4 Inhibition of autophagy leads in most cases to an increase susceptibility to apoptotic stimuli. Moreover, a growing number of proteins that play a negative regulatory role in both events have been identiﬁed [33]. Autophagy and apoptosis may be triggered by common upstream signals. Recent reports have shown that Akt inhibits apoptosis by phosphorylation of the Bcl-2 protein family member, Bad, allowing for cell survival. In addition, activation of the PI3K/Akt/mTOR pathway can cause inhibitory eﬀects of Akt on apoptosis and mTOR on autophagy and enhance survival capacity in neoplastic cells [34]. In addition, several Atg proteins, including Atg5 and Beclin 1 (Atg6), can be cleaved by calpain or caspases that are activated during apoptosis [35]. Caspase-dependent cleavage of Beclin 1 occurred in HeLa cells treated with a death recep- tor ligand [36]. Chemotherapy-induced apoptosis suppresses autophagy at the execution stage following cytochrome c release, at least in part through caspase 8-mediated cleavage of Beclin 1 at Asp133 and Asp146 [37]. Caspase 3 cleaved Beclin 1 at Asp149 in apoptosis induced by Bax overexpression [38]. Caspase-9 can also cleave Beclin 1, thereby destroying its proautophagic activity [39]. Moreover, the C-terminal fragment of Beclin 1 that results from this cleavage acquires a new function, which can amplify mitochondrion-mediated apoptosis. These ﬁndings provide important insights into the molecular cross-talk between autophagy and apopto- sis. Apoptosis can begin with autophagy, which can end with apoptosis. Some links between the two types of cell death are indicated via mitochondria. Induction of mitochondrial membrane permeabilization at a low level, below the threshold required for induction of apoptosis, results in sequestering damaged mitochondria in autophagic vacuoles. When mitochondrial membrane permeabilization is suﬃciently high to sustain the active execution of cell death, apoptosis is induced [40]. Therefore, it is likely that induction of apoptotic or autophagic cell death may depend on the level of mitochondrial membrane permeabilization. 6. ER and Autophagy ER is an essential intracellular organelle providing apparatus for synthesizing nascent proteins as well as their further modiﬁcation and correct folding, such as the formation of N-linked glycans and disulphide bonds. Disruption of any of these processes, such as with glucose depletion that prevents the proper glycosylation of proteins or with alterations in calcium homeostasis such that calcium-dependent chaper- ones cannot function properly, leads to the accumulation of misfolded proteins that triggers ER stress. ER stress has been implicated in diﬀerent stages of tumor development. The ER has by now been established as an essential site for the regulation of apoptotic pathways and has recently been recognized as an important component of autophagic signaling. ER stress appears to signal autophagy by pathways that all depend on eIF2α (eukaryotic initiation factor 2α). How eIF2α regulates autophagy is presently unknown, but the induction of Atg12 expression via ATF4 (activating transcription factor 4) is likely to participate in this process. International Journal of Cell Biology In cancer cells, when the amount of unfolded or misfolded proteins exceeds the capacity of the proteasome-mediated degradation system, autophagy is triggered to remove these proteins. Bcl-2 has been mainly studied in the context of cell death, but it is also known to carry out other functions in dif- ferent cellular processes, such as cell cycle progression, glu- cose homeostasis, transcriptional repression by p53, and autophagy. Beclin 1 has been identiﬁed as a novel BH3- (Bcl- 2-homology-3-) only protein. Beclin 1 induces autophagy by promoting autophagosome formation when in complex with hVps34 (vacuolar protein sorting 34)/class III PI3K. Beclin 1-Bcl-2 (Bcl-xL) complexes normally inhibit autophagy, which points to organelle-speciﬁc regulation of autophagy [41]. Beclin 1 binding with Bcl-2 has been suggested to interfere with the ability of Beclin 1 to form a complex with hVps34/PI3K, thus resulting in a loss of Beclin 1-associated PI3K autophagy-inducing activity. The interaction between Beclin 1 and Bcl-2 is abolished when key residues within the BH3 domain of Beclin 1 or the BH3-binding groove of Bcl- 2 are mutated. ER-localized Bcl-2, but not mitochondria- localized Bcl-2, has been shown to be important for the inhibition of autophagy [42]. The ER functions to synthesize proteins that store high intracellular calcium that can activate calcium-dependent chaperone proteins that assist in protein folding. The autophagy inhibition by Bcl-2 is evident only when Bcl-2 resides in the ER, where it has been suggested to regulate cellular Ca2+ homeostasis. Ca2+ regulates autophagy via a signaling pathway involving AMPK and mTOR, and ER-located Bcl-2 eﬀectively inhibits this pathway. ER-located Bcl-2 inhibits autophagy induced by Ca2+ mobilizing agents by regulating the Ca2+ homeostasis in a Beclin 1-independent manner [43]. 7. Golgi and Autophagy Eukaryotic cells possess an internal endomembrane system that compartmentalizes the cell for various diﬀerent cellular functions. The main components of this membrane system are the ER, Golgi complex, vesicles, plasma membrane, vacuole/lysosome, and nuclear envelope. Autophagy dis- plays unique membrane dynamics, distinct from classical membrane traﬃcking. The Golgi complex is required for double-membrane cytoplasm to vacuole targeting vesicle and autophagosome formation. A number of Rab GTPases which regulate secretory and endocytic membrane traf- ﬁc have been shown to play either critical or accessory roles in autophagy. Rab33B, a member of the Rab small GTPase family, which was originally described as a Golgi- resident protein involved in Golgi-to-ER transport [44], directly interacts with an autophagosome precursor marker, Atg16L, in a GTP-dependent manner, and the activation and inactivation of Rab33B modulate autophagy. Based on these results, the possible role of the interaction between Rab33B and Atg16L was suggested in autophagosome formation [45]. The autophagosomes are not formed by Golgi-derived vesicles/membranes alone because single- membrane structures, the so-called isolation membranes,