Regulation of cell proliferation and migration by p62 through stabilization of Twist1

EMT Regulation by Autophagy: A New Perspective in Glioblastoma Biology

Epithelial-to-mesenchymal transition (EMT) and its reverse process MET naturally occur during development and in tissue repair in vertebrates. EMT is also recognized as the crucial event by which cancer cells acquire an invasive phenotype through the activation of specific transcription factors and signalling pathways. Even though glial cells have a mesenchymal phenotype, an EMT-like process tends to exacerbate it during gliomagenesis and progression to more aggressive stages of the disease. Autophagy is an evolutionary conserved degradative process that cells use in order to maintain a proper homeostasis, and defects in autophagy have been associated to several pathologies including cancer. Besides modulating cell resistance or sensitivity to therapy, autophagy also affects the migration and invasion capabilities of tumor cells. Despite this evidence, few papers are present in literature about the involvement of autophagy in EMT-like processes in glioblastoma (GBM) so far. This review summarizes the current understanding of the interplay between autophagy and EMT in cancer, with special regard to GBM model. As the invasive behaviour is a hallmark of GBM aggressiveness, defining a new link between autophagy and EMT can open a novel scenario for targeting these processes in future therapeutical approaches.

FAT4 regulates the EMT and autophagy in colorectal cancer cells in part via the PI3K-AKT signaling axis

BACKGROUND

FAT4 functions as a tumor suppressor, and previous findings have demonstrated that FAT4 can inhibit the epithelial-to-mesenchymal transition (EMT) and the proliferation of gastric cancer cells. However, few studies have investigated the role of FAT4 in the development of colorectal cancer (CRC). The current study aimed to detect the role of FAT4 in the invasion, migration, proliferation and autophagy of CRC and elucidate the probable molecular mechanisms through which FAT4 interacts with these processes.

METHODS

Transwell invasion assays, MTT assays, transmission electron microscopy, immunohistochemistry and western blotting were performed to evaluate the migration, invasion, proliferation and autophagy abilities of CRC cells, and the levels of active molecules involved in PI3K/AKT signaling were examined through a western blotting analysis. In addition, the function of FAT4 in vivo was assessed using a tumor xenograft model.

RESULTS

FAT4 expression in CRC tissues was weaker than that in nonmalignant tissues and could inhibit cell invasion, migration, and proliferation by promoting autophagy in vitro. Furthermore, the regulatory effects of FAT4 on autophagy and the EMT were partially attributed to the PI3K-AKT signaling pathway. The results in vivo also showed that FAT4 modulated CRC tumorigenesis.

CONCLUSION

FAT4 can regulate the activity of PI3K to promote autophagy and inhibit the EMT in part through the PI3K/AKT/mTOR and PI3K/AKT/GSK-3β signaling pathways.

Autophagy and cancer stem cells: molecular mechanisms and therapeutic applications

Autophagy and mitophagy act in cancer as bimodal processes, whose differential functions strictly depend on cancer ontogenesis, progression, and type. For instance, they can act to promote cancer progression by helping cancer cells survive stress or, instead, when mutated or abnormal, to induce carcinogenesis by influencing cell signaling or promoting intracellular toxicity. For this reason, the study of autophagy in cancer is the main focus of many researchers and several clinical trials are already ongoing to manipulate autophagy and by this way determine the outcome of disease therapy. Since the establishment of the cancer stem cell (CSC) theory and the discovery of CSCs in individual cancer types, autophagy and mitophagy have been proposed as key mechanisms in their homeostasis, dismissal or spread, even though we still miss a comprehensive view of how and by which regulatory molecules these two processes drive cell fate. In this review, we will dive into the deep water of autophagy, mitophagy, and CSCs and offer novel viewpoints on possible therapeutic strategies, based on the modulation of these degradative systems.

Proteome profiling of triple negative breast cancer cells overexpressing NOD1 and NOD2 receptors unveils molecular signatures of malignant cell proliferation

Background

Triple negative breast cancer (TNBC) is a malignancy with very poor prognosis, due to its aggressive clinical characteristics and lack of response to receptor-targeted drug therapy. In TNBC, immune-related pathways are typically upregulated and may be associated with a better prognosis of the disease, encouraging the pursuit for immunotherapeutic options. A number of immune-related molecules have already been associated to the onset and progression of breast cancer, including NOD1 and NOD2, innate immune receptors of bacterial-derived components which activate pro-inflammatory and survival pathways. In the context of TNBC, overexpression of either NOD1or NOD2 is shown to reduce cell proliferation and increase clonogenic potential in vitro. To further investigate the pathways linking NOD1 and NOD2 signaling to tumorigenesis in TNBC, we undertook a global proteome profiling of TNBC-derived cells ectopically expressing each one of these NOD receptors.

Results

We have identified a total of 95 and 58 differentially regulated proteins in NOD1- and NOD2-overexpressing cells, respectively. We used bioinformatics analyses to identify enriched molecular signatures aiming to integrate the differentially regulated proteins into functional networks. These analyses suggest that overexpression of both NOD1 and NOD2 may disrupt immune-related pathways, particularly NF-κB and MAPK signaling cascades. Moreover, overexpression of either of these receptors may affect several stress response and protein degradation systems, such as autophagy and the ubiquitin-proteasome complex. Interestingly, the levels of several proteins associated to cellular adhesion and migration were also affected in these NOD-overexpressing cells.

Conclusions

Our proteomic analyses shed new light on the molecular pathways that may be modulating tumorigenesis via NOD1 and NOD2 signaling in TNBC. Up- and downregulation of several proteins associated to inflammation and stress response pathways may promote activation of protein degradation systems, as well as modulate cell-cycle and cellular adhesion proteins. Altogether, these signals seem to be modulating cellular proliferation and migration via NF-κB, PI3K/Akt/mTOR and MAPK signaling pathways. Further investigation of altered proteins in these pathways may provide more insights on relevant targets, possibly enabling the immunomodulation of tumorigenesis in the aggressive TNBC phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5523-6) contains supplementary material, which is available to authorized users.

Autophagy inhibition specifically promotes epithelial-mesenchymal transition and invasion in RAS-mutated cancer cells

Macroautophagy/autophagy inhibition is a novel anticancer therapeutic strategy, especially for tumors driven by mutant RAS. Here, we demonstrate that autophagy inhibition in RAS-mutated cells induces epithelial-mesenchymal transition (EMT), which is associated with enhanced tumor invasion. This is at least partially achieved by triggering the NFKB/NF-κB pathway via SQSTM1/p62. Knockdown of ATG3 or ATG5 increases oncogenic RAS-induced expression of ZEB1 and SNAI2/Snail2, and activates NFKB activity. Depletion of SQSTM1 abolishes the activation of the NFKB pathway induced by autophagy inhibition in RAS-mutated cells. NFKB pathway inhibition by depletion of RELA/p65 blocks this EMT induction. Finally, accumulation of SQSTM1 protein correlates with loss of CDH1/E-cadherin expression in pancreatic adenocarcinoma. Together, we suggest that combining autophagy inhibition with NFKB inhibitors may therefore be necessary to treat RAS-mutated cancer.

Abbreviations: 4-OHT: 4-hydroxytamoxifen; DIC: differential interference contrast; EMT: epithelial-mesenchymal transition; ESR: estrogen receptor; MAPK/ERK: mitogen-activated protein kinase; iBMK: immortalized baby mouse kidney epithelial cells; MET: mesenchymal-epithelial transition; PI3K: phosphoinositide 3-kinase; RNAi: RNA interference; TGFB/TGF-β: transforming growth factor beta; TNF: tumor necrosis factor; TRAF6: TNF receptor associated factor 6.

