Tumor suppressor genes in the 9p21 gene cluster are selective targets of inactivation in neuroendocrine gastroenteropancreatic tumors.

Functional inactivation of the Rb and p53 pathways appears to be a rite of passage for all cancerous cells. However, p53 and Rb alterations are rare events in neuroendocrine gastroenteropancreatic (GEP) tumors. The CDKN2 locus on chromosome 9p21 sits at the nexus of both pathways harboring tumor suppressor genes, which restrain cell growth by affecting the function of pRb and p53. Therefore, we analyzed the implication of their inactivation in 37 primary neuroendocrine GEP tumors and two cell culture models. RT-PCR analysis revealed loss of expression of at least one of the tumor suppressor genes CDKN2A/p16, CDKN2B/p15, and CDKN2D/p14 with distinct genetic profiles, most frequently in nonfunctional pancreatic tumors (57%) and small intestinal carcinoids (44%), and less commonly in insulinomas (30%) and gastrinomas (22%). DNA analysis and methylation-specific PCR attributed loss of expression to either homozygous deletion or 5'CpG island hypermethylation. 5-Aza-2-deoxycytidine treatment reversed CDKN2A/p16 and CDKN2B/p15 silencing with concurrent growth restraint. Thus, tumor suppressor genes localized in the 9p21 gene cluster are specific targets of inactivation in neuroendocrine GEP tumors, and demethylating agents might hold promise for selective therapy.

mRNA expression patterns of insulin-like growth factor system components in human neuroendocrine tumours.

BACKGROUND: Insulin-like growth factors (IGF) and their corresponding receptors and binding proteins are important in carcinogenesis for several tumours, but their expression pattern in the functionally and biologically heterogeneous human neuroendocrine tumours of the gastroenteropancreatic tract is largely unknown. MATERIALS AND METHODS: This study searched for the mRNA expression patterns of components of the IGF system: IGF-1 and IGF-2, IGF receptors 1 and 2 (IGF-1R, IGF-2R), IGF-binding proteins 1-6 (IGFBP1-6)) in the most frequent human gastroenteropancreatic neuroendocrine tumours (gastrinomas, insulinomas, tumours associated with carcinoid syndrome and functionally inactive tumours) employing reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: In the 37 tumour samples analysed (nine gastrinomas, 10 insulinomas, nine tumours associated with carcinoid syndrome and nine functionally inactive tumours) IGFBP-2 was found in all tumour samples while the IGFBP-1 was expressed only at low frequency (10-22%) among the four tumour types. The IGF-2R was predominantly expressed in gastrinomas. Among the four tumour types the expression of IGF-1R, IGF-2R and IGFBP-6 varied significantly. In addition, 12 pairs of significantly coexpressed IGF system components were detected (IGF-1 <--> IGF-1R, IGF-1 <--> IGF-2R, IGF-1 <--> IGFBP-3, IGF-1 <--> IGFBP-6, IGFBP-3 <--> IGF-1R, IGFBP-6 <--> IGF-1R, IGFBP-1 <--> IGF-2R, IGFBP-3 <--> IGF-2R, IGFBP-5 <--> IGF-2R, IGFBP-3 <--> IGFBP-5, IGFBP-3 <--> IGFBP-6, IGFBP-5 <--> IGFBP-6). CONCLUSIONS: The described differences of the expression patterns of the IGF system components in neuroendocrine tumour subtypes suggest tumour type-dependent different pathways in tumour growth control by IGF system components.

Treatment of endocrine gastroenteropancreatic tumors with somatostatin analogues.

Somatostatin is a hormone that regulates the function of several exocrine and endocrine glands. The peptide mediates its actions via five different receptors. These proteins are expressed in a tissue-specific manner. Somatostatin receptors are also present in neuroendocrine gastroenteropancreatic tumors. Two long-acting somatostatin analogues, octreotide and lanreotide, are recognized by the receptor subtypes 2 and 5. Excessive hormone secretion in carcinoid syndrome can be controlled by these drugs. In addition, at least a subgroup of patients with carcinoid syndromes respond with delayed tumor growth during octreotide therapy. In the future, the availability of the somatostatin receptor cDNAs will allow the development of specific and even more potent receptor analogues.

