Monitoring Autophagic Flux by Using Lysosomal Inhibitors and Western Blotting of Endogenous MAP1LC3B.

Assays that monitor autophagic flux, or degradative completion of autophagy, are crucial for the assessment of the dynamic autophagy process in a variety of systems. Such assays help to distinguish between an increase in autophagosomes resulting from induced autophagic activity versus an increase in autophagosomes due to reduced lysosomal turnover. The majority of flux assays use autophagy protein MAP1LC3B (microtubule-associated proteins 1A/1B light chain 3B, here referred to as LC3B) as a marker for autophagy, and most are based on the use of reporters. Here, we describe a method, suitable for monitoring flux in primary cells and/or when reporters are not available or desirable, that uses lysosomal inhibitors and the analysis of endogenous LC3B-II (the lipidated form of LC3B that is associated with autophagosomes) by western blotting. A common application of this method, detailed here, is to test whether a treatment of interest (e.g., chemotherapy drug) induces autophagic flux in the cells of interest. If it is found that there is no difference in LC3B-II levels between treatment with lysosomal inhibitor alone versus drug plus lysosomal inhibitor, then this suggests that the drug is not inducing autophagic flux. Elevated levels of LC3B-II in treatments with drug plus lysosomal inhibitor, compared with drug treatment alone and inhibitor treatment alone, indicate that the drug is probably leading to an increase in autophagic flux.