Bases moleculares de la cancerización de cavidad oral / Molecular basis on oral cavity cancerization

Se presenta una revisión bibliográfica breve sobre los principales aspectos moleculares de interés en la cancerización de cavidad oral. Se hace referencia a los conocimientos más recientes sobre las aberraciones cromosómicas más comunes y las alteraciones de los oncogenes y genes supresores tumorales que están implicados en la carcinogénesis oral. Así mismo, se resume la teoría molecular actual que explica el proceso de cancerización de campo (AU)

A review about the main molecular aspects on oral cavity cancerization is presented, with special reference to the common chromosomal aberration, oncogenes and tumour suppressor genes implied in oral carcinogenesis. A summary about molecular theory explaining the field cancerization process is also presented (AU)

Analysis of UV-induced mutation spectra in Escherichia coli by DNA polymerase eta from Arabidopsis thaliana.

DNA polymerase eta belongs to the Y-family of DNA polymerases, enzymes that are able to synthesize past template lesions that block replication fork progression. This polymerase accurately bypasses UV-associated cis-syn cyclobutane thymine dimers in vitro and therefore may contributes to resistance against sunlight in vivo, both ameliorating survival and decreasing the level of mutagenesis. We cloned and sequenced a cDNA from Arabidopsis thaliana which encodes a protein containing several sequence motifs characteristics of Pol eta homologues, including a highly conserved sequence reported to be present in the active site of the Y-family DNA polymerases. The gene, named AtPOLH, contains 14 exons and 13 introns and is expressed in different plant tissues. A strain from Saccharomyces cerevisiae, deficient in Pol eta activity, was transformed with a yeast expression plasmid containing the AtPOLH cDNA. The rate of survival to UV irradiation in the transformed mutant increased to similar values of the wild type yeast strain, showing that AtPOLH encodes a functional protein. In addition, when AtPOLH is expressed in Escherichia coli, a change in the mutational spectra is detected when bacteria are irradiated with UV light. This observation might indicate that AtPOLH could compete with DNA polymerase V and then bypass cyclobutane pyrimidine dimers incorporating two adenylates.

Combined exposure of ELF magnetic fields and x-rays increased mutant yields compared with x-rays alone in pTN89 plasmids.

We have examined mutations in the supF gene carried by pTN89 plasmids in Escherichia coli (E. coli) to examine the effects of extremely low frequency magnetic fields (ELFMFs) and/or X-rays to the plasmids. The plasmids were subjected to sham exposure or exposed to an ELFMF (5 mT), with or without X-ray irradiation (10 Gy). For the combined treatments, exposure to the ELFMF was immediately before or after X-ray irradiation. The mutant fractions were 0.94x10(-5 )for X-rays alone, 1.58x10(-5) for an ELFMF followed by X-rays, and 3.64x10(-5) for X-rays followed by an ELFMF. Increased mutant fraction was not detected following exposure to a magnetic field alone, or after sham exposure. The mutant fraction for X-rays followed by an ELFMF was significantly higher than those of other treatments. Sequence analysis of the supF mutant plasmids revealed that base substitutions were dominant on exposure to X-rays alone and X-rays plus an ELFMF. Several types of deletions were detected in only the combined treatments, but not with X-rays alone. We could not find any mutant colonies in sham irradiated and an ELFMF alone treatment, but exposure to ELFMFs immediately before or after X-ray irradiation may enhance the mutations. Our results indicate that an ELFMF increases mutation and alters the spectrum of mutations.

Mutation spectra in supF: approaches to elucidating sequence context effects.

Shuttle vectors carrying the supF suppressor tRNA gene were originally developed for mutagenesis experiments in primate and human cells. Since then, the supF gene has been used as a mutation reporter in other mammalian cells, yeast, Escherichia coli, and transgenic mice. The widespread use of the vector for studies of many DNA reactive agents has produced a large database of mutation spectra. These provide primary information on the kinds and distribution of mutations provoked by many agents and, in many instances, allow comparisons between related agents or the same agent in different cell backgrounds. In this review we will discuss some of these data with a primary focus on the interpretation of UV mutation spectra. We will also describe our development and application of custom supF marker genes as an approach to studying the effect of sequence context on mutation hotspots and cold spots. Our studies suggest that C-C photoproducts are not mutagenic in certain sequence contexts in which T-C photoproducts are mutation hotspots. In addition, we have found several examples of sequence context effects acting as much as 80 bases away from the site of mutation. We will consider some of the problems raised by these studies and the possible resolution of some of them offered by the newly discovered family of damage bypass DNA polymerases.

Mutation induction and mutation frequency decline in halogen light-irradiated Escherichia coli K-12 AB1157 strains.

