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

Rapamycin and Starvation Mitigate Indomethacin-Induced Intestinal Damage through Preservation of Lysosomal Vacuolar ATPase Integrity

Nonsteroidal anti-inflammatory drugs (NSAIDs) possess anti-inflammatory, antipyretic, and analgesic properties and are among the most commonly used drugs. Although the cause of NSAID-induced gastric ulcers is well understood, the mechanism behind small intestinal ulcers remains elusive. In this study, we examined the mechanism through which indomethacin (IM), a prominent NSAID, induces small intestinal ulcers, both in vitro and in vivo. In IEC6 cells, a small intestinal epithelial cell line, IM treatment elevated levels of LC3-II and p62. These expression levels remained unaltered after treatment with chloroquine or bafilomycin, which are vacuolar ATPase (V-ATPase) inhibitors. IM treatment reduced the activity of cathepsin B, a lysosomal protein hydrolytic enzyme, and increased the lysosomal pH. There was a notable increase in subcellular colocalization of LC3 with Lamp2, a lysosome marker, post IM treatment. The increased lysosomal pH and decreased cathepsin B activity were reversed by pretreatment with rapamycin (Rapa) or glucose starvation, both of which stabilize V-ATPase assembly. To validate the in vitro findings in vivo, we established an IM-induced small intestine ulcer mouse model. In this model, we observed multiple ulcerations and heightened inflammation following IM administration. However, pretreatment with Rapa or fasting, which stabilize V-ATPase assembly, mitigated the IM-induced small intestinal ulcers in mice. Coimmunoprecipitation studies demonstrated that IM binds to V-ATPase in vitro and in vivo. These findings suggest that IM induces small intestinal injury through lysosomal dysfunction, likely due to the disassembly of lysosomal V-ATPase caused by direct binding. Moreover, Rapa or starvation can prevent this injury by stabilizing the assembly. SIGNIFICANCE STATEMENT: This study elucidates the largely unknown mechanisms behind small intestinal ulceration induced by indomethacin and reveals the involvement of lysosomal dysfunction via vacuolar ATPase disassembly. The significance lies in identifying potential preventative interventions, such as rapamycin treatment or glucose starvation, offering pivotal insights that extend beyond nonsteroidal anti-inflammatory drugs-induced ulcers to broader gastrointestinal pathologies and treatments, thereby providing a foundation for novel therapeutic strategies aimed at a wide array of gastrointestinal disorders.

An Autophagy-Associated Prognostic Gene Signature for Breast Cancer

Autophagy is closely related to breast cancer and has the dual role of promoting and inhibiting the progression of breast cancer. In this study, we aimed to establish an autophagy-related gene signature for the prognosis of breast cancer. A gene signature composed of the eight most survival-relevant autophagy-associated genes was identified by least absolute shrinkage and selection operator (LASSO) regression analysis. A risk score was calculated based on the gene signature, which divided breast cancer patients into low- or high-risk groups and showed good and poor prognosis, respectively. The risk score displayed good prognostic performance in both the training cohort (TCGA, 1-10-year AUC > 0.63) and the validation cohort (GEO, 1-10-year AUC > 0.66). The multivariate Cox regression and stratified analysis revealed that the risk score was an independent prognostic factor for breast cancer patients. Moreover, the high-risk score was associated with higher infiltration of neutrophils and M2-polarized macrophages, and lower infiltration of resting memory CD4⁺ T cells, CD8⁺ T cells, and NK cells. Finally, the high-risk score was associated with myc target, glycolysis, and mTORC1 signaling. The risk score developed based on the autophagy-associated gene signature was an independent prognostic biomarker for breast cancer.

Three dimensions of autophagy in regulating tumor growth: cell survival/death, cell proliferation, and tumor dormancy

Autophagy is an intracellular lysosomal degradation process involved in multiple facets of cancer biology. Various dimensions of autophagy are associated with tumor growth and cancer progression, and here we focus on the dimensions involved in regulation of cell survival/cell death, cell proliferation and tumor dormancy. The first dimension of autophagy supports cell survival under stress within tumors and under certain contexts drives cell death, impacting tumor growth. The second dimension of autophagy promotes proliferation through directly regulating cell cycle or indirectly maintaining metabolism, increasing tumor growth. The third dimension of autophagy facilitates tumor cell dormancy, contributing to cancer treatment resistance and cancer recurrence. The intricate relationship between these three dimensions of autophagy influences the extent of tumor growth and cancer progression. In this review, we summarize the roles of the three dimensions of autophagy in tumor growth and cancer progression, and discuss unanswered questions in these fields.

