Regulation of paclitaxel-induced programmed cell death by autophagic induction: A model for cervical cancer

Abstract

Objective: Autophagy plays a vital role in homeostasis by combining organelles and cellular proteins with lysosome under starvation conditions. In addition, autophagy provides tumor cells with a source of energy. Continued autophagy will induce cells death. Here we aim to see if autophagic induction has an effect on conventional chemotherapeutic agents.

Methods: Rapamycin, or mammalian target of rapamycin and paclitaxel, apoptosis-inducing agents were used autophagy in HeLa cervical cancer cells.

Results: Growth inhibition of cells was not observed after the application of 0, 10, 20 nM of paclitaxel with or without rapamycin. Using a 5 nM concentration of paclitaxel, rapamycin administration inhibited cell growth significantly compared to no treatment. This implies the synergic antitumor effect of paclitaxel and rapamycin. Paclitaxel itself did not show any autophagic effect on cells but did show cell apoptosis by flow cytometry. Light chain 3, a microtubule-associated protein, which reflect autophagy, was increased with 5 nM of paclitaxel after pretreatment with 10 nM of rapamycin.

Conclusion: These findings suggest that the autophagic inducer, rapamycin, can potentiate autophagic cell death when added as an apoptosis-inducing chemotherapeutic agent. In conclusion, the control of autophagy may be a future target for chemotherapy.

Keywords: Apoptosis; Autophagy; Cervical neoplasms; Paclitaxel; mTOR protein.

Fig. 1

(A, B) Cell viability after treatment of paclitaxel and rapamycin in HeLa cervical cancer cells. (C) Cell viability after treatment with various doses of paclitaxel with or without 10 nM of rapamycin pretreatment. ^a)Rapamycin pretreatment followed by 5 nM of paclitaxel showed significant suppression of cellular growth (P<0.05).

Fig. 2

(A, B) Apoptotic cells stained by Anenxin V and autophagic cells stained by acridine orange counted at 24 hour after treatment with 5 nM of paclitaxel (detected by flow cytometry). (C) Paclitaxel exposure induced increased dose- and time-dependent caspase-3 expression.

Fig. 3

(A) Increased GFP-LC3-treated cells (arrows) in the process of autohpagy (×40). (B, C) Autophagic vacuoles in LC3-transfected cells increased in number after addition of 10 nM of rapamycin and a combination of 10 nM of rapamycin and 5 nM of paclitaxel for 24-hour to HeLa cells (×10).