Multiple OXPHOS deficiency in the liver of a patient with CblA methylmalonic aciduria sensitive to vitamin B(12)

An adult patient with methylmalonic aciduria due to defective cobalamin synthesis (CblA) responsive to vitamin B(12) presented suddenly with severe visual impairment ascribed to optic atrophy followed by a fatal multiorgan failure and lactic acidosis but low methylmalonic acid in plasma and urine. Multiple deficiency of oxidative phosphorylation was found in the patient's liver. We suggest that patients with B(12)-sensitive methylmalonic aciduria who have a milder clinical course should be carefully monitored for long-term complications.

Chromosome 11p15 paternal isodisomy in focal forms of neonatal hyperinsulinism

CONTEXT

Focal forms of congenital hyperinsulinism are due to a constitutional heterozygous mutation of paternal origin in the ABCC8 gene, more often than the KCNJ11 gene, located in the 11p15.1 region. This mutation is associated with the loss of the maternally inherited 11p15.1 to 11p15.5 region in the lesion. We investigated the possible occurrence of a compensatory duplication of the paternal 11p15.1-11p15.5 region.

MATERIALS AND METHODS

A combined immunohistochemistry and fluorescent in situ hybridization study on beta-cell interphase nuclei with probes covering two genes located in this region (ABCC8 and CDKN1C genes) was performed in four cases of focal forms of hyperinsulinism.

RESULTS

beta-Cells in the lesions of four cases of focal congenital hyperinsulinism were diploid for chromosomes 11 and 13. The 11p15.1 to 11p15.2 and 11p15.4 to 11p15.5 regions containing ABCC8 and CDKN1C genes, respectively, were present with two copies. Loss of the maternal allele was confirmed in these focal lesions with microsatellite markers flanking the ABCC8 and CDKN1C genes, whereas a heterozygous mutation in the ABCC8 gene was inherited from the father.

CONCLUSIONS

There is a duplication of the paternal allele on chromosome 11 in the focal forms of hyperinsulinism lesion. The paternal isodisomy observed rendered the beta-cells homozygous for ABCC8 mutation and harbored a K-channel defect in the lesion similar to that observed in diffuse forms of congenital hyperinsulinism.

Liver hepatoblastoma and multiple OXPHOS deficiency in the follow-up of a patient with methylmalonic aciduria

A boy who was diagnosed with methylmalonic aciduria (MMA) at the age of 10 days developed persistent hepatomegaly and raised transaminases from the age of 4 years. He was subsequently diagnosed with Leigh syndrome and required a kidney transplantation for end-stage renal failure. A massive hepatoblastoma led to his death by the age of 11 years. Methylmalonyl-CoA mutase activity was undetectable on both cultured skin fibroblasts and kidney biopsy and multiple respiratory chain deficiency was demonstrated in the kidney. Mitochondrial dysfunction and/or post-transplant immunosuppressive therapy should be considered as a possible cause of liver cancer in this patient.

Risk assessment of acute vascular events in congenital disorder of glycosylation type Ia

The congenital disorder of glycosylation type Ia (CDG-Ia) presents a broad clinical spectrum. Some patients suffer from acute vascular events (thrombosis and bleeding) and stroke-like events. No correlations have been made between the marked hemostasis abnormalities of CDG-Ia and the occurrence of acute vascular events. We report on 6 patients with CDG-Ia presenting vascular events, then we analyze the clinical and hemostasis data of 39 CDG-Ia patients described in the literature, 17 with vascular events (E) and 21 unscathed from any event (EF), to determine the risk factors for acute vascular events in CDG-Ia. Acute vascular events occurred in patients younger than 15 years, especially with fever and prolonged immobilization. Hemostasis and liver cytolysis were statistically abnormal in patients younger than 5 years whatever the occurrence of vascular events and they normalized with time. Higher factors VIII and IX activities were statistically observed in the E cluster (p=0.03) compared to the EF cluster. The activity/antigenicity ratio for protein C (p=0.02) was also higher in the E group. CDG-Ia patients younger than 15 years old are at risk of acute vascular events. The paradoxical results-abnormal VIII and IX factors in EF patients and normal results in E patients, while XI, antithrombin, protein C, ASAT and ALAT are abnormal in both groups, could suggest a disequilibrium between prothrombotic and antithrombotic factors in the E group. Vascular events may also occur in patients where glycoproteins are proportionally more hypoglycosylated, particularly protein C.

Tissue-specific programming expression of glucocorticoid receptors and 11 beta-HSDs by maternal perinatal undernutrition in the HPA axis of adult male rats

Maternal undernutrition leads to intrauterine growth retardation and predisposes to the development of pathologies in adulthood. The hypothalamo-pituitary-adrenal axis is a major target of early-life programming. We showed previously that perinatal maternal 50% food restriction leads to hypothalamo-pituitary-adrenal axis hyperactivity and disturbs glucocorticoid feedback in adult male rats. To try to better understand these alterations, we studied several factors involved in corticosterone sensitivity. We showed that unlike the restricted expression of 11 beta-HSD2 mRNA, the 11 beta-HSD1, glucocorticoid, and mineralocorticoid receptor genes are widely distributed in rat. In contrast to the hypothalamus, we confirmed that maternal undernutrition modulates hippocampal corticosterone receptor balance and leads to increased 11 beta-HSD1 gene expression. In the pituitary, rats exhibited a huge increase in both mRNA and mineralocorticoid receptor binding capacities as well as decreased 11 beta-HSD1/11 beta-HSD2 gene expression. Using IN SITU hybridization, we showed that the mineralocorticoid receptor gene was expressed in rat corticotroph cells and by other adenopituitary cells. In the adrenal gland, maternal food restriction decreased 11beta-HSD2 mRNA. This study demonstrated that maternal food restriction has both long-term and tissue-specific effects on gene expression of factors involved in glucocorticoid sensitivity and that it could contribute, via glucocorticoid excess, to the development of adult diseases.