Autophagy inhibition by TSSC4 (tumor suppressing subtransferable candidate 4) contributes to sustainable cancer cell growth

Cancer cell growth is dependent upon the sustainability of proliferative signaling and resisting cell death. Macroautophagy/autophagy promotes cancer cell growth by providing nutrients to cells and preventing cell death. This is in contrast to autophagy promoting cell death under some conditions. The mechanism regulating autophagy-mediated cancer cell growth remains unclear. Herein, we demonstrate that TSSC4 (tumor suppressing subtransferable candidate 4) is a novel tumor suppressor that suppresses cancer cell growth and tumor growth and prevents cell death induction during excessive growth by inhibiting autophagy. The oncogenic proteins ERBB2 (erb-b2 receptor tyrosine kinase 2) and the activation EGFR mutant (EGFRvIII, epidermal growth factor receptor variant III) promote cell growth and TSSC4 expression in breast cancer and glioblastoma multiforme (GBM) cells, respectively. In EGFRvIII-expressing GBM cells, TSSC4 knockout shifted the function of autophagy from a pro-cell survival role to a pro-cell death role during prolonged cell growth. Furthermore, the interaction of TSSC4 with MAP1LC3/LC3 (microtubule associated protein 1 light chain 3) via its conserved LC3-interacting region (LIR) contributes to its inhibition of autophagy. Finally, TSSC4 suppresses tumorsphere formation and tumor growth by inhibiting autophagy and maintaining cell survival in tumorspheres. Taken together, sustainable cancer cell growth can be achieved by autophagy inhibition via TSSC4 expression.ABBREVIATIONS: 3-MA: 3-methyladenine; ACTB: actin beta; CQ: chloroquine; EGFRvIII: epidermal growth factor receptor variant III; ERBB2: erb-b2 receptor tyrosine kinase 2; GBM: glioblastoma multiforme; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule Associated protein 1 light chain 3; TSSC4: tumor suppressing subtransferable candidate 4.

Revealing dynamic regulations and the related key proteins of myeloma-initiating cells by integrating experimental data into a systems biological model

MOTIVATION

The growth and survival of myeloma cells are greatly affected by their surrounding microenvironment. To understand the molecular mechanism and the impact of stiffness on the fate of myeloma-initiating cells (MICs), we develop a systems biological model to reveal the dynamic regulations by integrating reverse-phase protein array data and the stiffness-associated pathway.

RESULTS

We not only develop a stiffness-associated signaling pathway to describe the dynamic regulations of the MICs, but also clearly identify three critical proteins governing the MIC proliferation and death, including FAK, mTORC1 and NFκB, which are validated to be related with multiple myeloma by our immunohistochemistry experiment, computation and manually reviewed evidences. Moreover, we demonstrate that the systematic model performs better than widely used parameter estimation algorithms for the complicated signaling pathway.

AVAILABILITY AND IMPLEMENTATION

We can not only use the systems biological model to infer the stiffness-associated genetic signaling pathway and locate the critical proteins, but also investigate the important pathways, proteins or genes for other type of the cancer. Thus, it holds universal scientific significance.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Autophagy mediated lipid catabolism facilitates glioma progression to overcome bioenergetic crisis

BACKGROUND

Activation of mTORC1 plays a significant role in cancer development and progression. However, the metabolic mechanisms to sustain mTORC1 activation of cancer cells within stressed environments are still under-appreciated. We recently revealed high autophagy activity in tumour cells with mTORC1 hyper-activation. Nevertheless, the functions and mechanisms of autophagy in regulating mTORC1 in glioma are not studied.

METHODS

Using glioma patient database and human glioma cells, we assessed the mechanisms and function of selective autophagy to sustain mTORC1 hyper-activation in glioma.

