Transcription Factor Homeobox D9 Drives the Malignant Phenotype of HPV18-Positive Cervical Cancer Cells Via Binding to the Viral Early Promoter

Persistent infections with two types of human papillomaviruses (HPV), HPV16 and HPV18, are the most common cause of cervical cancer (CC). Two viral early genes, and , are associated with tumor development, and expressions of and are primarily regulated by a single viral promoter: in HPV16 and in HPV18. We previously demonstrated that the homeobox D9 (HOXD9) transcription factor is responsible for the malignancy of HPV16-positive CC cell lines via binding to the promoter. Here, we investigated whether HOXD9 is also involved in the regulation of the promoter using two HPV18-positive CC cell lines, SKG-I and HeLa. Following the HOXD9 knockdown, cell viability was significantly reduced, and expression was suppressed and was accompanied by increased protein levels of P53, while mRNA levels of did not change. expression was also downregulated and, while mRNA levels of and were unchanged, mRNA levels of E2F-target genes, and , were decreased, which indicates that the HOXD9 knockdown downregulates expression, thus leading to an inactivation of E2F and the cell-cycle arrest. Chromatin immunoprecipitation and promoter reporter assays confirmed that HOXD9 is directly associated with the promoter. Collectively, our results reveal that HOXD9 drives the HPV18 early promoter activity to promote proliferation and immortalization of the CC cells.