ATG4B promotes colorectal cancer growth independent of autophagic flux

Autophagy is reported to suppress tumor proliferation, whereas deficiency of autophagy is associated with tumorigenesis. ATG4B is a deubiquitin-like protease that plays dual roles in the core machinery of autophagy; however, little is known about the role of ATG4B on autophagy and proliferation in tumor cells. In this study, we found that ATG4B knockdown induced autophagic flux and reduced CCND1 expression to inhibit G₁/S phase transition of cell cycle in colorectal cancer cell lines, indicating functional dominance of ATG4B on autophagy inhibition and tumor proliferation in cancer cells. Interestingly, based on the genetic and pharmacological ablation of autophagy, the growth arrest induced by silencing ATG4B was independent of autophagic flux. Moreover, dephosphorylation of MTOR was involved in reduced CCND1 expression and G₁/S phase transition in both cells and xenograft tumors with depletion of ATG4B. Furthermore, ATG4B expression was significantly increased in tumor cells of colorectal cancer patients compared with adjacent normal cells. The elevated expression of ATG4B was highly correlated with CCND1 expression, consistently supporting the notion that ATG4B might contribute to MTOR-CCND1 signaling for G₁/S phase transition in colorectal cancer cells. Thus, we report that ATG4B independently plays a role as a positive regulator on tumor proliferation and a negative regulator on autophagy in colorectal cancer cells. These results suggest that ATG4B is a potential biomarker and drug target for cancer therapy.     

Involvement of autophagy in cardiac remodeling in transgenic mice with cardiac specific over-expression of human programmed cell death 5

Programmed cell death 5 (PDCD5) is a cytosolic protein suppressing growth of multiple types of cancer cells through activating p53. We hypothesized that PDCD5 plays an essential role in cardiac remodeling and function. PDCD5 was significantly up-regulated in the hearts from mice subjected to angiotensin II treatment or transverse aortic constriction. Thus, we generated transgenic mice over-expressing human PDCD5 under the control of alpha myosin heavy chain promoter to examine the role of PDCD5 in cardiac remodeling. Transgenic founder died spontaneously displayed enlarged heart. The high PDCD5 over-expressing line (10-fold) showed reduced survival rate, increase in heart weight normalized to body weight. Real-Time RT-PCR analysis revealed fetal gene program was up-regulated. Echocardiography and histopathological examination showed characteristics of dilated cardiomyopathy and heart failure in transgenic mice. Western blot and immunohistochemistry analysis showed autophagy was dramatically increased in transgenic mice as compared to WT littermates control mice, while apoptosis remained unchanged. The enhanced autophagy in high over-expressing line was associated with significant increase in p53 activity and its downstream target damage-regulated autophagy modulator expression. The low over-expressing line (3.5-fold) appeared normal, but was more susceptible to angiotensin II-induced cardiac hypertrophy. This study is the first providing evidence that PDCD5 plays an important role in cardiac remodeling.     

p73 regulates autophagy and hepatocellular lipid metabolism through a transcriptional activation of the ATG5 gene

p73, a member of the p53 tumor suppressor family, is involved in neurogenesis, sensory pathways, immunity, inflammation, and tumorigenesis. How p73 is able to participate in such a broad spectrum of different biological processes is still largely unknown. Here, we report a novel role of p73 in regulating lipid metabolism by direct transactivation of the promoter of autophagy-related protein 5 (ATG5), a gene whose product is required for autophagosome formation. Following nutrient deprivation, the livers of p73-deficient mice demonstrate a massive accumulation of lipid droplets, together with a low level of autophagy, suggesting that triglyceride hydrolysis into fatty acids is blocked owing to deficient autophagy (macrolipophagy). Compared with wild-type mice, mice functionally deficient in all the p73 isoforms exhibit decreased ATG5 expression and lower levels of autophagy in multiple organs. We further show that the TAp73α is the critical p73 isoform responsible for inducing ATG5 expression in a p53-independent manner and demonstrate that ATG5 gene transfer can correct autophagy and macrolipophagy defects in p73-deficient hepatocytes. These data strongly suggest that the p73–ATG5 axis represents a novel, key pathway for regulating lipid metabolism through autophagy. The identification of p73 as a major regulator of autophagy suggests that it may have an important role in preventing or delaying disease and aging by maintaining a homeostatic control.     