RESULTS

We revealed a strong association of altered mRNA levels in mTORC1 upstream and downstream genes with prognosis of glioma patients. Our results indicated that autophagy-mediated lipid catabolism was essential to sustain mTORC1 activity in glioma cells under energy stresses. We found that autophagy inhibitors or fatty acid oxidation (FAO) inhibitors in combination with 2-Deoxy-D-glucose (2DG) decreased energy production and survival of glioma cells in vitro. Consistently, inhibition of autophagy or FAO inhibitors with 2DG effectively suppressed the progression of xenografted glioma with hyper-activated mTORC1.

CONCLUSIONS

This study established an autophagy/lipid degradation/FAO/ATP generation pathway, which might be used in brain cancer cells under energy stresses to maintain high mTORC1 signalling for tumour progression.

The paradox of autophagy in Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder caused by germline mutations in TSC1 or TSC2 genes, which leads to the hyperactivation of the mTORC1 pathway, an important negative regulator of autophagy. This leads to the development of hamartomas in multiple organs. The variability in symptoms presents a challenge for the development of completely effective treatments for TSC. One option is the treatment with mTORC1 inhibitors, which are targeted to block cell growth and restore autophagy. However, the therapeutic effect of rapamycin seems to be more efficient in the early stages of hamartoma development, an effect that seems to be associated with the paradoxical role of autophagy in tumor establishment. Under normal conditions, autophagy is directly inhibited by mTORC1. In situations of bioenergetics stress, mTORC1 releases the Ulk1 complex and initiates the autophagy process. In this way, autophagy promotes the survival of established tumors by supplying metabolic precursors during nutrient deprivation; paradoxically, excessive autophagy has been associated with cell death in some situations. In spite of its paradoxical role, autophagy is an alternative therapeutic strategy that could be explored in TSC. This review compiles the findings related to autophagy and the new therapeutic strategies targeting this pathway in TSC.

Role of TSC1 in physiology and diseases

Since its initial discovery as the gene altered in Tuberous Sclerosis Complex (TSC), an autosomal dominant disorder, the interest in TSC1 (Tuberous Sclerosis Complex 1) has steadily risen. TSC1, an essential component of the pro-survival PI3K/AKT/MTOR signaling pathway, plays an important role in processes like development, cell growth and proliferation, survival, autophagy and cilia development by co-operating with a variety of regulatory molecules. Recent studies have emphasized the tumor suppressive role of TSC1 in several human cancers including liver, lung, bladder, breast, ovarian, and pancreatic cancers. TSC1 perceives inputs from various signaling pathways, including TNF-α/IKK-β, TGF-β-Smad2/3, AKT/Foxo/Bim, Wnt/β-catenin/Notch, and MTOR/Mdm2/p53 axis, thereby regulating cancer cell proliferation, metabolism, migration, invasion, and immune regulation. This review provides a first comprehensive evaluation of TSC1 and illuminates its diverse functions apart from its involvement in TSC genetic disorder. Further, we have summarized the physiological functions of TSC1 in various cellular events and conditions whose dysregulation may lead to several pathological manifestations including cancer.

Autophagy-mediated tumor cell survival and progression of breast cancer metastasis to the brain

Brain metastases represent a substantial amount of morbidity and mortality in breast cancer (BC). Metastatic breast tumor cells committed to brain metastases are unique because they escape immune surveillance, can penetrate the blood-brain barrier, and also adapt to the brain tissue microenvironment (TME) for colonization and outgrowth. In addition, dynamic intracellular interactions between metastatic cancer cells and neighboring astrocytes in the brain are thought to play essential roles in brain tumor progression. A better understanding of the above mechanisms will lead to developing more effective therapies for brain metastases. Growing literature suggests autophagy, a conserved lysosomal degradation pathway involved in cellular homeostasis under stressful conditions, plays essential roles in breast tumor metastatic transformation and brain metastases. Cancer cells must adapt under various microenvironmental stresses, such as hypoxia, and nutrient (glucose) deprivation, in order to survive and progress. Clinical studies reveal that tumoral expression of autophagy-related proteins is higher in brain metastasis compared to primary breast tumors. In this review, we outline the molecular mechanisms underlying autophagy-mediated BC cell survival and metastasis to the brain.

