Chaperone-mediated autophagy is required for tumor growth

High-fat diet feeding promotes stemness and precancerous changes in murine gastric mucosa mediated by leptin receptor signaling pathway

Obesity increases the risk for gastric cancers. However, the occurrence and mechanisms of precancerous atrophic gastritis induced by high-fat diet (HFD) remain unclear. Here, we show that HFD-associated lipotoxicity induces precancerous lesions that are accompanied by the disruption of organelle homeostasis, tissue integrity, and deregulated expression of stemness genes in the gastric epithelium mediated by leptin receptor (ObR) signaling. Following HFD feeding, ectopic fat accumulated and expression of LAMP2A in lysosome and COX IV in mitochondria increased in the gastric mucosa. HFD feeding also led to enhanced expression of activated-Notch1 and stem cell markers Lgr5, CD44, and EpCAM. In addition, HFD-fed mice showed intracellular β-catenin accumulation in the gastric mucosa with increased expression of its target genes, Nanog, Oct4, and c-Myc. These observations were abrogated in the leptin-deficient ob/ob mice and ObR-mutated db/db mice, indicating that these HFD-induced changes were responsible for effects downstream of the ObR. Consistent with this, the expression of the Class IA and III PI3Ks was increased following ObR activation in the gastric mucosa of HFD-fed mice. Together, these results suggest that HFD-induced lipotoxicity and deregulated organelle biosynthesis confer cancer stem cell-like properties to the gastric mucosa via signaling pathway mediated by leptin, PI3K and β-catenin.

Up-Regulated Expression of LAMP2 and Autophagy Activity during Neuroendocrine Differentiation of Prostate Cancer LNCaP Cells

Neuroendocrine (NE) prostate cancer (PCa) is a highly aggressive subtype of prostate cancer associated with resistance to androgen ablation therapy. In this study, we used LNCaP prostate cancer cells cultured in a serum-free medium for 6 days as a NE model of prostate cancer. Serum deprivation increased the expression of NE markers such as neuron-specific enolase (NSE) and βIII tubulin (βIII tub) and decreased the expression of the androgen receptor protein in LNCaP cells. Using cDNA microarrays, we compared gene expression profiles of NE cells and non-differentiated LNCaP cells. We identified up-regulation of 155 genes, among them LAMP2, a lysosomal membrane protein involved in lysosomal stability and autophagy. We then confirmed up-regulation of LAMP2 in NE cells by qRT-PCR, Western blot and confocal microscopy assays, showing that mRNA up-regulation correlated with increased levels of LAMP2 protein. Subsequently, we determined autophagy activity in NE cells by assessing the protein levels of SQSTM/p62 and LC3 by Western blot and LC3 and Atg5 mRNAs content by qRT-PCR. The decreased levels of SQSTM/p62 was accompanied by an enhanced expression of LC3 and ATG5, suggesting activation of autophagy in NE cells. Blockage of autophagy with 1μM AKT inhibitor IV, or by silencing Beclin 1 and Atg5, prevented NE cell differentiation, as revealed by decreased levels of the NE markers. In addition, AKT inhibitor IV as well as Beclin1 and Atg5 kwockdown attenuated LAMP2 expression in NE cells. On the other hand, LAMP2 knockdown by siRNA led to a marked blockage of autophagy, prevention of NE differentiation and decrease of cell survival. Taken together, these results suggest that LAMP2 overexpression assists NE differentiation of LNCaP cells induced by serum deprivation and facilitates autophagy activity in order to attain the NE phenotype and cell survival. LAMP2 could thus be a potential biomarker and potential target for NE prostate cancer.

Autophagy in the eye: Development, degeneration, and aging

Autophagy is a catabolic pathway that promotes the degradation and recycling of cellular components. Proteins, lipids, and even whole organelles are engulfed in autophagosomes and delivered to the lysosome for elimination. In response to stress, autophagy mediates the degradation of cell components, which are recycled to generate the nutrients and building blocks required to sustain cellular homeostasis. Moreover, it plays an important role in cellular quality control, particularly in neurons, in which the total burden of altered proteins and damaged organelles cannot be reduced by redistribution to daughter cells through cell division. Research has only begun to examine the role of autophagy in the visual system. The retina, a light-sensitive tissue, detects and transmits electrical impulses through the optic nerve to the visual cortex in the brain. Both the retina and the eye are exposed to a variety of environmental insults and stressors, including genetic mutations and age-associated alterations that impair their function. Here, we review the main studies that have sought to explain autophagy's importance in visual function. We describe the role of autophagy in retinal development and cell differentiation, and discuss the implications of autophagy dysregulation both in physiological aging and in important diseases such as age-associated macular degeneration and glaucoma. We also address the putative role of autophagy in promoting photoreceptor survival and discuss how selective autophagy could provide alternative means of protecting retinal cells. The findings reviewed here underscore the important role of autophagy in maintaining proper retinal function and highlight novel therapeutic approaches for blindness and other diseases of the eye.

Novel pharmacological modulators of autophagy: an updated patent review (2012-2015)

INTRODUCTION

Autophagy is a lysosome-dependent degradation pathway that maintains cellular homeostasis in response to a variety of cellular stresses. Accumulating reports based on animal models have indicated the importance of this catabolic program in many human pathophysiological conditions, including diabetes, neurodegenerative diseases, aging, and cancers. Therefore, autophagy has been highlighted as a novel therapeutic target with a wide range of beneficial effects on human diseases. Here, we review the recent advances of our knowledge toward autophagy, as well as the efforts for developing autophagy modulators. Areas covered: The relevant patents (published at 2012-2015) and the research literature claiming the pharmacological modulation of autophagy are reviewed. Also, their molecular mechanisms and potential therapeutic utilities are discussed. Expert opinion: Considering the molecular machinery involved in autophagy induction, the targeting of autophagy-specific protein is very important to design the therapeutic interventions for specifically treating a variety of autophagy-associated disorders. Many patents and the research literature described in this review have shown promising applications of the relevant autophagy modulators for cancer or neurodegeneration treatments, a few of which are already being considered for clinical evaluation. However, most patents have claimed the modulators of autophagy with little information regarding their mechanisms of action. To design highly potent therapeutics, further work, such as developing compounds that specifically target the autophagy-specific machinery, are required.

Applications of phototransformable fluorescent proteins for tracking the dynamics of cellular components

In the past few decades, fluorescent proteins have revolutionized the field of cell biology. Phototransformable fluorescent proteins are capable of changing their excitation and emission spectra after being exposed to specific wavelength(s) of light. The majority of phototransformable fluorescent proteins have originated from marine organisms. Genetic engineering of these proteins has made available many choices for different colors, modes of conversion, and other biophysical properties. Their phototransformative property has allowed the highlighting and tracking of subpopulations of cells, organelles, and proteins in living systems. Furthermore, phototransformable fluorescent proteins have offered new methods for superresolution fluorescence microscopy and optogenetics manipulation of proteins. One of the major advantages of phototransformable fluorescent proteins is their applicability for visualizing newly synthesized proteins that are en route to their final destinations. In this paper, we will discuss the biological applications of phototransformable fluorescent proteins with special emphasis on the application of tracking membrane proteins in vertebrate photoreceptor cells.