Development of liver disease despite mannose treatment in two patients with CDG-Ib

We report here the 6- and 2-year follow-up of two patients diagnosed at 2 months of age with CDG-Ib who were treated with mannose, with digestive symptoms, liver involvement and hyperinsulinemic hypoglycaemia. Both developed liver fibrosis while general condition improved and other symptoms disappeared.

RT-PCR analysis of corticotroph-associated genes expression in carcinoid tumours in the ectopic-ACTH syndrome

OBJECTIVE

ACTH is frequently produced in non-pituitary tumours, leading to the ectopic-ACTH syndrome, but the molecular mechanisms of its expression remain obscure. This study was aimed at understanding the transcription mechanisms of the ACTH-precursor gene in carcinoid tumours of the lung or thymus.

DESIGN

Transcripts coding for a series of corticotroph-associated transcription factor genes were detected, together with markers of the corticotroph phenotype. We studied a series of 41 carcinoid tumours including 15 with proven ectopic-ACTH syndrome.

METHODS

Specific RT-PCR reactions were designed for each gene including alternatively spliced isoforms.

RESULTS

The markers of the corticotroph phenotype were detected in all ACTH-positive tumours. Expression of the Tpit and Pitx1 genes were not restricted to ACTH-positive tumours but were also detected in many ACTH-negative carcinoids. Only a subset of ACTH-negative tumours expressed NAK-1/Nur77, and NeuroD1 expression was detected in approximately 50% of the tumours regardless of their secretory status. The glucocorticoid receptor alpha was detected in every tumour in contrast to its beta isoform detectable in a few tumours only. Chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) and peroxisome proliferator-activated receptor (PPAR) gamma2 were expressed in 50% of the tumours of each group whereas PPARgamma1 was expressed in almost every tumour.

CONCLUSIONS

ACTH-positive carcinoids do not share a characteristic expression pattern of the corticotroph-associated transcription factor genes, suggesting that the transcriptional mechanisms of the ACTH-precursor gene differ from those in normal pituitary corticotrophs. Expression of Tpit and Pitx1 genes in most carcinoids suggests that some aspects of the pituitary corticotroph phenotype may belong to general carcinoid differentiation.

Proopiomelanocortin, a polypeptide precursor with multiple functions: from physiology to pathological conditions

Proopiomelanocortin (POMC) is the polypeptide precursor of ACTH. First discovered in anterior pituitary corticotroph cells, it has more recently been revealed to have many other physiological aspects. The fine molecular mechanisms of ACTH biosynthesis show that ACTH is but one piece of a puzzle which contains many other peptides. Present in various tIssues, among which are pituitary, hypothalamus, central nervous system and skin, POMC undergoes extensive post-translational processing. This processing is tIssue-specific and generates, depending on the case, various sets of peptides involved in completely diverse biological functions. POMC expressed in corticotroph cells of the pituitary is necessary for adrenal function. Recent developments have shown that POMC-expressing neurons in the brain play a major role in the control of pain and energy homeostasis. Local production of POMC-derived peptides in skin may influence melanogenesis. A still unknown function in the placenta is likely.POMC has become a paradigmatic polypeptide precursor model illustrating the variable roles of a single gene and its various products in different localities.

Overexpression of the V3 vasopressin receptor in transgenic mice corticotropes leads to increased basal corticosterone

The vasopressin V3 receptor (V3) is specifically expressed in pituitary corticotropes and mediates the stimulatory effect of vasopressin on adrenocorticotropic hormone (ACTH) release. The V3 gene is overexpressed in corticotrope pituitary tumours compared to normal pituitaries. We hypothesized that V3 overexpression might induce changes in corticotrope function and alter the regulation of the hypothalamic-pituitary-adrenal axis. Thus, we generated transgenic mice (POMV3) expressing the human V3 receptor in the pituitary under the control of rat pro-opiomelanocortin (POMC) promoter sequences. The transgene was efficiently transcribed and vasopressin binding was increased in both corticotropes and melanotropes. In-vitro ACTH release and inositol phosphate formation were unchanged in POMV3 pituitaries, but the responses to vasopressin were significatively increased. In vivo, basal circulating concentrations of ACTH in POMV3 mice were similar to those of controls but corticosterone concentrations were moderately increased. In addition, the levels of POMC mRNA in the transgenic pituitaries were comparable to those of control mice. Finally, POMV3 mice responded with a similar maximal increase of ACTH and corticosterone to a 20-min acute restraint stress. Together, these results show that hypophyseal V3 overexpression led to increased basal concentrations of corticosterone and suggest that the negative glucocorticoid feedback may be altered at the pituitary level.

Ectopic ACTH Cushing's syndrome: V3 vasopressin receptor but not CRH receptor gene expression in a pulmonary carcinoid tumor

In the etiological diagnosis of ACTH-dependent Cushing's syndrome, it may be difficult to distinguish pituitary disease from ectopic ACTH production, specially when this is due to a benign neuroendocrine tumor. We describe a patient with partial dexamethasone suppression consistent with Cushing's disease, an absent response to CRH suggesting ectopic ACTH production and an atypical, apparent circadian rhythm. Bilateral cavernous sinus catheterization suggested a nonpituitary source of ACTH and, in the search of an ectopic tumor, somatostatin receptor scintigraphy, abdominal CT scan, and duodenopancreatic endoscopic echography were performed and failed to reveal any abnormality. Thoracic CT scan disclosed a tiny right lung nodule that showed a definite tracer uptake on MIBG scintigraphy. After resection, the nodule proved to be an 8-mm typical pulmonary carcinoid, with positive immunostaining for the classical neuroendocrine markers and for ACTH, and showing tissue expression of the POMC gene. However, the CRH receptor gene was not expressed, explaining the absent CRH response in vivo, whereas the V3 vasopressin receptor gene was expressed in the tumor tissue. The latter feature appears to be characteristic of benign carcinoids and may contribute to explaining the CRH-independent circadian rhythm observed in this case.