Control of the Epithelial-to-Mesenchymal Transition and Cancer Metastasis by Autophagy-Dependent SNAI1 Degradation

Autophagy, an intracellular degradation process, is essential for maintaining cell homeostasis by removing damaged organelles and proteins under various conditions of stress. In cancer, autophagy has conflicting functions. It plays a key role in protecting against cancerous transformation by maintaining genomic stability against genotoxic components, leading to cancerous transformation. It can also promote cancer cell survival by supplying minimal amounts of nutrients during cancer progression. However, the molecular mechanisms underlying how autophagy regulates the epithelial-to-mesenchymal transition (EMT) and cancer metastasis are unknown. Here, we show that starvation-induced autophagy promotes Snail (SNAI1) degradation and inhibits EMT and metastasis in cancer cells. Interestingly, SNAI1 proteins were physically associated and colocalized with LC3 and SQSTM1 in cancer cells. We also found a significant decrease in the levels of EMT and metastatic proteins under starvation conditions. Furthermore, ATG7 knockdown inhibited autophagy-induced SNAI1 degradation in the cytoplasm, which was associated with a decrease in SNAI1 nuclear translocation. Moreover, cancer cell invasion and migration were significantly inhibited by starvation-induced autophagy. These findings suggest that autophagy-dependent SNAI1 degradation could specifically regulate EMT and cancer metastasis during tumorigenesis.

Autophagy resists EMT process to maintain retinal pigment epithelium homeostasis

Proliferative vitreoretinopathy (PVR) is the most serious fibrous complication that causes vision loss after intraocular surgery, and there is currently no effective treatment in clinical. Autophagy is an important cell biological mechanism in maintaining the homeostasis of tissues and cells, resisting the process of EMT. However, it is still unclear whether autophagy could resist intraocular fibrosis and prevent PVR progression. In this study, we investigated the expression of mesenchymal biomarkers in autophagy deficiency cells and found these proteins were increased. The mesenchymal protein transcription factor Twist can bind to autophagy related protein p62 and promote the degradation of Twist, which reduced the expression of mesenchymal markers. By constructing an EMT model of retinal pigment epithelial (RPE) cells in vitro, we found that autophagy was activated in the EMT process of RPE cells. Moreover, in autophagy deficient RPE cell line via knockdown autophagy related protein 7 (Atg7), the expression of epithelial marker claudin-1 was suppressed and the mesenchymal markers were increased, accompanied by an increase in cell migration and contractility. Importantly, RPE epithelial properties can be maintained by promoting autophagy and effectively reversing TFG-β2-induced RPE fibrosis. These observations reveal that autophagy may be an effective way to treat PVR.

The role of autophagy in morphogenesis and stem cell maintenance

During embryonic development, cells need to undergo a number of morphological changes that are decisive for the shaping of the embryo's body, initiating organogenesis and differentiation into functional tissues. These remodeling processes are accompanied by profound changes in the cell membrane, the cytoskeleton, organelles, and extracellular matrix composition. While considerably detailed insight into the role of autophagy in stem cells biology has been gained in the recent years, information regarding the participation of autophagy in morphogenetic processes is only sparse. This review, therefore, focuses on the role of autophagy in cell morphogenesis through its regulatory activity in TGFβ signaling, expression of adhesion molecules and cell cycle modification. It also discusses the role of autophagy in stem cell maintenance which is very fundamental for cell renewal and replacement during development, pathogenesis of certain diseases and development of therapies. We are thus addressing here perspectives for further potentially rewarding research topics.

Knockdown of long noncoding RNA urothelial carcinoma associated 1 inhibits colorectal cancer cell proliferation and promotes apoptosis via modulating autophagy

Long noncoding RNA urothelial carcinoma associated 1 (UCA1) has been implicated in the growth and metastasis of colorectal cancer (CRC), and autophagy contributes to tumorigenesis and cancer cell survival. However, the regulatory role of UCA1 in CRC cell viability by modulating autophagy remains unclear. In the present study, a significant positive correlation was observed between UCA1 and microtubule-associated protein 1 light chain 3 (LC3) levels, and the elevated UCA1 was negatively correlated with the PKB/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway in 293T cells. Downregulation of UCA1 inhibited autophagy activation and cell proliferation, whereas the apoptosis was increased and the cell cycle was arrested in G2 stage. The next results showed that UCA1 was markedly upregulated in Caco-2 cells. Knockdown of UCA1 significantly decreased the LC3-II and autophagy-related gene 5 (ATG5) protein levels and resulted in an increase in p62 expression. Conversely, the autophagy activator rapamycin (RAPA) reversed the effects. Furthermore, downregulated UCA1 decreased Caco-2 cells population in the G1 phase and increased the cells number in G2 phage. The cell proliferation was inhibited, and apoptosis rate was promoted. More important, RAPA could also abrogate the changes induced by knockdown of UCA1. Collectively, these data demonstrated that downregulated UCA1 induced autophagy inhibition, resulting in suppressing cell proliferation and promoting apoptosis, which suggested that UCA1 might serve as a potential new oncogene to regulate CRC cells viability by modulating autophagy.

Endothelial cells promote metastasis of prostate cancer by enhancing autophagy

BACKGROUND

Prostate cancer is one of the most common malignancies. Increasing evidence suggested that endothelial cells may contribute to prostate cancer progression and metastasis. Most recently, autophagy has been proposed to plays a significant role in tumorigenesis and metastasis. Also, it is reported that downregulation of androgen receptor (AR) induces autophagy in prostate cancer cells. However, the underlying mechanisms remain unclear. Here, we aim to explore the role and mechanisms of endothelial cell in prostate cancer progression.

METHODS

The coculture system was established to test the effect of endothelial cells on prostate cancer cells. We performed antibody array and ELISA were used to profile the cytokine expression pattern of endothelial cells in supernatant. Western blot and RT-PCR were used to determine the mechanism by endothelial cells to promote invasion ability of prostate cancer cells. Maraviroc and chloroquine were used to block the CCL5/CCR5 and autophagy pathway respectively. Orthotopic xenograft mouse models and drug treatment study were conducted to determine the role of endothelial cells in promoting metastatic potential in vivo.

RESULTS

We use CPRC prostate cancer model and demonstrate that endothelial cells secrete large amount of CCL5 and induces autophagy by suppressing AR expression in prostate cancer cell lines. Consequently, elevated autophagy accelerates focal adhesions proteins disassembly and promoted prostate cancer invasion. Inhibition of both CCL5/CCR5 signaling and autophagy significantly reduces metastasis in vivo.

CONCLUSIONS

Together, our data establish the function for endothelial cells in tumor metastasis and propose new drug target for mCRPC.

Autophagic degradation of SQSTM1 inhibits ovarian cancer motility by decreasing DICER1 and AGO2 to induce MIRLET7A-3P

The relationship between macroautophagy/autophagy and miRNA in regulating cancer cell motility is not clearly delineated. Here, we found that induction of BECN1-dependent or -independent autophagy decreased ubiquitin-binding proteins SQSTM1/p62 and CALCOCO2/NDP52. Downregulation of SQSTM1 (but not CALCOCO2) led to a decrease of the miRNA-processing enzyme DICER1 and the miRNA effector AGO2. The autophagy-mediated reduction of levels of SQSTM1, DICER1 or AGO2 resulted in increased MIRLET7A-3P (but not MIRLET7A-5P or PRE-MIRLET7A miRNA) and suppressed ovarian cancer motility. The investigation of the MIRLET7A effects on cancer cell motility showed that synthetic MIRLET7A-3P (3 nM) inhibited, whereas MIRLET7A-5P (100 nM) increased cancer cell motility. Moreover, downregulation of MIRLET7A-3P with antisense of MIRLET7A-3P miRNA (MIRLET7A-3P inhibitor; 3 nM) reversed the nutrient depletion- and rVP1-mediated suppression of ovarian cancer cell motility. In addition, restoring SQSTM1, DICER1 and AGO2 with inhibition of autophagic degradation or overexpression of DICER1 and AGO2 reversed the autophagy-associated enhancement of MIRLET7A-3P and inhibition of motility. Examination of ovarian cancer tissue microarray further showed that the levels of SQSTM1, DICER1 and AGO2 in the tumor were higher than those in the non-tumor cells and negatively correlated with the levels of autophagy and MIRLET7A-3P. Our results demonstrated that induction of autophagy to decrease SQSTM1, DICER1 and AGO2 and increase MIRLET7A-3P is a potential therapeutic strategy for suppressing ovarian cancer cell motility. Abbreviations: ACTB: actin beta; AGO2: argonaute 2, RISC catalytic component; ATG: autophagy related; BCIP/NBT: 5-bromo-4-chloro-3-indolyl-phosphate/nitro blue tetrazolium; BECN1: beclin 1, autophagy related; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CQ: chloroquine; DICER1: dicer 1, ribonuclease III; EBSS: Earle balanced salt solution; FBS: fetal bovine serum; HGF: hepatocyte growth factor; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MIRLET7A: microRNA LET-7A: MIR16: microRNA 16; MIR29C: microRNA 29C; miRNA: microRNA; MMP: matrix metallopeptidase; PRE-MIRNA: precursor microRNA; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; RISC: RNA-induced silencing complex; rVP1: recombinant foot-and-mouth disease virus capsid protein VP1; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; WIPI: WD repeat domain, phosphoinositide interacting.