Chaperone-mediated autophagy prevents apoptosis by degrading BBC3/PUMA

Autophagy is a potentially inimical pathway and together with apoptosis, may be activated by similar stress stimuli that can lead to cell death. The molecular cues that dictate the cell fate choice between autophagy and apoptosis remain largely unknown. Here we report that the proapoptotic protein BBC3/PUMA (BCL2 binding component 3) is a bona fide substrate of chaperone-mediated autophagy (CMA). BBC3 associates with HSPA8/HSC70 (heat shock 70kDa protein 8), leading to its lysosome translocation and uptake. Inhibition of CMA results in stabilization of BBC3, which in turn sensitizes tumor cells to undergo apoptosis. We further demonstrate that upon TNF (tumor necrosis factor) treatment, IKBKB/IKKβ (inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase β)-mediated BBC3 Ser10 phosphorylation is crucial for BBC3 stabilization via blocking its degradation by CMA. Mechanistically, Ser10 phosphorylation facilitates BBC3 translocation from the cytosol to mitochondria. BBC3 stabilization resulting from either Ser10 phosphorylation or CMA inhibition potentiates TNF-induced apoptotic cell death. Our findings thus reveal that the selective degradation of BBC3 underlies the prosurvival role of CMA and define a previously unappreciated proapoptotic role of IKBKB that acts through phosphorylation-mediated stabilization of BBC3, thereby promoting TNF-triggered apoptosis.

Chaperone-mediated autophagy prevents apoptosis by degrading BBC3/PUMA

Autophagy is a potentially inimical pathway and together with apoptosis, may be activated by similar stress stimuli that can lead to cell death. The molecular cues that dictate the cell fate choice between autophagy and apoptosis remain largely unknown. Here we report that the proapoptotic protein BBC3/PUMA (BCL2 binding component 3) is a bona fide substrate of chaperone-mediated autophagy (CMA). BBC3 associates with HSPA8/HSC70 (heat shock 70kDa protein 8), leading to its lysosome translocation and uptake. Inhibition of CMA results in stabilization of BBC3, which in turn sensitizes tumor cells to undergo apoptosis. We further demonstrate that upon TNF (tumor necrosis factor) treatment, IKBKB/IKKβ (inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase β)-mediated BBC3 Ser10 phosphorylation is crucial for BBC3 stabilization via blocking its degradation by CMA. Mechanistically, Ser10 phosphorylation facilitates BBC3 translocation from the cytosol to mitochondria. BBC3 stabilization resulting from either Ser10 phosphorylation or CMA inhibition potentiates TNF-induced apoptotic cell death. Our findings thus reveal that the selective degradation of BBC3 underlies the prosurvival role of CMA and define a previously unappreciated proapoptotic role of IKBKB that acts through phosphorylation-mediated stabilization of BBC3, thereby promoting TNF-triggered apoptosis.

Autophagy in renal diseases

Autophagy is the cell biology process in which cytoplasmic components are degraded in lysosomes to maintain cellular homeostasis and energy production. In the healthy kidney, autophagy plays an important role in the homeostasis and viability of renal cells such as podocytes and tubular epithelial cells and of immune cells. Recently, evidence is mounting that (dys)regulation of autophagy is implicated in the pathogenesis of various renal diseases, and might be an attractive target for new renoprotective therapies. In this review, we provide an overview of the role of autophagy in kidney physiology and kidney diseases.

Role of chaperone-mediated autophagy in metabolism

Different types of autophagy coexist in most mammalian cells, and each of them fulfills very specific tasks in intracellular degradation. Some of these autophagic pathways contribute to cellular metabolism by directly hydrolyzing intracellular lipid stores and glycogen. Chaperone-mediated autophagy (CMA), in contrast, is a selective form of autophagy that can only target proteins for lysosomal degradation. Consequently, it was expected that the only possible contribution of this pathway to cellular metabolism would be by providing free amino acids resulting from protein breakdown. However, recent studies have demonstrated that disturbance in CMA leads to important alterations in glucose and lipid metabolism and in overall organism energetics. Here, we describe the unique mechanisms by which CMA contributes to the regulation of cellular metabolism and discuss the possible implications of these previously unknown functions of CMA for the pathogenesis of common metabolic diseases.

Regulation of Liver Metabolism by Autophagy

Intracellular components must be recycled for cells to maintain energy and ensure quality control of proteins and organelles. Autophagy is a highly conserved recycling process that involves degradation of cellular constituents in lysosomes. Although autophagy regulates a number of cell functions, it was first found to maintain energy balance in liver cells. As our understanding of autophagy has increased, we have found its connections to energy regulation in liver cells to be tight and complex. We review 3 mechanisms by which hepatic autophagy monitors and regulates cellular metabolism. Autophagy provides essential components (amino acids, lipids, and carbohydrates) required to meet the cell's energy needs, and it also regulates energy supply by controlling the number, quality, and dynamics of the mitochondria. Finally, autophagy also modulates levels of enzymes in metabolic pathways. In light of the multiple ways in which autophagy participates to control liver metabolism, it is no surprise that dysregulation of autophagy has been associated with metabolic diseases such as obesity, diabetes, or metabolic syndrome, as well as liver-specific disorders such as fatty liver, nonalcoholic steatohepatitis, and hepatocellular carcinoma. We discuss some of these connections and how hepatic autophagy might serve as a therapeutic target in common metabolic disorders.

Regulation of cell proliferation by hypoxia-inducible factors

Hypoxia is a physiological cue that impacts diverse physiological processes, including energy metabolism, autophagy, cell motility, angiogenesis, and erythropoiesis. One of the key cell-autonomous effects of hypoxia is as a modulator of cell proliferation. For most cell types, hypoxia induces decreased cell proliferation, since an increased number of cells, with a consequent increase in O2 demand, would only exacerbate hypoxic stress. However, certain cell populations maintain cell proliferation in the face of hypoxia. This is a common pathological hallmark of cancers, but can also serve a physiological function, as in the maintenance of stem cell populations that reside in a hypoxic niche. This review will discuss major molecular mechanisms by which hypoxia regulates cell proliferation in different cell populations, with a particular focus on the role of hypoxia-inducible factors.

