Small extracellular vesicle-mediated transfer of HPV16 transcripts from Ca Ski cells increases proliferation of HPV-negative recipient cancer cells

BACKGROUND: Tumor-produced extracellular vesicles (EVs) are key players in cancer progression by transferring their bioactive cargo (nucleic acids, lipids, proteins) to target cells leading to increase their proliferation, migration and invasive properties. EVs are involved in virus-associated carcinogenesis. Cervical cancer is due to a persistent infection with a high-risk human papillomavirus (HPV) whose integration into the cellular genome causes the continuous and deregulated expression of viral oncoproteins E6/E7, responsible for the carcinogenesis process. This study aimed to isolate EVs of HPV-infected cells, to explore their viral material content, to determine whether viral cargo can impact the proliferative status of HPV-lacking recipient cells. METHODS: EVs were isolated from HPV16-harboring Ca Ski cells by ultracentrifugation or a kit. Their metrological, microscopic and biochemical characterization was performed by NTA for size, TEM for morphology and western blotting for EV markers (CD9, CD63, CD81, ALIX, TSG101, Flotillin-1, Syntenin). Viral material cargo (HPV16 DNA; e6/e7, e6*I, e6^e7 early transcripts; E6/E7 oncoproteins) was analyzed by PCR/RTqPCR and immunoblotting. Confocal microscopy was used to observe the internalization of fluorescent EVs deposited over HPV-negative bladder cancer T24 cells. The effect of Ca Ski EVs on the proliferation of T24 cells was assessed by IncuCyte and CCK-8 assay. The involvement of early transcripts in proliferation was validated by siRNA experiments. RESULTS: A sEV-enriched fraction was obtained from Ca Ski cell supernatants. The unspliced e6/e7 transcripts and the spliced variants e6*I /e6^e7 were detected inside EVs but HPV16 DNA or E6/E7 proteins were not detected. After 24 h-incubation, EVs were internalized by T24 cells and led to an increase of their proliferation. This biological effect was partially due to e6/e7 transcripts loaded in EVs. CONCLUSIONS: After a complete characterization of Ca Ski sEVs (NTA, microscopy, PCR, western-blotting), our data show for the first time, a functional transfer of HPV16 early transcripts via EVs driving the proliferation of HPV-negative target cells. EV-loaded HPV16 e6/e7 mRNA could be used as early biomarkers before the disease sets in and to predict the evolution of cervical precancerous lesions towards cancer and facilitate patient monitoring through a simple liquid biopsy.