Paradoxical roles of autophagy in different stages of tumorigenesis: protector for normal or cancer cells

A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy

Autophagy (self-eating) is a conserved cellular degradation process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Autophagy dysfunction can have various pathological consequences, including tumor progression, pathogen hyper-virulence, and neurodegeneration. This review describes the mechanisms of autophagy and its associations with other cell death mechanisms, including apoptosis, necrosis, necroptosis, and autosis. Autophagy has both positive and negative roles in infection, cancer, neural development, metabolism, cardiovascular health, immunity, and iron homeostasis. Genetic defects in autophagy can have pathological consequences, such as static childhood encephalopathy with neurodegeneration in adulthood, Crohn's disease, hereditary spastic paraparesis, Danon disease, X-linked myopathy with excessive autophagy, and sporadic inclusion body myositis. Further studies on the process of autophagy in different microbial infections could help to design and develop novel therapeutic strategies against important pathogenic microbes. This review on the progress and prospects of autophagy research describes various activators and suppressors, which could be used to design novel intervention strategies against numerous diseases and develop therapeutic drugs to protect human and animal health.

Dormancy and cancer stem cells: An enigma for cancer therapeutic targeting

Dormancy occurs when cells remain viable but stop proliferating. When most of a cancer population undergoes this phenomenon, the result is called tumor dormancy, and when a single cancer cell undergoes this process, it is termed quiescence. Cancer stem cells (CSCs) share several overlapping characteristics and signaling pathways with dormant cancer cells, including therapy resistance, and an ability to metastasize and evade the immune system. Cancer cells can be broadly grouped into dormancy-competent CSCs (DCCs), cancer-repopulating cells (CRCs), dormancy-incompetent CSCs and disseminated tumor cells (DTCs). The settings in which cancer cells exploit the dormancy phase to survive and adapt are: (i) primary cancer dormancy; (ii) metastatic dormancy; (iii) therapy-induced dormancy; and (iv) immunologic dormancy. Dormancy, therapy resistance and plasticity of CSCs are fundamentally interconnected processes mediated through mechanisms involving reversible genetic alterations. Niches including metastatic, bone marrow, and perivascular are known to harbor dormant cancer cells. Mechanisms of dormancy induction are complex and multi-factorial and can involve angiogenic switching, addictive oncogene inhibition, immunoediting, anoikis, therapy, autophagy, senescence, epigenetic, and biophysical regulation. Therapy can have opposing effects on cancer cells with respect to dormancy; some therapies can induce dormancy, while others can reactivate dormant cells. There is a lack of consensus relative to the value of therapy-induced dormancy, i.e., some researchers view dormancy induction as a beneficial strategy as it can lead to metastasis inhibition, while others argue that reactivating dormant cancer cells and then eliminating them through therapy are a better approach. More focused investigations of intrinsic cell kinetics and environmental dynamics that promote and maintain cancer cells in a dormant state, and the long-term consequences of dormancy are critical for improving current therapeutic treatment outcomes.

MiRNA-224-5p inhibits autophagy in breast cancer cells via targeting Smad4

BACKGROUND/AIMS

Autophagy is known as a protective intracellular procedure, which can be regulated by several factors. MiRNA has been suggested as a potential element to mediate autophagy pathway in carcinomas. Our study was aim to investigate the role of autophagy in breast cancer cells and identify the involved molecular mechanism METHODS: The expression of LC3I/II, SQSTM1 and Smad4 were detected by western blot. The mRNA level were quantified by real-time PCR. MDC staining was used to directly visualize autophagosome formation. Target Scan 7.2 was used to predict biological targets of miR-224-5p RESULTS: MiR-224 -5p expression was upregulated in metastatic breast cancer and non-metastatic breast cancer cells compare with control. Moreover, miR-224-5p inhibition enhanced cellular autophagy levels in breast cancer cells. MiR-224-5p could suppress Smad4 expression in MDA-MB-231 cells, which indicated that Smad4 was identified as a target of miR-224-5p in breast cancer cells with high metastatic potential CONCLUSIONS: Our study revealed that miR-224-5p inhibited autophagy by targeting Smad4 in MDA-MB-231 cells. The results indicated that miR-224-5p/Smad4 regulating autophagy might be a novel regulatory network contributing to metastasis of breast cancer. MiR-224-5p and Smad4 is involved in breast tumorigenesis, which is possibly a novel target for breast cancer therapy.

