Dequalinium-induced cell death of yeast expressing alpha-synuclein-GFP fusion protein

Intracellular toxic effects of the dequalinium-induced protofibrils of alpha-synuclein have been investigated with the yeast system expressing alpha-synuclein-GFP fusion protein in single copy, which appears in the green halo around the plasma membrane. Intracellular responses of the green fluorescent protein were analyzed as the cells were treated with dequalinium (DQ) and lactacystin. Yeast cells expressing alpha-synuclein-GFP were susceptible to both compounds in alpha-synuclein-dependent manner. Upon DQ treatment, the green halo became smeared throughout the cytoplasm while lactacystin induced a few discrete green dots, reflecting intracellular formation of the protofibrils and the protein inclusions, respectively. The DQ-treated yeast cells were intensely stained with the nucleic acid stains of cell-permeable Hoechst 33342 and cell-impermeable propidium imidione, indicating that nucleus has been disrupted in addition to plasma membrane destabilization. Those DQ-treated yeast cells, however, still contained active mitochondria identified with MitoTracker Red. Therefore, the DQ-induced protofibrillar state of alpha-synuclein-GFP has been suggested to cause the nuclear damage either independently or in combination with the membrane destabilization without affecting mitochondria.