Growth factor receptor expression in human gastroenteropancreatic neuroendocrine tumours.

BACKGROUND: Human gastroenteropancreatic neuroendocrine tumours are functionally and biologically heterogeneous, but their exact growth factor receptor expression pattern, important for onco- and carcinogenesis, remains unknown. METHODS: This study searched for the mRNA expression pattern of six tyrosine- and serine/threonine kinase receptors [hepatocyte growth factor (HGFR), fibroblast growth factor (FGFR), epidermal growth factor (EGFR), insulin-like growth factor (IGF)-1R, transforming growth factor (TGF)-betaR1, TGF-betaR2] together with the five somatostatin receptors in human gastroenteropancreatic neuroendocrine tumours (gastrinomas, insulinomas, tumours with carcinoid syndrome, functionally inactive neuroendocrine tumours) using reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: EGF receptor was expressed almost exclusively in gastrinomas. Among the four tumour subtypes, expression frequencies of the somatostatin receptors 1 and 5, HGF-, IGF-1-, TGF-betaR1, TGF-betaR2 and the EGF-receptor varied significantly. CONCLUSIONS: In spite of the common cellular origin of these tumours, differences in growth factor receptor expression suggest the existence of different pathways during tumour subtype development.

A novel model for the first nucleotide binding domain of the cystic fibrosis transmembrane conductance regulator.

Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most frequent mutation is the deletion of F508 in the first nucleotide binding fold (NBF1). It induces a perturbation in the folding of NBF1, which impedes posttranslational maturation of CFTR. Determination of the three-dimensional structure of NBF1 would help to understand this defect. We present a novel model for NBF1 built from the crystal structure of bovine mitochondrial F1-ATPase protein. This model gives a reasonable interpretation of the effect of mutations on the maturation of the protein and, in agreement with the CD data, leads to reconsideration of the limits of NBF1 within CFTR.

Variation of immunocytochemical expression of transforming growth factor (TGF)-beta in hepatocytes in culture and liver slices.

Transforming growth factor beta (TGF-beta) is a major member of a cytokine family with pluripotent biological activity. In the liver, TGF-beta has pathophysiological significance with respect to hepatic fibrogenesis, regulation of liver cell growth, tumor development, and induction of hepatocellular apoptosis. We show that the expression of immunocytochemically detectable TGF-beta in cultured hepatocytes is strongly dependent on culture conditions and cellular microenvironment. Hepatocytes in situ and freshly isolated cells are TGF-beta negative. In contrast, hepatocytes in incubated liver slices are stained with a patch-like pattern, whereas parenchymal cells cultured as a monolayer exhibit strong diffuse positive immunostaining for TGF-beta within 2 h after seeding. The intensity of immunocytochemical staining is dependent on culture substrata, major expression being observed in cells maintained on glass or plastic surfaces. When collagen type-I and type-IV, or EHS-matrix are used as substrata, TGF-beta is absent or only weakly immunocytochemically apparent in cultured hepatocytes, irrespective of the culture medium used. The positive immunocytochemical expression of TGF-beta in hepatocytes arises neither by transcriptional and translational pathways nor by disturbed intracellular calcium homeostasis. However, calcium-dependent proteinases, such as calpain-I and -II, might be involved in the immunochemical presentation of intracellular TGF-beta, because respective calpain inhibitors strongly reduce the appearance of TGF-beta in cultured parenchymal liver cells. Thus, hepatocytes are a major cellular source of (latent) TGF-beta in liver, as becomes evident during culture.

Detection of more than 50 different CFTR mutations in a large group of German cystic fibrosis patients.