Chaperone-mediated autophagy: roles in neuroprotection

Chaperone-mediated autophagy (CMA), one of the main pathways of lysosomal proteolysis, is characterized by the selective targeting and direct translocation into the lysosomal lumen of substrate proteins containing a targeting motif biochemically related to the pentapeptide KFERQ. Along with the other two lysosomal pathways, macro- and micro-autophagy, CMA is essential for maintaining cellular homeostasis and survival by selectively degrading misfolded, oxidized, or damaged cytosolic proteins. CMA plays an important role in pathologies such as cancer, kidney disorders, and neurodegenerative diseases. Neurons are post-mitotic and highly susceptible to dysfunction of cellular quality-control systems. Maintaining a balance between protein synthesis and degradation is critical for neuronal functions and homeostasis. Recent studies have revealed several new mechanisms by which CMA protects neurons through regulating factors critical for their viability and homeostasis. In the current review, we summarize recent advances in the understanding of the regulation and physiology of CMA with a specific focus on its possible roles in neuroprotection.

Lysosomal mTORC2/PHLPP1/Akt Regulate Chaperone-Mediated Autophagy

Chaperone-mediated autophagy (CMA), a selective form of degradation of cytosolic proteins in lysosomes, contributes to maintenance of proteostasis and to the cellular adaptation to stress. CMA substrates are delivered by a cytosolic chaperone to the lysosomal surface, where, upon unfolding, they are internalized through a membrane translocation complex. The molecular components that participate in CMA substrate targeting and translocation are well characterized, but those involved in CMA regulation remain mostly unknown. In this study, we have identified that CMA is under the positive control of the phosphatase PHLPP1 that associates with the lysosomal membrane and counteracts the inhibitory effect of mTORC2 on CMA. Lysosomal Akt, a target of the mTORC2/PHLPP1 kinase-phosphatase pair, modulates CMA activity by controlling the dynamics of assembly and disassembly of the CMA translocation complex at the lysosomal membrane. The lysosomal mTORC2/PHLPP1/Akt axis could become a target to restore CMA dysfunction in aging and disease.

Autophagy and cancer metabolism

The metabolism of malignant cells is profoundly altered in order to maintain their survival and proliferation in adverse microenvironmental conditions. Autophagy is an intracellular recycling process that maintains basal levels of metabolites and biosynthetic intermediates under starvation or other forms of stress, hence serving as an important mechanism for metabolic adaptation in cancer cells. Although it is widely acknowledged that autophagy sustains metabolism in neoplastic cells under duress, many questions remain with regard to the mutual relationship between autophagy and metabolism in cancer. Importantly, autophagy has often been described as a "double-edged sword" that can either impede or promote cancer initiation and progression. Here, we overview such a dual function of autophagy in tumorigenesis and our current understanding of the coordinated regulation of autophagy and cancer cell metabolism in the control of tumor growth, progression, and resistance to therapy.

Methods to study chaperone-mediated autophagy

Chaperone-mediated autophagy (CMA) is a multistep process that involves selective degradation and digestion of a pool of soluble cytosolic proteins in lysosomes. Cytosolic substrates are selectively identified and targeted by chaperones to lysosomes where they are subsequently translocated into the organelle lumen through a dedicated CMA-associated lysosomal membrane receptor/translocation complex. CMA contributes to maintaining a functional proteome, through elimination of altered proteins, and participates in the cellular energetic balance through amino acid recycling. Defective or dysfunctional CMA has been associated with human pathologies such as neurodegeneration, cancer, immunodeficiency or diabetes, increasing the overall interest in methods to monitor this selective autophagic pathway. Here, we describe approaches used to study CMA in different experimental models.

Dual proteolytic pathways govern glycolysis and immune competence

Proteasomes and lysosomes constitute the major cellular systems that catabolize proteins to recycle free amino acids for energy and new protein synthesis. Tripeptidyl peptidase II (TPPII) is a large cytosolic proteolytic complex that functions in tandem with the proteasome-ubiquitin protein degradation pathway. We found that autosomal recessive TPP2 mutations cause recurrent infections, autoimmunity, and neurodevelopmental delay in humans. We show that a major function of TPPII in mammalian cells is to maintain amino acid levels and that TPPII-deficient cells compensate by increasing lysosome number and proteolytic activity. However, the overabundant lysosomes derange cellular metabolism by consuming the key glycolytic enzyme hexokinase-2 through chaperone-mediated autophagy. This reduces glycolysis and impairs the production of effector cytokines, including IFN-γ and IL-1β. Thus, TPPII controls the balance between intracellular amino acid availability, lysosome number, and glycolysis, which is vital for adaptive and innate immunity and neurodevelopmental health.

ATF4 Gene Network Mediates Cellular Response to the Anticancer PAD Inhibitor YW3-56 in Triple-Negative Breast Cancer Cells

We previously reported that a pan-PAD inhibitor, YW3-56, activates p53 target genes to inhibit cancer growth. However, the p53-independent anticancer activity and molecular mechanisms of YW3-56 remain largely elusive. Here, gene expression analyses found that ATF4 target genes involved in endoplasmic reticulum (ER) stress response were activated by YW3-56. Depletion of ATF4 greatly attenuated YW3-56-mediated activation of the mTORC1 regulatory genes SESN2 and DDIT4. Using the ChIP-exo method, high-resolution genomic binding sites of ATF4 and CEBPB responsive to YW3-56 treatment were generated. In human breast cancer cells, YW3-56-mediated cell death features mitochondria depletion and autophagy perturbation. Moreover, YW3-56 treatment effectively inhibits the growth of triple-negative breast cancer xenograft tumors in nude mice. Taken together, we unveiled the anticancer mechanisms and therapeutic potentials of the pan-PAD inhibitor YW3-56.

Autophagy, a major adaptation pathway shaping cancer cell death and anticancer immunity responses following photodynamic therapy

Autophagy is fundamentally a cytoprotective and pro-survival process yet studies have shown that it has an exceedingly contextual role in cancer biology; depending on the phase, location or type of oncogenic trigger and/or therapy, its role could fluctuate from pro- to anti-tumourigenic.

Chaperone-mediated autophagy components are upregulated in sporadic inclusion-body myositis muscle fibres

AIMS

Sporadic inclusion-body myositis (s-IBM) is an age-associated degenerative muscle disease. Characteristic features are muscle-fibre vacuolization and intramuscle-fibre accumulations of multiprotein aggregates, which may result from the demonstrated impairments of the 26S proteasome and autophagy. Chaperone-mediated autophagy (CMA) is a selective form of lysosomal degradation targeting proteins carrying the KFERQ motif. Lysosome-associated membrane protein type 2A (LAMP2A) and the heat-shock cognate protein 70 (Hsc70) constitute specific CMA components. Neither CMA components nor CMA activity has been studied in normal or disease human muscle, to our knowledge.