Nucleotide sequence and structural organization of the human vasopressin pituitary receptor (V3) gene

In the pituitary, vasopressin triggers ACTH release through a specific receptor subtype, termed V3 or V1b. We cloned the V3 cDNA and showed that its expression was almost exclusive to pituitary corticotrophs and some corticotroph tumors. To study the determinants of this tissue specificity, we have now cloned the gene for the human (h) V3 receptor and characterized its structure. It is composed of two exons, spanning 10kb, with the coding region interrupted between transmembrane domains 6 and 7. We established that the transcription initiation site is located 498 nucleotides upstream of the initiator codon and showed that two polyadenylation sites may be used, while the most frequent is the most downstream. Sequence analysis of the promoter region showed no TATA box but identified consensus binding motifs for Sp1, CREB, and half sites of the estrogen receptor binding site. However comparison with another corticotroph-specific gene, proopiomelanocortin, did not identify common regulatory elements in the two promoters except for a short GC-rich region. Unexpectedly, hV3 gene analysis revealed that a formerly cloned 'artifactual' hV3 cDNA indeed corresponded to a spliced antisense transcript, overlapping the 5' part of the coding sequence in exon 1 and the promoter region. This transcript, hV3rev, was detected in normal pituitary and in many corticotroph tumors expressing hV3 sense mRNA and may therefore play a role in hV3 gene expression.

Gene and cDNA cloning and characterization of the mouse V3/V1b pituitary vasopressin receptor

The gene of the mouse V3/V1b receptor was identified by homology cloning. One of the genomic clones contained the entire coding sequence. The cDNA presented high identity with rat (92%) and human (84%) sequences. Southern blot analysis indicated the existence of a single gene. Tissue distribution was studied by RT-PCR. The major site of expression was the pituitary. A faint signal was also present in hypothalamus, brain, adrenal, pancreas and colon. The mouse corticotroph cell line, AtT20, did not express the transcript. In order to confirm the identity of the sequence, the V3/V1b receptor cDNA was cloned and stably expressed in CHO-AA8 Tet-Off cells under the control of tetracycline. When transfected cells were treated with arginine vasopressin (AVP), inositol phosphate production increased in a dose-dependent manner, indicating that the V3/V1b receptor couples to phospholipase C. Moreover, AVP did not stimulate cAMP production. Binding studies with [3H]AVP indicated that the affinity of the mouse V3/V1b receptor (Kd=0.5 nM) is similar to that reported for rat and human receptors. The rank order of potency established in competition binding experiments with different analogues was representative of a V3/V1b profile, distinct from V1a and V2. However, significant differences were found between human and mouse receptors tested in parallel. Thus the pharmacology of V3/V1b receptors can not be transposed among different species.

Analysis of the human proopiomelanocortin gene promoter in a small cell lung carcinoma cell line reveals an unusual role for E2F transcription factors

The small cell lung carcinoma (SCLC) cell line DMS-79 has been used as a model for studying the molecular mechanism underlying the ectopic ACTH syndrome. We previously showed that two domains of the human Proopiomelanocortin (POMC) gene promoter were specifically active in DMS-79 cells. The present study focuses on the more distal one, Domain IV (-376/-417). DNaseI footprinting experiments identified a single binding site for DMS-79 cell proteins in this domain. Gel-shift and sequence analysis indicated that E2F proteins might bind this site. Indeed, proteins from DMS-79 cells which bind this site (i) have in vitro DNA binding properties indistinguishable from those of E2F proteins (ii) form, like E2F proteins, multiprotein complexes which can be dissociated by sodium deoxycholate and (iii) are recognized by antibodies directed against E2F proteins. Further, we show that the rat POMC distal promoter domain contains a homologous sequence which constitutes a natural mutant of the human POMC E2F binding site, since it does not bind E2F. We show by transient transfection that this natural mutant, in the context of the rat POMC promoter, is not active in DMS-79 cells by contrast to the human POMC E2F binding site. We conclude that E2F binding is required for the activity of Domain IV in DMS-79 cells and contributes to the expression of the POMC gene in SCLC. Further studies are required to elucidate the role of E2F factors in POMC gene transcription in SCLC cells, but our results have identified mechanisms different from those in pituitary corticotroph cells that are used by these SCLC tumor cells.

Analysis of proopiomelanocortin gene transcription mechanisms in bronchial tumour cells

The ectopic ACTH syndrome results from the transcription of the proopiomelanocortin (POMC) gene in non pituitary tumors. To determine its mechanisms, we examined in the human bronchial carcinoma cell line DMS-79 transacting factors binding to the human POMC gene promoter. Three binding sites were identified in the proximal promoter and proteins were studied by gel-shift assays. One of them is a binding site for Nur77/Nurr1 proteins in corticotroph cells but is bound in DMS-79 cells by factor(s) distinct from these proteins. The remaining two binding sites bound yet unidentified proteins and were both functionally active in DMS-79 cells. We also showed that DMS-79 cells lacked a factor required for tissue-restricted POMC gene expression in corticotroph cells. Altogether, our results indicate that POMC gene expression in DMS-79 cells is achieved without several of the corticotroph factors and provide a preliminary characterization of some factors involved in this process. They also reveal that DMS-79 cells are deficient in proteins involved in the regulation by cAMP and glucocorticoids.

Role for NF-kappa B in mediating the effects of hyperoxia on IGF-binding protein 2 promoter activity in lung alveolar epithelial cells

The surface of the pulmonary alveolus is a major target for oxidant injury, and its proper repair following injury is dependent on the proliferative response of the stem cells of the alveolar epithelium, the type 2 cells. In previous studies on the mechanisms controlling this response, we have documented involvement of several components of the IGF system, and mainly of the IGF binding protein-2 (IGFBP-2). We have provided evidence that this binding protein was associated with inhibition of DNA synthesis of type 2 cells exposed to oxidants and that its expression was regulated mostly at the level of transcription. In the present study, we focused on the factors involved in this regulation. From examination of the IGFBP-2 gene promoter sequence which revealed the presence of four potential binding sites for transcription factors of the NF-kappa B/Rel family, we hypothesized that NF-kappa B might be involved in the transcriptional activation of IGFBP-2 in oxidant-exposed cells. Data reported herein demonstrated that NF-kappa B activated IGFBP-2 promoter in transient transfection assays, and that exposure of cells to hyperoxia was associated with accumulation of the active form of NF-kappa B. Using gel shift analysis, we documented in O2-treated cells an increased binding to the four NF-kappa B binding sites. We also showed that accumulation of NF-kappa B was associated with a decrease in the inhibitory molecule I kappa B-alpha. Based on the current knowledge on NF-kappa B regulation, it is likely that in a number of situations associated with injury of lung alveolar epithelial cells signaling events involving accumulation of NF-kappa B converge to activate IGFBP-2 and to block entry into S phase.