The tumor suppressor gene ARHI (DIRAS3) inhibits ovarian cancer cell migration through multiple mechanisms

ARHI is an imprinted tumor suppressor gene that is downregulated in > 60% of ovarian cancers, associated with decreased progression-free survival. ARHI encodes a 26 kDa GTPase with homology to Ras. Re-expression of ARHI inhibits ovarian cancer growth, initiates autophagy and induces tumor dormancy. Recent studies have demonstrated that ARHI also plays a particularly important role in ovarian cancer cell migration. Re-expression of ARHI decreases motility of IL-6- and EGF-stimulated SKOv3 and Hey ovarian cancer cells, inhibiting both chemotaxis and haptotaxis. ARHI inhibits cell migration by binding and sequestering STAT3 in the cytoplasm, and preventing STAT3 translocation to the nucleus and localization in focal adhesion complexes. Re-expression of ARHI inhibits FAK^Y397 phosphorylation, disrupts focal adhesions and blocks FAK-mediated RhoA signaling, resulting in decreased levels of GTP-RhoA. Re-expression of ARHI disrupts formation of actin stress fibers in a FAK- and RhoA-dependent manner. Recent studies indicate that re-expression of ARHI inhibits expression of β-1 integrin which may also contribute to inhibition of migration, adhesion and invasion.     

Short interfering RNA against the PDCD5 attenuates cell apoptosis and caspase-3 activity induced by Bax overexpression

The programmed cell death 5 (PDCD5) protein plays an important apoptosis-accelerating role in cells undergoing apoptosis. Decreased expression of PDCD5 has been detected in various human carcinomas. Here we describe that one potent short interfering RNA (siRNA) against the PDCD5 (siPDCD5) specifically inhibits the expression of PDCD5 at both the mRNA and protein level. Cells with decreased PDCD5 expression displayed reduced sensitivity to an apoptotic stimulus induced by Bax overexpression in HeLa, HEK293 and 293T cell lines. Furthermore, we also show that siPDCD5 inhibited both caspase-3 activity and procaspase-3 cleavage. Suppressed expression of PDCD5 attenuates the release of cytochrome c from mitochondria to cytosol induced by Bax overexpression. This phenomenon is accompanied by the reduced translocation of Bax from the cytosol to mitochondria. MTT assay shows that targeted suppression of PDCD5 expression markedly promoted cell proliferation in Hela and HEK293 cell lines. Our data suggests that PDCD5 may exert its effects through pathway of mitochondria by modulating Bax translocation, cytochrome c release and caspase 3 activation directly or indirectly, and that decreased PDCD5 expression may be one of the mechanisms by which tumor cells achieve resistance to apoptotic stimulus induced by anticancer drugs.     

Enhanced Arginine Methylation of Programmed Cell Death 4 Protein during Nutrient Deprivation Promotes Tumor Cell Viability

The role of programmed cell death 4 (PDCD4) in tumor biology is context-dependent. PDCD4 is described as a tumor suppressor, but its coexpression with protein arginine methyltransferase 5 (PRMT5) promotes accelerated tumor growth. Here, we report that PDCD4 is methylated during nutrient deprivation. Methylation occurs because of increased stability of PDCD4 protein as well as increased activity of PRMT5 toward PDCD4. During nutrient deprivation, levels of methylated PDCD4 promote cell viability, which is dependent on an enhanced interaction with eIF4A. Upon recovery from nutrient deprivation, levels of methylated PDCD4 are regulated by phosphorylation, which controls both the localization and stability of methylated PDCD4. This study reveals that, in response to particular environmental cues, the role of PDCD4 is up-regulated and is advantageous for cell viability. These findings suggest that the methylated form of PDCD4 promotes tumor viability during nutrient deprivation, ultimately allowing the tumor to grow more aggressively.     

