Allelic expression of p73 in human ovarian cancers

Neoadjuvant chemotherapy for epithelial ovarian cancer—role of apoptosis

BACKGROUND

Ovarian cancer is one of the most frequently fatal gynecological cancers because most cases are diagnosed at an advanced stage. Loss of growth control and a marked resistance to apoptosis are considered major mechanisms driving tumor progression. Little is known about the effect of various treatment regimens on the distribution of molecular markers of apoptosis in epithelial ovarian cancer. The objective of this study was to compare the expression levels of both proapoptotic and antiapoptotic proteins p53, p73, Bcl-2, Bcl-XL and survivin in the ascitic cells and tumor samples of patients undergoing treatment with two different regimens.

METHODS

A total of 24 patients with untreated epithelial ovarian cancer were randomized into two groups of 12 each. Group 1 patients received three cycles of chemotherapy prior to surgery and three cycles after surgery and group 2 patients received six cycles of chemotherapy prior to surgery. The expression of apoptosis-related proteins was analyzed in ascitic fluid and tumor samples by Western blotting and immunohistochemistry. The apoptotic index was also determined in these samples by the TUNEL assay.

RESULTS

Significant decreases in antiapoptotic bcl-2 and survivin were seen, accompanied by increases in apoptotic index in tumors that had undergone chemotherapy as compared to the baseline ascites samples. No significant change in bcl-XL was observed. A significant decrease in proapoptotic p53 was also seen. No expression of p73 was observed in tumors or ascites. The findings were similar in groups 1 and 2 patients and were not statistically significantly different, perhaps due to the small sample size (n=12) of each group.

CONCLUSIONS

The above findings indicate that chemotherapy in ovarian carcinoma leads to an increase in apoptosis by a p53-independent pathway, which involves the downregulation of antiapoptotic Bcl-2 and survivin but not Bcl-XL. Furthermore, administering neoadjuvant chemotherapy (six cycles) as an alternative form of therapy for advanced epithelial ovarian cancer is more effective in inducing apoptosis than three cycles. However, the findings of this study need to be corroborated using a larger sample.

Overexpression of p16INK4a correlates with high expression of p73 in breast carcinomas

The p16-cyclin D-Cdk4(6)-pRB-E2F and p73 pathways are involved in the control of cell-cycle progression, and genetic lesions in both pathways frequently occur in breast carcinomas and other human cancers. The p16INK4a gene is involved in regulation of the G1/S transition, and when overexpressed, the p73 gene activates transcription of p53-responsive genes and promotes apoptosis. These pathways are related, for instance, p73 is also downstream of E2F-1, since E2F-1 induces p73-mediated apoptosis in the absence of p53. We studied 93 breast cancer patients to identify alterations in the expression of p16INK4a and p73 by semiquantitative RT-PCR analysis and possible interactions between them and correlations with clinicopathological parameters. p73 was overexpressed in 24 cases. Overexpression of p16INK4a was detected in 17 cases and underexpression in 32 cases. A significant correlation was observed between the overexpression of both genes (P = 0.05). Concurrent overexpression of p73 and p16INK4a was significantly correlated with metastases in three or more lymph nodes (P = 0.0007), positive immunohistochemistry for p53 (P = 0.014), vascular invasion (P = 0.048) and negative progesterone receptors (P = 0.004). These results indicate that concomitant overexpression of p16INK4a and p73 may be involved in breast cancer and associated with poor tumor characteristics.

Expression of p73 and c-Abl proteins in human ovarian carcinomas

The p73, a homologue of the p53 tumor suppressor protein, has a pro-apoptotic activity which is induced by the c-Abl, a protein tyrosine kinase appearing in the nucleus and cytoplasm of proliferating cells. However, the role of p73 and c-Abl in ovarian cancer is not well-defined. We investigated immunohistochemical expressions of p73 and c-Abl in 64 ovarian carcinomas, 13 borderline and 14 benign ovarian tumors to elucidate their clinicopathological relevances. Of the malignant, borderline, and benign ovarian tumors, respectively, 33 (51%), 10 (77%) and 13 (93%) had negative or low p73 expression, 31 (48%), 3 (23%) and 1 (7%) had high p73 expression, 23 (36%), 5 (38%) and 10 (71%) had negative or low c-Abl expression, and 41 (64%), 8 (61%) and 4 (29%) had high c-Abl expression. A high p73 or c-Abl expression was significantly associated with ovarian carcinomas as compared to benign tumors (p=0.003 and p=0.03 respectively). In addition, a significant correlation was found between the high p73 expression and disease stage (p=0.04) and patient's survival (p=0.02). No correlation was found with c-Abl expression. These results reveal an association of p73 overexpression with advanced ovarian carcinomas which may suggest the p73 overexpression as an indicator of poor prognosis.

Genetic alterations in ovarian cancer cells that might account for sensitivity to chemotherapy in patients

The cellular response to anticancer agent treatments is determined by many factors that could be altered in tumor cells. The induction of apoptosis of cancer cells is thought to be important for the overall response of these cells. Despite the introduction of new and potent anticancer agents, the survival rate for patients with ovarian cancer remains poor. In general ovarian cancer cells present a poor propensity to undergo apoptosis, which could be one of the reasons for this relatively poor response observed in the clinic. Induction of apoptosis is the result of activation and repression of pro- and antiapoptotic genes, which are regulated by complex mechanisms. Many cancer cells activate a "survival" program to escape disruption and allow propagation. In this review we have analyzed the role of genetic alterations observed in ovarian cancer cells in determining cellular response to drug treatment.