High precursor level in maternal blood results from the alternate mode of proopiomelanocortin processing in human placenta

OBJECTIVE

ACTH-producing non-pituitary tumours are often associated with altered precursor processing, particularly in the most aggressive ones. Since placental tissue is characterized by its ability to express the proopiomelanocortin (POMC) gene and rapid cellular proliferation, we examined whether intact POMC could be released physiologically during human gestation.

SUBJECTS

One hundred and fifty six normal pregnant women, 12 with multiple pregnancies, and 23 non-pregnant controls. Twenty-eight women were studied in the immediate postpartum period.

MEASUREMENTS

We measured plasma POMC levels with a specific immunoradiometric assay (IRMA) using a combination of antibodies directed against ACTH and beta endorphin. Results obtained with this first IRMA were confirmed in 22 subjects with a second assay using the same beta endorphin antibody and a more distal antibody directed against the N-terminal fragment of POMC. Reverse transcription-PCR detected full length, pituitary-like, POMC mRNA in human placenta.

RESULTS

Plasma POMC was undetectable (< 60 U/ml) in 23 normal subjects. In normal monofetal pregnancies, POMC became detectable in most women by the third month and then increased steadily until midgestation: 168 +/- 108 (U/ml; mean +/- SD) between 12 and 15 weeks, 190 +/- 103 between 16 and 19 weeks, 324 +/- 180 between 20 and 23 weeks, 276 +/- 171 between 24 and 27 weeks, 292 +/- 177 between 28 and 31 weeks, 290 +/- 235 between 32 and 35 weeks and 308 +/- 210 between 36 weeks and parturition. Plasma POMC was significantly higher in multiple pregnancies with very high levels in three triplet-bearing mothers: 671, 941, and 1731 U/ml at 31, 33 and 32 weeks, respectively. POMC levels felt quickly in post partum, becoming undetectable in five of 13 women on day 1, seven of eight on day 2 and five of six on day 3. Plasma POMC displayed no diurnal variation, was not suppressed by glucocorticoid administration and did not correlate with plasma ACTH or cortisol. In contrast, plasma POMC positively correlated with plasma CRH.

CONCLUSIONS

Pregnancy is the only condition in which POMC is produced and released physiologically, similar in some respects to the ectopic ACTH syndrome. POMC is derived solely from the placenta, with no interference from maternal pituitary secretion, and is thus a new and specific placental marker.

Overexpression of vasopressin (V3) and corticotrophin-releasing hormone receptor genes in corticotroph tumours

OBJECTIVE

The molecular mechanisms underlying ACTH-secreting tumour formation remain unknown. Transmembrane signalling pathways play an important role in several endocrine disorders including pituitary tumours. To investigate the role of the pituitary vasopressin (V3) receptor (R) in ACTH-secreting tumours we have qualitatively and quantitatively analysed its mRNA.

DESIGN

RT-PCR, denaturing gradient gel electrophoresis and S1 nuclease protection experiments were used to analyse V3 mRNA structure in ACTH-secreting tumours. We also developed a competitive RT-PCR system to compare the levels of expression of POMC, V3 and CRH-R genes. This system used as competitor a single mutant template (termed multi-mutant) containing primers for the three genes flanking an unrelated core sequence allowing multiple quantifications from the same cDNA preparations. We analysed 12 normal pituitaries, 15 corticotroph pituitary adenomas and 6 ACTH-secreting bronchial carcinoids.

RESULTS

The V3 mRNA structure and sequence were found to be identical in normal and tumoural pituitary indicating that the tumoural Vs mRNA codes for a normal receptor. POMC RT-PCR signals in the pituitary tumour group were approximately 7-fold higher than in the normal pituitary group. Similarly, V3 and CRH-R signal were increased in pituitary tumors (mean +/- SEM: 5.87 x 10(-6) +/- 1.73 x 10(-6), and 2.33 x 10(-4) +/- 1.4 x 10(-4), respectively), when compared to normal pituitaries (1.19 x 10(-7) +/- 2.39 x 10(-8), and 1.7 x 10(-6) +/- 4.65 x 10(-7), respectively) suggesting that these two genes are expressed at very high levels in corticotroph tumours. When expressed relative to the corresponding POMC signals, increases in V3 and CRH-R signals reached 49-fold and 137-fold, respectively, in pituitary tumours. In ACTH-secreting bronchial carcinoids V3 gene expression level was also higher than in normal pituitary, whereas CRH-R signals were detected in only 4 of the 6 tumours with wide variations.

CONCLUSION

Our results show that both vasopressin and CRH receptor genes are overexpressed in ACTH-secreting pituitary tumours. They suggest that overexpression of G protein-coupled receptors may be an additional mechanism through which membrane receptors may play a role in human tumours.