ATG4B promotes colorectal cancer growth independent of autophagic flux

Autophagy is reported to suppress tumor proliferation, whereas deficiency of autophagy is associated with tumorigenesis. ATG4B is a deubiquitin-like protease that plays dual roles in the core machinery of autophagy; however, little is known about the role of ATG4B on autophagy and proliferation in tumor cells. In this study, we found that ATG4B knockdown induced autophagic flux and reduced CCND1 expression to inhibit G₁/S phase transition of cell cycle in colorectal cancer cell lines, indicating functional dominance of ATG4B on autophagy inhibition and tumor proliferation in cancer cells. Interestingly, based on the genetic and pharmacological ablation of autophagy, the growth arrest induced by silencing ATG4B was independent of autophagic flux. Moreover, dephosphorylation of MTOR was involved in reduced CCND1 expression and G₁/S phase transition in both cells and xenograft tumors with depletion of ATG4B. Furthermore, ATG4B expression was significantly increased in tumor cells of colorectal cancer patients compared with adjacent normal cells. The elevated expression of ATG4B was highly correlated with CCND1 expression, consistently supporting the notion that ATG4B might contribute to MTOR-CCND1 signaling for G₁/S phase transition in colorectal cancer cells. Thus, we report that ATG4B independently plays a role as a positive regulator on tumor proliferation and a negative regulator on autophagy in colorectal cancer cells. These results suggest that ATG4B is a potential biomarker and drug target for cancer therapy.     

ATG7(2) Interacts With Metabolic Proteins and Regulates Central Energy Metabolism

Macroautophagy/autophagy is an essential catabolic process that targets a wide variety of cellular components including proteins, organelles, and pathogens. ATG7, a protein involved in the autophagy process, plays a crucial role in maintaining cellular homeostasis and can contribute to the development of diseases such as cancer. ATG7 initiates autophagy by facilitating the lipidation of the ATG8 proteins in the growing autophagosome membrane. The noncanonical isoform ATG7(2) is unable to perform ATG8 lipidation; however, its cellular regulation and function are unknown. Here, we uncovered a distinct regulation and function of ATG7(2) in contrast with ATG7(1), the canonical isoform. First, affinity-purification mass spectrometry analysis revealed that ATG7(2) establishes direct protein–protein interactions (PPIs) with metabolic proteins, whereas ATG7(1) primarily interacts with autophagy machinery proteins. Furthermore, we identified that ATG7(2) mediates a decrease in metabolic activity, highlighting a novel splice-dependent function of this important autophagy protein. Then, we found a divergent expression pattern of ATG7(1) and ATG7(2) across human tissues. Conclusively, our work uncovers the divergent patterns of expression, protein interactions, and function of ATG7(2) in contrast to ATG7(1). These findings suggest a molecular switch between main catabolic processes through isoform-dependent expression of a key autophagy gene.     

Role and regulation of starvation-induced autophagy in the Drosophila fat body

In response to starvation, eukaryotic cells recover nutrients through autophagy, a lysosomal-mediated process of cytoplasmic degradation. Autophagy is known to be inhibited by TOR signaling, but the mechanisms of autophagy regulation and its role in TOR-mediated cell growth are unclear. Here, we show that signaling through TOR and its upstream regulators PI3K and Rheb is necessary and sufficient to suppress starvation-induced autophagy in the Drosophila fat body. In contrast, TOR's downstream effector S6K promotes rather than suppresses autophagy, suggesting S6K downregulation may limit autophagy during extended starvation. Despite the catabolic potential of autophagy, disruption of conserved components of the autophagic machinery, including ATG1 and ATG5, does not restore growth to TOR mutant cells. Instead, inhibition of autophagy enhances TOR mutant phenotypes, including reduced cell size, growth rate, and survival. Thus, in cells lacking TOR, autophagy plays a protective role that is dominant over its potential role as a growth suppressor.     

DIRAS3 regulates the autophagosome initiation complex in dormant ovarian cancer cells

DIRAS3 is an imprinted tumor suppressor gene that is downregulated in 60% of human ovarian cancers. Re-expression of DIRAS3 at physiological levels inhibits proliferation, decreases motility, induces autophagy, and regulates tumor dormancy. Functional inhibition of autophagy with choroquine in dormant xenografts that express DIRAS3 significantly delays tumor regrowth after DIRAS3 levels are reduced, suggesting that autophagy sustains dormant ovarian cancer cells. This study documents a newly discovered role for DIRAS3 in forming the autophagosome initiation complex (AIC) that contains BECN1, PIK3C3, PIK3R4, ATG14, and DIRAS3. Participation of BECN1 in the AIC is inhibited by binding of BECN1 homodimers to BCL2. DIRAS3 binds BECN1, disrupting BECN1 homodimers and displacing BCL2. Binding of DIRAS3 to BECN1 increases the association of BECN1 with PIK3C3 and ATG14, facilitating AIC activation. Amino acid starvation of cells induces DIRAS3 expression, reduces BECN1-BCL2 interaction and promotes autophagy, whereas DIRAS3 depletion blocks amino acid starvation-induced autophagy. In primary ovarian cancers, punctate expression of DIRAS3, BECN1, and the autophagic biomarker MAP1LC3 are highly correlated (P < 0.0001), underlining the clinical relevance of these mechanistic studies. Punctate expression of DIRAS3 and MAP1LC3 was detected in only 21–23% of primary ovarian cancers but in 81–84% of tumor nodules found on the peritoneal surface at second-look operations following primary chemotherapy. This reflects a 4-fold increase (P < 0.0001) in autophagy between primary disease and post-treatment recurrence. We suggest that DIRAS3 not only regulates the AIC, but induces autophagy in dormant, nutrient-deprived ovarian cancer cells that remain after conventional chemotherapy, facilitating their survival.     