TSSC3 promotes autophagy via inactivating the Src-mediated PI3K/Akt/mTOR pathway to suppress tumorigenesis and metastasis in osteosarcoma, and predicts a favorable prognosis

BACKGROUND

Over the last two or three decades, the pace of development of treatments for osteosarcoma tends has been slow. Novel effective therapies for osteosarcoma are still lacking. Previously, we reported that tumor-suppressing STF cDNA 3 (TSSC3) functions as an imprinted tumor suppressor gene in osteosarcoma; however, the underlying mechanism by which TSSC3 suppresses the tumorigenesis and metastasis remain unclear.

METHODS

We investigated the dynamic expression patterns of TSSC3 and autophagy-related proteins (autophagy related 5 (ATG5) and P62) in 33 human benign bone tumors and 58 osteosarcoma tissues using immunohistochemistry. We further investigated the correlations between TSSC3 and autophagy in osteosarcoma using western blotting and transmission electronic microscopy. CCK-8, Edu, and clone formation assays; wound healing and Transwell assays; PCR; immunohistochemistry; immunofluorescence; and western blotting were used to investigated the responses in TSSC3-overexpressing osteosarcoma cell lines, and in xenografts and metastasis in vivo models, with or without autophagy deficiency caused by chloroquine or ATG5 silencing.

RESULTS

We found that ATG5 expression correlated positively with TSSC3 expression in human osteosarcoma tissues. We demonstrated that TSSC3 was an independent prognostic marker for overall survival in osteosarcoma, and positive ATG5 expression associated with positive TSSC3 expression suggested a favorable prognosis for patients. Then, we showed that TSSC3 overexpression enhanced autophagy via inactivating the Src-mediated PI3K/Akt/mTOR pathway in osteosarcoma. Further results suggested autophagy contributed to TSSC3-induced suppression of tumorigenesis and metastasis in osteosarcoma in vitro and in vivo models.

CONCLUSIONS

Our findings highlighted, for the first time, the importance of autophagy as an underlying mechanism in TSSC3-induced antitumor effects in osteosarcoma. We also revealed that TSSC3-associated positive ATG5 expression might be a potential predictor of favorable prognosis in patients with osteosarcoma.

Novel oncogene COPS3 interacts with Beclin1 and Raf-1 to regulate metastasis of osteosarcoma through autophagy

Background

Expression of COP9 signalosome subunit 3 (COPS3), an oncogene overexpressed in osteosarcoma, has been demonstrated to be significantly correlated with tumor metastasis. However, the underlying mechanism by which COPS3 promotes metastasis of osteosarcoma and its role in autophagy remain unknown.

Methods

The expression of COPS3 was detected in primary osteosarcoma tissues and matching lung metastasis tissues by immunohistochemistry (IHC). The effect of COPS3 on the metastasis of osteosarcoma cells was investigated by transwell, wound healing assays and animal studies. Indicated proteins was analyzed by western blotting when COPS3 was knockdown or overexpressed. The COPS3 Interacting protein was determined by immunoprecipitation assay. The relationship between COPS3 and autophagy was detected by western blotting and immunofluorescence.

Results

We found that knockdown of COPS3 significantly reduced the lung metastasis of osteosarcoma cells in a mouse model, coinciding with downregulation of mitogen-activated protein kinase (MEK) and extracellular signal-regulated kinase (ERK) signaling. The silencing of COPS3 also inhibited the epithelial–mesenchymal transition (EMT) through the 90 kDa ribosomal S6 kinases (RSK), a family of signal transduction proteins downstream of MEK/ERK. Reciprocal immunoprecipitation assays revealed that COPS3 directly interacts with Raf-1, an upstream regulator of MEK/ERK. Surprisingly, Beclin1, an important autophagic protein, appeared in the COPS3-immunoprecipitates, along with the autophagic markers LC3-I and LC3-II. Loss of COPS3 completely inhibited H₂O₂-induced autophagic flux and reduced Beclin1 expression. Additionally, autophagy inhibitor or silencing of Beclin1 both decreased cell metastasis.

Conclusions

Taken together, these data reveal a novel function of COPS3 in the regulation of autophagy and highlight the relationship between autophagy and metastasis in osteosarcoma cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0791-6) contains supplementary material, which is available to authorized users.

DRAM1 regulates the migration and invasion of hepatoblastoma cells via autophagy-EMT pathway

DNA-damage regulated autophagy modulator 1 (DRAM1) is known as a target of TP53-mediated autophagy, and has been reported to promote the migration and invasion abilities of glioblastoma stem cells. However, the precise contribution of DRAM1 to cancer cell invasion and migration, and the underlying mechanisms remain unclear. In the present study, small interfering (si)RNA or short hairpin RNA mediated knockdown of DRAM1 was performed in hepatoblastoma cells and the migration and invasion abilities were detected in vitro and in vivo. To investigate the underlying mechanisms, western blotting and immunofluorescence were used to detect the expression of autophagy-associated proteins and epithelial-mesenchymal-transition (EMT)-associated markers. The results showed that DRAM1 knockdown by specific siRNA abrogated cell autophagy, as well as inhibited the migration and invasion of HepG2 cells in Transwell assays, which may be reversed by rapamycin treatment. In addition, DRAM1 knockdown increased the expression of E-Cadherin while decreased the expression of vimentin in HepG2 cells, which was also be reversed by rapamycin treatment. Taken together, these results suggest that DRAM1 is involved in the regulation of the migration and invasion of HepG2 cells via autophagy-EMT pathway.

Mechanisms and context underlying the role of autophagy in cancer metastasis

Macroautophagy/autophagy is a fundamental cellular degradation mechanism that maintains cell homeostasis, regulates cell signaling, and promotes cell survival. Its role in promoting tumor cell survival in stress conditions is well characterized, and makes autophagy an attractive target for cancer therapy. Emerging research indicates that autophagy also influences cancer metastasis, which is the primary cause of cancer-associated mortality. However, data demonstrate that the regulatory role of autophagy in metastasis is multifaceted, and includes both metastasis-suppressing and -promoting functions. The metastasis-suppressing functions of autophagy, in particular, have important implications for autophagy-based treatments, as inhibition of autophagy may increase the risk of metastasis. In this review, we discuss the mechanisms and context underlying the role of autophagy in metastasis, which include autophagy-mediated regulation of focal adhesion dynamics, integrin signaling and trafficking, Rho GTPase-mediated cytoskeleton remodeling, anoikis resistance, extracellular matrix remodeling, epithelial-to-mesenchymal transition signaling, and tumor-stromal cell interactions. Through this, we aim to clarify the context-dependent nature of autophagy-mediated metastasis and provide direction for further research investigating the role of autophagy in cancer metastasis.

p53-Autophagy-Metastasis Link

The tumor suppressor p53 as the “guardian of the genome” plays an essential role in numerous signaling pathways that control the cell cycle, cell death and in maintaining the integrity of the human genome. p53, depending on the intracellular localization, contributes to the regulation of various cell death pathways, including apoptosis, autophagy and necroptosis. Accumulated evidence suggests that this function of p53 is closely involved in the process of cancer development. Here, present knowledge concerning a p53-autophagy-metastasis link, as well as therapeutic approaches that influence this link, are discussed.