Microsatellite analysis at 1p36.3 in malignant melanoma of the skin: fine mapping in search of a possible tumour suppressor gene region

Deletions in 1p36 in malignant melanoma have been found in high percentages in nodular melanomas and melanoma metastases. Despite many efforts, no candidate tumour suppressor gene associated with malignant melanoma has so far been found in this region. To further determine a possible tumour suppressor gene locus, we carried out a deletion mapping of chromosome 1p36 at nine microsatellite loci in 74 malignant melanomas. Loss of heterozygosity (LOH) in this region was found in 77% of nodular melanomas (NMs), 86% of metastatic melanomas, but only 20% of superficial spreading melanomas (SSMs). Regarding the allelic losses, the nodular and metastatic melanoma samples could be divided into three groups: one showing LOH at the more telomeric loci D1S243 and D1S468 (1p36.33), one displaying allelic loss at the more centromeric loci D1S214 and D1S253 (1p36.32-31) and one with LOH over all informative loci between D1S243 and D1S160. We did not find any significant correlation between a deletion in any of the investigated loci and the survival data of the patients. However, our results confine the deleted region in malignant melanoma to a very small area around 1p36.32, thus facilitating the search for the tumour suppressor gene with importance in malignant melanoma.

Restriction enzymes in the analysis of genetic alterations responsible for cancer progression

BACKGROUND

Molecular approaches are increasingly being employed to dissect the genetic changes accompanying tumour formation. These methods can often be confusing to the non-specialist as they include complex molecular steps. This can reduce the usefulness of such molecular data to clinicians. The authors aim to aid interpretation of molecular studies in general by presenting a comprehensive review of one molecular approach, i.e. the use of restriction enzymes in molecular studies of tumour development.

METHOD

A review was made of the molecular studies that have employed restriction enzymes in gastrointestinal cancer research. These studies have used restriction enzymes to analyse point mutation induction, gene methylation status and the deletion of chromosomal loci. In addition, emphasis is placed on some of the important considerations for the molecular analysis of tumours that can affect the molecular data obtained.

RESULTS

Restriction enzyme digestion has played, and continues to play, a major role in analysing the genetic changes in cancer. Many adaptations of basic restriction enzyme methodologies have enhanced the application of this approach in cancer genetics.

CONCLUSION

The availability of 200 different restriction enzymes, each recognizing different sequences in DNA, has been invaluable in studying cancer genetics. It is hoped that current advances in protein engineering will facilitate the creation of novel restriction enzymes with tailor-made sequence specificities. This will further improve the applicability of restriction enzymes in cancer genetics.

Frequent loss of heterozygosity at 1p36.3 and p73 abnormality in parathyroid adenomas

Although 1p is one of the most common loci showing loss of heterozygosity (LOH) in primary parathyroid adenoma, fine mapping has not been previously examined. In this study, we analyzed LOH in 32 primary parathyroid adenomas using five microsatellite markers at 1p36 (proximal-D1S507-D1S450-D1S2893-D1S468-D1S243-distal). All cases were heterozygous for at least one marker. The frequency of LOH varied from 41.2% (D1S468) to 7.1% (D1S507) among the different markers. LOH was detected consistently in a group of nine adenomas (28.1%, 9/32). A single region (7 cM) showing a consistent LOH at 1p36.3 was obtained that was flanked distally by D1S468 and proximally by D1S2893. Because the p73 gene is localized within this region and acts as a tumor suppressor gene, we examined the possible involvement of p73 in the development of parathyroid tumor. Allelic loss of p73 was identified in four adenomas (25%, 4/16 informative cases) that were all from the group of the nine adenomas with LOH, but somatic mutation was not detected in the remaining allele. At the StyI polymorphism of Exon 2, four of the six adenomas with LOH at 1p36 were heterozygous and expressed the GC allele. Of the six heterozygous adenomas without LOH, 4 showed biallelic and 2 monoallelic expressions (GC allele). All adenomas mainly expressed the p73alpha isoform. p73 protein was observed in five of the six adenomas with LOH and in two of the six adenomas without LOH. There were no differences in p73 protein levels between the samples with and without LOH. In conclusion, a candidate gene for parathyroid tumorigenesis is present within a 7-cM region at 1p36.3, however p73 is unlikely to be the target of the LOH at 1p36.3.

Wild type p73 overexpression and high-grade malignancy in breast cancer

The overexpression of wild type p73 is the most frequent alteration of p73 in malignancies. We investigated, in 70 breast carcinomas, p73 mRNA expression and its relationship to p53 mutations, determined by an immunohistochemical method, and loss heterozygosity (LOH) status of the 1p36 region, together with its possible implication in the pathogenesis of breast carcinomas. LOH, amplifying DNA by PCR using 5 markers, of 1p36 region (one intragenic to p73 gene) was found in 17% of cases but no significant correlation was observed with p73 overexpression. p53 positive immunostaining was present in 33% of breast carcinomas, and these exhibited a statistically significant relation with p73 overexpressed tumors. Overexpression of p73 mRNA was observed in 19 tumors (27%). The analysis of cases with p73 overexpression and cases with normal mRNA expression, in terms of age and pathologic characteristics of the tumors showed a significant association of p73 overexpression and tumors with lymph node metastases, vascular invasion and higher pathologic stage. These results suggest that p73 overexpression is a molecular alteration that could be implicated in the tumorigenesis of breast carcinomas and, eventually, in a poor clinical behavior.