ATG12–ATG3 connects basal autophagy and late endosome function

In addition to supporting cell survival in response to starvation or stress, autophagy promotes basal protein and organelle turnover. Compared to our understanding of stress-induced autophagy, little is known about how basal autophagy is regulated and how its activity is coordinated with other cellular processes. We recently identified a novel interaction between the ATG12–ATG3 conjugate and the ESCRT-associated protein PDCD6IP/Alix that promotes basal autophagy and endolysosomal trafficking. Moreover, ATG12–ATG3 is required for diverse PDCD6IP-mediated functions including late endosome distribution, exosome secretion, and viral budding. Our results highlight the importance of late endosomes for basal autophagic flux and reveal distinct roles for the core autophagy proteins ATG12 and ATG3 in controlling late endosome function.     

细胞程序性死亡因子家族分子在细胞凋亡中的调控作用

细胞程序性死亡因子(programmed cell death,PDCD)是一类与肿瘤发展相关并在进化上高度保守的蛋白质。PDCD家族由多个成员构成。其中,研究较为深入的包括PDCD1、PDCD2、PDCD4、PDCD5、PDCD6、PDCD7、PDCD8及PDCD10。PDCD在人类的各组织及细胞中广泛分布,其主要功能是对细胞凋亡的调控。目前研究发现,PDCD家族成员可通过不同信号通路实现对肿瘤细胞活力的调控,且某些家族成员的缺失或过表达都会引起机体发生病变,证明其在多种疾病当中具有重要作用。本文汇总了PDCD1、PDCD2、PDCD4、PDCD5、PDCD6、PDCD7、PDCD8、PDCD9、PDCD10、PDCD11、PDCD12的基因结构与蛋白质结构,介绍了各家族成员在细胞程序性死亡过程中的关系,并总结目前所报道的PDCD家族成员在肿瘤,以及多种疾病中所发挥的调控作用,以期帮助科研工作者了解其在细胞凋亡中的作用,以及为肿瘤和相关疾病发生发展的分子机制提供参考。     

Dual inhibition of autophagy and the AKT pathway in prostate cancer

Genetic inactivation of PTEN through either gene deletion or mutation is common in metastatic prostate cancer, leading to activation of the phosphoinositide 3-kinase (PI3K-AKT) pathway, which is associated with poor clinical outcomes. The PI3K-AKT pathway plays a central role in various cellular processes supporting cell growth and survival of tumor cells. To date, therapeutic approaches to develop inhibitors targeting the PI3K-AKT pathway have failed in both pre-clinical and clinical trials. We showed that a novel AKT inhibitor, AZD5363, inhibits the AKT downstream pathway by reducing p-MTOR and p-RPS6KB/p70S6K. We specifically reported that AZD5363 monotherapy induces G2 growth arrest and autophagy, but fails to induce significant apoptosis in PC-3 and DU145 prostate cancer cell lines. Blocking autophagy using pharmacological inhibitors (3-methyladenine, chloroquine and bafilomycin A₁) or genetic inhibitors (siRNA targeting ATG3 and ATG7) enhances cell death induced by AZD5363 in these prostate cancer cells. Importantly, the combination of AZD5363 with chloroquine significantly reduces tumor volume compared with the control group, and compared with either drug alone in prostate tumor xenograft models. Taken together, these data demonstrate that AKT inhibitor AZD5363, synergizes with the lysosomotropic inhibitor of autophagy, chloroquine, to induce apoptosis and delay tumor progression in prostate cancer models that are resistant to monotherapy, with AZD5363 providing a new therapeutic approach potentially translatable to patients.     

