secretion and the presence of both peptides in cultured chromaffin cells indicates that this system can be used as a model for studying natriuretic neuropeptide production.

Adrenal Glands↗
PubMed1988

Distribution of a novel pituitary protein (7B2) in mammalian gastrointestinal tract and pancreas.

The distribution of a novel pituitary protein (7B2) was determined in the gastrointestinal tract and pancreas of four mammalian species (man, pig, guinea pig, and rat) by a specific radioimmunoassay. The highest concentrations of cross-reacting immunoreactive 7B2 (IR-7B2) were observed in the pancreas and the proximal gut (antrum or duodenum). While the intestinal concentrations varied widely among species, pancreatic IR-7B2 concentrations appeared to be similar in all four species. In the rat, pancreatic islets were found to contain high concentrations of IR-7B2 (5.73 +/- 0.14 fmol/islet, mean +/- SEM). Neonatal capsaicin treatment and enteric nerve section did not affect the concentrations of IR-7B2 in the rat intestine. Layer separation of human gut showed that IR-7B2 is mainly (71 +/- 8%) present in the epithelial fraction. Chromatographic analysis of intestinal and pancreatic extracts from the four species on Sephadex G-100 showed the presence of two immunoreactive peaks at Kav 0.3 and 0.6, but there were both inter- and intraspecies variations in the proportions of the larger and smaller molecular forms.

Animals↗
PubMed1988

Structural and immunological homology of human and porcine pituitary and plasma IRCM-serine protease 1 to plasma kallikrein: marked selectivity for pairs of basic residues suggests a widespread role in pro-hormone and pro-enzyme processing.

IRCM-serine protease 1 (SP1), originally isolated from porcine pituitaries and exhibiting preference for cleavage at pairs of basic residues has now been isolated in sufficient quantities to be structurally characterized from both porcine and human pituitaries and plasmas. Whereas the porcine protease shows a high degree of amino acid sequence homology to human plasma pre-kallikrein, the human homologue exhibits an identity of sequence in the first 25 residues of each chain (regulatory and catalytic chains). In addition, human plasma and pituitary IRCM-SP1 and human plasma pre-kallikrein show virtually identical immunological and molecular properties. These data strongly suggest that IRCM-SP1 and plasma pre-kallikrein originate from the same gene product. Purified extracts from perfused rat pituitaries show that 32% of the IRCM-SP1 activity found in normal rat pituitaries, still remain. These data together with the demonstrated association of IRCM-SP1 with particulate fractions of the pituitary suggest that IRCM-SP1 represents a tissue form of plasma pre-kallikrein. The characterization of the digestion products obtained upon reaction of IRCM-SP1 with pro-insulin, ACTH1-39, pro-dynorphin and pro-enkephalin-derived peptides, somatostatin-28, and a pro-renin-like peptide confirmed the high degree of cleavage selectivity of this enzyme for pairs of basic residues.

Amino Acid Sequence↗
PubMed1987

Chromogranin B (secretogranin I), a putative precursor of two novel pituitary peptides through processing at paired basic residues.

During the course of reversed-phase high-pressure liquid chromatography (RP-HPLC) purification of the 7B2 peptide originally isolated in our laboratory from human pituitary gland extracts, two novel peptides were identified and purified to homogeneity. The complete amino acid sequence of the first one was established in 1985 and recently found to be entirely homologous to positions 420-493 of the just published chromogranin B sequence. This peptide, denoted GAWK, could originate from chromogranin B following specific cleavage at the basic amino acids flanking both termini of GAWK. Moreover, another peptide isolated in our laboratory from the same source and denoted CCB has been discovered and its sequence is also part of the same chromogranin B molecule. Here again, this peptide, occupying positions 597-653 and located at the COOH-terminal region of chromogranin B, could derive from specific processing at basic amino acids, Arg-Lys-Lys, present at positions 594-596. In a manner reminiscent of the relationship between pancreastatin and chromogranin A, it is proposed that both GAWK and CCB are produced from chromogranin B after specific processing at basic amino acids. These data are thus in favor of a putative role of chromogranins as precursors to potentially bioactive peptides.

Amino Acid Sequence↗