Repression of Memo1, a Novel Target of Human Papillomavirus Type 16 E7, Increases Cell Proliferation in Cervical Cancer Cells.

ABSTRACT

Human papillomavirus (HPV)-induced carcinogenesis is associated with unregulated expression of the oncoproteins E6 and E7. HPV E7 is a viral protein that lacks enzymatic activity; however, it can target several cellular proteins to induce cell transformation and promote uncontrolled proliferation. Although several E7 targets have been described, there are still gaps in the understanding of how this oncoprotein drives cells toward malignancy. Here, using a small HPV type 16 (HPV16) E7 peptide in a proteomic approach, we report Memo1 as a new E7 binding partner, interacting through the aspartic and glutamic acid residues (E80 and D81) in the C-terminal region of HPV16 E7. Furthermore, we demonstrate that HPV16 E7 targets Memo1 for proteasomal degradation through a Cullin2-dependent mechanism. In addition, we show that overexpression of Memo1 decreases cell transformation and proliferation and that reduction of Memo1 levels correlate with activation of Akt and an increase in invasion of HPV-positive cervical cancer cell lines. Our results show a novel HPV E7 interacting partner and describe novel functions of Memo1 in the context of HPV-induced malignancy. IMPORTANCE Although numerous targets have been reported to interact with the HPV E7 oncoprotein, the mechanisms involved in HPV-induced carcinogenesis and the maintenance of cell transformation are still lacking. Here, through pulldown assays using a peptide encompassing the C-terminal region of HPV16 E7, we report Memo1 as a novel E7 interactor. High levels of Memo1 correlated with reduced cell proliferation and, concordantly, knockdown of Memo1 resulted in Akt activation in HPV-positive cell lines. These results highlight new mechanisms used by HPV oncoproteins to modulate proliferation pathways in cervical cancer cells and increase our understanding of the link between Memo1 protein and cancer.