Autophagy-independent induction of LC3B through oxidative stress reveals its non-canonical role in anoikis of ovarian cancer cells

Cancer cells display abnormal redox metabolism. Autophagy, anoikis and reactive oxygen species (ROS) play a regulatory role during metastasis. LC3 is a well-known essential molecule for autophagy. Therefore, we wanted to explore the molecular interplay between autophagy, anoikis, and ROS in relation to LC3B. We observed enhanced LC3B level along with increased expression of p62 and modulation of other autophagy-related molecules (Atg 3, 5, 7, 12, 16L1 and Beclin1) by inducing oxidative-stress in ovarian cancer cells using a ROS-producing pro-oxidant molecule. Surprisingly, enhanced LC3B was unable to induce autophagosome formation rather promoted anoikis. ROS-induced inhibition of autophagosome-formation is possibly due to the instability of autophagy initiator, ULK1 complex. Moreover, such upregulation of LC3B via ROS enhanced several apoptotic molecules. Silencing LC3B reduced these apoptotic molecules and increased when overexpressed, suggesting its role in apoptosis. Furthermore, LC3B-dependent apoptosis was decreased by inhibiting ROS, indicating a possible link between ROS, LC3B, and apoptosis. Additionally, ROS-induced enhanced LC3B promoted detachment-induced cell death (anoikis). This was further reflected by reduced cell adhesion molecules (integrin-β3 and focal adhesion kinase) and mesenchymal markers (snail and slug). Our in vitro experimental data was further confirmed in primary tumors developed in syngeneic mice, which also showed ROS-mediated LC3B enhancement along with reduced autophagosomes, integrin-β3 and focal adhesion kinase ultimately leading to the decreased tumor mass. Additionally, primary cells from high-grade serous carcinoma patient's ascites exhibited LC3B enhancement and autophagy inhibition through ROS which provided a clinical relevance of our study. Taken together, this is the first evidence for a non-canonical role of LC3B in promoting anoikis in contrast to autophagy and may, therefore, consider as a potential therapeutic target molecule in ovarian cancer. Taken together, autophagy-inhibition may be an alternative approach to induce apoptosis/anoikis in cancer.

Heme oxygenase-1 induction mediates chemoresistance of breast cancer cells to pharmorubicin by promoting autophagy via PI3K/Akt pathway

Background

Concerns about breast cancer had become the most dangerous cancer to women over the world, more and more anti‐cancer agents are developed to treat this malignancy. Pharmorubicin is a cytotoxic drug, widely used in the treatment of breast cancer, but its role is limited because of chemoresistance produced by cells. This study focused on exploring the influence of autophagy on the resistance of pharmorubicin in breast cancer cells.

Methods

The cell survival of breast cancer cells was detected by MTT. The mRNA expression of heme oxygenase‐1 (HO‐1) was tested by qRT‐PCR. The protein expression of HO‐1, autophagic proteins (LC3‐I,LC3‐II and Beclin‐1), PI3K and Akt was detected by Western blot. Cell autophagy was examined by Cyto‐ID Autophagy Detection Kit.

Results

After being treated with pharmorubicin, the expression of HO‐1 and autophagy related proteins was significantly enhanced, but the cell survival ratio in the two cell lines decreased. After autophagy was inhibited, HO‐1 expression in two cells was down‐regulated. When pharmorubicin‐resistant cells were transfected with si‐HO‐1, the cell survival decreased and the protein expression of HO‐1, autophagic proteins (LC3‐II/LC3‐I and Beclin‐1) as well as autophagy were all down‐regulated, while in pharmorubicin‐resistant cells transfected with pcDNA3.1‐HO‐1, the results were reverse. When the PI3K or Akt was inhibited, PI3K, p‐Akt, HO‐1, autophagic proteins and autophagy were decreased remarkably.

Conclusion

It was proved that HO‐1 induction mediated chemoresistance of pharmorubicin in breast cancer cells by promoting autophagy via PI3K/Akt pathway.

miR-338 modulates proliferation and autophagy by PI3K/AKT/mTOR signaling pathway in cervical cancer

