p53 codon 72 polymorphism and risk of cervical cancer in UK.

BACKGROUND: A polymorphism at codon 72 of the human tumour-suppressor gene, p53, results in translation to either arginine or proline. A recent report suggested that the risk of human-papillomavirus-associated cervical cancer in white women is higher for those homozygous for the arginine allele than for those who are heterozygous. We examined a similar number of cervical cancers and a larger control group for their p53 codon 72 polymorphism status to see if we could confirm this result. METHODS: Three different groups of UK white women were studied: 96 who had volunteered to take part in a trial of ovarian-cancer screening; 150 attending for routine antenatal care in the Oxford region; and 50 women with cervical cancer. DNA from peripheral blood samples and from archival tissue samples was examined by PCR with allele-specific primers. FINDINGS: The proportions of individuals homozygous for the arginine allele, homozygous for the proline allele, and heterozygous for the two alleles were 59%, 4%, and 36% among women screened for ovarian cancer; 65%, 8%, and 27% among the antenatal-care group; and 54%, 6%, and 40% in women with cervical cancer. Chi2 analysis showed no significant differences in these proportions. INTERPRETATION: In the population studied, individuals homozygous for the arginine variant of codon 72 of the p53 gene were not at increased risk of cervical cancer.

No evidence exists for methylation inactivation of the p16 tumor suppressor gene in ovarian carcinogenesis.

The p16ink4/CDKN2/MTS1 tumor suppressor gene encodes a cyclin-dependent kinase inhibitor which plays an important role in regulation of the G1/S phase cell cycle checkpoint. Loss of heterozygosity (LOH) at the p16 locus, 9p21, has been documented in a wide variety of tumors including ovarian carcinoma. However, inactivating mutations of the remaining allele and homozygous deletions are relatively infrequent events in primary tumors, even in cases where expression of p16 at the mRNA and protein level is clearly absent. These findings initially cast doubt on the role of p16 as a tumor suppressor gene in vivo. Recently, an alternative mechanism of p16 inactivation involving methylation of the CpG island in the 5' region of the gene has been demonstrated in a number of malignancies and cell lines. In this study we have analyzed the methylation status of four CpG dinucleotides in a panel of 23 ovarian tumors using a multiplex PCR approach to correlate our findings with the LOH data in this region. Using the microsatellite markers D9S171 and D9S1679 LOH was demonstrated in 4/22 (18%) informative cases. All 23 tumors showed no evidence of methylation at the p16 locus including the 4 tumors demonstrating LOH at 9p21. These results suggest that methylation inactivation of the p16 gene does not play an important role in ovarian carcinogenesis.

Correlation of loss of heterozygosity with cytogenetic analysis using G-banding and fluorescence in situ hybridization in aneuploid cultures from two human testicular germ-cell tumors.

A detailed karyotype analysis using fluorescence in situ hybridization (FISH), with 24 chromosome-specific paint probes has been carried out on newly established cell lines from two testicular tumors, an i(12p)-positive teratoma, and an i(12p)-negative combined seminoma/teratoma. This has been correlated with loss of heterozygosity (LOH) and allelic imbalance, using DNA RFLP analysis to clarify the genetic changes and to identify any common regions of deletion or rearrangement. With G-banding alone, a total of 11 breakpoints were recognized. After FISH, the position of seven required revision, and 21 new ones were identified. The chromosomes involved most frequently in both tumors were numbers 1, 12, and 18. Breakpoints in 11q and 16q were also seen in both, and seven or more copies of 12p per cell were found in all clones. LOH was found for 18q in both tumors, and overall was much more frequent in underrepresented regions (one or two copies). On the whole, there was good agreement between the cytogenetic and DNA RFLP data; loci showing allelic imbalance generally had an odd number of copies of the chromosome region in which they were known to be located. Combined data on the chromosome 1 translocations in both tumors suggested that rearrangements were more complicated than cytogenetics alone had predicted.

Loss of heterozygosity on chromosome arms 5q, 11p, 11q, 13q, and 16p in human testicular germ cell tumors.

To identify common regions of deletion in human testicular germ cell tumors (TGCTs), we have screened tumors from 33 patients for loss of heterozygosity (LOH) using Southern blot analysis with 39 polymorphic markers covering 21 chromosome arms. Losses in more than 2 tumors and occurring at a frequency of > 10% were found on chromosome arms 5q, 11p, 11q, 13q, and 16p, the highest being on chromosome arm 5q (19%). It is suggested that tumor suppressor genes on 5q among others may be involved in testicular tumorigenesis and that LOH in this region requires further investigation. No losses were found on 12q and 17p despite the fact that the most common cytogenetic abnormality in TGCTs is an i(12p) and that the TP53 gene on 17p is the most frequently mutated gene in human cancers. The level of allelic imbalance varied considerably from one chromosome region to another (0-80%) and did not generally reflect the pattern of LOH. It tended to be high in overrepresented regions of the genome, 1q, 7p, and 12p. The tumor from one patient had a seminomatous component and a less differentiated component. We provide evidence for a common origin of both components and show that it is likely that this tumor has progressed from the seminoma to the less differentiated histology.