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

• Main Authors: Shigenori Hayashi, Takashi Iwata, Ryotaro Imagawa, Masaki Sugawara, Guanliang Chen, Satoko Tanimoto, Yo Sugawara, Ikumo Tanaka, Tomoya Matsui, Hiroshi Nishio, Masaru Nakamura, Yuki Katoh, Seiichiro Mori, Iwao Kukimoto, Daisuke Aoki
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Cancers
• Subjects: cervical cancer; HOXD9; HPV18; <i>P105</i> promoter
• Online Access: https://www.mdpi.com/2072-6694/13/18/4613

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, <i>E6</i> and <i>E7</i>, are associated with tumor development, and expressions of <i>E6</i> and <i>E7</i> are primarily regulated by a single viral promoter: <i>P97</i> in HPV16 and <i>P105</i> 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 <i>P97</i> promoter. Here, we investigated whether HOXD9 is also involved in the regulation of the <i>P105</i> promoter using two HPV18-positive CC cell lines, SKG-I and HeLa. Following the HOXD9 knockdown, cell viability was significantly reduced, and <i>E6</i> expression was suppressed and was accompanied by increased protein levels of P53, while mRNA levels of <i>TP53</i> did not change. <i>E7</i> expression was also downregulated and, while mRNA levels of <i>RB1</i> and <i>E2F</i> were unchanged, mRNA levels of E2F-target genes, <i>MCM2</i> and <i>PCNA</i>, were decreased, which indicates that the HOXD9 knockdown downregulates <i>E7</i> 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 <i>P105</i> promoter. Collectively, our results reveal that HOXD9 drives the HPV18 early promoter activity to promote proliferation and immortalization of the CC cells.