Curcumin steers THP-1 cells under LPS and mTORC1 challenges toward phenotypically resting, low cytokine-producing macrophages

The persistent activation of intestinal mechanistic target of rapamycin complex 1 (mTORC1) triggered by mucosal stress has been linked to deregulation of the gut immune response resulting in intestinal inflammation and cell death. The present study investigated the regulatory properties of food-derived mTORC1 modulators, curcumin, and piperine, toward the polarization of stimulated macrophages and the differentiation of monocytes at two mTORC1 activity levels (baseline and elevated). To that end, we created stable human THP-1 monocytes exhibiting normal or constitutively active mTORC1. Curcumin or its combination with piperine, but not piperine alone, suppressed mTORC1 kinase activity, curtailed lipopolysaccharide-mediated inflammatory response of THP-1 macrophages, and repressed macrophage activation by inhibiting signaling pathways involved in M1 (mTORC1) and M2 (mTORC2 and cAMP response element binding protein) polarization. The effects of piperine in the curcumin/piperine combination were modest overall, indicating it was curcumin that modulated differentiating monocytes into acquiring a M0 macrophage phenotype characterized by low inflammatory cytokine output.

Curcumin represses mTORC1 signaling in Caco-2 cells by a two-sided mechanism involving the loss of IRS-1 and activation of AMPK

The mechanistic target of rapamycin complex 1 (mTORC1) is a central modulator of inflammation and tumorigenesis in the gastrointestinal tract. Growth factors upregulate mTORC1 via the PI3K/AKT and/or Ras/MAPK signal pathways. Curcumin (CUR), a polyphenol found in turmeric roots (Curcuma longa) can repress mTORC1 kinase activity in colon cancer cell lines; however, key aspects of CUR mechanism of action remain to be elucidated including its primary cellular target. We investigated the molecular effects of physiologically attainable concentration of CUR (20 μM) in the intestinal lumen on mTORC1 signaling in Caco-2 cells. CUR markedly inhibited mTORC1 kinase activity as determined by the decreased phosphorylation of p70S6K (Thr389, -99%, P < 0.0001) and S6 (Ser235/236, -92%, P < 0.0001). Mechanistically, CUR decreased IRS-1 protein abundance (-80%, P < 0.0001) thereby downregulating AKT phosphorylation (Ser473, -94%, P < 0.0001) and in turn PRAS40 phosphorylation (Thr246, -99%, P < 0.0001) while total PRAS40 abundance was unchanged. The use of proteasome inhibitor MG132 showed that CUR-mediated loss of IRS-1 involved proteasomal degradation. CUR lowered Raptor protein abundance, which combined with PRAS40 hypophosphorylation, suggests CUR repressed mTORC1 activity by inducing compositional changes that hinder the complex assembly. In addition, CUR activated AMPK (Thr172 phosphorylation, P < 0.0001), a recognized repressor of mTORC1, and AMPK upstream regulator LKB1. Although cargo adapter protein p62 was decreased by CUR (-49%, P < 0.004), CUR did not significantly induce autophagy. Inhibition of AKT/mTORC1 signaling by CUR may have lifted the cross-inhibition onto MAPK signaling, which became induced; p-ERK1/2 (+670%, P < 0.0001), p-p38 (+1433%, P < 0.0001). By concomitantly targeting IRS-1 and AMPK, CUR's mechanism of mTORC1 inhibition is distinct from that of rapamycin.

FAK activates AKT-mTOR signaling to promote the growth and progression of MMTV-Wnt1-driven basal-like mammary tumors

BACKGROUND

Breast cancer is a heterogeneous disease. Hence, stratification of patients based on the subtype of breast cancer is key to its successful treatment. Among all the breast cancer subtypes, basal-like breast cancer is the most aggressive subtype with limited treatment options. Interestingly, we found focal adhesion kinase (FAK), a cytoplasmic tyrosine kinase, is highly overexpressed and activated in basal-like breast cancer.