METHODS

We studied CMA components by immunocytochemistry, immunoblots, real-time PCR and immunoprecipitation in: (a) 16 s-IBM, nine aged-matched normal and nine disease control muscle biopsies; and (b) cultured human muscle fibres (CHMFs) with experimentally inhibited activities of either the 26S proteasome or autophagy.

RESULTS

Compared with age-matched controls, in s-IBM muscle, LAMP2A and Hsc70 were on a given transverse section accumulated as aggregates in approximately 5% of muscle fibres, where they (a) colocalized with each other and α-synuclein (α-syn), a CMA-targeted protein; and (b) were bound to each other and to α-syn by immunoprecipitation. By immunoblots, LAMP2A was increased sevenfold P < 0.001 and Hsc70 2.6-fold P < 0.05. LAMP2A mRNA was increased 4.4-fold P < 0.001 and Hsc70 mRNA 1.9-fold P < 0.05. In CHMFs inhibition of either the 26S proteasome or autophagy induced CMA, evidenced by a significant increase of both LAMP2A and Hsc70.

CONCLUSIONS

Our study demonstrates, for the first time, up-regulation of CMA components in s-IBM muscle, and it provides further evidence that altered protein degradation is likely an important pathogenic aspect in s-IBM.

Chaperone-mediated autophagy regulates T cell responses through targeted degradation of negative regulators of T cell activation

Chaperone-mediated autophagy (CMA) targets soluble proteins for lysosomal degradation. Here we found that CMA was activated in T cells in response to engagement of the T cell antigen receptor (TCR), which induced expression of the CMA-related lysosomal receptor LAMP-2A. In activated T cells, CMA targeted the ubiquitin ligase Itch and the calcineurin inhibitor RCAN1 for degradation to maintain activation-induced responses. Consequently, deletion of the gene encoding LAMP-2A in T cells caused deficient in vivo responses to immunization or infection with Listeria monocytogenes. Impaired CMA activity also occurred in T cells with age, which negatively affected their function. Restoration of LAMP-2A in T cells from old mice resulted in enhancement of activation-induced responses. Our findings define a role for CMA in regulating T cell activation through the targeted degradation of negative regulators of T cell activation.

Phosphorylation-regulated degradation of the tumor-suppressor form of PED by chaperone-mediated autophagy in lung cancer cells

PED/PEA-15 is a death effector domain (DED) family member with a variety of effects on cell growth and metabolism. To get further insight into the role of PED in cancer, we aimed to find new PED interactors. Using tandem affinity purification, we identified HSC70 (Heat Shock Cognate Protein of 70 kDa)-which, among other processes, is involved in chaperone-mediated autophagy (CMA)-as a PED-interacting protein. We found that PED has two CMA-like motifs (i.e., KFERQ), one of which is located within a phosphorylation site, and demonstrate that PED is a bona fide CMA substrate and the first example in which phosphorylation modifies the ability of HSC70 to access KFERQ-like motifs and target the protein for lysosomal degradation. Phosphorylation of PED switches its function from tumor suppression to tumor promotion, and we show that HSC70 preferentially targets the unphosphorylated form of PED to CMA. Therefore, we propose that the up-regulated CMA activity characteristic of most types of cancer cell enhances oncogenesis by shifting the balance of PED function toward tumor promotion. This mechanism is consistent with the notion of a therapeutic potential for targeting CMA in cancer, as inhibition of this autophagic pathway may help restore a physiological ratio of PED forms.

Deficient chaperone-mediated autophagy in liver leads to metabolic dysregulation

The activity of chaperone-mediated autophagy (CMA), a catabolic pathway for selective degradation of cytosolic proteins in lysosomes, decreases with age, but the consequences of this functional decline in vivo remain unknown. In this work, we have generated a conditional knockout mouse to selectively block CMA in liver. We have found that blockage of CMA causes hepatic glycogen depletion and hepatosteatosis. The liver phenotype is accompanied by reduced peripheral adiposity, increased energy expenditure, and altered glucose homeostasis. Comparative lysosomal proteomics revealed that key enzymes in carbohydrate and lipid metabolism are normally degraded by CMA and that impairment of their regulated degradation contributes to the metabolic abnormalities observed in CMA-defective animals. These findings highlight the involvement of CMA in regulating hepatic metabolism and suggest that the age-related decline in CMA may have a negative impact on the energetic balance in old organisms.

Cyclin-dependent kinases regulate lysosomal degradation of hypoxia-inducible factor 1α to promote cell-cycle progression

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates adaptive responses to oxygen deprivation. In addition, the HIF-1α subunit has a nontranscriptional role as a negative regulator of DNA replication through effects on minichromosome maintenance helicase loading and activation. However, some cell types continue to replicate under hypoxic conditions. The mechanism by which these cells maintain proliferation in the presence of elevated HIF-1α levels is unclear. Here we report that HIF-1α physically and functionally interacts with cyclin-dependent kinase 1 (Cdk1) and Cdk2. Cdk1 activity blocks lysosomal degradation of HIF-1α and increases HIF-1α protein stability and transcriptional activity. By contrast, Cdk2 activity promotes lysosomal degradation of HIF-1α at the G1/S phase transition. Blocking lysosomal degradation by genetic or pharmacological means leads to HIF-1α-dependent cell-cycle arrest, demonstrating that lysosomal degradation of HIF-1α is an essential step for the maintenance of cell-cycle progression under hypoxic conditions.

p62/SQSTM1 synergizes with autophagy for tumor growth in vivo

Autophagy is crucial for cellular homeostasis and plays important roles in tumorigenesis. FIP200 is an essential autophagy gene that promotes mammary tumorigenesis. Here, Wei et al. find that ablation of FIP200 reduces growth of established tumors. p62 knockdown or deficiency in established FIP200-null tumors dramatically impairs tumor growth, and this is associated with the up-regulated activation of the NF-κB pathway by p62. This study demonstrates that p62 and autophagy synergize to promote tumor growth.

Autophagy is crucial for cellular homeostasis and plays important roles in tumorigenesis. FIP200 (FAK family-interacting protein of 200 kDa) is an essential autophagy gene required for autophagy induction, functioning in the ULK1–ATG13–FIP200 complex. Our previous studies showed that conditional knockout of FIP200 significantly suppressed mammary tumorigenesis, which was accompanied by accumulation of p62 in tumor cells. However, it is not clear whether FIP200 is also required for maintaining tumor growth and how the increased p62 level affects the growth in autophagy-deficient FIP200-null tumors in vivo. Here, we describe a new system to delete FIP200 in transformed mouse embryonic fibroblasts as well as mammary tumor cells following their transplantation and show that ablation of FIP200 significantly reduced growth of established tumors in vivo. Using similar strategies, we further showed that either p62 knockdown or p62 deficiency in established FIP200-null tumors dramatically impaired tumor growth. The stimulation of tumor growth by p62 accumulation in FIP200-null tumors is associated with the up-regulated activation of the NF-κB pathway by p62. Last, we showed that overexpression of the autophagy master regulator TFEB^S142A increased the growth of established tumors, which correlated with the increased autophagy of the tumor cells. Together, our studies demonstrate that p62 and autophagy synergize to promote tumor growth, suggesting that inhibition of both pathways could be more effective than targeting either alone for cancer therapy.

