Maintenance of protein homeostasis and organelle integrity and function is critical for cellular homeostasis and cell viability. Autophagy is the principal mechanism that mediates the delivery of various cellular cargoes to lysosomes for degradation and recycling. A myriad of studies demonstrate important protective roles for autophagy against disease. However, in cancer, seemingly opposing roles of autophagy are observed in the prevention of early tumour development versus the maintenance and metabolic adaptation of established and metastasizing tumours. Recent studies have addressed not only the tumour cell intrinsic functions of autophagy, but also the roles of autophagy in the tumour microenvironment and associated immune cells. In addition, various autophagy-related pathways have been described, which are distinct from classical autophagy, that utilize parts of the autophagic machinery and can potentially contribute to malignant disease. Growing evidence on how autophagy and related processes affect cancer development and progression has helped guide efforts to design anticancer treatments based on inhibition or promotion of autophagy. In this Review, we discuss and dissect these different functions of autophagy and autophagy-related processes during tumour development, maintenance and progression. We outline recent findings regarding the role of these processes in both the tumour Nature Reviews Molecular Cell Biology
Review articleATG3 and ATG7. These proteins facilitate the lipid conjugation of the ATG8 family members (consisting of the microtubule-associated protein 1A/1B-light chain 3 (LC3) and GABARAP subfamilies), which are important during cargo recruitment and autophagosome maturation 3,4 (Fig. 1), as well as other processes that involve ATG8-lipid conjugation (see below and Supplementary Box 1). Although cargo recruitment can be non-selective, for example in nutrient-depleted cells where autophagosomes take up different cargoes to recycle crucial nutrients such as amino acids or lipids, autophagy is largely highly selective. This selectivity is facilitated by autophagy cargo receptors (ACRs) (Fig. 1 and Supplementary Box 2), which bind to specific cargoes that have been tagged for degradation via ubiquitindependent or ubiquitin-independent processes 5 . To add further to this complexity, recent studies have unravelled additional roles of ATG proteins beyond autophagosome formation, thereby expanding their functions and implications in disease 6 (Box 1). Two additional lysosomal degradation processes exist that are related to (macro) autophagy but do not require the activities of ATG proteins. These include chaperone-mediated autophagy and microautophagy, in which cargo delivery to the lysosome relies on chaperone activity and invagination of the lysosomal membrane to encapsulate cellular material, respectively 1 .Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author sel...