We have conducted a comprehensive study of the molecular basis of cystic fibrosis (CF) in 350 German CF patients. A screening approach based on single-strand conformation analysis and direct sequencing of genomic polymerase chain reaction products has allowed us to detect the molecular defects on 95.4% of the CF chromosomes within the coding region and splice sites of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The spectrum of sequence changes comprises 54 different mutations, including 17 missense mutations, 14 nonsense mutations, 11 frameshift mutations, 10 splice site variants and two amino acid deletions. Eleven of these mutations have not previously been described. Our results reflect the marked mutational heterogeneity of CF in a large sample of patients from a non-isolated population.

Cystic fibrosis: the impact of analytical technology for genotype-phenotype studies.

The generalized exocrinopathy cystic fibrosis (CF) is the most common severe genetic disease in Caucasian populations. A panel of more than 700 chromosomes from German and Turkish CF patients was screened for disease-causing mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene by chemical cleavage of mismatch, single strand conformation polymorphism, restriction analysis and direct sequencing of genomic DNA amplified by polymerase chain reaction. Besides the major 3-bp deletion, delta F508 that was found on 73% of German CF chromosomes, more than 50 other missense, nonsense, frame-shift, and splice-site mutations have already been identified. In general, a CFTR mutation is linked with a single 10-marker haplotype which indicates that in most cases a particular mutation spread from a common ancestor. The comparison of mutation genotypes with the disease phenotype emphasized the causative role of the type and localization of the CFTR mutation for clinical course and prognosis. Pancreatic status and the risk of colonization of airways with opportunistic pathogens are genetically determined. Most patients who are harbouring mutations in the nucleotide binding folds were suffering from severe CF disease. Mild or even aberrant forms of CF were observed for many missense mutations located in the putative transmembrane domains or for mutations that are expected to result in a truncated protein of half of wild-type CFTR.

Four novel cystic fibrosis mutations in splice junction sequences affecting the CFTR nucleotide binding folds.

Single cases of the four novel splice site mutations 1525-1 G-->A (intron 9), 3601-2 A-->G (intron 18), 3850-3 T-->G (intron 19), and 4374 + 1 G-->T (intron 23) were detected in the CFTR gene of cystic fibrosis patients of Indo-Iranian, Turkish, Polish, and German descent. The nucleotide substitutions at the +1, -1, and -2 positions all destroy splice sites and lead to severe disease alleles associated with features typical of gastrointestinal and pulmonary cystic fibrosis disease. The 3850-3 T-to-G change was discovered in a very mildly affected 33-year-old delta F508 compound heterozygote, suggesting that the T-to-G transversion at the less conserved -3 position of the acceptor splice site may retain some wildtype function.

Genetic determinants of airways' colonisation with Pseudomonas aeruginosa in cystic fibrosis.

Exocrine pancreatic insufficiency and lung infection with Pseudomonas aeruginosa are major features of cystic fibrosis (CF). This monogenic disease is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. 267 children and adolescents with CF who were regularly seen at the same centre were assessed for an association of the CFTR mutation genotype with exocrine pancreatic function and the age of onset of chronic colonisation with P aeruginosa. The major mutation delta F508 accounted for 74% of CF alleles; 33 further CFTR mutations had been detected on the CF chromosomes of the study population by June, 1992. With the exception of delta F508/R347P compound heterozygotes, patients of the same mutation genotype were either pancreas insufficient (PI) or pancreas sufficient (PS). The age-specific colonisation rates with P aeruginosa were significantly lower in PS than in PI patients. The missense and splice site mutations that are "mild" CF alleles with respect to exocrine pancreatic function were also "low risk" alleles for the acquisition of P aeruginosa. On the other hand, the proportion of P aeruginosa-positive patients increased most rapidly in the PI delta F508 compound heterozygotes who were carrying a termination mutation in the nucleotide binding fold-encoding exons. Pancreatic status and the risk of chronic airways' colonisation with P aeruginosa are predisposed by the CFTR mutation genotype and can be differentiated by the type and location of the mutations in the CFTR gene.

