Search Results
Search for other papers by Adrian J L Clark in
Google Scholar
PubMed
proopiomelanocortin (POMC) was first coined by Chrétien and coworkers and will be used hereafter ( Chrétien et al. 1979 ). Figure 1 Anatomy of the POMC gene and its transcription and translation. (A) POMC is located on the short arm of human chromosome 2
Search for other papers by Sandra Navarro in
Google Scholar
PubMed
Search for other papers by Lucia Soletto in
Google Scholar
PubMed
Search for other papers by Sara Puchol in
Google Scholar
PubMed
Search for other papers by Josep Rotllant in
Google Scholar
PubMed
Search for other papers by Jose Luis Soengas in
Google Scholar
PubMed
Search for other papers by Jose Miguel Cerdá-Reverter in
Google Scholar
PubMed
Introduction Proopiomelanocortin ( POMC ) gene encodes a protein precursor whose posttranslational processing yields the melanocortins among other biologically active peptides. In tetrapods, this precursor integrates three main domains: the N
Search for other papers by Y. de Keyzer in
Google Scholar
PubMed
Search for other papers by M.-F. Rousseau-Merck in
Google Scholar
PubMed
Search for other papers by J.-P. Luton in
Google Scholar
PubMed
Search for other papers by F. Girard in
Google Scholar
PubMed
Search for other papers by A. Kahn in
Google Scholar
PubMed
Search for other papers by X. Bertagna in
Google Scholar
PubMed
ABSTRACT
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.
Search for other papers by Michel Chrétien in
Google Scholar
PubMed
Search for other papers by Majambu Mbikay in
Google Scholar
PubMed
-melanocyte-stimulating hormone (β-MSH), a pituitary octadecapeptide discovered 10 years earlier ( Geschwind et al. 1956 , Harris & Roos 1956 ). In this review, we describe how the LPH model unfolded into the pro-opiomelanocortin (POMC) story and how the prohormone theory
Search for other papers by A. J. L. Clark in
Google Scholar
PubMed
Search for other papers by P. M. Lavender in
Google Scholar
PubMed
Search for other papers by G. M. Besser in
Google Scholar
PubMed
Search for other papers by L. H. Rees in
Google Scholar
PubMed
ABSTRACT
As an approach to understanding the abnormalities of pro-opiomelanocortin (POMC) gene regulation in human ACTH-secreting tumours, we have analysed the POMC mRNA content of nine such tumours using the Northern blot technique. Most of the tumours and normal human pituitary contained easily detectable quantities of POMC mRNA. The length of this message in most tumours was similar to, or slightly larger than, that in the normal pituitary (1150–1200 bases). Ribonuclease H studies suggested that the origin of any size heterogeneity was a longer poly(A) tail in the tumour RNA. Some tumours, however, expressed a short POMC mRNA (800 bases) which may lack the first two exons of the POMC gene as has been described. A third POMC mRNA size variant (1500 bases) was also seen in low levels in two cases, and as the principal mRNA species in one case. Primer extension and S1 nuclease protection studies suggested that most transcripts in the tumours analysed originated from the conventional promoter, and thus the use of an alternative promoter is not an adequate explanation for the expression of this gene in ectopic ACTH-secreting tumours.
Search for other papers by P. Lavender in
Google Scholar
PubMed
Search for other papers by A. J. L. Clark in
Google Scholar
PubMed
Search for other papers by G. M. Besser in
Google Scholar
PubMed
Search for other papers by L. H. Rees in
Google Scholar
PubMed
ABSTRACT
The pro-opiomelanocortin gene is widely expressed in human tissues, although both transcriptional initiation sites and regulation appear to be tissue specific. In order to determine how promoter and enhancer choice is effected, we have studied the methylation pattern of the gene in a number of normal tissues, tumours and cell lines. Variability of this pattern was observed in the 5′-flanking DNA, particularly at the HpaII site located at −304 bp upstream from the pituitary CAP site. This site was generally methylated in tissues likely to express the predominant extrapituitary (800 nucleotide) message, while in tissues known to express the normal pituitary (1150 nucleotide) message and longer species, a tendency towards undermethylation was observed. Although the sites at which variable methylation occurs did not correspond to established binding sites for regulatory proteins, many of these regions remain to be determined and thus it is possible that methylation may be influential in the tissue-specific regulation of this gene.