The effects of halogen light irradiation on reversion of argE3-->Arg+ in E. coli K12 strain AB1157 and its mfd- mutant, and on mutation frequency decline (MFD) after transiently incubating irradiated bacteria under non-growing conditions were studied. The induction of mutations, the mutational specificity, and the MFD effect had the same characteristic features as those seen in E. coli B strains after irradiation with 254 nm UV light. MFD which is due to repair of premutagenic lesion in the transcribed strand of glnU gene and prevents mutations leading to supB formation, was not observed in halogen light-induced mutations in the mfd-1 strain. Overproduction of UmuD'C proteins led to a large increase in mutation frequency, which was much greater in mfd- than in mfd+ strains. In bacteria irradiated with halogen light and incubated immediately in a rich medium to express mutations, the formation of supB predominated strongly over that of supE(ochre) in mfd- cells but was at a similar level in mfd+ cells. Introduction of zcf117::Tn10 to AB1157 strain makes cells more sensitive to halogen light irradiation, whereas introduction of mfd-1 does not.

UV-induced mutations of supF gene on a shuttle vector plasmid in p53-deficient mouse cells are qualitatively different from those in wild-type cells.

To verify the genetic instability of p53-deficient cells, UV-induced mutation of the supF gene on a shuttle vector was analyzed. UV-irradiated or non-irradiated shuttle vector plasmid carrying the supF gene as a target of mutation (pYZ289) was introduced into p53-deficient and p53-proficient mouse embryonic fibroblasts, and then the plasmid DNA replicated in mouse cells was recovered. Survival of UV-irradiated plasmid was almost equivalent in both p53-deficient and p53-proficient cells. The frequencies of UV-induced mutation of the supF gene were also the same in both types of cells. However, the distributions of base change mutations in the supF sequence were different between p53-deficient and p53-proficient cells; especially the locations of tandem CpC to TpT changes exhibited a marked difference. Since DNA repair activities of these two types of cell were almost the same, these qualitative differences in UV-induced mutations were probably caused by as yet unidentified differences in other than DNA repair activity.

[Immunohistochemical study of radiation-induced apoptosis and oncogenes].

Relationships between radiation-induced apoptosis and oncogenes or suppressor genes (p53, MDM2, c-myc, p21ras and bcl-2) were immunohistochemically studied in 7 human tumors transplanted to nude mice. The most radiosensitive ependymoblastoma was negative for p53 and c-myc, however, the other 6 tumors were positive for them. Following irradiation, the ependymoblastoma became p53 positive, and showed the highest incidence of apoptosis among the 7 tumors. In addition, bcl-2 expression in this tumor was slightly different from that in the others.

Mutation spectra in Salmonella of sunlight, white fluorescent light, and light from tanning salon beds: induction of tandem mutations and role of DNA repair.

We evaluated the mutagenicity of sunlight (SUN), uncovered coolwhite fluorescent light (FLR), and light from a tanning salon bed (TAN) at the base-substitution allele hisG46 of Salmonella in four DNA repair backgrounds (wild type, uvrB, pKM101, and uvrB + pKM101). Approximately 80% of the radiation emitted by TAN was within the ultraviolet (UV) range, whereas only approximately 10% of the SUN and approximately 1% of the FLR radiation was UV. TAN emitted similar amounts of UVA and UVB, whereas SUN emitted 50-60x and FLR emitted 5-10x more UVA relative to UVB. Based on total dose (UV + visible), the mutagenic potency ranking was TAN > FLR > SUN. Using colony probe hybridization and PCR/DNA sequence analysis, approximately 3000 revertants were analyzed to determine the mutational specificity of the three light sources. The mutation spectra and those induced by 254-nm UV had common features. The uvrB mutation enhanced the mutagenicity of the environmental UV sources more (20-216x) than did the pKM101 plasmid (approximately 20x) relative to wild type DNA repair. All light sources induced equal proportions of transitions and transversions in excision repair-proficient strains, but they induced more transitions relative to transversions in uvrB-containing strains. The majority of the mutations were G.C-->A.T transitions that were induced equally frequently at the first or second position of the CCC codon of the hisG46 allele in all strains except TA1535 (uvrB), where SUN and FLR induced transitions preferentially at the first position, and TAN induced them preferentially at the second position. Identified or presumptive multiple mutations, which constituted the only mutational class enhanced by all three light sources in the presence of uvrB and pKM101 either alone or together, accounted for 3-5% of the induced mutations in the plasmid-containing strains, and their increases (38-82-fold) in TA100 (uvrB, pKM101) were the highest of any mutational class. Of the TAN-induced multiple mutations, 83% (19/23) were CC-->TT tandem transitions. These results show that exposures to the nonsolar environmental UV sources FLR and TAN produce mutations similar to those produced by SUN, a known carcinogen.