Inhibition of autophagy contributes to the toxicity of cadmium telluride quantum dots in Saccharomyces cerevisiae

Abstract

Cadmium telluride quantum dots (CdTe QDs) are used as near-infrared probes in biologic and medical applications, but their cytological effects and mechanism of potential toxicity are still unclear. In this study, we evaluated the toxicity of CdTe QDs of different sizes and investigated their mechanism of toxicity in the yeast Saccharomyces cerevisiae. A growth inhibition assay revealed that orange-emitting CdTe (O-CdTe) QDs (half inhibitory concentration [IC₅₀] =59.44±12.02 nmol/L) were more toxic than green-emitting CdTe QDs (IC₅₀ =186.61±19.74 nmol/L) to S. cerevisiae. Further studies on toxicity mechanisms using a transmission electron microscope and green fluorescent protein tagged Atg8 processing assay revealed that O-CdTe QDs could partially inhibit autophagy at a late stage, which differs from the results reported in mammalian cells. Moreover, autophagy inhibited at a late stage by O-CdTe QDs could be partially recovered by enhancing autophagy with rapamycin (an autophagy activator), combined with an increased number of living cells. These results indicate that inhibition of autophagy acts as a toxicity mechanism of CdTe QDs in S. cerevisiae. This work reports a novel toxicity mechanism of CdTe QDs in yeast and provides valuable information on the effect of CdTe QDs on the processes of living cells.

Keywords:

• CdTe quantum dots
• Saccharomyces cerevisiae
• toxicity
• autophagy

Supplementary materials

Figure S1 Proportion of cells belonging to diagrammed fluorescence phenotypes when treated with CdTe QDs for 16 hours.

Notes: Cells transformed with a plasmid encoding GFP-Atg8 were treated with 50 nmol/L O-CdTe QDs or G-CdTe QDs for 16 hours. More than 50 cells were counted and classified into certain phenotypes. The results are expressed as mean ± standard deviation, n=3.

Abbreviations: CdTe, cadmium telluride; G-CdTe, green-emitting CdTe; O-CdTe, orange-emitting CdTe.

Figure S2 Raw data of cell cycle distribution analysis obtained by flow cytometry.

Notes: Cells were treated with CdTe QDs for 8 hours and stained with propidium iodide before flow cytometry analysis.

Abbreviations: CdTe QDs, cadmium telluride quantum dots; G-CdTe, green-emitting CdTe; O-CdTe, orange-emitting CdTe.

Acknowledgments

This work was supported by the National Basic Research Program of China (973 Program, no 2013CB933904) and the National Natural Science Foundation of China (21272182, 21225313, and 31570090). This project is partially supported by the Chinese 111 Project Grant B06018, the National Fund for Fostering Talents in Basic Sciences (J1103513), and the Laboratory (Innovative) Research Fund of Wuhan University.

Disclosure

The authors report no conflicts of interest in this work.