METHODS

To understand the role of FAK in this subtype, we generated mice with conditional deletion of FAK and a knock-in mutation in its kinase domain in MMTV-Wnt1-driven basal-like mammary tumors. Tumor initiation, growth, and metastasis were characterized for these mice cohorts. Immunohistochemical and transcriptomic analysis of Wnt1-driven tumors were also performed to elucidate the mechanisms underlying FAK-dependent phenotypes. Pharmacological inhibition of FAK and mTOR in human basal-like breast cancer cell lines was also tested.

RESULTS

We found that in the absence of FAK or its kinase function, growth and metastasis of the tumors were significantly suppressed. Furthermore, immunohistochemical analyses of cleaved caspase 3 revealed that loss of FAK results in increased tumor cell apoptosis. To further investigate the mechanism by which FAK regulates survival of the Wnt1-driven tumor cells, we prepared an isogenic pair of mammary tumor cells with and without FAK and found that FAK ablation increased their sensitivity to ER stress-induced cell death, as well as reduced tumor cell migration and tumor sphere formation. Comparative transcriptomic profiling of the pair of tumor cells and gene set enrichment analysis suggested mTOR pathway to be downregulated upon loss of FAK. Immunoblot analyses further confirmed that absence of FAK results in reduction of AKT and downstream mTOR pathways. We also found that inhibition of FAK and mTOR pathways both induces apoptosis, indicating the importance of these pathways in regulating cell survival.

CONCLUSIONS

In summary, our studies show that in a basal-like tumor model, FAK is required for survival of the tumor cells and can serve as a potential therapeutic target.

SPAG5: An Emerging Oncogene

Sperm-associated Antigen 5 (SPAG5) is a mitotic spindle protein. Recent studies have found that it is overexpressed in many human cancers and functions as an oncogene. Here, we summarize the current underlying mechanisms for its oncogenic roles in regulating cellular behaviors of cancer cells and discuss the possibility of targeting SPAG5 for cancer treatment.

Ductal Carcinoma In Situ Progression in Dog Model of Breast Cancer

The mechanisms that drive ductal carcinoma in situ (DCIS) progression to invasive cancer are not clear. Studying DCIS progression in humans is challenging and not ethical, thus necessitating the characterization of an animal model that faithfully resembles human disease. We have characterized a canine model of spontaneous mammary DCIS and invasive cancer that shares histologic, molecular, and diagnostic imaging characteristics with DCIS and invasive cancer in women. The purpose of the study was to identify markers and altered signaling pathways that lead to invasive cancer and shed light on early molecular events in breast cancer progression and development. Transcriptomic studies along the continuum of cancer progression in the mammary gland from healthy, through atypical ductal hyperplasia (ADH), DCIS, and invasive carcinoma were performed using the canine model. Gene expression profiles of preinvasive DCIS lesions closely resemble those of invasive carcinoma. However, certain genes, such as SFRP2, FZD2, STK31, and LALBA, were over-expressed in DCIS compared to invasive cancer. The over-representation of myoepithelial markers, epithelial-mesenchymal transition (EMT), canonical Wnt signaling components, and other pathways induced by Wnt family members distinguishes DCIS from invasive. The information gained may help in stratifying DCIS as well as identify actionable targets for primary and tertiary prevention or targeted therapy.

Autophagic lipid metabolism sustains mTORC1 activity in TSC-deficient neural stem cells

Although mTORC1 negatively regulates autophagy in cultured cells, how autophagy impacts mTORC1 signaling, in particular in vivo, is less clear. Here we show that autophagy supports mTORC1 hyperactivation in NSCs lacking Tsc1, thereby promoting defects in NSC maintenance, differentiation, tumourigenesis, and the formation of the neurodevelopmental lesion of Tuberous Sclerosis Complex (TSC). Analysing mice that lack Tsc1 and the essential autophagy gene Fip200 in NSCs we find that TSC-deficient cells require autophagy to maintain mTORC1 hyperactivation under energy stress conditions, likely to provide lipids via lipophagy to serve as an alternative energy source for OXPHOS. In vivo, inhibition of lipophagy or its downstream catabolic pathway reverses defective phenotypes caused by Tsc1-null NSCs and reduces tumorigenesis in mouse models. These results reveal a cooperative function of selective autophagy in coupling energy availability with TSC pathogenesis and suggest a potential new therapeutic strategy to treat TSC patients.