Search for other papers by A. White in
Google Scholar
PubMed
Search for other papers by M. F. Stewart in
Google Scholar
PubMed
Search for other papers by W. E. Farrell in
Google Scholar
PubMed
Search for other papers by S. R. Crosby in
Google Scholar
PubMed
Search for other papers by P. M. Lavender in
Google Scholar
PubMed
Search for other papers by P. R. Twentyman in
Google Scholar
PubMed
Search for other papers by L. H. Rees in
Google Scholar
PubMed
Search for other papers by A. J. L. Clark in
Google Scholar
PubMed
ABSTRACT
Expression of the RNA coding for the ACTH—β-lipotrophin precursor, pro-opiomelanocortin (POMC), has been demonstrated in five human small-cell lung cancer (SCLC) cell lines. Using Northern and slot-blot hybridization analysis of RNA and a bovine POMC cDNA as probe, the processed POMC RNA from SCLC cells was found to be approximately 1350 nucleotides in length, which is larger than that found in the normal human pituitary. Expression of the POMC gene was confirmed by measurement of ACTH precursors secreted by the cells, using a novel two-site immunoradiometric assay based on monoclonal antibodies, which directly quantifies both POMC and pro-ACTH but does not recognize ACTH. Levels of POMC in medium accumulated throughout the growth of the cells, in contrast to POMC RNA which showed a relatively constant level of expression. We conclude that human SCLC cell lines are valuable models for studying the aberrant expression and regulation of the human POMC gene.
Search for other papers by I. C. McMillen in
Google Scholar
PubMed
Search for other papers by J. E. Mercer in
Google Scholar
PubMed
Search for other papers by G. D. Thorburn in
Google Scholar
PubMed
ABSTRACT
In order to clarify the corticotrophic capacity of the fetal sheep anterior pituitary in late gestation, we have measured the relative levels of messenger RNA for the ACTH precursor molecule proopiomelanocortin (POMC) in individual fetal sheep anterior pituitaries collected between 100 and 144 days of gestation. The mean relative POMC mRNA:poly(A)+ RNA ratio of the pituitary glands collected between 100 and 135 days (1·35 ± 0·15) was significantly greater than the mean relative POMC mRNA:poly(A)+ RNA ratio of the pituitaries collected between 141 and 144 days (0·81 ± 0·09). Northern blot analysis showed that a single band of RNA hybridized with the human POMC cDNA probe in adult and fetal sheep pituitaries.
Our results do not contradict the hypothesis that an increase in basal ACTH concentrations after 140 days of gestation could reflect a change in the post-translational processing of POMC in the fetal sheep anterior pituitary.
Search for other papers by T. S. Grewal in
Google Scholar
PubMed
Search for other papers by P. J. Lowry in
Google Scholar
PubMed
Search for other papers by D. Savva in
Google Scholar
PubMed
ABSTRACT
A large portion of the human pro-opiomelanocortin (POMC) peptide corresponding to amino acid residues 59–241 has been cloned and expressed in Escherichia coli. A 1·0 kb DNA fragment encoding this peptide was cloned into the expression vectors pUC8 and pUR291. Plasmid pJMBG51 (a pUC8 recombinant) was found to direct the expression of a 24 kDa peptide. The recombinant pUR291 (pJMBG52) was shown to produce a β-galactosidase fusion protein of 140 kDa. Western blot analysis showed that both the 24 kDa and 140 kDa peptides are recognized by antibodies raised against POMC-derived peptides. The β-galactosidase fusion protein has been partially purified from crude E. coli cell lysates using affinity chromatography on p-aminobenzyl-1-thio-β-d-galactopyranoside agarose.
Search for other papers by T. Usui in
Google Scholar
PubMed
Search for other papers by Y. Nakai in
Google Scholar
PubMed
Search for other papers by T. Tsukada in
Google Scholar
PubMed
Search for other papers by H. Takahashi in
Google Scholar
PubMed
Search for other papers by J. Fukata in
Google Scholar
PubMed
Search for other papers by Y. Naito in
Google Scholar
PubMed
Search for other papers by S. Nakaishi in
Google Scholar
PubMed
Search for other papers by T. Tominaga in
Google Scholar
PubMed
Search for other papers by N. Murakami in
Google Scholar
PubMed
Search for other papers by H. Imura in
Google Scholar
PubMed
ABSTRACT
A fragment of human genomic DNA containing the entire pro-opiomelanocortin (POMC) gene was introduced by transfection into the rat glial cell line C6. Blot analysis using poly(A)-rich RNA from the transformed C6 cells showed several hybridization bands. One band was similar in size (1·2 kb) to the POMC mRNA of human pituitary, while two were larger (2·6 and 2·2 kb) and the fourth smaller (800 bp). S1 nuclease mapping revealed that the POMC transcripts in transformed C6 cells were similar to those in non-pituitary tissues. Immunoreactive ACTH (ir-ACTH) was measurable in both the culture medium and cells. Gel chromatography showed that ir-ACTH in the medium eluted at a position identical to that of so-called big ACTH (approximately 40 kDa) which is found in the plasma of patients with ectopic ACTH syndrome. The human POMC gene could thus be expressed in the non-pituitary rat glial cell line C6, although the transcripts and translation products in C6 cells differ from those in the human pituitary. These results suggest that the transformed C6 cell may be a useful tool for studying the regulation of human POMC gene expression in non-pituitary cells.