Cervical cancer (CC) is a malignant solid tumor, which is one of the main causes of morbidity and mortality in women. Given that autophagy is an important factor promoting tumor progression, we aim to investigate the functional role of miR-338 in autophagy and proliferation of cervical cancer. In our study, expression of miR-338 was validated by quantitative RT-PCR in 30 paired cervical cancer tissues and normal tissues. We performed MTT, colony formation and cell cycle assay to explore the effect of miR-338 on cell proliferation. The level of autophagy was evaluated by observing the expression of LC3 formation under fluorescence microscope and detected the LC3 expression by western blot. We used luciferase reporter assays to identify the target gene about miR-338. We not only found that the level of miR-338 is decreased in cervical cancer tissues and cells, but also negatively correlated with the protein level of ATF2. In turn, restoring the expression of miR-338 inhibited proliferation in Hela and SiHa cells. Further mechanistic study identified that ATF2 as a direct target of miR-338. Forced lowexpression of miR-338 directly led to increased the level of autophagy in cervical cancer cells, which was similar to the mTOR signaling inhibitor rapamycin. The western blot analysis show that inhibited miR-338 expression could decrease the p-mTOR and p-p70S6 expression. Thus, we infer that miR-338 decreases autophagy level in cervical cancer cells by activating mTOR signaling pathway. In summary, our study demonstrate that miR-338 could inhibites proliferation and autophagy by targeting ATF2 via mTOR signaling pathway on cervical cancer cells. These results suggest a potential application of miR-338 in cervical cancer as a novel mechanism of tumor therapeutic.

Late-stage inhibition of autophagy enhances calreticulin surface exposure

Calreticulin (CRT) exposure on the cell surface is essential for inducing immunogenic cell death by chemotherapy. Recent studies have shown conflicting effects of chemotherapy-induced autophagy on CRT exposure in cancer cells. Our data revealed that surface-exposed CRT (Ecto-CRT) emission was attenuated by inhibition of autophagy at early stages; however, inhibition of autophagy at late stages resulted in increased Ecto-CRT. Furthermore, neither autophagy activation nor endoplasmic reticulum (ER) stress induction alone was sufficient for CRT surface exposure. Moreover, chemotherapeutic agents that only activated autophagy without inducing ER stress could not increase Ecto-CRT; therefore, combined use of an autophagy activator and ER stress inducer could effectively promote CRT translocation to the plasma membrane. Together, our results highlight the potential of the combined use of ER stress inducers and autophagy late-stage inhibitors to reestablish and strengthen both the CRT exposure and immunogenicity of chemotherapeutic agents induced death cells.

Phytochemicals as potent modulators of autophagy for cancer therapy

The dysregulation of autophagy is involved in the pathogenesis of a broad range of diseases, and accordingly universal research efforts have focused on exploring novel compounds with autophagy-modulating properties. While a number of synthetic autophagy modulators have been identified as promising cancer therapy candidates, autophagy-modulating phytochemicals have also attracted attention as potential treatments with minimal side effects. In this review, we firstly highlight the importance of autophagy and its relevance in the pathogenesis and treatment of cancer. Subsequently, we present the data on common phytochemicals and their mechanism of action as autophagy modulators. Finally, we discuss the challenges associated with harnessing the autophagic potential of phytochemicals for cancer therapy.

Auramine O, an incense smoke ingredient, promotes lung cancer malignancy

Burning incense to worship deities is a popular religious ritual in large parts of Asia, and is a popular custom affecting more than 1.5 billion adherents. Due to incomplete combustion, burning incense has been well recognized to generate airborne hazards to human health. However, the correlation between burning incense and lung cancer in epidemiological studies remains controversy. Therefore, we speculated that some unknown materials in incense smoke are involved in the initiation or progression of lung cancer. Based on this hypothesis, we identified a major compound auramine O (AuO) from the water-soluble fraction of incense burned condensate using mass spectrometry. AuO is commonly used in incense manufacture as a colorant. Due to thermostable, AuO released from burned incenses becomes an unexpected air pollutant. AuO is classified as a Group 2B chemical by the International Agency of Research on Cancer (IARC), however, the damage of AuO to the respiratory system remains elusive. Our study revealed that AuO has no apparent effect on malignant transformation; but, it dramatically promotes lung cancer malignancy. AuO accumulates in the nucleus and induces the autophagy activity in lung tumor cells. AuO significantly enhances migration and invasive abilities and the in vitro and in vivo stemness features of lung tumor cells through activating the expression of aldehyde dehydrogenase family 1 member A1 (ALDH1A1), and ALDH1A1 knockdown attenuates AuO-induced autophagy activity and blocks AuO-induced lung tumor malignancy. In conclusion, we found that AuO, an ingredient of incense smoke, significantly increases the metastatic abilities and stemness characters of lung tumor cells through the activation of ALDH1A1, which is known to be associated with poor outcome and progression of lung cancer. For public health, reducing or avoiding the use of AuO in incense is recommended.