Compression of morbidity in a progeroid mouse model through the attenuation of myostatin/activin signalling

BACKGROUND

One of the principles underpinning our understanding of ageing is that DNA damage induces a stress response that shifts cellular resources from growth towards maintenance. A contrasting and seemingly irreconcilable view is that prompting growth of, for example, skeletal muscle confers systemic benefit.

METHODS

To investigate the robustness of these axioms, we induced muscle growth in a murine progeroid model through the use of activin receptor IIB ligand trap that dampens myostatin/activin signalling. Progeric mice were then investigated for neurological and muscle function as well as cellular profiling of the muscle, kidney, liver, and bone.

RESULTS

We show that muscle of Ercc1^Δ/- progeroid mice undergoes severe wasting (decreases in hind limb muscle mass of 40-60% compared with normal mass), which is largely protected by attenuating myostatin/activin signalling using soluble activin receptor type IIB (sActRIIB) (increase of 30-62% compared with untreated progeric). sActRIIB-treated progeroid mice maintained muscle activity (distance travel per hour: 5.6 m in untreated mice vs. 13.7 m in treated) and increased specific force (19.3 mN/mg in untreated vs. 24.0 mN/mg in treated). sActRIIb treatment of progeroid mice also improved satellite cell function especially their ability to proliferate on their native substrate (2.5 cells per fibre in untreated progeroids vs. 5.4 in sActRIIB-treated progeroids after 72 h in culture). Besides direct protective effects on muscle, we show systemic improvements to other organs including the structure and function of the kidneys; there was a major decrease in the protein content in urine (albumin/creatinine of 4.9 sActRIIB treated vs. 15.7 in untreated), which is likely to be a result in the normalization of podocyte foot processes, which constitute the filtration apparatus (glomerular basement membrane thickness reduced from 224 to 177 nm following sActRIIB treatment). Treatment of the progeric mice with the activin ligand trap protected against the development of liver abnormalities including polyploidy (18.3% untreated vs. 8.1% treated) and osteoporosis (trabecular bone volume; 0.30 mm³ in treated progeroid mice vs. 0.14 mm³ in untreated mice, cortical bone volume; 0.30 mm³ in treated progeroid mice vs. 0.22 mm³ in untreated mice). The onset of neurological abnormalities was delayed (by ~5 weeks) and their severity reduced, overall sustaining health without affecting lifespan.

CONCLUSIONS

This study questions the notion that tissue growth and maintaining tissue function during ageing are incompatible mechanisms. It highlights the need for future investigations to assess the potential of therapies based on myostatin/activin blockade to compress morbidity and promote healthy ageing.

The lysosomal TRPML1 channel regulates triple negative breast cancer development by promoting mTORC1 and purinergic signaling pathways

The triple-negative breast cancer (TNBC) that comprises approximately 10%-20% of breast cancers is an aggressive subtype lacking effective therapeutics. Among various signaling pathways, mTORC1 and purinergic signals have emerged as potentially fruitful targets for clinical therapy of TNBC. Unfortunately, drugs targeting these signaling pathways do not successfully inhibit the progression of TNBC, partially due to the fact that these signaling pathways are essential for the function of all types of cells. In this study, we report that TRPML1 is specifically upregulated in TNBCs and that its genetic downregulation and pharmacological inhibition suppress the growth of TNBC. Mechanistically, we demonstrate that TRPML1 regulates TNBC development, at least partially, through controlling mTORC1 activity and the release of lysosomal ATP. Because TRPML1 is specifically activated by cellular stresses found in tumor microenvironments, antagonists of TRPML1 could represent anticancer drugs with enhanced specificity and potency. Our findings are expected to have a major impact on drug targeting of TNBCs.

