Blockade of Autophagy Aggravates Endoplasmic Reticulum Stress and Improves Paclitaxel Cytotoxicity in Human Cervical Cancer Cells

PURPOSE: Autophagy is one of the ways to degrade unfolded proteins after endoplasmic reticulum (ER) stress. The purpose of this study is to determine whether a blockade of autophagy leads to aggravated endoplasmic reticulum stress, which then induces cells apoptosis in HeLa cells treated with paclitaxel. MATERIALS AND METHODS: Autophagy activation and the proapoptotic effects were characterized using monodansylcadaverine labeling and Hoechest staining, respectively. A Western blot analysis was used to detect the expression of apoptotic and autophagy-related genes. A flow cytometry was used to assess the cell apoptosis ratio. RESULTS: Paclitaxel exposure induced the aggregation of autophagosomes in the cytoplasms of cervical cancer HeLa cells. The expression of Beclin 1 and LC3 II were upregulated, but p62 was downregulated, which suggests that autophagy was promoted by paclitaxel. On the other hand, the expression of GRP78 obviously increased, suggesting that ER stress was induced after paclitaxel treatment. The cell proliferation assay indicated that a knockdown of Beclin 1 sensitized HeLa cells to paclitaxel. Furthermore, paclitaxel-mediated apoptotic cell death was further potentiated by the pretreatment with autophagy inhibitor chloroquine or small interfering RNA against Beclin 1. These results suggest that an induction of autophagy by paclitaxel may induce cell survival rather than cell death in HeLa cells; moreover, inhibition of autophagy led to an aggravated ER stress and an induction of downstream apoptosis. CONCLUSION: Our results reveal autophagy induced by paclitaxel conferred protection of tumor cells against apoptosis, and blockade of autophagy subsequently aggravated ER stress, enhancing the apoptosis associated with paclitaxel treatment in HeLa cells.