Sevoflurane Ameliorates Myocardial Cell Injury by Inducing Autophagy via the Deacetylation of LC3 by SIRT1

Misfolded and aberrant proteins have been found to be associated with myocardial cell injury. Thus, increased clearance of misfolded or aggregated proteins via autophagy might be a potential option in preventing myocardial cell injury. Sevoflurane may ameliorate myocardial cell injury by affecting sirtuin 1- (SIRT1-) mediated autophagy. Rat models with myocardial cell injury were induced by limb ischemia reperfusion. The model rats received different treatments: sevoflurane, nicotinamide, and autophagy inhibitor 3-methyladenine (3-MA). Autophagy was observed by SEM. The levels of SIRT1 and microtubule-associated protein 1A/1B-light chain 3 (LC3) were measured. Present findings demonstrated that limb ischemia reperfusion induced autophagy. Sevoflurane increased the level of SIRT1, which deacetylated LC3 and further increased autophagic rates. On the other hand, the autophagy was inhibited by sevoflurane and or the inhibitors of SIRT1 and LC3. Present results demonstrated a novel molecular mechanism by which sevoflurane induced autophagy by increasing the level of SIRT1 and reducing the acetylation of LC3.

Therapeutic Implications of Autophagy Inducers in Immunological Disorders, Infection, and Cancer

Autophagy is an essential catabolic program that forms part of the stress response and enables cells to break down their own intracellular components within lysosomes for recycling. Accumulating evidence suggests that autophagy plays vital roles in determining pathological outcomes of immune responses and tumorigenesis. Autophagy regulates innate and adaptive immunity affecting the pathologies of infectious, inflammatory, and autoimmune diseases. In cancer, autophagy appears to play distinct roles depending on the context of the malignancy by either promoting or suppressing key determinants of cancer cell survival. This review covers recent developments in the understanding of autophagy and discusses potential therapeutic interventions that may alter the outcomes of certain diseases.

Oxysterols in adipose tissue-derived mesenchymal stem cell proliferation and death

Mesenchymal stem cells (MSCs) are multipotent cells characterized by self-renewal and cellular differentiation capabilities. Oxysterols comprise a very heterogeneous group derived from cholesterol through enzymatic and non-enzymatic oxidation. Potent effects in cell death processes, including cytoxicity and apoptosis induction, were described in several cell lines. Very little is known about the effects of oxysterols in MSCs. 7-ketocholesterol (7-KC), one of the most important oxysterols, was shown to be cytotoxic to human adipose tissue-derived MSCs. Here, we describe the short-term (24h) cytotoxic effects of cholestan-3α-5β-6α-triol, 3,5 cholestan-7-one, (3α-5β-6α)- cholestane-3,6-diol, 7-oxocholest-5-en-3β-yl acetate, and 5β-6β epoxy-cholesterol, on MSCs derived from human adipose tissue. MSCs were isolated from adipose tissue obtained from three young, healthy women. Oxysterols, with the exception of 3,5 cholestan-7-one and 7-oxocholest-5-en-3β-yl acetate, led to a complex mode of cell death that include apoptosis, necrosis and autophagy, depending on the type of oxysterol and concentration, being cholestan-3α-5β-6α-triol the most effective. Inhibition of proliferation was also promoted by these oxysterols, but no changes in cell cycle were observed.

Autophagy inhibition impairs the epithelial-mesenchymal transition and enhances cisplatin sensitivity in nasopharyngeal carcinoma

Drug resistance restricts the efficacy of cisplatin in the treatment of nasopharyngeal carcinoma (NPC). Increasing evidence indicates that autophagy and the epithelial-mesenchymal transition (EMT) participate in cancer progression and drug sensitivity. The aim of the present study was to investigate the function of autophagy and EMT in cisplatin treatment, and to reveal the underlying impact of autophagy on the EMT process in NPC. Transmission electron microscopy assays and western blot analyses confirmed that cisplatin activates autophagy in NPC cells. Alterations in cell morphology and biomolecular markers confirmed that cisplatin induces the EMT phenotype in NPC cells. Cell viability assays showed that the combination of the autophagy inhibitor chloroquine (CQ) increased the cytotoxicity of cisplatin in NPC cells and that the EMT inducer transforming growth factor β1 promoted the resistance to cisplatin in NPC cells. Moreover, autophagy inhibition by CQ and microtubule-associated protein 1 light chain 3B-knockdown reversed the EMT phenotype in NPC cells. In conclusion, autophagy and the EMT process promote cisplatin resistance in NPC cells, while the inhibition of autophagy impairs the EMT process.

