A quantitative TR-FRET plate reader immunoassay for measuring autophagy

Autophagy involves the isolation and targeting of unwanted cellular components to lysosomes for their digestion and reuse. Autophagic dysregulation has recently been implicated in a wide range of disease processes, yet facile methods for quantifying autophagy have been lacking in the field. Here we describe the generation of a quantitative plate reader assay for measuring the autophagic activity of cells. One of the best characterized autophagy markers is the protein LC3B, which normally resides in the cytosol (LC3B-I) but upon induction of autophagy becomes lipidated and embedded in autophagosomal membranes (LC3B-II). To quantify autophagy, we reasoned that GFP-tagged LC3B could serve as a time-resolved fluorescence resonance energy transfer (TR-FRET) acceptor upon cell lysis in the presence of terbium-labeled LC3B antibodies. Using this TR-FRET immunoassay approach, we screened a panel of LC3B antibodies and identified an antibody that exhibits strong preferential affinity toward autophagosome-associate...