Low risk HPV-6E6 induces apoptosis in bone marrow-derived dendritic cells

The present study assessed the subcellular localization and apoptotic potential of low-risk human papilloma virus 6E6 (HPV-6E6), expressed in bone marrow-derived dendritic cells (DCs). DCs were obtained from C57BL/6 mice and transfected with a pGFP-6E6 plasmid. The subcellular localization of E6 was determined by tracing green fluorescent protein (GFP) using fluorescence microscopy. Apoptosis was assessed by staining nuclei with DAPI and performing an apoptosis-based flow cytometry assay. The co-localization of E6 and p53 was also investigated using confocal microscopy. In addition, the expression of apoptosis-associated proteins was analyzed using immunoblotting. The results of the present study demonstrated that low-risk HPV-6E6 is predominantly localized in the cytoplasm of DCs. Furthermore, p53 was upregulated in DCs transfected with pGFP-6E6 and co-localized with GFP-6E6 in the cytoplasm. DCs transfected with a control pGFP plasmid did not undergo apoptosis, whereas cells transfected with pGFP-6E6 did, as indicated by the presence of cell debris and condensation of the nuclei. Furthermore, the expression of apoptosis-associated proteins, including p53, BCL2 associated X apoptosis regulator (Bax), BCL2 homologous antagonist/killer (Bak) and cytochrome c, were significantly higher in DCs expressing low-risk E6 than in control cells. Therefore, the current study demonstrated that low-risk HPV-6E6 is predominantly located in the cytoplasm of DCs and induces apoptosis. This may be an important mechanism that explains why low-risk HPV is unable to induce malignant transformation.