Background: High-risk human papillomaviruses (HPVs) are the major causative agents of cervical cancer. The E7 protein of high-risk HPV disturbs cell cycle control and down-regulates components of the antigen presentation pathway, suggesting an ideal target for development of the immunotherapy in HPV-positive cervical cancers. We previously reported that HPV16 E7 could down-regulate cell-surface HLA class I antigen accompanying decreased expression of transporter associated with antigen processing 1 (TAP-1). The purpose of this study was to determine whether knockdown of HPV16 E7 could up-regulate surface HLA class I antigen expression in HPV16 E7 expressing HaCaT cells (HaCaT-E7).

Methods: An E7-specific small interfering RNA (siRNA) was transfected into the HaCaT-E7 cells, and the expression of HPV16 E7 was measured by real-time reverse transcriptase polymerase chain reaction and Western blot. With the use of flow cytometry analysis, the levels of cell surface HLA class I antigen and intracellular TAP-1 expression were detected.

Results: It was found that transfection of HPV16 E7-siRNA reduced HPV16 E7 expression as measured on messenger RNA and protein levels. The flow cytometry analysis showed that, compared with mock transfection, a statistically significant increase of approximately 75% in surface HLA class I levels was observed in HaCaT-E7 cells at 72 hours after transfection of E7 siRNA. Moreover, he knockdown of E7 in HaCaT-E7 cells could result in an increase of intracellular TAP-1 expression, which is essential for the expression of HLA class I at cell surface.

Conclusions: Our study showed that the knockdown of HPV16 E7 could increase cell surface HLA class I antigen expression in HaCaT-E7 cells. In addition, for HPV-positive human cervical cancer, our observations indicate that the HPV E7 gene is a target of choice.