Biological significance of allele specific loss of the p53 gene in breast carcinomas

Altered expression and loss of heterozygosity of the migration and invasion inhibitory protein (MIIP) gene in breast cancer

Previous studies have characterized the migration and invasion inhibitory protein (MIIP) as a novel putative tumor-suppressor gene that regulates cell migration and invasion as well as the mitotic checkpoint. The MIIP gene is located on chromosome 1p36.22, a common site for deletion in many solid tumors including breast cancer. In the present study, we evaluated MIIP expression and allelic deletion to gain insight into the role of the MIIP gene in breast cancer. MIIP gene mRNA and protein expression was assessed in 86 matched breast cancer and adjacent normal tissues. Loss of heterogeneity (LOH) of the MIIP gene was determined using single-nucleotide polymorphism (SNP) and microsatellite (MS) markers in 149 breast carcinomas and the corresponding normal lymphocytes. The analysis revealed that the expression levels of MIIP mRNA and protein were downregulated in tumor specimens compared to those in corresponding adjacent tissues. Advanced clinical stage and tumor size >2 cm were associated with a decreased MIIP expression level. Twenty-six percent (37/142) of tumors were shown to have LOH at the MIIP locus by MS and SNP markers. Breast cancer patients with LOH at the SNP marker rs2295283 experienced shorter survival time. The attenuated expression and LOH of the MIIP gene may contribute to the poor prognosis of breast cancer, supporting a tumor-suppressing role of MIIP gene in the pathogenesis of this disease.

Coordination of TP53 abnormalities in breast cancer: data from analysis of TP53 polymorphisms, loss of heterozygosity, methylation, and mutations

AIMS

We have studied whether TP53 rs1042522, rs17878362, and rs1625895 alleles having a protective effect against breast cancer (BC) will be lost in tumors, whereas those allowing disease development will be retained.

METHODS

Analysis of TP53 polymorphisms was performed in blood leukocytes and tumors from 80 Caucasian BC patients. In addition, TP53 loss of heterozygosity (LOH), methylation, and mutations were studied in tumor DNA of BC individuals with loss of alleles of TP53 polymorphisms.

RESULTS

In breast tumors of patients heterozygous for TP53 polymorphisms, we detected loss of rs1042522 C and G and rs17878362 A2 alleles; however, the loss of the C allele was preferential. We found that loss of TP53 alleles, namely rs1042522 C, has been caused by an LOH mechanism, namely TP53 deletions, whereas TP53 point mutations frequently occurred in the retained G allele (p=0.03). In addition, we showed that BC patients with rs1042522 CC genotype were characterized by only unifocal tumors and decreased frequency of lymph node metastases (p=0.03).

CONCLUSIONS

Taken together, we showed the preferential loss of the rs1042522 C allele, which is protective against BC progression, in breast tumors. Also, the loss of the C allele, which encodes p53 protein with the best DNA repair capability according to literature data, may create prerequisites for mutations, but not for methylation in a retained G variant, as we found here. However, these results need to be confirmed because of the limited statistical power of the present study and the small sampling.

Overexpressions of Cyclin B1, cdc2, p16 and p53 in human breast cancer: the clinicopathologic correlations and prognostic implications

PURPOSE

The molecular mechanisms that are responsible for the initiation and progression of breast cancers are largely unknown. This study was to analyze the cyclin B1, cdc2, p53 and p16 tumor suppressor genes in human breast cancer.

MATERIALS AND METHODS

To investigate the role of cyclin B1, cdc2, p53 and p16 in the pathogenesis and progression of breast carcinomas, 98 cases of breast cancers were examined by immunohistochemical method. The correlations of cyclin B1, cdc2, p53 and p16 expression with various clinico-pathologic findings were analysed.

RESULTS

In the normal breast tissues, cyclin B1, cdc2 and p16 were weakly expressed, while p53 was not expressed. On the other hand, cyclin B1, cdc2, p53 and p16 were overexpressed in breast cancer, showing correlation between the expression of cyclin B1 and cdc2 and breast cancers (p=0.00). The overexpressions of cdc2 and p16 were correlated with an infiltrative tumor border pattern and this was statistically significant (p<0.05). In addition, the overexpression of cdc2 was correlated with histologic high grade carcinomas (p=0.00).

CONCLUSION

Cyclin B1 and cdc2 appeared to be involved in the genesis or progression of breast cancers. In addition, the overexpressions of p16 and p53 may play important roles in more aggressive tumor and the overexpression of cdc2 is associated with progression of tumor to a higher grade of breast carcinomas. The deranged overexpressions of cyclin B1, cdc2, p16 and p53 may play an important role in human breast carcinogenesis.

Common alleles in candidate susceptibility genes associated with risk and development of epithelial ovarian cancer

Common germline genetic variation in the population is associated with susceptibility to epithelial ovarian cancer. Microcell-mediated chromosome transfer and expression microarray analysis identified nine genes associated with functional suppression of tumorogenicity in ovarian cancer cell lines; AIFM2, AKTIP, AXIN2, CASP5, FILIP1L, RBBP8, RGC32, RUVBL1 and STAG3. Sixty-three tagging single nucleotide polymorphisms (tSNPs) in these genes were genotyped in 1,799 invasive ovarian cancer cases and 3,045 controls to look for associations with disease risk. Two SNPs in RUVBL1, rs13063604 and rs7650365, were associated with increased risk of serous ovarian cancer [HetOR = 1.42 (1.15-1.74) and the HomOR = 1.63 (1.10-1.42), p-trend = 0.0002] and [HetOR = 0.97 (0.80-1.17), HomOR = 0.74 (0.58-0.93), p-trend = 0.009], respectively. We genotyped rs13063604 and rs7650365 in an additional 4,590 cases and 6,031 controls from ten sites from the United States, Europe and Australia; however, neither SNP was significant in Stage 2. We also evaluated the potential role of tSNPs in these nine genes in ovarian cancer development by testing for allele-specific loss of heterozygosity (LOH) in 286 primary ovarian tumours. We found frequent LOH for tSNPs in AXIN2, AKTIP and RGC32 (64, 46 and 34%, respectively) and one SNP, rs1637001, in STAG3 showed significant allele-specific LOH with loss of the common allele in 94% of informative tumours (p = 0.015). Array comparative genomic hybridisation indicated that this nonrandom allelic imbalance was due to amplification of the rare allele. In conclusion, we show evidence for the involvement of a common allele of STAG3 in the development of epithelial ovarian cancer.