Immunofluorescences

Cells plated on glass coverslips were fixed with 100% methanol at −20°C for 5 minutes. Cells were permeabilized with 0.1% saponin, blocked with PBS containing 0.1% saponin and 1% BSA for 30 minutes, and incubated with primary antibody for 1 hour at 37°C. Coverslips were washed and incubated with Alexa Fluor–labeled secondary antibodies for 30 minutes at room temperature. Finally, coverslips were washed and mounted using DAPI Fluoromount-G and analyzed by confocal microscope. The following antibodies were used: GPT2 (1:100, Proteintech, 16757-1-AP, RRID: AB_2112098), TOM20 (1:2,000, Santa Cruz Biotechnology, 17764, RRID: AB_628381), goat anti-mouse IgG Alexa Fluor 555 conjugate (1:1,000, Thermo Fisher Scientific, A-21422, RRID: AB_2535844), and goat anti-rabbit IgG Alexa Fluor 488 (1:1,000, Thermo Fisher Scientific, A-11008, RRID: AB_143165).