Autophagy: Molecular mechanisms and their implications for anticancer therapies

Autophagy is a catabolic process whereby cells maintain homeostasis by eliminating unnecessary proteins and damaged organelles. It may be triggered under physiological conditions, such as nutrient starvation, or in response to a variety of stress stimuli, such as exposure to radiations or cytotoxic compounds. Although autophagy is basically a protective mechanism that sustains cell survival under adverse conditions, it has been recently demonstrated that the induction of autophagic process may ultimately lead to cell death. As for the role of autophagy in cancer, it is still very controversial whether it suppresses tumorigenesis or provides cancer cells with a rescue mechanism under unfavourable conditions. Therefore, the dual role of autophagy in tumor progression and in the response of cancer cells to chemotherapeutic drugs is still open to debate. The first part of this review describes the cellular events occurring during the various phases of the autophagic process. Special attention has been given to the morphological aspects and the regulatory molecules involved in autophagic cell death. Specifically, we have focused on the proteins necessary for autophagosome formation, encoded by the ATG (AuTophaGy-related gene) gene family, and their role in the regulation of the process of autophagy. We also examined the effects of autophagy modulators on cell survival and cell death and discussed the recent efforts aimed at finding novel agents that activate or inhibit autophagy by targeting regulatory molecules of the complex autophagy pathways.