Autophagy regulation and its role in gastric cancer and colorectal cancer

BACKGROUND

Autophagy is associated with the occurrence, development, cellular adaptation, progression, treatment and prognosis of gastric cancer (GC) and colorectal cancer (CRC). The effect of autophagy in these two cancers has attracted our attention.

OBJECTIVE

The aim of this study was to describe the functional and regulatory mechanisms associated with autophagy in GC and CRC.

METHODS

We reviewed recent publications describing the role of autophagy in GC and CRC, including the functional characteristics, clinical significance and regulatory mechanisms.

RESULTS

Autophagy plays context-dependent dual roles in the development and progression of GC and CRC. It can either promote tumor growth and cell survival or can contribute to tumor suppression and promote cell death. Both of these effects employ complex regulatory networks, such as those mediated by p53, PI3K/Akt/mTOR, Ras and microRNA. Among the cellular process associated with these pathways, autophagy is a potential target for anti-tumor therapy.

CONCLUSION

Autophagy is associated with both tumorigenic and protective effects in cancer. However, the role of autophagy in GC and CRC remains unclear. Although the translation of the basic science of autophagy into clinical practice is a long process, the modulation of autophagy as a potential therapeutic approach in GC and CRC merits further investigation.

Autophagy-deficient Kupffer cells promote tumorigenesis by enhancing mtROS-NF-κB-IL1α/β-dependent inflammation and fibrosis during the preneoplastic stage of hepatocarcinogenesis

As a cellular degradation mechanism, autophagy exerts crucial and complicated effects on HCC development. Liver non-parenchymal cells, including hepatic resident macrophage Kupffer cells, also play important roles in this process. However, most associated studies have focused on the influence of the autophagy level in hepatic cells and HCC cells, but not liver non-parenchymal cells. Based on our previous study, we confirmed that Atg5 silence in the liver during the preneoplastic stage facilitated liver fibrosis, inflammation and, ultimately, tumorigenesis. We further found that autophagy deficiency promotes the production of inflammatory and fibrogenic factors in macrophages. Moreover, Kupffer cell depletion rescued the tumor-promoting effect of autophagy deficiency during the preneoplastic stage. In autophagy-deficient macrophages, mitochondrial ROS mediated inflammation- and fibrosis-promoting effects by increasing IL1α/β production via enhancing NF-κB-associated pathways. Both blocking of mitochondrial ROS and blocking the IL1 receptor stopped the promotion of fibrosis, inflammation and tumorigenesis resulting from Atg5 knockdown during the preneoplastic stage. In conclusion, autophagy-deficient Kupffer cells promote liver fibrosis, inflammation and, finally, hepatocarcinogenesis during the preneoplastic stage by enhancing mitochondrial ROS- NF-κB-IL1α/β pathways.

Induction of autophagy promotes the growth of early preneoplastic rat liver nodules

Although inhibition of autophagy has been implicated in the onset and progression of cancer cells, it is still unclear whether its dysregulation at early stages of tumorigenesis plays an oncogenic or a tumor suppressor role. To address this question, we employed the Resistant-Hepatocyte rat model to study the very early stages of hepatocellular carcinoma (HCC) development. We detected a different autophagy-related gene expression and changes in the ultrastructural profile comparing the most aggressive preneoplastic lesions, namely those positive for the putative progenitor cell marker cytokeratin-19 (KRT-19) with the negative ones. The ultrastructural and immunohistochemical analyses of KRT-19-positive preneoplastic hepatocytes showed the presence of autophagic vacuoles which was associated with p62, Ambra1 and Beclin1 protein accumulation suggesting that a differential modulation of autophagy occurs at early stages of the oncogenesis in KRT-19-positive vs negative lesions. We observed an overall decrease of the autophagy-related genes transcripts and a strong up-regulation of miR-224 in the KRT-19-positive nodules. Interestingly, the treatment with the autophagy inducer, Amiodarone, caused a marked increase in the proliferation of KRT-19 positive preneoplastic lesions associated with a strong increase of their size; by contrast, Chloroquine, an inhibitor of the autophagic process, led to their reduction. These results show that autophagy modulation is a very early event in hepatocarcinogenesis and is restricted to a hepatocytes subset in the most aggressive preneoplastic lesions. Our findings highlight the induction of autophagy as a permissive condition favouring cancer progression indicating in its inhibition a therapeutic goal to interfere with the development of HCC.

