Chromosomal assignment of human uracil-DNA glycosylase to chromosome 12

The mouse uracil-DNA glycosylase gene: isolation of cDNA and genomic clones and mapping ung to mouse chromosome 5

Uracil-DNA glycosylase (UDG) is the enzyme responsible for the first step in the base-excision repair pathway that specifically removes uracil from DNA. Here we report the isolation of the cDNA and genomic clones for the mouse uracil-DNA glycosylase gene (ung) homologous to the major placental uracil-DNA glycosylase gene (UNG) of humans. The complete characterization of the genomic organization of the mouse uracil-DNA glycosylase gene shows that the entire mRNA coding region for the 1.83-kb cDNA of the mouse ung gene is contained in an 8.2-kb SstI genomic fragment which includes six exons and five introns. The cDNA encodes a predicted uracil-DNA glycosylase (UDG) protein of 295 amino acids (33 kDa) that is highly similar to a group of UDGs that have been isolated from a wide variety of organisms. The mouse ung gene has been mapped to mouse chromosome 5 using fluorescence in situ hybridization (FISH).

Nuclear and mitochondrial forms of human uracil-DNA glycosylase are encoded by the same gene

Recent cloning of a cDNA (UNG15) encoding human uracil-DNA glycosylase (UDG), indicated that the gene product of M(r) = 33,800 contains an N-terminal sequence of 77 amino acids not present in the presumed mature form of M(r) = 25,800. This led to the hypothesis that the N-terminal sequence might be involved in intracellular targeting. To examine this hypothesis, we analysed UDG from nuclei, mitochondria and cytosol by western blotting and high resolution gel filtration. An antibody that recognises a sequence in the mature form of the UNG protein detected all three forms, indicating that they are products of the same gene. The nuclear and mitochondrial form had an apparent M(r) = 27,500 and the cytosolic form an apparent M(r) = 38,000 by western blotting. Gel filtration gave essentially similar estimates. An antibody with specificity towards the presequence recognised the cytosolic form of M(r) = 38,000 only, indicating that the difference in size is due to the presequence. Immunofluorescence studies of HeLa cells clearly demonstrated that the major part of the UDG activity was localised in the nuclei. Transfection experiments with plasmids carrying full-length UNG15 cDNA or a truncated form of UNG15 encoding the presumed mature UNG protein demonstrated that the UNG presequence mediated sorting to the mitochondria, whereas UNG lacking the presequence was translocated to the nuclei. We conclude that the same gene encodes nuclear and mitochondrial uracil-DNA glycosylase and that the signals for mitochondrial translocation resides in the presequence, whereas signals for nuclear import are within the mature protein.

Relationships between Ki-67 labelling index, amplification of the epidermal growth factor receptor gene, and prognosis in human glioblastomas

The aim of this study was to determine possible relationships between Ki-67 labelling index (Ki-67 LI), amplification of the epidermal growth factor receptor (EGFR) gene, and prognosis in human glioblastomas. Ki-67 LI was determined on cryosections of biopsy specimens of 20 human glioblastomas with a mouse anti-human Ki-67 monoclonal antibody. Amplification of the EGFR gene was determined by slot blot and Southern blot analyses of DNA extracted from the tumour biopsies. The Ki-67 LI was higher in the glioblastoma group with EGFR gene amplification (8 tumours, median value of Ki-67 LI 4.2, range 0.4-24.6) than in those without EGFR gene amplification (12 tumours, median value of Ki-67 LI 0.8, range 0.2-11.8) (0.05 p less than 0.1). The glioblastoma patients with Ki-67 LI greater than 1.5 (10 tumours) had a statistically significant shorter survival than those with Ki-67 LI less than 1.5 (10 tumours) (p less than 0.05). The glioblastoma patients with EGFR gene amplification lived shorter time than those without EGFR gene amplification (p greater than 0.05).