Vasopressin receptors modulate the pharmacological phenotypes of Cushing's syndrome

We have examined the expression profiles of the different vasopressin receptors (V1, V2, V3) that can be expressed in the three different types of tumors associated with Cushing's syndrome. V3 (V1b) receptor cDNA was cloned from a pituitary tumor responsible for Cushing's disease. We show that it is overexpressed in these tumors and can respond to DD-AVP. High expression of the V3 receptor on highly differentiated, ACTH-secreting, bronchial carcinoid tumors explain why these non-pituitary tumors occasionally respond to vasopressin, mimicking a "pituitary-like" behavior. A retrospective analysis showed that vasopressin induced an ACTH-independent cortisol rise in 27% of the adrenocortical tumors responsible for Cushing's syndrome. V1 mRNA was detected in normal adrenal cortex and in all tumors. Adenomas had significantly higher levels than carcinomas. V1 mRNA levels were higher in responders than in non-responders. One adenoma which had a brisk cortisol response in vivo, also had in vitro cortisol responses that were inhibited by a specific V1 antagonist. In situ hybridization showed the presence of V1 mRNA in the normal human adrenal cortex where the signal predominated in the compact cells of the zona reticularis. A positive signal was also present in the tumors with high V1 mRNA levels determined by RT-PCR; its distribution pattern was heterogeneous and showed preferential association with compact cells. High-and not ectopic-expression of the V1 receptor occurs in a minority of adrenal cortical tumors which become directly responsive to vasopressin stimulation.

Variable expression of the V1 vasopressin receptor modulates the phenotypic response of steroid-secreting adrenocortical tumors

We studied the putative role of the vasopressin receptors in the phenotypic response of steroid-secreting adrenocortical tumors. A retrospective analysis of a series of 26 adrenocortical tumors responsible for Cushing's syndrome (19 adenomas and 7 carcinomas) showed that vasopressin (10 IU, i.m., lysine vasopressin) induced an ACTH-independent cortisol response (arbitrarily defined as a cortisol rise above baseline of 30 ng/mL or more) in 7 cases (27%). In comparison, 68 of 90 patients with Cushing's disease (76%) had a positive cortisol response. We then prospectively examined the expression of vasopressin receptor genes in adrenocortical tumors of recently operated patients (20 adenomas and 19 adrenocortical carcinomas). We used highly sensitive and specific quantitative RT-PCR techniques for each of the newly characterized human vasopressin receptors: V1, V2, and V3. The V1 messenger ribonucleic acid (mRNA) was detected in normal adrenal cortex and in all tumors. Its level varied widely between 2.0 x 10(2) and 4.4 x 10(5) copies/0.1 microgram total RNA, and adenomas had significantly higher levels than carcinomas, although there was a large overlap. Among the 6 recently operated patients who had been subjected to the vasopressin test in vivo, the tumor V1 mRNA levels were higher in the 4 responders (9.5 x 10(3) to 5.0 x 10(4)) than in the 2 nonresponders (2.0 x 10(2) and 1.8 x 10(3)). One adenoma that had a brisk cortisol response in vivo, also had in vitro cortisol responses that were inhibited by a specific V1 antagonist. In situ hybridization showed the presence of V1 mRNA in the normal human adrenal cortex where the signal predominated in the compact cells of the zona reticularis. A positive signal was also present in the tumors with high RT-PCR V1 mRNA levels; its distribution pattern was heterogeneous and showed preferential association with compact cells. RT-PCR studies for the other vasopressin receptors showed a much lower signal for V2 and no evidence for V3 mRNA. We could not establish whether the V2 mRNA signal observed in normal and tumoral specimens was present within adrenocortical cells or merely within tissue vessels. We conclude that the vasopressin V1 receptor gene is expressed in normal and tumoral adrenocortical cells. High, and not ectopic, expression occurs in a minority of tumors that become directly responsive to vasopressin stimulation tests.

Widespread transcription of the growth hormone-releasing peptide receptor gene in neuroendocrine human tumors

GH-releasing peptides are a new class of potent GH secretagogs (GHS) in vivo and in vitro. In normal man GHS also elicit low but definite ACTH and prolactin secretion. Recently it was shown that patients with pituitary corticotrope adenomas respond to GHS with a dramatic rise in ACTH secretion, and it has been suggested that GHS may provide a diagnostic tool to differentiate Cushing's disease from the ectopic ACTH syndrome. GHS actions are mediated by a G protein-coupled receptor recently characterized and cloned in man and rat. In this study we analyzed GHS receptor (GHS-R) expression in various types of pituitary adenoma and in endocrine and non-endocrine lung tumors by RT-PCR. GHS-R transcription was detected in all normal pituitaries and GH-secreting adenomas as expected. The receptor was also transcribed in some prolactin-secreting adenomas and non-functioning adenomas, and, more strikingly, in all 18 ACTH-secreting pituitary adenomas studied. Furthermore, it was frequently expressed in endocrine bronchial tumors, especially carcinoids, whereas it was not found or barely detectable in non-endocrine bronchial tumors. Again ACTH-secreting carcinoids of the lung were all positive for GHS-R expression. These results show that GHS-R transcription is a common feature of endocrine tumors independent of their type and origin.

V3 vasopressin receptor and corticotropic phenotype in pituitary and nonpituitary tumors

Pituitary corticotropic cells express a specific vasopressin receptor, called V1b or V3, through which vasopressin stimulates corticotropin secretion. We recently cloned a cDNA coding for this receptor and showed that it belongs to the G protein-coupled receptor family. V3 mRNA is readily detected by RT-PCR in normal human pituitaries and corticotropic pituitary adenomas but not in PRL or GH-secreting adenomas, thus demonstrating that, like POMC itself and the CRH receptor, V3 is a marker of the corticotropic phenotype. Nuclease protection experiments suggest that V3 is overexpressed in some corticotropic adenomas, and thus may play a role in tumor development by activating the phospholipase C-signalling pathway. In addition analysis of its expression in nonpituitary neuroendocrine tumors showed a striking association with carcinoids of the lung responsible for the ectopic ACTH syndrome.

