Apoptosis is one of the causes of cell death in cervical cancer following radiotherapy (S. S. Liu et al., Eur. J. Cancer, 37: 1104 -1110, 2001). By studying the gene expression profile with cDNA apoptotic array, the p73 gene was found overexpressed in radiosensitive cervical cancers when compared with radioresistant ones. To investigate the role of the p73 gene in relation to clinical assessment of radiosensitivity in cervical cancer based on the findings of residual tumor cells in cervical biopsies after completion of radiotherapy, we studied the protein expression of p73 in 59 cervical cancers after radiotherapy and 68 normal cervices using immunohistochemistry. The expression of p73 was found to be significantly increased in cancer samples and, more importantly, in those samples sensitive to radiotherapy (P < 0.001). The overexpression of p73 actually predicted a better prognosis in cervical cancer patients (P < 0.001). To investigate the possible involvement of p73 downstream genes, the protein expressions of p21 and Bax were studied. The expression of p21, but not Bax, was found to be positively correlated with the expression of p73 (P ‫؍‬ 0.001). Furthermore, the epigenetic regulation of p73 expression via DNA methylation was also investigated in 103 cervical cancers and 124 normals. Hypermethylation of p73 gene was observed in 38.8% of cervical cancers, and it was significantly associated with reduced or absent p73 expression (P < 0.001). Reactivation of p73 expression in two cervical cancer cell lines by demethylation treatment supported the role of methylation in the regulation of p73 expression. Our findings suggested that p73 expression was related to the radiosensitivity of cervical cancer cells and may play an important role in the regulation of cellular radiosensitivity.

Radiation therapy is the most effective therapy for cervical cancer in advanced stages. p53 plays a critical role in the cellular response to radiation-induced DNA damage. However, p53 function is often impaired in the presence of the oncoprotein E6 from human papillomavirus, which is often associated with the development of cervical cancer. p73, a p53 family member, is highly similar to p53, but is resistant to the degradation by human papillomavirus E6. In this study, we investigated the role of p73A in relation to cellular radiosensitivity in the p53-impaired cervical cancer cells. Radiosensitivity and irradiation-induced apoptotic cell death were examined in the exogenous overexpressed p73A-and p53-impaired cells. Our results showed that the endogenous p73A expressed only in the radiosensitive cervical cancer C4-1

Abstract. This study was aimed at investigating the deathassociated protein kinase (DAPK) promoter methylation and its clinical relevance in cervical cancer. The DAPK promoter methylation was detected by methylation-specific PCR (MSP) and correlated with DAPK mRNA and protein expression. The effect of DAPK expression on the radiosensitivity of the cervical cancer cell line was assessed by overexpressing DAPK in the radioresistant cell line SiHa. DAPK hypermethylation was found in 56.08% of the cervical cancer samples and was associated with the tumor histological cell type of squamous cell carcinoma (p=0.002) and advanced tumor stage (p=0.005). Subsequently, DAPK protein expression was found to significantly decrease in cervical cancer samples when compared to normal tissues. The DAPK mRNA and protein expression levels were absent or remarkably reduced in SiHa and HeLa in which the DAPK promoter was hypermethylated. The expression levels of DAPK could be restored after demethylation treatment with 5-aza-2'-deoxycytidine. Overexpressing DAPK in vitro had no significant influence to the survival of the radioresistant SiHa cell after being challenged by irradiation. Our findings suggest that DAPK might not directly be responsible for the cellular radiosensitivity, however, DAPK hypermethylation appeared to be of prognostic significance in the advanced stages of cervical cancer. IntroductionCervical cancer is one of the most common gynecological cancers worldwide. The inactivation of tumor suppressor genes and activation of oncogenes are important in cervical tumorigenesis. Transcriptional silencing by hypermethylation of the CpG islands located in the promoter region is a frequent mechanism leading to the inactivation of tumor suppressor genes (1). Aberrant promoter methylation of tumor suppressor genes was found in cervical cancer. The use of the aberrant gene promoter methylation in cervical cancer was shown to be a potential molecular marker (2).Radiotherapy is an effective treatment for cervical cancer. Failure of therapy is usually due to the resistance of the tumor towards radiotherapy. One cellular mechanism common to various therapeutic regimens, including radiation, is tumor cell death via apoptosis. Our previous study demonstrated a close relationship between spontaneous apoptosis and patients' survival (3). Apoptosis may thus play a role in the response of cervical cancer to radiation treatment.The death-associated protein kinase (DAPK) gene is a tumor suppressor gene frequently investigated among various cancers. It is a pro-apoptotic gene and participates in various apoptotic systems. The DAPK C-terminal serine-rich tail peptide, which is conserved in death-domain-containing proteins, plays a negative regulatory role in the inhibition of DAPK, whereas the removal of this region enhances the killing activity (4). Hypermethylation of DAPK was frequently reported in various cancers including colon (5), head and neck (6), urinary bladder (7), lung (8-10), B cell lymphoma (11) and ovary (12). In addition, i...