The roles ofHPV16E6,E7 andE6/E7 genes inSTK31 promoter/exon1 methylation and expression levels in cervical cancer cell lines
10.3969/j.issn.1007-3969.2015.09.001
- VernacularTitle:宫颈癌细胞系中HPV16 E6、E7及E6/E7基因对STK31基因甲基化状态及表达的影响
- Author:
Fufen YIN
;
Ning WANG
;
Xiao YU
;
Xiaoning BI
;
Xiaohui XU
;
Yankui WANG
- Publication Type:Journal Article
- Keywords:
Serine/threonine kinases 31 gene;
Methylation;
HPV16;
Cervical cancer;
Biomarker
- From:
China Oncology
2015;(9):641-651
- CountryChina
- Language:Chinese
-
Abstract:
Background and purpose:Studies have proved that the serine/threonine kinases 31 (STK31) gene plays important roles in human cancers. TheSTK31 gene expression was demonstrated to be regulated by the methylation status of its promoter/exon1 region. Viral infection was revealed to be associated with the hypermethylation of some tumor suppressor genes in some tumor samples. The purposes of this paper were to study the roles ofHPV16E6,E7, orE6/E7 oncogenes in methylation status and expression of theSTK31 gene, and potential effects of DNA methyltransferases (DNMTs) onSTK31 gene methylation status.Methods:Ectopically-expressed HPV16 E6, E7, or E6/E7 cells were estab-lished by transfectingHPV16E6,E7, orE6/E7 oncogenes with lentivirus vectors into HPV-negative cervical cancer cell lines HT-3 and C33A. Bisulfite genomic sequencing PCR (BGS) combined with TA clone and MSP (methylation-specific PCR) were used to analyze methylation status of theSTK31 gene promoter/exon1 region in HPV-positive cervical cancer cell lines (HeLa, SiHa, CaSki), HPV-negative cervical carcinoma cell lines (C33A, HT-3) and the transfected cells. The mRNA and protein expression of STK31, DNMT1, DNMT2, DNMT3a, DNMT3b and DNMT3L were detected by RT-PCR and Western blot.Results:Transfection efficiency was tested by Western blot, which showed that the transfected cells successfully expressed E6, E7, or E6/E7 proteins, respectively. TheSTK31 gene promoter/exon1 was hypomethylated in HPV-positive cell lines HeLa, SiHa and CasKi resulting in detection of mRNA and protein expression.STK31 gene promoter/exon1 showed hypermethylation leading to silenced expression in the two HPV-negative cervical cancer cells HT-3 and C33A. Compared with primary HT-3 and C33A cells, the methylation status ofSTK31 promoter/exon1 was down-regulated that led to expression of STK31 in the ectopically-expressed HPV16 E7 and E6/E7 cells. Expressions of DNMT1,DNMT3a andDNMT3b genes at the level of transcription were higher in C33AE6/E7 and HT-3E6/E7 cells than those in C33A-vector and HT-3 vector cells, respectively (P<0.001). mRNA levels of DNMT1, DNMT3a and DNMT3b were higher in HPV16-positive cervical cancer tissues than those in HPV-negative cervical cancer tissues, respectively (t=5.997,P<0.001;t=6.743,P<0.001;t=7.926,P<0.001). DNMT2 mRNA level was lower in C33AE6/E7 and HT-3E6/E7 cells than those in C33A-vector and HT-3 vector cells, respectively (t=7.451,P<0.001;t=2.451,P<0.05). mRNA level of DNMT2 gene was lower in HPV16-positive cervical cancer tissues than in HPV-negative cervical cancer tissues (t=9.134, P<0.001). There was no statistically significant difference in expression levels of DNMT3L mRNA between cervical cancer cell lines before and after transfection, or HPV16-positive and HPV-negative cervical cancer tissues, respectively (P>0.05, data not shown).Conclusion:HPV infection leads to the down-regulated methylation status ofSTK31 promoter/exon1 that results in the expression of STK31.STK31 gene expression is regulated by methylation status of its promoter/exon1 region. HPV16E7 andE6/E7 oncogenes may influence the methylation status ofSTK31 gene promoter/exon1 region by regulating the expression of DNMT2.