Therapeutic targeting of autophagy in cancer. Part II: pharmacological modulation of treatment-induced autophagy

Autophagy, the catabolic pathway in which cells recycle organelles and other parts of their own cytoplasm, is increasingly recognised as an important cytoprotective mechanism in cancer cells. Several cancer treatments stimulate the autophagic process and when autophagy is inhibited, cancer cells show an enhanced response to multiple treatments. These findings have nourished the theory that autophagy provides cancer cells with a survival advantage during stressful conditions, including exposure to therapeutics. Therefore, interference with the autophagic response can potentially enhance the efficacy of cancer therapy. In this review we examine two approaches to modulate autophagy as complementary cancer treatment: inhibition and induction. Inhibition of autophagy during cancer treatment eliminates its cytoprotective effects. Conversely, induction of autophagy combined with conventional cancer therapy exerts severe cytoplasmic degradation that can ultimately lead to cell death. We will discuss how autophagy can be therapeutically manipulated in cancer cells and how interactions between the conventional cancer therapies and autophagy modulation influence treatment outcome.

Autophagy and human disease: emerging themes

Malfunction of autophagy, the process that mediates breakdown and recycling of intracellular components in lysosomes, has been linked to a variety of human diseases. As the number of pathologies associated with defective autophagy increases, emphasis has switched from the mere description of the status of autophagy in these conditions to a more mechanistic dissection of the autophagic changes. Understanding the reasons behind the autophagic defect, the immediate consequences of the autophagic compromise and how autophagy changes with the evolution of the disease has become a 'must,' especially now that manipulation of autophagy is being considered as a therapeutic strategy. Here, we comment on some of the common themes that have emerged from such detailed analyses of the interplay between autophagy and disease conditions.

Low intensity focused ultrasound (LOFU) modulates unfolded protein response and sensitizes prostate cancer to 17AAG

The hypoxic tumor microenvironment generates oxidative Endoplasmic Reticulum (ER) stress, resulting in protein misfolding and unfolded protein response (UPR). UPR induces several molecular chaperones including heat-shock protein 90 (HSP90), which corrects protein misfolding and improves survival of cancer cells and resistance to tumoricidal therapy although prolonged activation of UPR induces cell death. The HSP90 inhibitor, 17AAG, has shown promise against various solid tumors, including prostate cancer (PC). However, therapeutic doses of 17AAG elicit systemic toxicity. In this manuscript, we describe a new paradigm where the combination therapy of a non-ablative and non-invasive low energy focused ultrasound (LOFU) and a non-toxic, low dose 17AAG causes synthetic lethality and significant tumoricidal effects in mouse and human PC xenografts. LOFU induces ER stress and UPR in tumor cells without inducing cell death. Treatment with a non-toxic dose of 17AAG further increased ER stress in LOFU treated PC and switch UPR from a cytoprotective to an apoptotic response in tumors resulting significant induction of apoptosis and tumor growth retardation. These observations suggest that LOFU-induced ER stress makes the ultrasound-treated tumors more susceptible to chemotherapeutic agents, such as 17AAG. Thus, a novel therapy of LOFU-induced chemosensitization may be designed for locally advanced and recurrent tumors.

Autophagy and cancer therapy

Autophagy is the process by which cellular material is delivered to lysosomes for degradation and recycling. There are three different types of autophagy, but macroautophagy, which involves the formation of double membrane vesicles that engulf proteins and organelles that fuse with lysosomes, is by far the most studied and is thought to have important context-dependent roles in cancer development, progression, and treatment. The roles of autophagy in cancer treatment are complicated by two important discoveries over the past few years. First, most (perhaps all) anticancer drugs, as well as ionizing radiation, affect autophagy. In most, but not all cases, these treatments increase autophagy in tumor cells. Second, autophagy affects the ability of tumor cells to die after drug treatment, but the effect of autophagy may be to promote or inhibit cell death, depending on context. Here we discuss recent research related to autophagy and cancer therapy with a focus on how these processes may be manipulated to improve cancer therapy.

Selective autophagy: talking with the UPS

Far from now are the days when investigators raced to identify the proteolytic system responsible for the degradation of their favorite protein. Nowadays, it is well accepted that a given protein can be degraded by different systems depending on factors such as cell type, cellular conditions, or functionality of each proteolytic pathway. The realization of this sharing of substrates among pathways has also helped to unveil deeper levels of communication among the different proteolytic systems. Thus, cells often respond to blockage of one degradative mechanism by upregulating any of the other available pathways. In addition, effectors and regulators of one proteolytic system can be degraded by a different proteolytic pathway that exerts, in this way, a regulatory function. In this mini review, we describe the different levels of cross-talk among autophagic pathways and the ubiquitin/proteasome system. We also provide examples of how this proteolytic communication is used for compensatory purposes in different pathological conditions and discuss the possible therapeutic potential of targeting the modulators of the cross-talk among proteolytic pathways.

p62/SQSTM1 accumulation in squamous cell carcinoma of head and neck predicts sensitivity to phosphatidylinositol 3-kinase pathway inhibitors

The phosphoinositol-3 kinase (PI3K) pathway is highly dysregulated in squamous cell carcinoma of the head and neck (SCCHN). While inhibitors of the PI3K/AKT pathway are being developed in cancer, their efficacy does not appear to be related to the presence of mutations or amplification in pathway genes. The PI3K pathway is a major regulator of macro-autophagy, an evolutionarily conserved catabolic process that degrades cellular materials to promote cellular homeostasis and survival under stress. Employing a panel of SCCHN cell lines, we observed a significant correlation between the activity of PI3K/AKT inhibitors and their ability to induce autophagy. More specifically, resistance to these inhibitors was associated with accumulation of p62/SQSTM1, a pleotropic protein that is consumed during autophagy, while loss of autophagy was, for the first time, found to be due to silencing of an essential autophagy gene, ATG7. Moreover, modulating ATG7 and p62/SQSTM1 could regulate sensitivity to PI3K/AKT inhibitors, underscoring a mechanistic link between autophagy and drug sensitivity. Analysis of human tissues revealed progressive accumulation of p62/SQSTM1 in a significant proportion of cancer samples compared to normal tissue, suggesting that defective autophagy has relevance to SCCHN. These findings are further validated by analysis of TCGA data confirming homozygous deletion and mRNA down-regulation of ATG7 in 10.0% of SCCHN samples. Taken together, these data indicate that p62/SQSTM1 levels modulate sensitivity to PI3K/AKT inhibitors; cancers vary in their capacity to undergo autophagy through epigenetic modification and, when deficient, accumulate p62/SQSTM1; and expression of autophagy-related proteins may serve as markers for resistance to PI3K/AKT inhibitors in SCCHN.