The Autophagy Receptor Adaptor p62 is Up-regulated by UVA Radiation in Melanocytes and in Melanoma Cells

UVA (315-400 nm) is the most abundant form of UV radiation in sunlight and indoor tanning beds. However, much remains to be understood about the regulation of the UVA damage response in melanocytes and melanoma. Here, we show that UVA, but not the shorter waveband UVB (280-315 nm), up-regulates adaptor protein p62 in an Nrf2- and reactive oxygen species (ROS)-dependent manner, suggesting a UVA-specific effect on p62 regulation. UVA-induced p62 up-regulation was inhibited by a mitochondria-targeted antioxidant or Nrf2 knockdown. In addition, p62 knockdown inhibited UVA-induced ROS production and Nrf2 up-regulation. We also report here a novel regulatory feedback loop between p62 and PTEN in melanoma cells. PTEN overexpression reduced p62 protein levels, and p62 knockdown increased PTEN protein levels. As compared with normal human skin, p62 was up-regulated in human nevus, malignant melanoma and metastatic melanoma. Furthermore, p62 was up-regulated in melanoma cells relative to normal human epidermal melanocytes, independent of their BRAF or NRAS mutation status. Our results demonstrated that UVA up-regulates p62 and induces a p62-Nrf2 positive feedback loop to counteract oxidative stress. Additionally, p62 forms a feedback loop with PTEN in melanoma cells, suggesting p62 functions as an oncogene in UVA-associated melanoma development and progression.

GABARAPL1 suppresses metastasis by counteracting PI3K/Akt pathway in prostate cancer

Metastasis remains the primary cause of prostate cancer (CaP)-related death. Using a genome wide shRNA screen, we identified GABARAPL1 as a potential CaP metastasis suppressor. GABARAPL1 mRNA levels inversely correlate with the invasive potential of a panel of human CaP cell lines. Lower mRNA levels correlate with higher Gleason scores in clinical CaP tumor samples. Moreover, Kaplan-Meier curves analysis showed that GABARAPL1 down-regulation in cancer tissues is associated with decreased disease-free survival in CaP patients. Knockdown of GABARAPL1 in human LNCaP cells results in increased invasion in vitro and lymph node metastasis in vivo. Vice versa, ectopic expression of GABARAPL1 decreases the invasiveness of CWR22Rv1 cells. Our previous in vitro shRNA screening identified FOXO4, a PI3K/Akt-inactivating downstream target, as a potential CaP metastasis suppressor. We show here that silencing FOXOs leads to reduced GABARAPL1 expression and enhanced invasion in LNCaP cells. Transfection of constitutively-activated Akt (myr-Akt) increased the invasion of LNCaP cells, which is associated with the inactivation of FOXOs and decreased GABARAPL1 expression. Indeed, forced expression of GABARAPL1 reversed the increased invasiveness of LNCaP/myr-Akt cells. Finally, immunohistochemistry analysis shows that Akt phosphorylation is negatively correlated with GABARAPL1 expression in human CaP tissues. Taken together, our data indicate that the suppression of FOXOs-GABARAPL1 signaling by Akt is an important mechanism for CaP progression and metastasis.

Mesenchymal stem cells promote cell invasion and migration and autophagy-induced epithelial-mesenchymal transition in A549 lung adenocarcinoma cells

Mesenchymal stem cells (MSCs) are recruited into the tumour microenvironment and promote tumour growth and metastasis. Tumour microenvironment-induced autophagy is considered to suppress primary tumour formation by impairing migration and invasion. Whether these recruited MSCs regulate tumour autophagy and whether autophagy affects tumour growth are controversial. Our data showed that MSCs promote autophagy activation, reactive oxygen species production, and epithelial-mesenchymal transition (EMT) as well as increased migration and invasion in A549 cells. Decreased expression of E-cadherin and increased expression of vimentin and Snail were observed in A549 cells cocultured with MSCs. Conversely, MSC coculture-mediated autophagy positively promoted tumour EMT. Autophagy inhibition suppressed MSC coculture-mediated EMT and reduced A549 cell migration and invasion slightly. Furthermore, the migratory and invasive abilities of A549 cells were additional increased when autophagy was further enhanced by rapamycin treatment. Taken together, this work suggests that microenvironments containing MSCs can promote autophagy activation for enhancing EMT; MSCs also increase the migratory and invasive abilities of A549 lung adenocarcinoma cells. Mesenchymal stem cell-containing microenvironments and MSC-induced autophagy signalling may be potential targets for blocking lung cancer cell migration and invasion.

Deconvoluting the relationships between autophagy and metastasis for potential cancer therapy

Autophagy is a highly conserved lysosome-dependent degradation process that may digest some long-lived proteins and damaged organelles. As an essential homeostasis maintaining system in normal cells, autophagy plays a key role in several pathological settings, especially cancer. Metastasis, known as a crucial hallmark of cancer progression, is the primary cause of cancer lethality. The role of autophagy in metastasis is quite complex as supportive evidence has indicated both pro-metastatic and anti-metastatic functions of autophagy. Autophagy can inhibit metastasis by restricting necrosis and mediating autophagic cell death, whereas it may also promote metastasis by enhancing cancer cell fitness in response to stress. Moreover, the function of autophagy is context- and stage-dependent. Specifically, during the early steps of metastasis, autophagy mainly serves as a suppressor, while it plays a pro-metastatic role in the later steps. Here, we focus on highlighting the dual roles of autophagy in metastasis and address the molecular mechanisms involved in this process, which may provide a new insight into cancer biology. While, we also summarize several anti-metastatic agents manipulating autophagy, in the hope of shedding light on exploration of potential novel drugs for future cancer therapy.

Autophagy suppresses cell migration by degrading GEF-H1, a RhoA GEF

Cell migration is a process crucial for a variety of biological events, such as morphogenesis and wound healing. Several reports have described the possible regulation of cell migration by autophagy; however, this remains controversial. We here demonstrate that mouse embryonic fibroblasts (MEFs) lacking autophagy protein 5 (Atg5), an essential molecule of autophagy, moved faster than wild-type (WT) MEFs. Similar results were obtained for MEFs lacking Atg7 and unc-51-like kinase 1 (Ulk1), which are molecules required for autophagy. This phenotype was also observed in Atg7-deficient macrophages. WT MEFs moved by mesenchymal-type migration, whereas Atg5 knockout (KO) MEFs moved by amoeba-like migration. This difference was thought to be mediated by the level of RhoA activity, because Atg5 KO MEFs had higher RhoA activity, and treatment with a RhoA inhibitor altered Atg5 KO MEF migration from the amoeba type to the mesenchymal type. Autophagic regulation of RhoA activity was dependent on GEF-H1, a member of the RhoA family of guanine nucleotide exchange factors. In WT MEFs, GEF-H1 directly bound to p62 and was degraded by autophagy, resulting in low RhoA activity. In contrast, the loss of autophagy increased GEF-H1 levels and thereby activated RhoA, which caused cells to move by amoeba-like migration. This amoeba-like migration was cancelled by the silencing of GEF-H1. These results indicate that autophagy plays a role in the regulation of migration by degrading GEF-H1.

Algal oil rich in n-3 polyunsaturated fatty acids suppresses B16F10 melanoma lung metastasis by autophagy induction

Melanoma is a malignant tumor that arises from epidermal melanocytes with high morbidity and mortality, and currently, there are no effective conventional genotoxic treatments or systematic treatment.