Defective autophagy leads to the suppression of stem-like features of CD271+ osteosarcoma cells

Background

As an important stress-response mechanism, autophagy plays crucial role in the tumor formation and drug resistance of cancer cells including osteosarcoma (OS). OS cancer stem cells (CSCs) also are considered a key factor of tumorigenesis, drug resistance and tumor recurrence. However, the relationship between autophagy and OS CSCs still remains unclear.

Methods

CD271+ OS CSCs and CD271- OS cells were isolated by magnetic activated cell sorting. The autophagy level was evaluated by the mRNA expression of autophagy genes, the protein level of LC3II and p62, and the mean number of GFP-LC3 dot per cell. Lentivirus-delivered specific shRNA was utilized to inhibit the corresponding gene expression. The cell viability was examined with CCK8 assay. The cell proliferation level was detected with BrdU staining assay. Cell death was determined by Annexin V/PI double staining of fluorescence activated cell sorting, lactate dehydrogenase release and caspase-3 activity. Tumorigenicity ability was evaluated by colony and sphere formation assay, the protein expression of stemness markers and tumor formation in nude mice.

Results

Our data indicated that CD271+ OS CSCs had a similar basic autophagy level with CD271- OS cells. Autophagy deficiency had no observable effects on the levels of cell proliferation and death both in CD271+ and CD271- OS cells under normal condition. However, CD271+ OS cells showed a higher autophagy activity than CD271- OS cells under hypoxia and low nutrient (LH) condition. Moreover, autophagy-deficient CD271+ OS cells lost the advantage of tolerance to LH condition compared to CD271- OS cells. Meanwhile, autophagy deficiency enhanced the sensitivity to chemotherapeutics in the CD271+ cells to the comparable level in the CD271- cells. More importantly, deficient-autophagy decreased the protein expression of stemness markers and caused the disappearance of the superiority in tumorigenicity in vitro and vivo in CD271+ OS cells.

Conclusion

The results above demonstrated that autophagy contributes to the stem-like features of CD271+ OS CSCs. Inhibition of autophagy is a promising strategy in the CSCs-targeting OS therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0297-5) contains supplementary material, which is available to authorized users.

miR-224-3p inhibits autophagy in cervical cancer cells by targeting FIP200

Cervical cancer (CC) is a malignant solid tumor, which is one of the main causes of morbidity and mortality in women. Persistent High-risk human papillomavirus (hrHPV) infection is closely related to cervical cancer and autophagy has been suggested to inhibit viral infections. miRNAs have been reported to regulate autophagy in many solid tumors with many studies implicating miR-224-3p in the regulation of autophagy. In this study, we performed a miRNA microarray analysis on CC tissues and found that a large number of miRNAs with differential expressions in hrHPV-infected tissues. We identified miR-224-3p as a candidate miRNA selectively up regulated in HPV-infected tissues and cell lines. Further analysis revealed that miR-224-3p regulates autophagy in cervical cancer tissues and cell lines. While the overexpression of miR-224-3p inhibits autophagy in HPV-infected cells, knocking down endogenous miR-224-3p increases autophagy activity in the same cells. In addition, we found that miR-224-3p directly inhibits the expression of autophagy related gene, FAK family-interacting protein of 200 kDa (FIP200). In summary, we found that miR-224-3p regulates autophagy in hrHPV-induced cervical cancer cells through targeting FIP200 expression.

Poly C binding protein 1 represses autophagy through downregulation of LC3B to promote tumor cell apoptosis in starvation

Accumulating evidences indicate that poly C binding protein (PCBP1) is downregulated in various carcinomas as a tumor suppressor, but the underlying mechanism in suppression of tumorigenesis still remains elusive. Here, we found that PCBP1 overexpression attenuates tumor cell growth upon serum-free starvation. Notably, the autophagic degradation inhibitor, chloroquine, could mimic this suppressive effect in tumor cell growth. Autophagy analyses demonstrated that PCBP1 overexpression blocked autophagic flux of tumor cells under starvation conditions, while PCBP1 downregulation in turn refueled this autophagic flux, protecting cells from death. Mechanistically, PCBP1 overexpression attenuated microtubule-associated protein Light chain 3 (LC3B) mRNA stability to repress LC3B expression, resulting in the autophagy inhibition. Consequently, PCBP1 overexpression strongly triggered the caspase 3 and 8-mediated apoptosis of tumor cells and downregulated anti-apoptotic Bcl-2 expression upon starvation, which could be further synergized by autophagic inhibitor, indicating that PCBP1 not only inhibits tumor cell autophagy, but also renders them to apoptosis. Taken together, our results uncovered a novel mechanism of PCBP1 in repressing autophagy-mediated cell survival and indicated that inhibition of tumor cell autophagy by PCBP1 upregulation or with autophagic inhibitors could be an effective therapeutical strategy to colon and ovary tumors with low PCBP1 expression.