Liver autophagy: much more than just taking out the trash

Studies performed in the liver in the 1960s led to the identification of lysosomes and the discovery of autophagy, the process by which intracellular proteins and organelles are degraded in lysosomes. Early studies in hepatocytes also uncovered how nutritional status regulates autophagy and how various circulating hormones modulate the activity of this catabolic process in the liver. The intensive characterization of hepatic autophagy over the years has revealed that lysosome-mediated degradation is important not only for maintaining liver homeostasis in normal physiological conditions, but also for an adequate response of this organ to stressors such as proteotoxicity, metabolic dysregulation, infection and carcinogenesis. Autophagic malfunction has also been implicated in the pathogenesis of common liver diseases, suggesting that chemical manipulation of this process might hold potential therapeutic value. In this Review--intended as an introduction to the topic of hepatic autophagy for clinical scientists--we describe the different types of hepatic autophagy, their role in maintaining homeostasis in a healthy liver and the contribution of autophagic malfunction to liver disease.

Chaperone-mediated autophagy: roles in disease and aging

This review focuses on chaperone-mediated autophagy (CMA), one of the proteolytic systems that contributes to degradation of intracellular proteins in lysosomes. CMA substrate proteins are selectively targeted to lysosomes and translocated into the lysosomal lumen through the coordinated action of chaperones located at both sides of the membrane and a dedicated protein translocation complex. The selectivity of CMA permits timed degradation of specific proteins with regulatory purposes supporting a modulatory role for CMA in enzymatic metabolic processes and subsets of the cellular transcriptional program. In addition, CMA contributes to cellular quality control through the removal of damaged or malfunctioning proteins. Here, we describe recent advances in the understanding of the molecular dynamics, regulation and physiology of CMA, and discuss the evidence in support of the contribution of CMA dysfunction to severe human disorders such as neurodegeneration and cancer.

Hyperactivation of mammalian target of rapamycin complex 1 (mTORC1) promotes breast cancer progression through enhancing glucose starvation-induced autophagy and Akt signaling

The mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth and proliferation. Recent studies have suggested that constitutive activation of mTORC1 in normal cells could lead to malignant tumor development in several tissues. However, the mechanisms of mTORC1 hyperactivation to promote the growth and metastasis of breast or other cancers are still not well characterized. Here, using a new inducible deletion system, we show that deletion of Tsc1 in mouse primary mammary tumor cells, either before or after their transplantation, significantly increased their growth in vivo. The increase in tumor growth was completely rescued by rapamycin treatment, suggesting a major contribution from mTORC1 hyperactivation. Interestingly, glucose starvation-induced autophagy, but not amino acid starvation-induced autophagy, was increased significantly in Tsc1-null tumor cells. Further analysis of these cells also showed an increased Akt activation but no significant changes in Erk signaling. Together, these results provide insights into the mechanism by which hyperactivation of mTORC1 promotes breast cancer progression through increasing autophagy and Akt activation in vivo.

Chaperone-mediated autophagy in the kidney: the road more traveled

Chaperone-mediated autophagy (CMA) is a lysosomal proteolytic pathway in which cytosolic substrate proteins contain specific chaperone recognition sequences required for degradation and are translocated directly across the lysosomal membrane for destruction. CMA proteolytic activity has a reciprocal relationship with macroautophagy: CMA is most active in cells in which macroautophagy is least active. Normal renal proximal tubular cells have low levels of macroautophagy, but high basal levels of CMA activity. CMA activity is regulated by starvation, growth factors, oxidative stress, lipids, aging, and retinoic acid signaling. The physiological consequences of changes in CMA activity depend on the substrate proteins present in a given cell type. In the proximal tubule, increased CMA results from protein or calorie starvation and from oxidative stress. Overactivity of CMA can be associated with tubular lysosomal pathology and certain cancers. Reduced CMA activity contributes to protein accumulation in renal tubular hypertrophy, but may contribute to oxidative tissue damage in diabetes and aging. Although there are more questions than answers about the role of high basal CMA activity, this remarkable feature of tubular protein metabolism appears to influence a variety of chronic diseases.

Down-regulation of autophagy-related protein 5 (ATG5) contributes to the pathogenesis of early-stage cutaneous melanoma

The role of autophagy in cancer is controversial: Both tumor-suppressing and tumor-promoting functions have been reported. We show that a key regulator of autophagy, autophagy-related protein 5 (ATG5), is often down-regulated in primary melanomas compared to benign nevi, leading to a reduction of basal autophagy as evidenced by a reduced expression of LC3. A follow-up of 158 primary melanoma patients showed that patients with low levels of ATG5 in their tumors had a reduced progression-free survival. In an in vitro model of melanoma tumorigenesis, where the BRAF oncogene was transduced into normal melanocytes, we observed that lowering ATG5 expression promoted proliferation by precluding oncogene-induced senescence. Hence, it appears that down-regulation of ATG5 contributes to tumorigenesis in early-stage cutaneous melanoma, and the expression of ATG5 and LC3 correlates with melanoma diagnosis and prognosis.

Why is autophagy important for melanoma? Molecular mechanisms and therapeutic implications

As the principle lysosomal mediated mechanism for the degradation of aged or damaged organelles and proteins, autophagy (self-eating) is generally considered a pro-survival process activated by cells to sustain life in presence of adverse environmental conditions such as nutrient shortage and/or in presence of cytotoxic compounds. Upon activation, cytoplasmic material is sequestered into double-membrane vesicles (autophagosomes) then targeted for degradation by fusion with lysosomes (autolysosomes); metabolic activity and cell survival are consequently sustained by recycling the degradation products. Basal autophagy occurs in almost all cell types, though at different degree, as a finely regulated "quality control" process to prevent cell damage, for the demolition of cellular structures during cell/tissue remodelling, and to ensure the maintenance of cellular homeostasis through recycling cellular components/molecules. Autophagy is stimulated in response to both physiological and pathological conditions such as starvation, hypoxia and low energy, pathogen infection and protein aggregates. Although it's clear that autophagy is also involved in cancer, its role, however, is complex since it can both suppress and promote tumorigenesis. Consequently, it is generally accepted that while autophagy is used by advanced stage cancers to maintain tumour survival, loss of autophagy in earlier stages is associated with tumour development. Accordingly, it is now apparent that aberrant control of autophagy is among key hallmarks of cancer, with several studies now demonstrating this process is deregulated also in melanoma.