Dual role of autophagy in hallmarks of cancer

Evolutionarily conserved across eukaryotic cells, macroautophagy (herein autophagy) is an intracellular catabolic degradative process targeting damaged and superfluous cellular proteins, organelles, and other cytoplasmic components. Mechanistically, it involves formation of double-membrane vesicles called autophagosomes that capture cytosolic cargo and deliver it to lysosomes, wherein the breakdown products are eventually recycled back to the cytoplasm. Dysregulation of autophagy often results in various disease manifestations, including neurodegeneration, microbial infections, and cancer. In the case of cancer, extensive attention has been devoted to understanding the paradoxical roles of autophagy in tumor suppression and tumor promotion. In this review, while we summarize how this self-eating process is implicated at various stages of tumorigenesis, most importantly, we address the link between autophagy and hallmarks of cancer. This would eventually provide a better understanding of tumor dependence on autophagy. We also discuss how therapeutics targeting autophagy can counter various transformations involved in tumorigenesis. Finally, this review will provide a novel insight into the mutational landscapes of autophagy-related genes in several human cancers, using genetic information collected from an array of cancers.

Autophagy acts through TRAF3 and RELB to regulate gene expression via antagonism of SMAD proteins

Macroautophagy can regulate cell signalling and tumorigenesis via elusive molecular mechanisms. We establish a RAS mutant cancer cell model where the autophagy gene ATG5 is dispensable in A549 cells in vitro, yet promotes tumorigenesis in mice. ATG5 represses transcriptional activation by the TGFβ-SMAD gene regulatory pathway. However, autophagy does not terminate cytosolic signal transduction by TGFβ. Instead, we use proteomics to identify selective degradation of the signalling scaffold TRAF3. TRAF3 autophagy is driven by RAS and results in activation of the NF-κB family member RELB. We show that RELB represses TGFβ target promoters independently of DNA binding at NF-κB recognition sequences, instead binding with SMAD family member(s) at SMAD-response elements. Thus, autophagy antagonises TGFβ gene expression. Finally, autophagy-deficient A549 cells regain tumorigenicity upon SMAD4 knockdown. Thus, at least in this setting, a physiologic function for autophagic regulation of gene expression is tumour growth.

Macroautophagy can regulate cell signalling and tumorigenesis but the molecular mechanisms are unclear. Here the authors show selective degradation of the signalling scaffold TRAF3 by autophagy and consequent activation of the NF-κB family member RELB regulate gene expression via antagonism of SMAD proteins.

Regulation of XPC deubiquitination by USP11 in repair of UV-induced DNA damage

Nucleotide excision repair (NER) is the most versatile DNA repair pathway for removing DNA damage caused by UV radiation and many environmental carcinogens. NER is essential for suppressing tumorigenesis in the skin, lungs and brain. Although the core NER proteins have been identified and characterized, molecular regulation of NER remains poorly understood. Here we show that ubiquitin-specific peptidase 11 (USP11) positively regulates NER by deubiquitinating xeroderma pigmentosum complementation group C (XPC) and promoting its retention at the DNA damage sites. In addition, UV irradiation induces both USP11 recruitment to the chromatin and USP11 interaction with XPC in an XPC-ubiquitination-dependent manner. Furthermore, we found that USP11 is down-regulated in chronically UV-exposed mouse skin and in skin tumors from mice and humans. Our findings indicate that USP11 plays an important role in maintaining NER capacity, and suggest that USP11 acts as a tumor suppressor via its role in DNA repair.

p62/SQSTM1 interacts with vimentin to enhance breast cancer metastasis

The signalling adaptor p62 is frequently overexpressed in numerous cancer types. Here, we found that p62 expression was elevated in metastatic breast cancer and its overexpression correlated with reduced metastasis- and relapse-free survival times. Analysis of p62 expression in breast cancer cell lines demonstrated that high p62 expression was associated with the invasive phenotypes of breast cancer. Indeed, silencing p62 expression attenuated the invasive phenotypes of highly metastatic cells, whereas overexpressing p62 promoted the invasion of non-metastatic cells in in vitro microfluidic model. Moreover, MDA-MB-231 cells with p62 depletion which were grown in a three-dimensional culture system exhibited a loss of invasive protrusions. Consistently, genetic ablation of p62 suppressed breast cancer metastasis in both zebrafish embryo and immunodeficient mouse models, as well as decreased tumourigenicity in vivo. To explore the molecular mechanism by which p62 promotes breast cancer invasion, we performed a co-immunoprecipitation–mass spectrometry analysis and revealed that p62 interacted with vimentin, which mediated the function of p62 in promoting breast cancer invasion. Vimentin protein expression was downregulated upon p62 suppression and upregulated with p62 overexpression in breast cancer cells. Linear regression analysis of clinical breast cancer specimens showed a positive correlation between p62 and vimentin protein expression. Together, our findings provide strong evidence that p62 functions as a tumour metastasis promoter by binding vimentin and promoting its expression. This finding might help to develop novel molecular therapeutic strategies for breast cancer metastasis treatment.

GBP3 promotes glioma cell proliferation via SQSTM1/p62-ERK1/2 axis

Guanylate binding proteins (GBPs) are interferon-inducible large GTPases and play a crucial role in cell-autonomous immunity. However, the biology function of GBPs in cancer remains elusive. GBP3 is specifically expressed in adult brain. Here we show that GBP3 is highly elevated in human glioma tumors and glioma cell lines. Overexpression of GBP3 dramatically increased glioma cell proliferation whereas silencing GBP3 by RNA interference produced opposite effects. We further showed that GBP3 expression was able to induce sequestosome-1(SQSTM1, also named p62) expression and activate extracellular signal-regulated kinase (ERK1/2). The SQSTM1-ERK1/2 signaling cascade was essential for GBP3-promoted cell growth because depletion of SQSTM1 markedly reduced the phosphorylated ERK1/2 levels and GBP3-mediated cell growth, and inhibition of mitogen-activated protein kinase/ERK kinase abolished GBP3-induced glioma cell proliferation. Consistently, GBP3 overexpression significantly promoted glioma tumor growth in vivo and its expression was inversely correlated with the survival rate of glioma patients. Taken together, these results for the first time suggest that GBP3 contributes to the proliferation of glioma cells via regulating SQSTM1-ERK1/2 pathway, and GBP3 might represent as a new potential therapeutic target against glioma.

Autophagy Roles in the Modulation of DNA Repair Pathways

Autophagy and DNA repair are biological processes vital for cellular homeostasis maintenance and when dysfunctional, they lead to several human disorders including premature aging, neurodegenerative diseases, and cancer. The interchange between these pathways is complex and it may occur in both directions. Autophagy is activated in response to several DNA lesions types and it can regulate different mechanisms and molecules involved in DNA damage response (DDR), such as cell cycle checkpoints, cell death, and DNA repair. Thus, autophagy may modulate DNA repair pathways, the main focus of this review. In addition to the already well-documented autophagy positive effects on homologous recombination (HR), autophagy has also been implicated with other DNA repair mechanisms, such as base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). Given the relevance of these cellular processes, the clinical applications of drugs targeting this autophagy-DNA repair interface emerge as potential therapeutic strategies for many diseases, especially cancer.