Autophagy promotes resistance to photodynamic therapy-induced apoptosis selectively in colorectal cancer stem-like cells

Recent studies have indicated that cancer stem-like cells (CSCs) exhibit a high resistance to current therapeutic strategies, including photodynamic therapy (PDT), leading to the recurrence and progression of colorectal cancer (CRC). In cancer, autophagy acts as both a tumor suppressor and a tumor promoter. However, the role of autophagy in the resistance of CSCs to PDT has not been reported. In this study, CSCs were isolated from colorectal cancer cells using PROM1/CD133 (prominin 1) expression, which is a surface marker commonly found on stem cells of various tissues. We demonstrated that PpIX-mediated PDT induced the formation of autophagosomes in PROM1/CD133⁺ cells, accompanied by the upregulation of autophagy-related proteins ATG3, ATG5, ATG7, and ATG12. The inhibition of PDT-induced autophagy by pharmacological inhibitors and silencing of the ATG5 gene substantially triggered apoptosis of PROM1/CD133⁺ cells and decreased the ability of colonosphere formation in vitro and tumorigenicity in vivo. In conclusion, our results revealed a protective role played by autophagy against PDT in CSCs and indicated that targeting autophagy could be used to elevate the PDT sensitivity of CSCs. These findings would aid in the development of novel therapeutic approaches for CSC treatment.     

Pdcd4 deficiency enhances macrophage lipoautophagy and attenuates foam cell formation and atherosclerosis in mice