STUB1/CHIP is required for HIF1A degradation by chaperone-mediated autophagy

The transcription factor HIF1 is mostly regulated by the oxygen-dependent proteasomal degradation of the labile subunit HIF1A. Recent data showed degradation of HIF1A in the lysosome through chaperone-mediated autophagy (CMA). However the molecular mechanism involved has not been elucidated. This study shows that the KFERQ-like motif, that has been identified in all CMA substrates, is required to mediate the interaction between HIF1A and the chaperone HSPA8. Moreover, mutations in the KFERQ-like motif of HIF1A preclude the interaction with the CMA receptor LAMP2A, thus inhibiting its lysosomal degradation. Importantly, we show for the first time that the ubiquitin ligase STUB1 is required for degradation of HIF1A in the lysosome by CMA. Indeed, mutations in STUB1 that inhibit either the ubiquitin ligase activity or its ability to bind to HSPA8, both prevent degradation of HIF1A by CMA. Moreover, we show that HIF1A binds to and is translocated into intact lysosomes isolated from rat livers. This new pathway for degradation of HIF1A does not depend on the presence of oxygen and is activated in response to nutrient deprivation such that the levels of HIF1A bound to CMA positive lysosomes significantly increase in starved animal livers and the binding of HIF1A to LAMP2A increases in response to serum deprivation. Moreover, excessive degradation of HIF1A by CMA compromises cells' ability to respond to and survive under hypoxia, suggesting that this pathway might be of pathophysiological importance in conditions that combine hypoxia with starvation.

Balance between autophagic pathways preserves retinal homeostasis

Aging contributes to the appearance of several retinopathies and is the largest risk factor for aged-related macular degeneration, major cause of blindness in the elderly population. Accumulation of undegraded material as lipofuscin represents a hallmark in many pathologies of the aged eye. Autophagy is a highly conserved intracellular degradative pathway that plays a critical role in the removal of damaged cell components to maintain the cellular homeostasis. A decrease in autophagic activity with age observed in many tissues has been proposed to contribute to the aggravation of age-related diseases. However, the participation of different autophagic pathways to the retina physiopathology remains unknown. Here, we describe a marked reduction in macroautophagic activity in the retina with age, which coincides with an increase in chaperone-mediated autophagy (CMA). This increase in CMA is also observed during retinal neurodegeneration in the Atg5(flox/flox) ; nestin-Cre mice, a mouse model with downregulation of macroautophagy in neuronal precursors. In contrast to other cell types, this autophagic cross talk in retinal cells is not bi-directional and CMA inhibition renders cone photoreceptor very sensitive to stress. Temporal and cell-type-specific differences in the balance between autophagic pathways may be responsible for the specific pattern of visual loss that occurs with aging. Our results show for the first time a cross talk of different lysosomal proteolytic systems in the retina during normal aging and may help the development of new therapeutic intervention for age-dependent retinal diseases.

Autophagy: a potential therapeutic target in lung diseases

Macroautophagy (hereafter referred to as autophagy) is an evolutionally conserved intracellular process to maintain cellular homeostasis by facilitating the turnover of protein aggregates, cellular debris, and damaged organelles. During autophagy, cytosolic constituents are engulfed into double-membrane-bound vesicles called "autophagosomes," which are subsequently delivered to the lysosome for degradation. Accumulated evidence suggests that autophagy is critically involved not only in the basal physiological states but also in the pathogenesis of various human diseases. Interestingly, a diverse variety of clinically approved drugs modulate autophagy to varying extents, although they are not currently utilized for the therapeutic purpose of manipulating autophagy. In this review, we highlight the functional roles of autophagy in lung diseases with focus on the recent progress of the potential therapeutic use of autophagy-modifying drugs in clinical medicine. The purpose of this review is to discuss the merits, and the pitfalls, of modulating autophagy as a therapeutic strategy in lung diseases.

Chemical modulation of chaperone-mediated autophagy by retinoic acid derivatives

Chaperone-mediated autophagy (CMA) contributes to cellular quality control and the cellular response to stress through the selective degradation of cytosolic proteins in lysosomes. Decrease in CMA activity occurs in aging and in age-related disorders (for example, neurodegenerative diseases and diabetes). Although prevention of this age-dependent decline through genetic manipulation in mouse has proven beneficial, chemical modulation of CMA is not currently possible, due in part to the lack of information on the signaling mechanisms that modulate this pathway. In this work, we report that signaling through the retinoic acid receptor alpha (RARα) inhibits CMA and apply structure-based chemical design to develop synthetic derivatives of all-trans-retinoic acid (ATRA) to specifically neutralize this inhibitory effect. We demonstrate that chemical enhancement of CMA protects cells from oxidative stress and from proteotoxicity, supporting a potential therapeutic opportunity when reduced CMA contributes to cellular dysfunction and disease.

Chaperone-mediated autophagy targets hypoxia-inducible factor-1α (HIF-1α) for lysosomal degradation

Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor that mediates adaptive responses to hypoxia. We demonstrate that lysosomal degradation of the HIF-1α subunit by chaperone-mediated autophagy (CMA) is a major regulator of HIF-1 activity. Pharmacological inhibitors of lysosomal degradation, such as bafilomycin and chloroquine, increased HIF-1α levels and HIF-1 activity, whereas activators of chaperone-mediated autophagy, including 6-aminonicotinamide and nutrient starvation, decreased HIF-1α levels and HIF-1 activity. In contrast, macroautophagy inhibitors did not increase HIF-1 activity. Transcription factor EB, a master regulator of lysosomal biogenesis, also negatively regulated HIF-1 activity. HIF-1α interacts with HSC70 and LAMP2A, which are core components of the CMA machinery. Overexpression of HSC70 or LAMP2A decreased HIF-1α protein levels, whereas knockdown had the opposite effect. Finally, hypoxia increased the transcription of genes involved in CMA and lysosomal biogenesis in cancer cells. Thus, pharmacological and genetic approaches identify CMA as a major regulator of HIF-1 activity and identify interplay between autophagy and the response to hypoxia.

Interplay of LRRK2 with chaperone-mediated autophagy

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease. We found LRRK2 to be degraded in lysosomes by chaperone-mediated autophagy (CMA), whereas the most common pathogenic mutant form of LRRK2, G2019S, was poorly degraded by this pathway. In contrast to the behavior of typical CMA substrates, lysosomal binding of both wild-type and several pathogenic mutant LRRK2 proteins was enhanced in the presence of other CMA substrates, which interfered with the organization of the CMA translocation complex, resulting in defective CMA. Cells responded to such LRRK2-mediated CMA compromise by increasing levels of the CMA lysosomal receptor, as seen in neuronal cultures and brains of LRRK2 transgenic mice, induced pluripotent stem cell-derived dopaminergic neurons and brains of Parkinson's disease patients with LRRK2 mutations. This newly described LRRK2 self-perpetuating inhibitory effect on CMA could underlie toxicity in Parkinson's disease by compromising the degradation of α-synuclein, another Parkinson's disease-related protein degraded by this pathway.

