International Journal of Cell Biology stress and was independent of the MEK1/2-ERK1/2 pathway [59]. 9.1.4. Farnesyltransferase Inhibitors. Farnesylation is a post- translational modiﬁcation of proteins in which farnesyl- transferase catalyzes the attachment of the isoprenoid group from farnesyl pyrophosphate to a cysteine residue at the C-terminus of proteins. The farnesyltransferase inhibitors manumycin A, FTI-276, and lonafarnib (sarasar) induced autophagy in human cancer cell lines [60]. Treatment with a combination of oridonin and manumycin A (a natural product of Streptomyces parvulus) downregulated phospho- rylation of Akt, downstream of PI3K. Oridonin triggers apoptosis of cancer cells and is partially eﬀective through mitochondrial depolarization. Lonafarnib decreased phos- phorylation of mTOR and S6 kinase, which is downstream of mTOR, in a dose-dependent manner. FTI-276 is a CAAX peptidomimetic of the carboxyl terminal of Ras proteins. FTI-276 was identiﬁed as a highly selective suppressor of Ras-dependent oncogenicity, and FTI-276 inhibited Akt phosphorylation. 9.1.5. Golgi-Associated Agents. Brefeldin A inhibits the acti- vation and membrane-binding properties of most ADP- ribosylation factors and causes the redistribution of Golgi proteins into the ER. Brefeldin A leads to dramatic changes in the structure of the Golgi apparatus causing the conversion of the staked cisternae into vesicular/cisternal remnants. Brefeldin A even when acting alone, increases the volume fraction of autophagic vacuoles. The destabilization of the Golgi apparatus by brefeldin A interrupts the intracellular traﬃcking of N-linked glycoproteins along the secretory pathway [61]. Treatment of cells with paclitaxel (taxol) results in polymerization of microtubules. After incubation with paclitaxel, the Golgi apparatus is fragmented and is conspicuously present in areas of the cytoplasm enriched in microtubules. Paclitaxel treatment could lead to the formation of acidic vesicular organelles, the induction of Atg5, Beclin 1, and LC3 expressions, and an increase in punctate ﬂuorescent signals in A549 cells pretransfected with GFP-tagged LC3 [62]. 9.1.6. HDAC Inhibitors. Histone acetylation is mediated by histone acetyltransferases and deacetylases (HDACs), which inﬂuence chromatin dynamics, protein turnover, and the DNA damage response. The HDAC inhibitor SAHA (sub- eroylanilide hydroxamic acid, vorinostat) can induce both caspase-dependent apoptosis and caspase-independent auto- phagic cell death, so it has clear therapeutic implications [63]. SAHA induced autophagy through downregulation of Akt/mTOR signaling and induction of the ER stress response. Moreover, SAHA treatment upregulated expression of Beclin 1 and Atg7 and promoted formation of the Atg5-Atg12 con- jugate [64]. Valproic acid was identiﬁed as a potent selective histone deacetylase inhibitor, which induces autophagy in glioma cells. Valproic acid is capable of producing elevated levels of mitochondrial ROS in glioma cells. ROS production results in autophagosome development and autolysosomal 7 degradation [65]. FK228 (romidepsin) is a unique cyclic peptide and is among the most potent inhibitors of both Class I and II HDACs. FK228 converted LC3-I to LC3-II and induced localization of LC3 to autophagosomes. FK228- mediated autophagy in rhabdomyosarcoma cells coincided with nuclear translocation of AIF, while knockdown of AIF abrogated autophagy following FK228 exposure [66]. 9.1.7. Mitochondrial Agents. An essential trace element, selenite, is preferentially cytotoxic to various human glioma cells over normal astrocytes via autophagic cell death. Before selenite-induced cell death in glioma cells, disruption of the mitochondrial cristae, loss of mitochondrial mem- brane potential, and subsequent entrapment of disorganized mitochondria within autophagosomes or autophagolyso- somes, along with degradation of mitochondrial proteins, were noted, showing that selenite induces autophagy in which mitochondria serve as the main target [7]. The phytoalexin resveratrol (trans-3,5,4 -trihydroxystilbene), a defensive substance produced by plants in response to infection by pathogenic microorganisms, displays a wide range of biological eﬀects in mammalian cells. Resveratrol induced autophagy through any of numerous mechanisms that involve activation of mitochondria, downregulation of cell survival proteins, inhibition of cell survival kinases, and survival transcription factors [67]. 9.1.8. mTOR Inhibitors. Rapamycin (sirolimus) and its ana- logues (such as CCI-779, RAD001, and AP23573) inhibit mTOR (mTORC1), the kinase that normally suppresses both apoptosis and autophagy. Rapamycin activates the autophagic process, and silencing of mTOR with siRNA increases the inhibitory eﬀect of rapamycin on tumor cell viability by stimulating autophagy [68]. Berberine, a small molecule derived from Coptidis rhizome, can induce both autophagy and apoptosis in hepatocellular carcinoma cells. Berberine may also induce autophagic cell death in HepG2 and MHCC97-L cells through activation of Beclin 1 and inhibition of the mTOR-signaling pathway by suppressing the activity of Akt and upregulating p38 MAPK signaling [69]. Treatment with torin1 signiﬁcantly enhanced lysosomal accumulation of mTOR and Raptor. Torin1 inhibits mTOR by directly competing with ATP for binding to the kinase domain. Thus, torin1 inhibits both mTORC1 and mTORC2 [70]. The small molecule Ku-0063794, which inhibits both mTORC1 and mTORC2 with an IC50, induced a much greater dephosphorylation of the mTORC1 substrate 4E- BP1 (eukaryotic initiation factor 4E-binding protein 1) than rapamycin [71]. PM02734 (elisidepsin) causes cell death by a complex mechanism that involves increased autophagosome content, due for the most part to impairment of autophagic ﬂux, inhibition of the Akt/mTOR pathway, and activation of DAPK. This unique mechanism of action justiﬁes the continued development of this agent for the treatment of lung cancer [72]. 9.1.9. Pathogens. Autophagy has recently emerged as an im- portant mechanism for controlling intracellular pathogens.