The spectrum of p53 mutations in colorectal adenomas differs from that in colorectal carcinomas

BACKGROUND

p53 mutations are frequently observed in colorectal carcinomas but they have also been found in colorectal adenomas, although considerably less frequently.

AIMS

To explore p53 mutations in benign tumours, we have screened 70 colorectal adenomas for allelic loss at, and point mutations in, TP53 by analysis of selected microdissected cell populations.

RESULTS

Sixteen (22.8%) adenomas were found to have allelic loss, of which 11 (15.7%) had p53 mutations. In adenomas with mild, moderate, or severe dysplasia, mutation or allelic loss occurred in 4.8%, 16.7%, and 52.6%, respectively (p<0.001). Seven different mutations were found, all missense changes or inframe deletions: one (Thr150Arg) has not been found before while three (Gln144His, Gly245Arg, and Glu285Gln) have not been described previously in colorectal tumours. The other three mutations (Arg175Gly, DeltaPro190, and Gly245Ser) have been found in colorectal carcinomas, the last commonly. Adenomas harboured a spectrum of p53 mutations which was significantly different from cancers as regards the position in the gene and a higher frequency of G-->C/C-->G changes.

CONCLUSIONS

Combining our data on adenomas with data already published and in comparison with the spectrum of mutations in colorectal carcinomas, it is suggested that some p53 mutations have a weaker effect than others and are therefore more likely to be found in adenomas which have not progressed to carcinomas.

A 700-kb physical map of a region of 16q23.2 homozygously deleted in multiple cancers and spanning the common fragile site FRA16D

We have identified a >600-kb region at 16q23.2 that is homozygously deleted from malignant ovarian ascites using representational difference analysis. Overlapping homozygous deletions were also observed in the colon carcinoma cell line HCT116 and a xenograft established from the small cell lung cancer cell line WX330. This region coincides with that described previously by others as showing loss of heterozygosity in prostate and breast cancers (C. Li et al., Genes Chromosomes Cancer, 24: 175-182, 1999; A. Latil et al., Cancer Res., 57: 1058-1062, 1997; K. Driouch et al., Genes Chromosomes Cancer, 19: 185-191, 1997; A. Iida et al., Br. J. Cancer, 75: 264-267, 1997). In addition, the minimally deleted region spans the common fragile site FRA16D. We have constructed a 700-kb physical map encompassing the deleted region. By fluorescence in situ hybridization of aphidicolin-induced metaphase chromosomes, we have preliminary data to suggest that P1-derived bacterial artificial chromosome clones from the contig lie on both sides of FRA16D. This is confirmed by extensive fluorescence in situ hybridization analysis of the region reported in the accompanying article (M. Mangelsdorf et al., Cancer Res., 60: 1683-1689, 2000) and is consistent with an involvement of this common fragile site in the loss of 16q23.2 material in various cancer types. The minimally deleted region of approximately 210 kb has been characterized using our own markers and public domain markers. Eleven distinct expressed sequences mapped to the region, providing a basis for identifying the predicted tumor suppressor gene in this region.

A "living fossil" sequence: primary structure of the coelacanth (Latimeria chalumnae) hemoglobin--evolutionary and functional aspects

The coelacanth (Latimeria chalumnae, Actinistia) has a single hemoglobin component. The primary structures of the alpha- and beta-chains are presented. They could be separated by reversed-phase HPLC. Peptides obtained by tryptic digestion of the native and oxidized chains were isolated by reversed-phase HPLC and sequenced in liquid and gas-phase sequenators. The alignment was achieved by employing the N-terminal sequences of the native chains and those of a beta-chain cyanogen bromide peptide as well as fragments obtained by acid hydrolysis. The Latimeria alpha-chains consist of 142 amino-acid residues, due to a fish-specific insertion between positions 46 and 47, whereas the beta-chains are of normal length (146 residues). Latimeria alpha- and beta-chains share 72 (51.1%) and 70 (47.9%) identical residues with human hemoglobin, respectively. Numerous heme contacts and positions involved in subunit interface contacts are replaced. The most interesting of them were studied by molecular modeling. The loss of an alpha 1/beta 2-contact by the exchanges alpha 92(FG4)Arg----Leu and beta 43(CD2)Glu----Lys might be responsible for the easy dissociation of the tetrameric hemoglobin molecule. A comparison of the residues replaced in contact positions with fishes and amphibians revealed the highest number of matches between Latimeria and tadpoles. The same result was obtained by the evaluation of other regions relevant for structure and function of the molecule, like exon-intron boundary regions, phosphate binding sites and salt bridges responsible for the Bohr effect.