Macrophage foam cells, a major component of the atherosclerotic lesion, have vital roles in the development of atherosclerosis. Lipoautophagy, a type of autophagy characterized by selective delivery of lipid droplet for lysosomal degradation, may impact atherosclerosis by regulating macrophage foam cell formation. Previously, we reported that programmed cell death 4 (PDCD4), a tumor suppressor, negatively regulated autophagy in tumor cells. However, its roles in macrophage lipoautophagy, foam cell formation and atherosclerosis remain to be established. Here we found that Pdcd4 deficiency clearly improved oxidized low-density lipoproteins-impaired autophagy efflux, promoted autophagy-mediated lipid breakdown in murine macrophages and thus prevented macrophage conversion into foam cells. Importantly, Pdcd4 deficiency in mice significantly upregulated macrophage autophagy in local plaques along with attenuated lipid accumulation and atherosclerotic lesions in high-fat-fed Apolipoprotein E knockout mice. Bone marrow transplantation experiment demonstrated that PDCD4-mediated autophagy in hematopoietic cells contributed to the development of atherosclerosis. These results indicate that endogenous PDCD4 promotes for macrophage foam cell formation and atherosclerosis development via inhibiting autophagy and provides new insights into atherogenesis, suggesting that promoting macrophage autophagy through downregulating PDCD4 expression may be beneficial for treating atherosclerosis.Atherosclerosis is a lipid dysfunction-derived chronic inflammatory process in large and medium arterial wall.¹ Macrophage foam cell, as a major component in the lesion of atherosclerosis, has vital role in the development of atherosclerosis. In the initial step of atherosclerotic development, circulating monocytes migrate into arterial wall via dysfunctional endothelial cells and differentiate into macrophages.^{2, 3, 4} The infiltrated macrophages ingest and digest oxidized low-density lipoprotein (ox-LDL), and then transport lipid out of vascular wall.⁵ However, macrophage with overloaded lipids stored in the form of lipid droplets (LDs) will transform into foam cells. Macrophage foam cell formation could promote the development of atherosclerosis.⁶ Thus, decreasing the formation of macrophage foam cell would be an attractive strategy to reverse plaque lipid buildup.⁷The macroautophagy (hereafter referred to as autophagy) is an evolutionarily conserved and well-controlled cellular catabolic process. During the process, cytoplasmic components are sequestered in double-membrane vesicles (which is called autophagosome) and degraded by fusion with lysosomal compartments (autophagolysosome) for recycling application.⁸ The process of autophagy is regulated by several autophagy-related genes (ATGs) encoded proteins, such as ATG5, ATG6 (also known as BECN1), ATG8 (also known as microtubule-associated protein 1 light chain 3, LC3) and ATG12. ATG5 is involved in the early stage of autophagosome formation. ATG5 is conjugated with ATG12 and ATG16L to form ATG12–ATG5–ATG16L complex, which contributes to the elongation and closure of the autophagosomes in the generation of lipidated forms of LC3 family proteins.⁹ Lipoautophagy, a type of autophagy that selectively delivers LDs for lysosomal degradation,¹⁰ regulates lipid metabolism and is involved in the process of atherosclerosis.^{11, 12, 13, 14} In advanced atherosclerosis, macrophage autophagy becomes dysfunctional. However, the basic autophagy deficiency in macrophage by specific Atg5 knockout accelerates atherosclerotic plaques in high-fat-fed ldlr^−/− mice via promoting oxidative stress, plaque necrosis¹² or inflammasome hyperactivation.¹³ More interestingly, autophagy can enhance brokendown of lipid in LD, cholesterol efflux from macrophage foam cells and further inhibit atherogenisis.¹⁴ Stent-based delivery of everolimus (mTOR inhibitor) in atherosclerotic plaques of cholesterol-fed rabbits leads to a marked reduction of macrophages via autophagic cell death.¹⁵ Therefore, regulating the level of macrophage autophagy and macrophage conversion into foam cells would be a potential target for preventing the atherosclerotic plaques formation.¹⁶Programmed cell death 4 (PDCD4), an inhibitor of protein translation, inhibits translation initiation via binding to the translation initiation factor eIF4A or translation elongation by direct or indirectly binding to the coding region of specific RNAs.^{17, 18} Accumulated evidence has demonstrated PDCD4 as a tumor suppressor.¹⁹ PDCD4 can inhibit promotion and progression of tumors, such as lung cancer,²⁰ hepatocellular carcinoma cells,²¹ colon cancer,²² ovarian cancer²³ and glioma.²⁴ In addition, it has been reported that PDCD4 is also involved in the development of inflammatory diseases.^{25, 26, 27, 28, 29, 30} For example, Pdcd4-deficient mice are resistant to experimental allergic encephalitis,²⁵ LPS-induced endotoxin shock²⁶ and type-1 diabetes.²⁷ In addition, Pdcd4-deficient mice are sensitive to LPS/D-galactosamine-induced acute liver injury.²⁸ Recently, we reported that Pdcd4 deficiency attenuated adipocyte foam cells, diet-induced obesity, obesity-associated inflammation and insulin resistance,²⁹ and increased IL-10 expression by macrophages that partly involved in atherosclerosis in hyperlipidemic mice,³⁰ suggesting that PDCD4 may be involved in the metabolism-related diseases. Furthermore, we found that PDCD4 negatively regulated autophagy by inhibiting ATG5 expression in tumor cells.³¹ However, its role in macrophage lipoautophagy and foam formation, and association with atherosclerosis remain to be investigated.In the present study, we found that Pdcd4 deficiency improved ox-LDL-impaired autophagy efflux in murine macrophage and subsequently attenuated macrophage conversion into foam cells in an autophagy-dependent manner and further attenuated the formation of atherosclerotic lesions in hyperlipidemia mice. These results indicate that PDCD4 is critical for macrophage foam cell formation in atherosclerosis development and provides new insights into atherogenesis, and potential therapeutic avenues to treat atherosclerosis-associated diseases.     

Autophagy is a regulator of TRAIL-induced apoptosis in NSCLC A549 cells

Autophagy, a catabolic process by which cytoplasmic components are degraded in lysosomes, plays an important role in the maintenance of cellular homeostasis. Dysregulation of autophagy is associated with several diseases. However, few studies have addressed the role of autophagy in the lung, and its role in lung diseases remains unclear. In the present study, we examined the effect of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on autophagy in A549 cells and explored the underlying mechanisms. We showed that TRAIL promoted autophagosome formation, as detected by the levels of LC3-II, and its effect on promoting autophagy was dependent on the expression of the autophagy related genes (ATGs) Atg5, Atg7, and beclin-1. TRAIL-induced ATG expression was attenuated by JNK silencing or treatment with the JNK inhibitor SP600125, indicating the involvement of the JNK pathway. Crosstalk between autophagy and apoptosis was demonstrated by silencing the autophagy related genes Atg5, Atg7, and beclin-1, and the dependence of TRAIL-induced apoptosis on autophagy-related gene expression. Taken together, our results indicate that TRAIL promotes autophagy in A549 cells via a mechanism involving the modulation of ATG expression through the JNK pathway. Inhibition of autophagy enhanced TRAIL-induced cell proliferative inhibition and apoptosis in A549 cells.