Expression of epidermal growth factor receptor in human meningiomas and meningeal tissue

The aim of this study was to examine meningeal tissue under normal, reactive, and neoplastic conditions for expression of epidermal growth factor receptor (EGFR) using an improved histochemical method, namely biotinylated epidermal growth factor. EGFR was found in all the examined meningiomas (12 benign and three anaplastic) and in neonatal rat meninges, whereas normal and injured adult human and rat meninges did not exhibit detectable EGFR. These observations indicate that EGFR is involved in the development of meningeal tissue. Further, EGFR is abnormally expressed in meningeal tumours, indicating a role of EGFR in the neoplastic process of these tumours. The regular expression of EGFR in human meningiomas suggests EGFR as a tumour marker for this tumour type.

Expression of the epidermal growth factor receptor gene in human brain metastases

Biopsy specimens of human brain metastases were examined for amplification and expression of the proto-oncogene c-erbB1 (located on chromosome 7) encoding the epidermal growth factor receptor (EGFR). Moreover, the tumour DNA was also examined for amplification of other cancer-related genes on this chromosome: the proto-oncogene c-met, the gene for platelet-derived growth factor A-chain, and the gene for plasminogen activator inhibitory type 1. All 18 brain metastases demonstrated positive binding of biotinylated EGF on cryosections. Three out of 18 metastases had amplification of the EGFR gene; the other chromosome-7 genes tested were not amplified. Thus, an increased EGFR gene expression seems to be a general finding in a wide range of carcinomas metastatic to the brain, whereas we found only occasional selective EGFR gene amplifications in single cases.

Cell cycle regulation and in vitro hybrid arrest analysis of the major human uracil-DNA glycosylase

Uracil-DNA glycosylase (UDG) is the first enzyme in the excision repair pathway for removal of uracil in DNA. In vitro transcription/translation of a cloned human cDNA encoding UDG resulted in easily measurable UDG activity. The apparent size of the primary translation product was 34 kD. Two lines of evidence indicated that this cDNA encodes the major nuclear UDG. First, in vitro translation of human fibroblast mRNA isolated from S-phase cells resulted in measurable UDG activity and this UDG translation was specifically inhibited 90% by an anti-sense UDG mRNA transcript. Secondly, cell cycle analysis revealed an 8-12 fold increase in transcript level late in the G1-phase preceding a 2-3 fold increase in total UDG activity in the S-phase. UDG degradation was found to be very slow (T1/2 approximately 30h), therefore, the rate of UDG synthesis could be derived from the rate of UDG accumulation, and was found to correlate temporarily and quantitatively with the transcript level. Inhibitor studies showed that RNA and protein synthesis was required for induction of UDG. However, specific inhibition of DNA replication with aphidicolin indicated that entrance of fibroblasts into the S-phase was not required for UDG accumulation.

Human uracil-DNA glycosylase complements E. coli ung mutants

We have previously isolated a cDNA encoding a human uracil-DNA glycosylase which is closely related to the bacterial and yeast enzymes. In vitro expression of this cDNA produced a protein with an apparent molecular weight of 34 K in agreement with the size predicted from the sequence data. The in vitro expressed protein exhibited uracil-DNA glycosylase activity. The close resemblance between the human and the bacterial enzyme raised the possibility that the human enzyme may be able to complement E. coli ung mutants. In order to test this hypothesis, the human uracil-DNA glycosylase cDNA was established in a bacterial expression vector. Expression of the human enzyme as a LacZ alpha-humUNG fusion protein was then studied in E. coli ung mutants. E. coli cells lacking uracil-DNA glycosylase activity exhibit a weak mutator phenotype and they are permissive for growth of phages with uracil-containing DNA. Here we show that the expression of human uracil-DNA glycosylase in E. coli can restore the wild type phenotype of ung mutants. These results demonstrate that the evolutionary conservation of the uracil-DNA glycosylase structure is also reflected in the conservation of the mechanism for removal of uracil from DNA.