Doxorubicin-Induced Cancer Cell Senescence Shows a Time Delay Effect and Is Inhibited by Epithelial-Mesenchymal Transition (EMT)

BACKGROUND: Senescence is a natural barrier for the body to resist the malignant transformation of its own cells. This work investigated the senescence characteristics of cancer cells in vitro. MATERIAL/METHODS: Human cervical cancer HeLa cells were treated with different concentrations of doxorubicin for 3 days, with or without subsequent extended culture in drug-free medium for 6 days. Senescent cell ratios between these 2 culture schemes were calculated. Expression of 2 senescence-associated secretory factors, IL-6 and IL-8, were detected by RT-PCR and ELISA. Doxorubicin treatment induced epithelial-mesenchymal transition in cancer cells. The proportions of senescent cells in epithelial-like and mesenchymal-like sub-groups were calculated. Doxorubicin-treated HeLa cells were stained with Vimentin antibody and sorted by flow cytometry. Senescent cell marker p16(INK4a) and IL-8 expression in Vimentin-high and Vimentin-low cells were detected by Western blot. RESULTS: We found that less than 1% of HeLa cells showed senescence phenotype after treatment with doxorubicin for 3 days. However, the proportion of senescent cells was significantly increased when the doxorubicin-treated cells were subsequently cultured in drug-free medium for another 6d. RT-PCR and ELISA results showed that this prolonged culture method could further improve the expression of IL-6 and IL-8. We also found that the senescent cells were mainly epithelial-like type and few presented mesenchymal-like shape. p16(INK4a) and IL-8 expression were decreased in cell fraction with higher Vimentin expression. CONCLUSIONS: Our results suggested the existence of time delay effect in doxorubicin-induced senescence of HeLa cells, and epithelial-mesenchymal transition may resist doxorubicin-induced cell senescence.