Endogenous HMGB1 regulates autophagy. High mobility group box 1 (HMGB1) is a chromatin-associated nuclear protein and extracellular damage-associated molecular pattern molecule that regulates autophagy. Stimuli that enhance reactive oxygen species (ROS) promote cytosolic translocation of HMGB1, which enhances autophagic flux. HMGB1 directly interacts with the autophagy protein Beclin1, displacing Bcl-2. Mutation of cysteine 106 (C106) of HMGB1 promotes cytosolic localization and sustained autophagy. The intramolecular disulfide bridge (C23/45) of HMGB1 is required for binding to Beclin1 and sustaining autophagy. Endogenous HMGB1 is a critical pro-autophagic protein that enhances cell survival and limits programmed apoptotic cell death. Autophagy is a major mechanism by which starving cells reallocate nutrients from unnecessary to more essential processes. During autophagy, a cytosolic form of light chain 3 (LC3; LC3-I) is cleaved and then conjugated to phosphatidylethanolamine to form the LC3-phosphatidylethanolamine conjugate (LC3-II), which is recruited to autophagosomal membranes. Autophagy is a process that clears long-lived proteins and dysfunctional organelles and generates substrates for adenosine triphosphate production during periods of starvation and other types of cellular stress. HMGB1 is a highly conserved nuclear protein that acts as an architectural chromatin-binding factor that bends DNA and promotes protein assembly at specific DNA targets. In addition to its intranuclear role, HMGB1 also functions as an extracellular signaling molecule during inflammation, cell differentiation, cell migration, and tumor metastasis. HMGB1 is released from necrotic cells and secreted by activated macrophages, natural killer cells, and mature dendritic cells, where it mediates the response to infection, injury, and inflammation. In contrast, after DNA damage induced by UV light irradiation or platination, HMGB1 is sequestered in the nucleus, which is classically associated with apoptotic, but not necrotic, cell death. Autophagic stimuli promote translocation of HMGB1 to the cytosol. Classical autophagic stimuli, such as starvation (HBSS) or rapamycin treatment, promote HMGB1 translocation from the nucleus to the cytosol in cultured mouse embryonic fibroblasts (MEFs), human Panc2.03 (Fig. 1 A), and other cell lines. Treatment with rapamycin or starvation induced HMGB1 translocation unaccompanied by measurable lactate dehydrogenase release. This suggests that the HMGB1 translocation, observed during early events with heightened autophagy, is an active process. Furthermore,Endogenous HMGB1 regulates autophagy. High mobility group box 1 (HMGB1) is a chromatin-associated nuclear protein and extracellular damage-associated molecular pattern molecule that regulates autophagy. Stimuli that enhance reactive oxygen species (ROS) promote cytosolic translocation of HMGB1, which enhances autophagic flux. HMGB1 directly interacts with the autophagy protein Beclin1, displacing Bcl-2. Mutation of cysteine 106 (C106) of HMGB1 promotes cytosolic localization and sustained autophagy. The intramolecular disulfide bridge (C23/45) of HMGB1 is required for binding to Beclin1 and sustaining autophagy. Endogenous HMGB1 is a critical pro-autophagic protein that enhances cell survival and limits programmed apoptotic cell death. Autophagy is a major mechanism by which starving cells reallocate nutrients from unnecessary to more essential processes. During autophagy, a cytosolic form of light chain 3 (LC3; LC3-I) is cleaved and then conjugated to phosphatidylethanolamine to form the LC3-phosphatidylethanolamine conjugate (LC3-II), which is recruited to autophagosomal membranes. Autophagy is a process that clears long-lived proteins and dysfunctional organelles and generates substrates for adenosine triphosphate production during periods of starvation and other types of cellular stress. HMGB1 is a highly conserved nuclear protein that acts as an architectural chromatin-binding factor that bends DNA and promotes protein assembly at specific DNA targets. In addition to its intranuclear role, HMGB1 also functions as an extracellular signaling molecule during inflammation, cell differentiation, cell migration, and tumor metastasis. HMGB1 is released from necrotic cells and secreted by activated macrophages, natural killer cells, and mature dendritic cells, where it mediates the response to infection, injury, and inflammation. In contrast, after DNA damage induced by UV light irradiation or platination, HMGB1 is sequestered in the nucleus, which is classically associated with apoptotic, but not necrotic, cell death. Autophagic stimuli promote translocation of HMGB1 to the cytosol. Classical autophagic stimuli, such as starvation (HBSS) or rapamycin treatment, promote HMGB1 translocation from the nucleus to the cytosol in cultured mouse embryonic fibroblasts (MEFs), human Panc2.03 (Fig. 1 A), and other cell lines. Treatment with rapamycin or starvation induced HMGB1 translocation unaccompanied by measurable lactate dehydrogenase release. This suggests that the HMGB1 translocation, observed during early events with heightened autophagy, is an active process. Furthermore,