Human Papillomavirus E6/E7 and Long Noncoding RNA TMPOP2 Mutually Upregulated Gene Expression in Cervical Cancer Cells

Abstract

Human papillomaviruses 16 and 18 (HPV16/18) are the main causative agents of cervical cancer. Viral proteins HPV16/18 E6 and E7 are constitutively expressed in cancer cells to maintain oncogenic phenotypes. Accumulating evidences suggest that HPVs are correlated with the deregulation of long noncoding RNAs (lncRNAs) in cervical cancer, although the mechanism was unexplored in most cases. TMPOP2 is a newly identified lncRNA excessively expressed in cervical cancer. However, the mechanism for the upregulation of TMPOP2 in cervical cancer cells remains largely unknown and its relationship with HPVs is still elusive. The significance of our research is in revealing the mutual upregulation of HPV16/18 E6/E7 and TMPOP2 with the molecular mechanisms explored. This study will expand our understandings of the oncogenic activities of human papillomaviruses and lncRNAs. TMPOP2 was previously suggested to be an oncogenic long noncoding RNA which is excessively expressed in cervical cancer cells and inhibits E-cadherin gene expression by recruiting transcription repressor EZH2 to the gene promoter. So far, the function and regulation of TMPOP2 in cervical cancer remain largely unknown. Herein, we found that TMPOP2 expression was correlated with human papillomavirus 16/18 (HPV16/18) E6 and E7 in cervical cancer cell lines CaSki and HeLa. Tumor suppressor p53, which is targeted for degradation by HPV16/18, was demonstrated to associate with two p53 response elements in the TMPOP2 promoter to repress the transcription of the TMPOP2 gene. Reciprocally, ectopic expression of TMPOP2 was demonstrated to sequester tumor repressor microRNAs (miRNAs) miR-375 and miR-139 which target HPV16/18 E6/E7 mRNA and resulted in an upregulation of HPV16/18 E6/E7 genes. Thereby, HPV16/18 E6/E7 and the long noncoding RNA (lncRNA) TMPOP2 form a positive feedback loop to mutually derepress gene expression in cervical cancer cells. Moreover, results of RNA sequencing and cell cycle analysis showed that knockdown of TMPOP2 impaired the expression of cell cycle genes, induced cell cycle arrest, and inhibited HeLa cell proliferation. Together, our results indicate that TMPOP2 and HPV16/18 E6/E7 mutually strengthen their expression in cervical cancer cells to enhance tumorigenic activities. IMPORTANCE Human papillomaviruses 16 and 18 (HPV16/18) are the main causative agents of cervical cancer. Viral proteins HPV16/18 E6 and E7 are constitutively expressed in cancer cells to maintain oncogenic phenotypes. Accumulating evidences suggest that HPVs are correlated with the deregulation of long noncoding RNAs (lncRNAs) in cervical cancer, although the mechanism was unexplored in most cases. TMPOP2 is a newly identified lncRNA excessively expressed in cervical cancer. However, the mechanism for the upregulation of TMPOP2 in cervical cancer cells remains largely unknown and its relationship with HPVs is still elusive. The significance of our research is in revealing the mutual upregulation of HPV16/18 E6/E7 and TMPOP2 with the molecular mechanisms explored. This study will expand our understandings of the oncogenic activities of human papillomaviruses and lncRNAs.