Intimacy and a deadly feud: the interplay of autophagy and apoptosis mediated by amino acids.

Autophagy (i.e., "self-eating") and apoptosis (i.e., type I programmed cell death) are essential and intimately involved in molecular, cellular, and whole-body homeostasis in humans and animals. Autophagy has been categorized as a mechanism of intracellular degradation, recycling, defense, and survival. To date, three types of autophagy have been identified: macroautophagy, microautophagy, and chaperone-mediated autophagy. Recent discoveries strongly suggest that macroautophagy also modulates type II programmed cell death under specific circumstances. Autophagy and apoptosis are fundamentally distinct processes, but are interconnected by common stress initiators and intermediate regulators. During the past two decades, the role of amino acid metabolism and signaling in the regulation of apoptosis and autophagy has been intensively studied. In this review, we summarize recent advances in our understanding of the molecular mechanisms that regulate both autophagy and apoptosis in the context of amino acid signaling.