HPV E6 promotes cell proliferation of cervical cancer cell by accelerating accumulation of RBM15 dependently of autophagy inhibition

The mechanism of m6A modification in HPV-related cervical cancer remains unclear. This study explored the role of methyltransferase components in HPV-related cervical cancer and the mechanism. The levels of methyltransferase components and autophagy, ubiquitylation of RBM15 protein and the co-localization of lysosomal markers LAMP2A and RBM15 were measured. CCK-8 assay, flow cytometry, clone formation experiment and immunofluorescence assay were conducted to measure cell proliferation. The mouse tumor model was developed to study the cell growth in vivo. The binding of RBM15 to c-myc mRNA and m6A modifcation of c-myc mRNA were analyzed. The expressions of METTL3, RBM15 and WTAP were higher in HPV-positive cervical cancer cell lines than those in HPV-negative cells, especially RBM15. HPV-E6 knock-down inhibited the expression of RBM15 protein and promoted its degradation, but couldn't change its mRNA level. Autophagy inhibitor and proteasome inhibitor could reverse those effects. HPV-E6 siRNA could not enhance ubiquitylation modification of RBM15, but could enhance autophagy and the co-localization of RBM15 and LAMP2A. RBM15 overexpression could enhance cell proliferation, block the inhibitory effects of HPV-E6 siRNA on cell growth, and these effects could be reserved by cycloeucine. RBM15 could bind to c-myc mRNA, resulting in an increase to m6A level and protein expression of c-myc, which could be blocked by cycloeucine. HPV-E6 can downregulate autophagy, inhibit the degradation of RBM15 protein, induce the accumulation of intracellular RBM15, and increase the m6A modification on c-myc mRNA, resulting in an increase of c-myc protein and a growth promotion for cervical cancer cells.

High risk HPV E6 oncoproteins impair the subcellular distribution of the four and a half LIM-only protein 2 (FHL2)

HPVs are the causative agents of approximately 5% of all human cancers, with cervical cancer being the most predominant. To understand the mechanism of action of the viral E6 oncoprotein, we analysed the effects of E6 upon potential cellular target proteins. One candidate is FHL-2, involved in the regulation of signal transduction pathways from the multimeric complexes assembled at focal adhesions. We show that both HPV E6 and E6(⁎) can interact with FHL-2 in vitro, but unlike most E6 targets, FHL-2 does not appear to be an E6 degradation target. Analysis of the patterns of FHL-2 distribution within HPV-positive tumour-derived cells shows a significant alteration in the pattern of FHL-2 localisation when compared to non-HPV containing cells. This perturbation of FHL-2 distribution is proteasome-dependent and inhibition of E6 expression restores the normal distribution of FHL-2. These results confirm FHL-2 as a new interacting partner of the HPV-E6 oncoproteins.