Metabolic alterations in lung cancer-associated fibroblasts correlated with increased glycolytic metabolism of the tumor

Cancer cells undergo a metabolic reprogramming but little is known about metabolic alterations of other cells within tumors. We use mass spectrometry-based profiling and a metabolic pathway-based systems analysis to compare 21 primary human lung cancer-associated fibroblast lines (CAF) to "normal" fibroblast lines (NF) generated from adjacent nonneoplastic lung tissue. CAFs are protumorigenic, although the mechanisms by which CAFs support tumors have not been elucidated. We have identified several pathways whose metabolite abundance globally distinguished CAFs from NFs, suggesting that metabolic alterations are not limited to cancer cells. In addition, we found metabolic differences between CAFs from high and low glycolytic tumors that might reflect distinct roles of CAFs related to the tumor's glycolytic capacity. One such change was an increase of dipeptides in CAFs. Dipeptides primarily arise from the breakdown of proteins. We found in CAFs an increase in basal macroautophagy which likely accounts for the increase in dipeptides. Furthermore, we show a difference between CAFs and NFs in the induction of autophagy promoted by reduced glucose. In sum, our data suggest that increased autophagy may account for metabolic differences between CAFs and NFs and may play additional as yet undetermined roles in lung cancer.

Loss of stress response as a consequence of viral infection: implications for disease and therapy

Herein, we propose that viral infection can induce a deficient cell stress response and thereby impairs stress tolerance and makes tissues vulnerable to damage. Having a valid paradigm to address the pathological impacts of viral infections could lead to effective new therapies for diseases that have previously been unresponsive to intervention. Host response to viral infections can also lead to autoimmune diseases like type 1 diabetes. In the case of Newcastle disease virus, the effects of viral infection on heat shock proteins may be leveraged as a therapy for cancer. Finally, the search for a specific virus being responsible for a condition like chronic fatigue syndrome may not be worthwhile if the disease is simply a nonspecific response to viral infection.

LAMP2A overexpression in breast tumors promotes cancer cell survival via chaperone-mediated autophagy

Lysosome-associated membrane protein type 2A (LAMP2A) is a key protein in the chaperone-mediated autophagy (CMA) pathway. LAMP2A helps in lysosomal uptake of modified and oxidatively damaged proteins directly into the lumen of lysosomes for degradation and protein turnover. Elevated expression of LAMP2A was observed in breast tumor tissues of all patients under investigation, suggesting a survival mechanism via CMA and LAMP2A. Reduced expression of the CMA substrates, GAPDH and PKM, was observed in most of the breast tumor tissues when compared with the normal adjacent tissues. Reactive oxygen species (ROS) mediated oxidative stress damages regulatory cellular components such as DNA, proteins and/or lipids. Protein carbonyl content (PCC) is widely used as a measure of total protein oxidation in cells. Ectopic expression of LAMP2A reduces PCC and thereby promotes cell survival during oxidative stress. Furthermore, inhibition of LAMP2A stimulates accumulation of GAPDH, AKT1 phosphorylation, generation of ROS, and induction of cellular apoptosis in breast cancer cells. Doxorubicin, which is a chemotherapeutic drug, often becomes ineffective against tumor cells with time due to chemotherapeutic resistance. Breast cancer cells deficient of LAMP2A demonstrate increased sensitivity to the drug. Thus, inhibiting CMA activity in breast tumor cells can be exploited as a potential therapeutic application in the treatment of breast cancer.

Chaperones in autophagy

Cells continuously turn over proteins through cycles of synthesis and degradation in order to maintain a functional proteome and to exert a tight control in the levels of regulatory proteins. Selective degradation of proteins was initially thought to be an exclusive function of the ubiquitin-proteasome system, however, over the years, the contribution of lysosomes to this selective degradation, through the process of autophagy, has become consolidated. In this context, molecular chaperones, classically associated with protein folding, unfolding and assembling have been revealed as important modulators of selectivity during the autophagic process. Here, we review this relatively new role of chaperones in mediating selective autophagy and comment on how alterations of this function can lead to human pathologies associated to proteotoxicity.

Small molecule activators of the heat shock response: chemical properties, molecular targets, and therapeutic promise

All cells have developed various mechanisms to respond and adapt to a variety of environmental challenges, including stresses that damage cellular proteins. One such response, the heat shock response (HSR), leads to the transcriptional activation of a family of molecular chaperone proteins that promote proper folding or clearance of damaged proteins within the cytosol. In addition to its role in protection against acute insults, the HSR also regulates lifespan and protects against protein misfolding that is associated with degenerative diseases of aging. As a result, identifying pharmacological regulators of the HSR has become an active area of research in recent years. Here, we review progress made in identifying small molecule activators of the HSR, what cellular targets these compounds interact with to drive response activation, and how such molecules may ultimately be employed to delay or reverse protein misfolding events that contribute to a number of diseases.

Autophagy in pancreatic cancer pathogenesis and treatment

Pancreatic cancer is the fourth most common cancer to cause death due to advanced stage at diagnosis and poor response to current treatment. Autophagy is the lysosome-mediated degradation pathway which plays a critical role in cellular defense, quality control, and energy metabolism. Targeting autophagy is now an exciting field for translational cancer research, as autophagy dysfunction is among the hallmarks of cancer. Pancreatic tumors have elevated autophagy under basal conditions when compared with other epithelial cancers. This review describes our current understanding of the interaction between autophagy and pancreatic cancer development, including risk factors (e.g., pancreatitis, smoking, and alcohol use), tumor microenvironment (e.g., hypoxia and stromal cells), and molecular biology (e.g., K-Ras and p53) of pancreatic cancer. The importance of the HMGB1-RAGE pathway in regulation of autophagy and pancreatic cancer is also presented. Finally, we describe current studies involving autophagy inhibition using either pharmacological inhibitors (e.g., chloroquine) or RNA interference of essential autophagy genes that regulate chemotherapy sensitivity in pancreatic cancer. Summarily, autophagy plays multiple roles in the regulation of pancreatic cancer pathogenesis and treatment, although the exact mechanisms remain unknown.

Chaperone-mediated autophagy: a unique way to enter the lysosome world

All cellular proteins undergo continuous synthesis and degradation. This permanent renewal is necessary to maintain a functional proteome and to allow rapid changes in levels of specific proteins with regulatory purposes. Although for a long time lysosomes were considered unable to contribute to the selective degradation of individual proteins, the discovery of chaperone-mediated autophagy (CMA) changed this notion. Here, we review the characteristics that set CMA apart from other types of lysosomal degradation and the subset of molecules that confer cells the capability to identify individual cytosolic proteins and direct them across the lysosomal membrane for degradation.