Human papillomavirus type 16 E6 suppresses microRNA-23b expression in human cervical cancer cells through DNA methylation of the host gene C9orf3.

Chi Lam Au Yeung,Tim Tak Kwok,Tsun Yee Tsang,Pak Lun Yau

doi:10.18632/oncotarget.14555

Abstract

Oncogenic protein E6 of human papillomavirus type 16 (HPV-16) is believed to involve in the aberrant methylation in cervical cancer as it upregulates DNA methyltransferase 1 (DNMT1) through tumor suppressor p53. In addition, DNA demethylating agent induces the expression of one of the HPV-16 E6 regulated microRNAs (miRs), miR-23b, in human cervical carcinoma SiHa cells. Thus, the importance of DNA methylation and miR-23b in HPV-16 E6 associated cervical cancer development is investigated. In the present study, however, it is found that miR-23b is not embedded in any typical CpG island. Nevertheless, a functional CpG island is predicted in the promoter region of C9orf3, the host gene of miR-23b, and is validated by methylation-specific PCR and bisulfite genomic sequencing analyses. Besides, c-MET is confirmed to be a target gene of miR-23b. Silencing of HPV-16 E6 is found to increase the expression of miR-23b, decrease the expression of c-MET and thus induce the apoptosis of SiHa cells through the c-MET downstream signaling pathway. Taken together, the tumor suppressive miR-23b is epigenetically inactivated through its host gene C9orf3 and this is probably a critical pathway during HPV-16 E6 associated cervical cancer development.

Highlights

MicroRNA, a class of small non-coding single-stranded RNA of 19 to 24 nucleotides in length, is recently believed to participate in the development of cancer, including cervical cancer
Reduced miR-23b expression in DNMT knockout cells miR-23b is suggested to be epigenetically regulated in the previous study. miR-23b together with a number of miRs were found to be overexpressed in human colorectal carcinoma HCT116 double DNA methyltransferase 1 (DNMT1) and DNMT3b knockout (DK) cells as compared to the HCT116 parental cells [21]
Similar to DK cells, the miR was overexpressed in DNMT1 knockout (D1) cells (Figure 1A), suggesting that DNMT1 may suppress the expression of miR-23b, presumably by methylation, in cells

Summary

Introduction

MicroRNA (miR), a class of small non-coding single-stranded RNA of 19 to 24 nucleotides in length, is recently believed to participate in the development of cancer, including cervical cancer. “Knowing” the mechanisms that regulate the expression of miRNAs is critical in understanding the role of miRs in cervical cancer development. MiRNAs may probably be controlled by nuclear transcription factors through either transactivation or transrepression in ways similar as that for the protein-coding genes [5]. The transcription factors, such as p53, c-myc, E2F and NFκB, were reported to be involved in the regulation of miRNA expressions [5,6,7,8]. Previous studies showed that a large fraction of miRNA might be regulated at the Drosha processing step [4, 9]

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