Intra- and extragenic marker haplotypes of CFTR mutations in cystic fibrosis families.

In order to facilitate the screening for the less common mutations in the cystic fibrosis (CF) gene viz., the CF transmembrane conductance regulator gene (CFTR), marker haplotypes were determined for German non-CF (N) and CF chromosomes by polymerase chain reaction analysis of four polymorphisms upstream of the CF gene (XV-2c, KM.19, MP6-D9, J44) and six intragenic polymorphisms (GATT, TUB9, M470V, T854T, TUB18, TUB20) that span the CFTR gene from exon 6 through exon 21. Novel informative sequence variants of CFTR were detected in front of exons 10 (1525-61 A or G), 19 (3601-65 C or A), and 21 (4006-200 A or G). The CF locus exhibits strong long-range marker-marker linkage disequilibrium with breakpoints of recombination between XV-2c and KM.19, and between exons 10 and 19 of CFTR. Marker alleles of GATT-TUB9 and TUB18-TUB20 were found to be in absolute linkage disequilibrium. Four major haplotypes encompass more than 90% of German N and CF chromosomes. Fifteen CFTR mutations detected on 421 out of 500 CF chromosomes were each identified on one of these four predominant 7-marker haplotypes. Whereas all analysed delta F508 chromosomes carried the same KM.19-D9-J44-GATT-TUB9-M470V-T854T haplotype, another frequent mutation in Germany, R553X, was identified on two different major haplotypes. Hence, a priori haplotyping cannot exclude a particular CF mutation, but in combination with population genetic data, enables mutations to be ranked by decreasing probability.

Mild course of cystic fibrosis associated with heterozygosity for infrequent mutations in the first nucleotide-binding fold of CFTR.

The mild clinical course of a patient with cystic fibrosis is presented who inherited the two mutations Gly551----Asp and Arg553----Stop in the cystic fibrosis transmembrane conductance regulator gene. The missense mutation Arg553----Stop discovered in American Blacks is also present on cystic fibrosis chromosomes of Caucasian ancestry.

Cystic fibrosis with three mutations in the cystic fibrosis transmembrane conductance regulator gene.

Three mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene were discovered in a pancreas-insufficient patient with cystic fibrosis (CF) who displayed an uncommon combination of almost normal chloride concentration in sweat tests and typical symptoms of gastrointestinal and pulmonary disease. The R553Q mutation was found on the maternal delta F508-CFTR gene. Codon 553 is located within a consensus motif of the ATP-binding cassette transport proteins at a less conserved position. Other members of this protein superfamily contain a glutamine instead of arginine at the homologous position, suggesting a modulating rather than disease-causing role of the R553Q mutation in CFTR. The amplification refractory mutation system did not detect the R553Q mutation in a further 65 normal, 113 delta F508, and 91 non-delta F508 CF chromosomes. The index case carried the R553X nonsense mutation on the paternal chromosome. The R553X mutation was present on a further 9 out of 86 German non-delta F508 CF chromosomes linked with the XV2c-KM19-Mp6d9-J44-GATT haplotypes 2-2-2-1-1 and 1-1-2-1-2. The location of R553X on separate haplotypes including both alleles of the intragenic GATT repeat suggests an ancient and/or multiple origins of the R553X mutations. The association of the genotype of the CFTR mutation and the clinical phenotype was assessed for the patients carrying the related genotypes delta F508/delta F508 (n = 80), delta F508/R553X (n = 9) and delta F508-R553Q/R553X (n = 1). In compound heterozygotes, the median chloride concentration in pilocarpine iontophoresis sweat tests was significantly lower than in the delta F508 homozygotes (P less than 0.01). The patient groups were significantly different with respect to the distributions of the centiles for height (P less than 0.001) and weight (P less than 0.01) as the most sensitive predictors of the course and prognosis in CF. Growth retardation was more pronounced in the compound heterozygotes.