RESUMEN
BACKGROUND: Radiosensitivity is limited in cervical cancer (CC) patients due to acquired radiation resistance. In our previous studies, we found that immediate-early response 5 (IER5) is upregulated in CC cells upon radiation exposure and decreases cell survival by promoting apoptosis. The details on the transcriptional regulation of radiation-induced IER5 expression are unknown. Studies in recent years have suggested that Pol II-associated factor 1 (PAF1) is a pivotal transcription factor for certain genes "induced" during tumor progression. In this study, we investigated the role of PAF1 in regulating IER5 expression during CC radiotherapy. METHODS: PAF1 expression in CC cells was measured by western blotting, immunohistochemistry, and qRT-PCR, and the localization of PAF1 and IER5 was determined by immunofluorescence. The effect of PAF1 and IER5 knockdown by siRNA in Siha and Hela cells was studied by western blotting, qRT-PCR, CCK-8 assay, and flow cytometry. The physical interaction of PAF1 with the IER5 promoter and enhancers was confirmed using chromatin immunoprecipitation and qPCR with or without enhancers knockout by CRISPR/Cas9. RESULTS: We confirmed that PAF1 was highly expressed in CC cells and that relatively low expression of IER5 was observed in cells with highly expressed PAF1 in the nucleus. PAF1 knockdown in Siha and Hela cells was associated with increased expression of IER5, reduced cell viability and higher apoptosis rate in response to radiation exposure, while simultaneous PAF1 and IER5 knockdown had little effect on the proportion of apoptotic cells. We also found that PAF1 hindered the transcription of IER5 by promoting Pol II pausing at the promoter-proximal region, which was primarily due to the binding of PAF1 at the enhancers. CONCLUSIONS: PAF1 reduces CC radiosensitivity by inhibiting IER5 transcription, at least in part by regulating its enhancers. PAF1 might be a potential therapeutic target for overcoming radiation resistance in CC patients.
Asunto(s)
Regulación Neoplásica de la Expresión Génica , Proteínas Inmediatas-Precoces/antagonistas & inhibidores , Proteínas Nucleares/antagonistas & inhibidores , Tolerancia a Radiación , Factores de Transcripción/fisiología , Neoplasias del Cuello Uterino/radioterapia , Elementos de Facilitación Genéticos , Femenino , Células HeLa , Humanos , Proteínas Inmediatas-Precoces/genética , Proteínas Nucleares/genética , Regiones Promotoras Genéticas , Factores de Transcripción/antagonistas & inhibidores , Factores de Transcripción/genéticaRESUMEN
The aim of the present study was to identify novel methylation markers for cervical cancer screening and to test the clinical application of the most promising biomarker in cervical scrapings. Methylated-CpG island recovery assay-based microarray analysis was carried out on a discovery set consisting of cervical cancer tissue and normal cervical tissue to identify significantly hypermethylated genes. Five hundred and four CpG islands, corresponding to 378 genes, were differentially methylated between cervical cancer tissue and normal cervical tissue. Among them, 30 genes were significantly hypermethylated. Of the 30 genes, SOX9, PKLR and DLX4 were selected for further validation by direct bisulfite sequencing. The SOX9 gene revealed complete methylation in the cervical cancer tissue and complete non-methylation in the normal control tissue. A TaqMan-based real-time PCR assay was performed to detect the methylation levels of the SOX9 gene in 156 cervical scrapings, including 48 normal cervical scrapings, 30 scrapings with cervical intraepithelial neoplasia 1 (CIN1), 30 scrapings with CIN2-3 and 48 scrapings with squamous cell carcinoma (SCC). The methylation levels (methylation score) of the SOX9 gene increased significantly with the severity of cervical squamous lesions. The area under the receiver operating characteristic (ROC) curve (AUC) revealed that the methylation score of the SOX9 gene could be used to segregate SCC/CIN2-3 from CIN1/normal (AUC, 0.961; p=0.000). At the optimal cut-off value, a sensitivity of 92.3% and a specificity of 89.7% were obtained. In conclusion, SOX9 methylation is frequently involved in cervical carcinogenesis, and may provide a valuable molecular biomarker for early detection of cervical cancer.