Epidermal SIRT1 regulates inflammation, cell migration, and wound healing

Sirtuins (SIRT1-7) are NAD-dependent proteins with the enzymatic activity of deacetylases and ADP ribosyltransferases. SIRT1 is the proto member of the proteins in the mammalian sirtuin family and plays multiple roles in aging and disease. Using mice with epidermis-specific SIRT1 deletion, we show that SIRT1 is required for efficient wound healing. SIRT1 deficiency in the epidermis inhibited the regeneration of both the epidermis and the dermal stroma. SIRT1 loss altered the production of many cytokines, inhibited the recruitment of macrophages, neutrophils, and mast cells, the recruitment and activation of fibroblasts, and angiogenesis in the granulation tissue. In keratinocytes, SIRT1 knockdown inhibited EMT, cell migration, and TGF-β signaling. For the first time, using skin-specific mouse model, we demonstrate that epidermal SIRT1 plays a crucial role in wound repair. These findings are novel in understanding how wound healing is regulated. Our findings provide in vivo and in vitro evidence that SIRT1 in the epidermis regulates cell migration, redox response, inflammation, epidermis re-epithelialization, granulation formation, and proper wound healing in mice.

A Prognostic Bio-Model Based on SQSTM1 and N-Stage Identifies Nasopharyngeal Carcinoma Patients at High Risk of Metastasis for Additional Induction Chemotherapy

Purpose: Metastasis is one of the most important causes of treatment failure in nasopharyngeal carcinoma (NPC). In T4 or N2-3 patients at high-risk of metastasis, concurrent chemoradiotherapy (CCRT) is inadequate and additional induction chemotherapy (IC) is controversial. There is a critical need to develop a better patient stratification to efficiently identify patients at high-risk of metastasis for additional IC. Recently, Sequestosome 1 (SQSTM1)/p62, an autophagy adaptor protein, was identified as one of the metastasis-related proteins in NPC. However, the mechanism by which SQSTM1 is involved in NPC metastasis was not investigated.Experimental Design: The effect of SQSTM1 on cell migration and invasion was examined in vitro and in vivo SQSTM1 expression was analyzed in clinical NPC samples using IHC. Luciferase reporter analyses were conducted to identify the effects of SQSTM1 on NF-κB transcriptional activity. A prediction bio-model was constructed by Cox analysis. Retrospective and prospective randomized clinical data were adopted to build and test the model, respectively.Results: SQSTM1 mediated epithelial to mesenchymal transition (EMT) through the NF-κB pathway to promote NPC metastasis. Inhibiting SQSTM1 enhanced sensitivity to cisplatin in NPC cells. In NPC patients, high SQSTM1 expression was associated with increased risk of distant metastasis. Furthermore, we propose a prognostic bio-model based on SQSTM1 and N-stage to predict NPC metastasis. Most importantly, our prospective randomized study suggested that IC is beneficial for NPC patients with high metastasis risk.Conclusions: The prognostic bio-model identifies NPC patients at high-risk of metastasis for additional IC. Clin Cancer Res; 24(3); 648-58. ©2017 AACR.

Autophagy attenuates endothelial-to-mesenchymal transition by promoting Snail degradation in human cardiac microvascular endothelial cells

Endothelial-to-mesenchymal transition (EndMT) mainly exists in cardiovascular development and disease progression, and is well known to contribute to cardiac fibrosis. Recent studies indicated that autophagy also participates in the regulation of cardiac fibrosis. However, the precise role of autophagy in cardiac fibrosis and the underlying molecular mechanism remain unclear. The present study aimed to explore the role of autophagy in EndMT, reveal the underlying molecular mechanism, and seek new therapy for cardiac fibrosis. In the present study, we found that EndMT and autophagy were induced simultaneously by hypoxia in human cardiac microvascular endothelial cells (HCMECs). Rapamycin, an autophagy enhancer, attenuated EndMT with promoting angiogenesis, while 3-methyladenine (3-MA) and chloroquine (CQ), agents that inhibit autophagy, accelerated the progression accompanied by the decrease in counts of tube formation under hypoxia conditions. Interestingly, intervening autophagy by rapamycin, 3-MA, or CQ did not affect hypoxia-induced autocrine TGFβ signaling, but changed the expression of Snail protein without alterations in the expression of Snail mRNA. Furthermore, the colocalization of LC3 and Snail indicated that autophagy might mediate Snail degradation under hypoxia conditions in HCMECs. Interaction of p62, the substrate of autophagy, with Snail by co-immunoprecipitation especially in hypoxia-incubated cells confirmed the hypothesis. In conclusion, autophagy serves as a cytoprotective mechanism against EndMT to promote angiogenesis by degrading Snail under hypoxia conditions, suggesting that autophagy targetted therapeutic strategies may be applicable for cardiac fibrosis by EndMT.

LC3-Associated Phagocytosis and Inflammation

LC3-associated phagocytosis (LAP) is a novel form of non-canonical autophagy where LC3 (microtubule-associated protein 1A/1B-light chain 3) is conjugated to phagosome membranes using a portion of the canonical autophagy machinery. The impact of LAP to immune regulation is best characterized in professional phagocytes, in particular macrophages, where LAP has instrumental roles in the clearance of extracellular particles including apoptotic cells and pathogens. Binding of dead cells via receptors present on the macrophage surface results in the translocation of the autophagy machinery to the phagosome and ultimately LC3 conjugation. These events promote a rapid form of phagocytosis that produces an "immunologically silent" clearance of the apoptotic cells. Consequences of LAP deficiency include a decreased capacity to clear dying cells and the establishment of a lupus-like autoimmune disease in mice. The ability of LAP to attenuate autoimmunity likely occurs through the dampening of pro-inflammatory signals upon engulfment of dying cells and prevention of autoantigen presentation to other immune cells. However, it remains unclear how LAP shapes both the activation and outcome of the immune response at the molecular level. Herein, we provide a detailed review of LAP and its known roles in the immune response and provide further speculation on the putative mechanisms by which LAP may regulate immune function, perhaps through the metabolic reprogramming and polarization of macrophages.

Metalloprotease-dependent activation of EGFR modulates CD44+/CD24- populations in triple negative breast cancer cells through the MEK/ERK pathway

PURPOSE

The CD44⁺/CD24^- cell phenotype is enriched in triple negative breast cancers, is associated with tumor invasive properties, and serves as a cell surface marker profile of breast cancer stem-like cells. Activation of Epidermal Growth Factor Receptor (EGFR) promotes the CD44⁺/CD24^- phenotype, but the specific signaling pathway downstream of EGFR responsible for this effect is not clear. The purpose of this study was to determine the role of the MEK/ERK pathway in the expansion of CD44⁺/CD24^- populations in TNBC cells in response to EGFR activation.

METHODS

Representative TNBC cell lines SUM159PT (claudin-low) and SUM149PT (basal) were used to evaluate cell surface expression of CD44 and CD24 by flow cytometry in response to EGFR and MEK inhibition or activation. EGFR and ERK phosphorylation levels were analyzed by Western blotting. The relationship between EGFR phosphorylation and MEK activation score in basal and claudin-low tumors from the TCGA database was examined.

RESULTS

Inhibition of ERK activation with selumetinib, a MEK1/2 inhibitor, blocked EGF-induced expansion of CD44⁺/CD24^- populations. Sustained activation of ERK by overexpression of constitutively active MEK1 was sufficient to expand CD44⁺/CD24^- populations in cells in which EGFR activity was blocked by either erlotinib, an EGFR kinase inhibitor, or BB-94, a metalloprotease inhibitor that prevents generation of soluble EGFR ligands. In basal and claudin-low tumors from the TCGA database, there was a positive correlation between EGFR_pY1068 and MEK activation score in tumors without genomic loss of DUSP4, a negative regulator of ERK, but not in tumors harboring DUSP4 deletion.

CONCLUSION

Our results demonstrate that ERK activation is a key event in EGFR-dependent regulation of CD44⁺/CD24^- populations. Furthermore, our findings highlight the role of ligand-mediated EGFR signaling in the control of MEK/ERK pathway output in TNBC tumors without DUSP4 loss.

