Switching p53-dependent growth arrest to apoptosis via the inhibition of DNA damage-activated kinases.

Cisplatin and doxorubicin are widely used anticancer drugs that cause DNA damage, which activates the ATM-Chk2-p53 pathway in cancer cells. This activation leads to cell cycle block or apoptosis, depending on the nature of the DNA damage. In an attempt to enhance the effects of these agents, we inhibited ATM/ATR and Chk2, which are known upstream regulators of p53. The cancer cell lines A2780 and ARN8, bearing the wild-type p53 protein, were used to study changes in p53 activation and trans-activation. Our results suggest that the G(1)-checkpoint, normally activated by DNA damage, is functionally overcome by the action of kinase inhibitors that sensitize cells to apoptosis. Both inhibitors show these effects, albeit with variable intensity in different cell lines, which is promising for other studies and theoretically for use in clinical practice.

Prediction of human papillomavirus 16 e6 gene expression and cervical intraepithelial neoplasia progression by methylation status.

INTRODUCTION: Human papillomavirus (HPV) infection represents the most important risk factor for the development of cervical intraepithelial neoplasia (CIN) and cervical cancer. We aimed to analyze the consequences of methylation of the E6 gene promoter in distinct stages of HPV-16-induced cellular transformation to assess its importance for disease progression. METHODS: Human papillomavirus 16 was detected by sensitive polymerase chain reaction (PCR). Determination of E6 gene promoter methylation was analyzed by digestion with specific restriction endonuclease McrBC followed by PCR amplification. Expression of the E6 gene was determined by quantitative real-time PCR. RESULTS: Of 103 cervical smears from asymptomatic women with no cytological and colposcopic abnormalities, 20.4% were HPV-16-positive. Human papillomavirus 16 was present in 44.4% of 18 patients with CIN I, in 62.2% of 143 patients with CIN II/III, and in 74.2% of 31 cervix carcinoma specimens. The incidence of HPV-16 in all lesions compared with asymptomatic women was statistically significant (P < 0.001, Pearson chi test). Methylation was detected in 81% (n = 21) of HPV-16-positive asymptomatic smears compared with 62.5% in CIN I (n = 8), 31.5% (n = 89) in CIN II/III, and 43.4% (n = 23) in carcinomas; a statistical significance between lesions and healthy women was found (P < 0.001, Pearson chi test). Expression of E6 mRNA correlated with methylation status (P = 0.010, Mann-Whitney U test). CONCLUSIONS: We conclude that methylation of the E6 gene promoter in HPV-16 genome is a predictive biomarker for cervical cancer progression by regulating the expression of the E6 oncogene.

The histone H2B-specific ubiquitin ligase RNF20/hBRE1 acts as a putative tumor suppressor through selective regulation of gene expression.

Histone monoubiquitylation is implicated in critical regulatory processes. We explored the roles of histone H2B ubiquitylation in human cells by reducing the expression of hBRE1/RNF20, the major H2B-specific E3 ubiquitin ligase. While H2B ubiquitylation is broadly associated with transcribed genes, only a subset of genes was transcriptionally affected by RNF20 depletion and abrogation of H2B ubiquitylation. Gene expression dependent on RNF20 includes histones H2A and H2B and the p53 tumor suppressor. In contrast, RNF20 suppresses the expression of several proto-oncogenes, which reside preferentially in closed chromatin and are modestly transcribed despite bearing marks usually associated with high transcription rates. Remarkably, RNF20 depletion augmented the transcriptional effects of epidermal growth factor (EGF), increased cell migration, and elicited transformation and tumorigenesis. Furthermore, frequent RNF20 promoter hypermethylation was observed in tumors. RNF20 may thus be a putative tumor suppressor, acting through selective regulation of a distinct subset of genes.