High expression of the POU factor Brn3a in aggressive neuroendocrine tumors

A new family of POU transcription factors called Brn plays a role in development of the brain and some neuroendocrine structure. Because a member of this family, Brn3a, is present in the ACTH-producing mouse pituitary tumor AtT-20, binds to POMC promoter, and stimulates its activity, we studied its human homolog in ACTH-secreting or nonsecreting tumors of pituitary and bronchial origins. A specific and quantitative reverse transcription-PCR assay was developed to assess Brn3a transcripts in tumor ribonucleic acid. Brn3a transcript levels were invariably low (< 5 x 10(-6) arbitrary units) in four GH-, two PRL-, three gonadotropin-, and seven of eight ACTH-producing pituitary adenomas. A single highly invasive ACTH-secreting pituitary adenoma in a patient who ultimately died with liver metastases, and the mouse corticotroph tumor cell line AtT-20 had high Brn3a transcripts levels at 3 x 10(-5) and 4 x 10(-4) arbitrary units, respectively. Five typical bronchial carcinoids had barely detectable levels (< 5 x 10(-6) arbitrary units), whereas seven of eight small cell carcinomas of the lung (SCCLs) had extremely high levels (between 10(-3)-10(-1) arbitrary units); six of seven atypical bronchial carcinoids had intermediate values, between 10(-6) and 5 x 10(-3) arbitrary units. Although nine bronchial tumors produced POMC, there was no association between Brn3a levels and POMC gene expression; the two tumors with the highest POMC messenger ribonucleic acid contents were two bronchial carcinoids with barely detectable Brn3a levels. A gel mobility shift assay was performed with a rat CRH promoter probe that binds Brn3a; extracts of the POMC-producing human SCCL line DMS-79, which contained high levels of Brn3a transcripts, generated the same specific complex as did AtT-20 cell extracts. These data show that Brn3a gene expression in neuroendocrine tumors is not correlated with POMC gene expression; rather, it is strikingly elevated in the highly aggressive tumors, independently of their POMC status and their pituitary or nonpituitary origin.

The pituitary V3 vasopressin receptor and the corticotroph phenotype in ectopic ACTH syndrome

Ectopic ACTH secretion occurs in highly differentiated and rather indolent tumors like bronchial carcinoids or, in contrast, in various types of aggressive and poorly differentiated neuroendocrine tumors. We explored this phenomenon using the recently cloned human pituitary V3 vasopressin receptor as an alternate molecular marker of the corticotroph phenotype. Expression of V3 receptor, corticotrophin releasing hormone (CRH) receptor, and proopiomelanocortin (POMC) genes was examined in tumors of pituitary and nonpituitary origin. A comparative RT-PCR approach revealed signals for both V3 receptor and CHR receptor mRNAs in 17 of 18 ACTH-secreting pituitary adenomas, and 6 of 6 normal pituitaries; in six growth hormone- or prolactin-secreting adenomas, a very faint V3 receptor signal was observed in three cases, and CRH receptor signal was undetected in all. Six of eight bronchial carcinoids responsible for the ectopic ACTH syndrome had both POMC and V3 receptor signals as high as those in ACTH-secreting pituitary adenomas; in contrast, no POMC signal and only a very faint V3 receptor signal were detected in six of eight nonsecreting bronchial carcinoids. Northern blot analysis showed V3 receptor mRNA of identical size in ACTH-secreting bronchial carcinoids and pituitary tumors. Other types of nonpituitary tumors responsible for ectopic ACTH syndrome presented much lower levels of both POMC and V3 receptor gene expression than those found in ACTH-secreting bronchial carcinoids. In contrast with the V3 receptor, CRH receptor mRNA was detected in the majority of neuroendocrine tumors irrespective of their POMC status. These results show that expression of the V3 receptor gene participates in the corticotroph phenotype. Its striking association with ACTH-secreting bronchial carcinoids defines a subset of nonpituitary tumors in which ectopic POMC gene expression is but one aspect of a wider process of corticotroph cell differentiation, and opens new possibilities of pharmacological investigations and even manipulations of this peculiar ACTH hypersecretory syndrome.

Functional analysis of the human pro-opiomelanocortin promoter in the small cell lung carcinoma cell line DMS-79

DMS-79 is a human cell line derived from a small cell lung carcinoma (SCLC), which expresses the pro-opiomelanocortin (POMC) gene. We took it as a model in which to study the mechanism of POMC gene expression in these tumors: precursor processing is altered and gene expression is essentially unresponsive to glucocorticoids. POMC gene structure appeared normal by Southern blot analysis, indicating that gene rearrangement was not responsible for its expression in DMS-79. Indeed, using transient expression of human POMC-luciferase fusion genes in DMS-79, we showed that (1) the normal human POMC promoter was functional in DMS-79, and (2) the same proximal promoter region (-417; + 21) produced the full transcriptional activity in DMS-79 and in the mouse pituitary cell line AtT-20. Progressive 5' deletion analysis revealed differences between AtT-20 and DMS-79: region (-611; -376) was active in AtT-20 and not in DMS-79, whereas region (-95; -161) was active in both cell lines and (-376; -417) was only active in DMS-79. The latter partially overlaps a motif homologous to the DE-2 rat element which confers the tissue-specific expression of POMC in AtT-20 cells; however, this motif had no effect in DMS-79. These data suggest that POMC gene transcription is achieved through a different set of transacting factors in DMS-79 and AtT-20. Altogether, our results provide evidence that DMS-79 is a valid model of tumors responsible for the ectopic ACTH syndrome and that the mechanism of POMC gene expression in these SCLC cells is different from that in pituitary cells.

Cloning and characterization of the human V3 pituitary vasopressin receptor

Arginine-vasopressin (AVP) plays a determinant role in the normal ACTH response to stress in mammals. We cloned a human cDNA coding a 424 amino acid G-protein coupled receptor structurally related to the vasopressin/oxytocin receptor family. When expressed in COS cells, this receptor binds AVP with a high affinity (Kd = 0.55 +/- 0.13 nM) and is functionally coupled to phospholipase C. Competition studies with peptidic or non peptidic AVP analogues reveal that it is pharmacologically distinct from V1a and V2 AVP receptors and therefore it is designated V3. RT-PCR analysis shows that the human V3 receptor is expressed in normal pituitary and also in kidney, but is undetectable in liver, myometrium and adrenal gland. Northern blot analysis reveals a approximately 4.8 kb messenger in human corticotropic pituitary adenomas.