Glutathione-S-transferase omega 1 (GSTO1-1) acts as mediator of signaling pathways involved in aflatoxin B1-induced apoptosis-autophagy crosstalk in macrophages

Aflatoxin B1 (AFB1) is the most toxic aflatoxin species and has been shown to be associated with specific as well as non-specific immune responses. In the present study, using murine macrophage Raw 264.7 cells as a model, we report that short exposure (6h) to AFB1 caused an increase in the cellular calcium pool in mitochondria, which in turn elevated reactive oxygen species (ROS)-mediated oxidative stress and led to loss of mitochondrial membrane potential and ultimately c-Jun N-terminal kinases (JNK)-mediated caspase-dependent cell death. On the contrary, longer exposure (12h) to AFB1 reduced JNK phosphorylation and cell death in macrophages. Measurement of autophagic flux demonstrated that autophagy induction through the canonical pathway was responsible for suppressing AFB1-induced apoptosis after 12h. As a detailed molecular mechanism, we found that the unfolded protein response (UPR) machinery was active at 12h post-exposure to AFB1 and induced cytoprotective autophagy as confirmed by determination of major autophagic markers. Inhibition of autophagy by Beclin-1 siRNA also resulted in JNK-mediated cell death. We further established that glutathione S transferase omega1-1 (GSTO1-1), a specific class of GST, was the responsible factor between apoptosis and autophagy crosstalk. Targeting of GSTO1-1 increased JNK-mediated apoptosis by 2-fold compared to the control, whereas autophagy rate was reduced. Thus, increased expression of GSTO1-1 was associated with increased protein glutathionylation, an important protein modification in response to cellular redox status.

Truncating mutation in the autophagy gene UVRAG confers oncogenic properties and chemosensitivity in colorectal cancers

Autophagy-related factors are implicated in metabolic adaptation and cancer metastasis. However, the role of autophagy factors in cancer progression and their effect in treatment response remain largely elusive. Recent studies have shown that UVRAG, a key autophagic tumour suppressor, is mutated in common human cancers. Here we demonstrate that the cancer-related UVRAG frameshift (FS), which does not result in a null mutation, is expressed as a truncated UVRAG(FS) in colorectal cancer (CRC) with microsatellite instability (MSI), and promotes tumorigenesis. UVRAG(FS) abrogates the normal functions of UVRAG, including autophagy, in a dominant-negative manner. Furthermore, expression of UVRAG(FS) can trigger CRC metastatic spread through Rac1 activation and epithelial-to-mesenchymal transition, independently of autophagy. Interestingly, UVRAG(FS) expression renders cells more sensitive to standard chemotherapy regimen due to a DNA repair defect. These results identify UVRAG as a new MSI target gene and provide a mechanism for UVRAG participation in CRC pathogenesis and treatment response.

Pirarubicin induces an autophagic cytoprotective response through suppression of the mammalian target of rapamycin signaling pathway in human bladder cancer cells

Pirarubicin is widely used in intravesical chemotherapy for bladder cancer, but its efficacy is limited due to drug resistance; the mechanism has not been well studied. Emerging evidence shows that autophagy can be a novel target for cancer therapy. This study aimed to investigate the role of autophagy in pirarubicin-treated bladder cancer cells. Bladder cancer cells EJ and J82 were treated with pirarubicin, siRNA, 3-methyladenine or hydroxychloroquine. Cell proliferation and apoptosis were tested by cell survival assay and flow cytometric analysis, respectively. Autophagy was evaluated by immunoblotting before and after the treatments. The phosphorylated mammalian target of rapamycin, serine/threonine kinase p70 S6 kinase, and eukaryotic translation initiation factor 4E binding protein 1 were also investigated by immunoblotting. We found that pirarubicin could induce autophagy in bladder cancer cells. Inhibition of autophagy by 3-methyladenine, hydroxychloroquine or knockdown of autophagy related gene 3 significantly increased apoptosis in pirarubicin-treated bladder cancer cells. Pirarubicin-induced autophagy was mediated via the mTOR/p70S6K/4E-BP1 signaling pathway. In conclusion, autophagy induced by pirarubicin plays a cytoprotective role in bladder cancer cells, suggesting that inhibition of autophagy may improve efficacy over traditional pirarubicin chemotherapy in bladder cancer patients.