The first sequenced normal hemoglobin lacking histidine in position 146 of the beta-chains. The primary structures of the major and minor hemoglobin components of the great crested newt (Triturus cristatus, Urodela, Amphibia)

The hemoglobin of the Great Crested Newt (Triturus cristatus), an animal maintaining the gas exchange to about 85% through the skin, consists of a major (HbM = 65%) and a minor (Hbm = 35%) component. The primary structures of the four chains are presented. They could be separated by reversed-phase HPLC and were cleaved with trypsin and additionally by acid hydrolysis. Both the native chains and their peptides were sequenced by liquid and gas phase sequenators. At the N-terminus the alpha M-chains are by one amino-acid residue longer and the beta M-chains by one residue shorter, resulting in a chain length of 142 and 145, respectively. The alpha m-chains are of normal length whereas in the beta m-chains the C-terminal histidine in position 146 is missing. Both alpha-chains differ by 50 residues (35.2%) and the beta-chains by 63 (43.2%). The alpha-chains were compared with those of other salamandroid hemoglobins. The difference to human hemoglobin is marked by 61 (43.3%) amino-acid substitutions in both alpha-chains and by 78 (53.4%) in both beta-chains. Numerous heme contacts and positions involved in the subunit interface are affected by replacements. The most interesting of them were studied by molecular modeling. The importance of the missing beta m-146(HC3)His and of the substitution of several amino-acid residues involved in the binding of organic phosphates is discussed with respect to the reduced Bohr effect of Triturus cristatus hemoglobin.

The primary structure of the hemoglobin from the grey-headed flying fox (Pteropus poliocephalus) and the black flying fox (P. alecto, Megachiroptera)

The primary structures of the hemoglobins of two Flying Foxes of the genus Pteropus are presented. Both comprise two components: in P. alecto hemoglobin two alpha-chains at a ratio of 1:1 and two beta-chains at a ratio of 4:1 were detected. The hemoglobin of P. poliocephalus comprises one alpha-chain and two beta-chains, the latter at a ratio of 1:1. The globin chains were separated by high-performance liquid chromatography and the sequences determined by automatic liquid and gas phase Edman degradation of the chains and their tryptic peptides. Compared with human hemoglobin, the alpha-chains of P. alecto and P. poliocephalus show 18 and 19 exchanges, respectively, whereas in the beta-chains 16/17 substitutions are found in both cases. In the alpha-chains of P. alecto, one exchange involves an alpha 1/beta 1-contact. In the beta-chains of both species one heme-, one alpha 1/beta 2- and two alpha 1/beta 1-contacts are exchanged. The relevant side chains are the same in both species. The functional and systematic aspects of these findings are discussed.

The primary structure of the hemoglobin of the Indian false vampire (Megaderma lyra, Microchiroptera)

The hemoglobin of the Indian false vampire Megaderma lyra contains only one component. In this paper, we are presenting its primary structure. The globin chains were separated by high-performance liquid chromatography and the sequences determined by automatic liquid and gas phase Edman degradation of the chains and their tryptic peptides, as well as of the prolyl-peptides obtained by acid hydrolysis of the Asp-Pro bond in the alpha- and beta-chains. The alpha-chains show 23 and the beta-chains 20 exchanges compared with the human alpha- and beta-chains, respectively. In the alpha-chains, three exchanges involved alpha 1/beta 1 contacts. In the beta-chains one heme-and three alpha 1/beta 1 contacts are exchanged. The functional and systematic aspects of these replacements are discussed.

The primary structure of the hemoglobin of an Indian flying fox (Cynopterus sphinx, Megachiroptera)

The hemoglobin of the Indian flying fox Cynopterus sphinx contains only one component. In this work, we are presenting its primary structure. The globin chains were separated by high-performance liquid chromatography and the sequences determined by automatic liquid and gas-phase Edman degradation of the chains and their tryptic peptides, as well as of the peptide obtained by acid hydrolysis of the Asp-Pro bond in the beta-chains. The alpha-chains show 14 and the beta-chains 19 exchanges compared with the human alpha- and beta-chains, respectively. In the alpha-chains one amino-acid exchange involves an alpha 1/beta 1 contact. In the beta-chains one heme contact, three alpha 1/beta 1- and one alpha 1/beta 2-contacts are exchanged. The functional and evolutionary aspects of these findings are discussed.

The primary structure of the hemoglobin of the European marmot (Marmota marmota marmota, Rodentia)

The hemoglobin of the European marmot Marmota marmota marmota has been found to consist of only one component. In this work, we are presenting its primary structure. The globin chains have been separated by high performance liquid chromatography and the sequences have been determined by automated Edman degradation of the chains and their tryptic peptides, as well as of the peptide obtained by acid hydrolysis of the Asp-Pro bond in the beta-chains. In the alpha-chains we have found 13 and in the beta-chains 34 exchanges compared with the human alpha- and beta-chains, respectively. The amino acids which are substituted in the alpha-chains are not involved in any contacts, whereas in the beta-chains, one exchange involves a heme contact, two alpha 1/beta 1- and one alpha 1/beta 2-contacts. The functional and evolutionary aspects of these findings are discussed.