Benzo(a)pyrene enhances the EMT-associated migration of lung adenocarcinoma A549 cells by upregulating Twist1

Benzo(a)pyrene (BaP), an important toxic component of cigarette smoke, can cause lung cancer and lead to the progression of lung cancer. In the present study, we investigated the effect of BaP on the migration of lung adenocarcinoma A549 cells. BaP (1 µM) promoted the migration of A549 cells in a time-dependent manner and upregulated the expression of the Twist family BHLH transcription factor 1 (Twist1). BaP also induced upregulation of the mesenchymal markers N-cadherin and vimentin and downregulation of the epithelial marker E-cadherin. When the expression of Twist1 was knocked down in A549 cells that were treated with BaP for 4 weeks (A549BaP-4w), the expression of Twist1 decreased, which inhibited the migration capacity of A549BaP-4w cells, the expression of N-cadherin and vimentin was downregulated and the expression of E-cadherin was upregulated. In addition, morphological observations of A549BaP-4w cells revealed that the epithelial characteristics of A549 cells became mesenchymal characteristics. When the expression of Twist1 was knocked down, the A549BaP-4w cells were transformed back to cells with epithelial characteristics. In conclusion, the results from the present study indicate that BaP enhances the epithelial-mesenchymal transition-associated migration of lung adenocarcinoma A549 cells by upregulating Twist1.

Autophagy as a potential therapeutic target during epithelial to mesenchymal transition in renal cell carcinoma: An in vitro study

Cancer progression toward invasive and metastatic disease is aided by reactivation of epithelial-mesenchymal transition (EMT), involving transdifferentiation of epithelial cells into mesenchymal phenotype. This leads to increased migratory and stem cell-like features in the cells. These EMT cells are more resistant to chemotherapy and it is hypothesized that the phenomenon of autophagy induces resistance, providing a survival strategy for cells. In the present study, we induced EMT-like phenotype in renal carcinoma cells and identified corresponding higher autophagy flux in these cells. The EMT transformed cells may be a representative of the resistant cancer stem cell(CSC)-like phenotype. Autophagy was identified as a potential mechanism of cell survival in these cells thus implying that autophagy inhibition can lead to enhanced cell death. We also observed that tumor cells especially EMT transformed cells, have been 'primed' to undergo autophagy by mTOR inhibition. We observed that combined use of autophagy inhibitor and temsirolimus (TEM) improved antitumor activity against RCC in EMT transformed metastatic cells. One of the approaches for inhibiting autophagy was the use of lysosomotropic anti-malarial drug, chloroquine (CQ) and we explored the therapeutic potential of combination of CQ and the mTOR inhibitor, TEM. EMT transformed cells showed increased cell cytotoxicity when autophagy was impaired by addition CQ with TEM. This led us to conclude that inhibition of autophagy with the current therapeutic regimen could be useful in targeting the EMT transformed cells along with the bulk tumor cells in RCC.

Adaptor protein p62 promotes skin tumor growth and metastasis and is induced by UVA radiation

Skin cancer is the most common cancer, and exposure to ultraviolet (UV) radiation, namely UVA and UVB, is the major risk factor for skin cancer development. UVA is significantly less effective in causing direct DNA damage than UVB, but UVA has been shown to increase skin cancer risk. The mechanism by which UVA contributes to skin cancer remains unclear. Here, using RNA-Seq, we show that UVA induces autophagy and lysosomal gene expression, including the autophagy receptor and substrate p62. We found that UVA activates transcription factor EB (TFEB), a known regulator of autophagy and lysosomal gene expression, which, in turn, induces p62 transcription. Next, we identified a novel relationship between p62 and cyclooxygenase-2 (COX-2), a prostaglandin synthase critical for skin cancer development. COX-2 expression was up-regulated by UVA-induced p62, suggesting that p62 plays a role in UVA-induced skin cancer. Moreover, we found that p62 stabilizes COX-2 protein through the p62 ubiquitin-associated domain and that p62 regulates prostaglandin E₂ production in vitro In a syngeneic squamous cell carcinoma mouse model, p62 knockdown inhibited tumor growth and metastasis. Furthermore, p62-deficient tumors exhibited reduced immune cell infiltration and increased cell differentiation. Because prostaglandin E₂ is known to promote pro-tumorigenic immune cell infiltration, increase proliferation, and inhibit keratinocyte differentiation in vivo, this work suggests that UVA-induced p62 acts through COX-2 to promote skin tumor growth and progression. These findings expand our understanding of UVA-induced skin tumorigenesis and tumor progression and suggest that targeting p62 can help prevent or treat UVA-associated skin cancer.

Autophagy in UV Damage Response

UV radiation exposure from sunlight and artificial tanning beds is the major risk factor for the development of skin cancer and skin photoaging. UV-induced skin damage can trigger a cascade of DNA damage response signaling pathways, including cell cycle arrest, DNA repair and, if damage is irreparable, apoptosis. Compensatory proliferation replaces the apoptotic cells to maintain skin barrier integrity. Disruption of these processes can be exploited to promote carcinogenesis by allowing the survival and proliferation of damaged cells. UV radiation also induces autophagy, a catabolic process that clears unwanted or damaged proteins, lipids and organelles. The mechanisms by which autophagy is activated following UV exposure, and the functions of autophagy in UV response, are only now being clarified. Here, we summarize the current understanding of the mechanisms governing autophagy regulation by UV, the roles of autophagy in regulating cellular response to UV-induced photodamage and the implications of autophagy modulation in the treatment and prevention of photoaging and skin cancer.

Recent insights into the function of autophagy in cancer

In this review, Amaravadi et al. discuss recent developments in the role of autophagy in cancer, in particular how autophagy can promote cancer through suppressing p53 and preventing energy crisis, cell death, senescence, and an anti-tumor immune response.

Macroautophagy (referred to here as autophagy) is induced by starvation to capture and degrade intracellular proteins and organelles in lysosomes, which recycles intracellular components to sustain metabolism and survival. Autophagy also plays a major homeostatic role in controlling protein and organelle quality and quantity. Dysfunctional autophagy contributes to many diseases. In cancer, autophagy can be neutral, tumor-suppressive, or tumor-promoting in different contexts. Large-scale genomic analysis of human cancers indicates that the loss or mutation of core autophagy genes is uncommon, whereas oncogenic events that activate autophagy and lysosomal biogenesis have been identified. Autophagic flux, however, is difficult to measure in human tumor samples, making functional assessment of autophagy problematic in a clinical setting. Autophagy impacts cellular metabolism, the proteome, and organelle numbers and quality, which alter cell functions in diverse ways. Moreover, autophagy influences the interaction between the tumor and the host by promoting stress adaptation and suppressing activation of innate and adaptive immune responses. Additionally, autophagy can promote a cross-talk between the tumor and the stroma, which can support tumor growth, particularly in a nutrient-limited microenvironment. Thus, the role of autophagy in cancer is determined by nutrient availability, microenvironment stress, and the presence of an immune system. Here we discuss recent developments in the role of autophagy in cancer, in particular how autophagy can promote cancer through suppressing p53 and preventing energy crisis, cell death, senescence, and an anti-tumor immune response.

Down-regulated miR-23a Contributes to the Metastasis of Cutaneous Melanoma by Promoting Autophagy

Melanoma is among the most aggressive tumors, and the occurrence of metastasis leads to a precipitous drop in the patients' survival. Therefore, identification of metastasis-associated biomarkers and therapeutic targets will contribute a lot to improving melanoma theranostics. Recently, microRNAs (miRNAs) have been implicated in modulating cancer invasion and metastasis, and are proved as potential non-invasive biomarkers in sera for various tumors. Here, we reported miR-23a as a novel metastasis-associated miRNA that played a remarkable role in modulating melanoma invasive and metastatic capacity and was of great value in predicting melanoma metastasis and prognosis. We found that serum miR-23a level was significantly down-regulated in metastatic melanoma patients and highly correlated with poor clinical outcomes. In addition, miR-23a level was also remarkably decreased in metastatic melanoma tissues and cell lines. Furthermore, overexpressed miR-23a suppressed the invasive and migratory property of melanoma cells by abrogating autophagy through directly targeting ATG12. Specially, miR-23a-ATG12 axis attenuated melanoma invasion and migration through autophagy-mediated AMPK-RhoA pathway. Finally, the overexpression of miR-23a prevented melanoma metastasis in vivo. Taken together, our findings demonstrate that the metastasis-associated miR-23a is not only a potential biomarker, but also a valuable therapeutic target for melanoma.