Autophagy promotes the survival and development of tumors by participating in the formation of vasculogenic mimicry

Autophagy, type II nonapoptotic cell death, is characterized by the formation of double-membrane cytosolic vesicles, the recycling of damaged cytoplasmic content and the maintenance of genetic stability and cellular homeostasis, under conditions of nutrient starvation, hypoxia or other therapeutic stress. In the present study, we comprehensively discuss its indispensable role in the formation of vasculogenic mimicry (VM), capillary-like tubes consisting of cells from the tumor itself instead of vascular endothelial cells. A short hairpin RNA (shRNA) to silence beclin1, an autophagy-specific gene, was designed, synthesized and subcloned into a vector to establish an autophagy-inhibited group, while negative control and blank groups were also established using human gastric cancer SGC7901 cells. We then investigated the VM formation ability of these three groups and detected changes in gene expression, survival and invasion correspondingly. The results showed that, following the formation of VM, the expression of pluripotent genes (c-myc, oct3/4, sox-2) and autophagy-specific genes (beclin1, ATG5, ATG7) were increased, which was consistent with the negative control cell group. However, the autophagy inhibited cell group did not form VM, and the expression of pluripotent genes was decreased. Moreover, the inhibition of autophagy reduced the survival and invasive ability of cancer cells under stress. We suggest that during the formation of VM, the stable expression of genes and the maintenance of survival and invasion are indispensable. Under a stress environment, autophagy is activated to maintain the stability of gene expression, maintain survival and invasive ability and facilitate VM formation, which can provide nutrients, oxygen and invasive channels to tumors, facilitating survival and development under stress.

Tetracycline derivative minocycline inhibits autophagy and inflammation in concanavalin-a-activated human hepatoma cells

Inhibition of soluble matrix metalloproteinase (MMP) activity is among the non-antibiotic cellular effects exerted by the anti-inflammatory tetracycline derivative minocycline. The impact of minocycline on the signal transduction functions of membrane-bound MMPs is however unknown. We assessed minocycline in a concanavalin-A (ConA)-activated human HepG2 hepatoma cell model, a condition known to increase the expression of membrane type-1 MMP (MT-MMP) and to trigger inflammatory and autophagy processes. We found that minocycline inhibited ConA-induced formation of autophagic acidic vacuoles, green fluorescent microtubule-associated protein 1 light chain 3 (GFP-LC3) puncta formation, gene and protein expression of autophagy biomarker BCL2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3), invasion biomarker MT1-MMP, and inflammation biomarker cyclooxygenase (COX)-2. Gene silencing of MT1-MMP abrogated ConA-induced formation of autophagic acidic vacuoles and ConA-induced expressions of BNIP3 and COX-2. Minocycline was also shown to inhibit ConA-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation as well as gene expression of NANOS1, a biomarker believed to colocalize with MT1-MMP and the specific silencing of which further inhibited ConA-induced STAT3 phosphorylation. Collectively, our data demonstrate that part of minocycline’s effects on autophagy could be exerted through the inhibition of MT1-MMP signaling functions, which contribute to the autophagy and inflammatory phenotype of ConA-activated HepG2 cells.

Short-term effects of 7-ketocholesterol on human adipose tissue mesenchymal stem cells in vitro

Oxysterols comprise a very heterogeneous group derived from cholesterol through enzymatic and non-enzymatic oxidation. Among them, 7-ketocholesterol (7-KC) is one of the most important. It has potent effects in cell death processes, including cytoxicity and apoptosis induction. Mesenchymal stem cells (MSCs) are multipotent cells characterized by self-renewal and cellular differentiation capabilities. Very little is known about the effects of oxysterols in MSCs. Here, we describe the short-term cytotoxic effect of 7-ketocholesterol on MSCs derived from human adipose tissue. MSCs were isolated from adipose tissue obtained from two young, healthy women. After 24 h incubation with 7-KC, mitochondrial hyperpolarization was observed, followed by a slight increase in the level of apoptosis and changes in actin organization. Finally, the IC50 of 7-KC was higher in these cells than has been observed or described in other normal or cancer cell lines.