Proopiomelanocortin gene expression in normal and tumoral human lung

Proopiomelanocortin (POMC) gene expression is not restricted to the pituitary corticotroph cell, but also takes place in many normal and tumoral nonpituitary tissues. In contrast, the ectopic ACTH syndrome is a rare event. Because it is most often associated with lung tumors, we specifically studied this tissue, analyzing the different forms of POMC RNAs in normal specimens as well as in various types of tumors. The endocrine nature of the tumors was assessed by both histological examination and measurements of secretogranin-I fragments in the tissue extracts. POMC RNA was first detected by Northern blot analysis; its absolute amounts and its various molecular forms were more precisely quantified and discriminated by S1 mapping studies using a single stranded DNA probe located at the 5' end of exon 3. In five bronchial carcinoid tumors associated with the ectopic ACTH syndrome, a highly predominant, if not single, POMC RNA identical to the 1200-nucleotide (nt) pituitary message was present, the high amounts of which were correlated with those of POMC peptides in the same tissues. In five bronchial carcinoid tumors not associated with the ectopic ACTH syndrome, the same message was detected (four of five), with a second, often predominant, short RNA of about 800 nt (five of five), and the overall amounts of POMC RNAs were low. Similar patterns of POMC RNAs were observed in squamous cell tumors, adenocarcinomas, and normal lung, where the short 800-nt RNA tended to be predominant. These results show that POMC gene expression can be demonstrated in normal lung tissue and in all types of lung tumors. The ectopic ACTH syndrome only occurs with tumors capable of generating high amounts of the pituitary-like message, a phenomenon that seems to be restricted to an occasional tumor with features of neuroendocrine differentiation.

Pituitary-like proopiomelanocortin transcripts in human Leydig cell tumors

Proopiomelanocortin is a polypeptide precursor molecule, the processing of which generates ACTH, beta-endorphin, the beta- and gamma-lipotropins, the joining peptide, and the NH2-terminal fragment. Anterior pituitary corticotrophs are the major site of proopiomelanocortin gene expression in man and the predominant, if not sole source of circulating ACTH. Recent data have established that proopiomelanocortin gene expression also occurs in various normal nonpituitary tissues, one of the best studied being the testis. In this latter organ the dominant gene products are short transcripts of approximately 800 nucleotides, which lack the first two exons of the gene and cannot encode a complete proopiomelanocortin molecule. In this report we show that the mode of proopiomelanocortin gene expression is occasionally modified in human Leydig cell tumors: a 1,200-nucleotide mRNA species identical to that in the pituitary is produced. It results from the usual (pituitary) start site of transcription and thus can encode the complete proopiomelanocortin molecule. In two out of six tumors, large amounts of the 1,200-nucleotide transcript led to a dramatic increase of approximately 1,000-fold in proopiomelanocortin peptide concentrations as compared with the normal and peritumoral testis. Proopiomelanocortin processing in these tumors generates various peptide fragments including ACTH. These results may help to understand the mechanism of proopiomelanocortin expression in nonpituitary tumors and have implications for the more general phenomenon of ectopic hormone secretion.

Pro-opiomelanocortin gene expression in human phaeochromocytomas

Phaeochromocytoma is an occasional cause of the ectopic ACTH syndrome. The mechanisms of proopiomelanocortin (POMC) gene expression were analysed in 11 human tumours not associated with Cushing's syndrome, by detecting and characterizing the POMC mRNA. A DNA probe corresponding to most of the protein-coding region of the third exon was used in Northern blot studies of total and poly(A)+ RNA. All tumours contained a short (800 bases) mRNA species different from the 1200 base mRNA species of the human pituitary. This short mRNA was also present in the normal adrenal, where S1 mapping showed that it resulted from transcription initiation within the third exon. However, in two tumours, equivalent amounts of the 1200 base mRNA were also present, and in one of them a third POMC mRNA of approximately 1450 bases was detected. These data show that POMC gene expression occurs in all phaeochromocytomas. It is suggested that excess production of the 1200 bases (or the larger, 1450 base) mRNA in some tumours may be responsible for the rare occurrence of the ectopic ACTH syndrome.

Variable modes of proopiomelanocortin gene transcription in human tumors

We studied the mechanism of POMC gene expression in human nonpituitary tumors that is responsible for the ectopic ACTH syndrome. All tumors contained a 1200-nucleotide (nt) POMC mRNA species identical to that in normal and tumoral pituitaries. In two of six nonpituitary tumors, equivalent amounts of a larger, ca. 1450-nt POMC mRNA species were also present. S1 mapping studies with probes encompassing the three exons of the gene revealed that this larger POMC mRNA species was 5' extended; the other regions were identical to that in the 1200-nt POMC mRNA. In order to analyze the 5'-end of the larger POMC mRNA species, a genomic clone starting at 3.0 kilobases upstream from the usual (pituitary) cap site was obtained, and single-stranded DNA probes were used for S1 mapping studies. They showed several upstream start sites of transcription located at -369, -217, and -108. Analysis of the human genomic sequence showed TATA and GC box-like motifs preceding the -369 and -217 sites and a GC-rich region preceding the -108 site. S1 mapping with a DNA probe, encompassing exon 1 and 93 nt of its 5'-flanking region, allowed quantitative determinations, which showed that the 5'-extended POMC mRNA species accounted for variable proportions of the overall POMC transcripts in different tissues: 0.3% or less in two normal pituitaries, 0.5-3% in five tumoral pituitaries, and up to 35% and 40% in two of six nonpituitary tumors. These results show that variable modes of human POMC gene expression are induced by upstream promotors whose relative activities appear increased in some nonpituitary tumors.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of human corticotrophin-releasing hormone and pro-opiomelanocortin-related peptides in a thymic carcinoid tumour responsible for Cushing's syndrome

Severe Cushing's syndrome developed in a man of 35 years. Plasma ACTH and lipotrophin hormone levels were supranormal, and dexamethasone failed to stop their production. An ACTH-producing thymic carcinoid tumour was found to be responsible for the Cushing's syndrome. The tumour tissue contained pro-opiomelanocortin (POMC)-mRNA and POMC-related peptides. In addition, human corticotrophin-releasing hormone (h-CRH) (0.25 ng/mg wet tissue) was identified in the tumour extract. Among a series of extracts from two normal and three tumoral (Nelson's syndrome) pituitary glands, six non-pituitary POMC-producing tumours and five normal thymuses examined, only the extract from the thymic tumour of our patient contained h-CRH. The molecule isolated had the same properties as synthetic h-CRH (dilution, Sephadex G 50 chromatography). Circulating h-CRH levels, however, were normal. The possible involvement of such ectopic CRH production in the aetiology of Cushing's syndrome remains uncertain.