Mammalian autophagy and the plasma membrane

Autophagy (literally 'self-eating') is an evolutionarily conserved degradation process where cytoplasmic components are engulfed by vesicles called autophagosomes, which are then delivered to lysosomes, where their contents are degraded. Under stress conditions, such as starvation or oxidative stress, autophagy is upregulated in order to degrade macromolecules and restore the nutrient balance. The source of membranes that participate in the initial formation of phagophores is still incompletely understood and many intracellular structures have been shown to act as lipid donors, including the endoplasmic reticulum, Golgi, nucleus, mitochondria and the plasma membrane. Here, we focus on the contributions of the plasma membrane to autophagosome biogenesis governed by ATG16L1 and ATG9A trafficking, and summarize the physiological and pathological implications of this macroautophagy route, from development and stem cell fate to neurodegeneration and cancer.

The Autophagy Machinery: A New Player in Chemotactic Cell Migration

Autophagy is a highly conserved self-degradative process that plays a key role in diverse cellular processes such as stress response or differentiation. A growing body of work highlights the direct involvement of autophagy in cell migration and cancer metastasis. Specifically, autophagy has been shown to be involved in modulating cell adhesion dynamics as well as epithelial-to-mesenchymal transition. After providing a general overview of the mechanisms controlling autophagosome biogenesis and cell migration, we discuss how chemotactic G protein-coupled receptors, through the repression of autophagy, may orchestrate membrane trafficking and compartmentation of specific proteins at the cell front in order to support the critical steps of directional migration.

The role of autophagy in the cross-talk between epithelial-mesenchymal transitioned tumor cells and cancer stem-like cells

Epithelial-mesenchymal transition (EMT) and cancer stem-like cells (CSC) are becoming highly relevant targets in anticancer drug discovery. A large body of evidence suggests that epithelial-mesenchymal transitioned tumor cells (EMT tumor cells) and CSCs have similar functions. There is also an overlap regarding the stimuli that can induce the generation of EMT tumor cells and CSCs. Moreover, direct evidence has been brought that EMT can give rise to CSCs. It is unclear however, whether EMT tumor cells should be considered CSCs or if they have to undergo further changes. In this article we summarize available evidence suggesting that, indeed, additional programs must be engaged and we propose that macroautophagy (hereafter, autophagy) represents a key trait distinguishing CSCs from EMT tumor cells. Thus, CSCs have often been reported to be in an autophagic state and blockade of autophagy inhibits CSCs. On the other hand, there is ample evidence showing that EMT and autophagy are distinct events. CSCs, however, represent, by themselves, a heterogeneous population. Thus, CSCs have been distinguished in predominantly non-cycling and cycling CSCs, the latter representing CSCs that self-renew and replenish the pool of differentiated tumor cells. We now suggest that the non-cycling CSC subpopulation is in an autophagic state. We propose also two models to explain the relationship between EMT tumor cells and these two major CSC subpopulations: a branching model in which EMT tumor cells can give rise to cycling or non-cycling CSCs, respectively, and a hierarchical model in which EMT tumor cells are first induced to become autophagic CSCs and, subsequently, cycling CSCs. Finally, we address the therapeutic consequences of these insights.

Arsenic Induces p62 Expression to Form a Positive Feedback Loop with Nrf2 in Human Epidermal Keratinocytes: Implications for Preventing Arsenic-Induced Skin Cancer

Exposure to inorganic arsenic in contaminated drinking water poses an environmental public health threat for hundreds of millions of people in the US and around the world. Arsenic is a known carcinogen for skin cancer. However, the mechanism by which arsenic induces skin cancer remains poorly understood. Here, we have shown that arsenic induces p62 expression in an autophagy-independent manner in human HaCaT keratinocytes. In mouse skin, chronic arsenic exposure through drinking water increases p62 protein levels in the epidermis. Nrf2 is required for basal and arsenic-induced p62 up-regulation. p62 knockdown reduces arsenic-induced Nrf2 activity, and induces sustained p21 up-regulation. p62 induction is associated with increased proliferation in mouse epidermis. p62 knockdown had little effect on arsenic-induced apoptosis, while it decreased cell proliferation following arsenic treatment. Our findings indicate that arsenic induces p62 expression to regulate the Nrf2 pathway in human keratinocytes and suggest that targeting p62 may help prevent arsenic-induced skin cancer.

Gastrin activates autophagy and increases migration and survival of gastric adenocarcinoma cells

BACKGROUND

The peptide hormone gastrin exerts a growth-promoting effect in both normal and malignant gastrointestinal tissue. Gastrin mediates its effect via the cholecystokinin 2 receptor (CCKBR/CCK2R). Although a substantial part of the gastric adenocarcinomas express gastrin and CCKBR, the role of gastrin in tumor development is not completely understood. Autophagy has been implicated in mechanisms governing cytoprotection, tumor growth, and contributes to chemoresistance. This study explores the role of autophagy in response to gastrin in gastric adenocarcinoma cell lines.

METHODS

Immunoblotting, survival assays and the xCELLigence system were used to study gastrin induced autophagy. Chemical inhibitors of autophagy were utilized to assess the role of this process in the regulation of cellular responses induced by gastrin. Further, knockdown studies using siRNA and immunoblotting were performed to explore the signaling pathways that activate autophagy in response to gastrin treatment.

RESULTS

We demonstrate that gastrin increases the expression of the autophagy markers MAP1LC3B-II and SQSTM1 in gastric adenocarcinoma cells. Gastrin induces autophagy via activation of the STK11-PRKAA2-ULK1 and that this signaling pathway is involved in increased migration and cell survival. Furthermore, gastrin mediated increase in survival of cells treated with cisplatin is partially dependent on induced autophagy.

CONCLUSION

This study reveals a novel role of gastrin in the regulation of autophagy. It also opens up new avenues in the treatment of gastric cancer by targeting CCKBR mediated signaling and/or autophagy in combination with conventional cytostatic drugs.

p62/SQSTM1 enhances breast cancer stem-like properties by stabilizing MYC mRNA

Aberrant p62 overexpression has been implicated in breast cancer development. Here, we found that p62 expression was elevated in breast cancer stem cells (BCSCs), including CD44⁺CD24^- fractions, mammospheres, ALDH1⁺ populations and side population cells. Indeed, short-hairpin RNA (shRNA)-mediated knockdown of p62 impaired breast cancer cells from self-renewing under anchorage-independent conditions, whereas ectopic overexpression of p62 enhanced the self-renewal ability of breast cancer cells in vitro. Genetic depletion of p62 robustly inhibited tumor-initiating frequencies, as well as growth rates of BCSC-derived tumor xenografts in immunodeficient mice. Consistently, immunohistochemical analysis of clinical breast tumor tissues showed that high p62 expression levels were linked to poorer clinical outcome. Further gene expression profiling analysis revealed that p62 was positively correlated with MYC expression level, which mediated the function of p62 in promoting breast cancer stem-like properties. MYC mRNA level was reduced upon p62 deletion by siRNA and increased with p62 overexpression in breast cancer cells, suggesting that p62 positively regulated MYC mRNA. Interestingly, p62 did not transactivate MYC promoter. Instead, p62 delayed the degradation of MYC mRNA by repressing the expression of let-7a and let-7b, thus promoting MYC mRNA stabilization at the post-transcriptional level. Consistently, let-7a and let-7b mimics attenuated p62-mediated MYC mRNA stabilization. Together, these findings unveiled a previously unappreciated role of p62 in the regulation of BCSCs, assigning p62 as a promising therapeutic target for breast cancer treatments.