PTH mRNA transcription analysis in infantile tumors associated with hypercalcemia

The ability of infantile hypercalcemic tumors (three rhabdoid renal tumors, one cellular mesoblastic nephroma, and one hepatoblastoma) to produce parathyroid hormone (PTH) was tested using RNA-DNA hybridization. Results were compared with those obtained in one lung epidermoid carcinoma and one parathyroid adenoma from adult patients. Elevated plasma immunoreactive PTH (iPTH) concentrations were observed in three of five children. The only tumor in which PTH-RNA hybridization could be detected was the parathyroid adenoma. The integrity of the RNA preparations was further confirmed by positive hybridization obtained with a glucagon DNA probe in both normal pancreas and the rhabdoid tumors. Quantitative bone histomorphometry of tumor-bearing nude mice showed a reduction in bone formation and increased bone resorption, the opposite of what occurs in hyperparathyroidism. The PTH-like protein, which was detected by radioimmunoassays (RIA) in the sera of three patients, could not be correlated with tumor PTH mRNA transcription within the limits of our assays. In order to explain this discrepancy, we suggest that the tumors produce a factor (not PTH) which, in turn, elicits the excess iPTH which we detected by RIA.

Characterization of proopiomelanocortin transcripts in human nonpituitary tissues

Proopiomelanocortin (POMC), the precursor to adrenocorticotropic hormone and other related peptides, was originally identified in the corticotropic cell. Recent evidence shows that POMC products are also normally present in a variety of nonpituitary tissues. To investigate this phenomenon in humans we looked for the presence and characteristics of POMC transcripts in various adult tissues. Blot hybridization analysis of normal adrenal, thymus, and testis RNAs revealed a small RNA species approximately 400 nucleotides shorter than the 1200-nucleotide pituitary species. Primer extension and S1 nuclease mapping studies showed that this small RNA lacked exon 1 and exon 2 of the gene, and it corresponded to a set of at least six molecules starting 41 to 162 nucleotides downstream from the 5' end of exon 3. These RNAs appear to result from heterogeneous transcription initiation sites presumably under the control of "GC box" promoter sequences located in the 3' end of intron 2. They cannot encode a complete POMC molecule, and the only truncated POMC molecules that could be translated would lack a signal peptide necessary for membrane translocation and precursor processing. The use of highly sensitive S1 nuclease mapping techniques with uniformly labeled single-stranded DNA probes allowed the detection of a small but definite amount of the "normal," 1200-nucleotide, mRNA species. It is suggested that it is this POMC mRNA that is responsible for the local production of all the POMC peptides.

Altered proopiomelanocortin gene expression in adrenocorticotropin-producing nonpituitary tumors. Comparative studies with corticotropic adenomas and normal pituitaries

In order to assess the mechanisms of proopiomelanocortin (POMC) gene expression in human ACTH-producing tumors, we performed the simultaneous evaluation of POMC products and messenger RNA (mRNA) in tissue fragments obtained from two corticotropic adenomas, five nonpituitary tumors, and two normal human pituitaries. The POMC products were examined using a combination of gel exclusion chromatography and four different radioimmunoassays directed against gamma 3 melanocyte stimulating hormone (gamma 3MSH), ACTH, gamma-lipotropin (gamma LPH), and beta-endorphin. The POMCmRNA was detected and analyzed by dot and northern blot hybridization using a single-stranded genomic DNA probe corresponding to the coding region of the human POMC gene. Tissue concentrations of POMC products and mRNA showed parallel distributions. Immunoreactive gamma 3MSH and gamma LPH patterns revealed only 16-kD fragment- and gamma LPH-like peptides in normal and tumoral pituitaries; additional gamma 3MSH- and/or beta MSH-like peptides were found in all five nonpituitary tumors. A single POMCmRNA of approximately 1,200 bases (b) was detected in normal and tumoral pituitaries; a single identical POMCmRNA was also found in four nonpituitary tumors. A thymic carcinoid tumor, in addition to the 1,200-b POMCmRNA, contained equal amounts of a second larger POMCmRNA of approximately 1,450 b. It is concluded that POMC gene expression appears qualitatively unaltered in corticotropic adenomas. In nonpituitary tumors, in contrast, abnormal POMC processing is frequent; in addition, an extra POMCmRNA was detected in a thymic tumor with a greater length than the normal mRNA; the mechanisms and pathophysiological implications of these modifications remain to be elucidated.

Detection of the messenger RNAs coding for the opioid peptide precursors in pituitary and adrenal by "in situ' hybridization: study in several mammal species

The messenger RNAs coding for opioid peptide precursors have been detected and mapped in histological sections by "in situ' hybridization using specific DNA probes labelled with 32P. Using bovine preproenkephalin A (PPA) cDNA, PPA mRNA was detected in adrenal medulla of bull, hamster and guinea pig. No signal was detected in adrenal of man, rat and cat. The pro-opiomelanocortin (POMC) mRNA was detected in pituitary of man, bull, cat, rat and pig, in all cells of the intermediate lobe as well as in scattered cells of the anterior lobe producing POMC. Adequate controls demonstrated the specificity of the labelling. These results provide evidence of the expression of the gene coding for PPA in the adrenal and for POMC in the pituitary. They show cross-hybridization of one DNA probe with mRNAs of various mammals and then provide evidence that one single probe can be used to analyze expression of a given gene in tissues of several animal species by "in situ' hybridization.