Small molecules bind human mTOR protein and inhibit mTORC1 specifically

Inhibition of mTOR activity (mechanistic target of rapamycin) is an anti-cancer therapeutic strategy. mTOR participates in two functional complexes, mTORC1 and mTORC2. Since mTORC1 is specifically activated in multiple tumors, novel molecules that inhibit mTORC1 could be therapeutically important. To identify potentially novel modulators of mTOR pathways, we screened 1600 small molecule human drugs for mTOR protein binding, using novel biolayer interferometry technology. We identified several small molecules that bound to mTOR protein in a dose-dependent manner, on multiple chemical scaffolds. As mTOR participates in two major complexes, mTORC1 and mTORC2, the functional specificities of the binders were measured by S6Kinase and Akt phosphorylation assays. Three novel 'mTOR general' binders were identified, carvedilol, testosterone propionate, and hydroxyprogesterone, which inhibited both mTORC1 and mTORC2. By contrast, the piperazine drug cinnarizine dose-dependently inhibited mTORC1 but not mTORC2, suggesting it as a novel mTORC1-specific inhibitor. Some of cinnarizine's chemical analogs also inhibited mTORC1 specifically, whereas others did not. Thus we report the existence of a novel target for some related piperazines including cinnarizine and hydroxyzine, i.e. specific inhibition of mTORC1 activity. Since mTOR inhibition is a general anti-cancer strategy, and mTORC1 is specifically activated in some tumors, we suggest the piperazine scaffold, including cinnarizine and hydroxyzine, could be proposed for rational therapy in tumors in which mTORC1 is specifically activated. Related piperazines have shown toxicity to cancer cells in vitro as single agents and in combination chemotherapy. Thus piperazine-based mTOR inhibitors could become a novel chemotherapeutic strategy.

Curcumin decreases Warburg effect in cancer cells by down-regulating pyruvate kinase M2 via mTOR-HIF1α inhibition

Warburg effect is an emerging hallmark of cancer cells with pyruvate kinase M2 (PKM2) as its key regulator. Curcumin is an extensively-studied anti-cancer compound, however, its role in affecting cancer metabolism remains poorly understood. Herein, we show that curcumin inhibits glucose uptake and lactate production (Warburg effect) in a variety of cancer cell lines by down-regulating PKM2 expression, via inhibition of mTOR-HIF1α axis. Stable PKM2 silencing revealed that PKM2 is required for Warburg effect and proliferation of cancer cells. PKM2 over-expression abrogated the effects of curcumin, demonstrating that inhibition of Warburg effect by curcumin is PKM2-mediated. High PKM2 expression correlated strongly with poor overall survival in cancer, suggesting the requirement of PKM2 in cancer progression. The study unravels novel PKM2-mediated inhibitory effect of curcumin on metabolic capacities of cancer cells. To the best of our knowledge, this is the first study linking curcumin with PKM2-driven cancer glycolysis, thus, providing new perspectives into the mechanism of its anticancer activity.

(-)-Guaiol regulates autophagic cell death depending on mTOR signaling in NSCLC

(-)-Guaiol, a sesquiterpene alcohol with the guaiane skeleton, has been found in many Chinese medicinal plants and been reported to comprise various guaiane natural products that are well known for their antibacterial activities. Previously, we have shown its antitumor activity by inducing autophagy in NSCLC cells. However, its potential mechanism in inducing autophagy is still under our investigation. Here, data from our western blotting assays showed that, in NSCLC cells, (-)-Guaiol significantly blocked the mTORC2-AKT signaling by suppressing mTOR phosphorylation at serine 2481 (S2481) to induce autophagy, illustrated by the increasing ratio of LC3II/I. Besides, it impaired the mTORC1 signaling by inhibiting the activity of its downstream factors, such as 4E-BP1 and p70 S6K, all of which could obviously rescued by the mTOR activator MHY1485. Afterwards, results from biofunctional assays, including cell survival analysis, colony formation assays and flow cytometry assays, suggested that (-)-Guaiol triggered autophagic cell death by targeting both mTORC1 and mTORC2 signaling pathways. In summary, our studies showed that (-)-Guaiol inhibited the proliferation of NSCLC cells by specifically targeting mTOR signaling pathways, including both mTORC1 and mTORC2 signaling, providing a better therapeutic option for substituting rapamycin in treating NSCLC patients.

MicroRNA-26a inhibits the growth and invasiveness of malignant melanoma and directly targets on MITF gene

Metastatic melanoma is the most aggressive form of skin cancer and is refractory to therapy. MicroRNAs have been recently discovered as novel molecules that provide therapeutic benefits against melanoma. This work aims to examine the effects of miR-26a and let-7a on the growth and invasiveness of malignant melanoma in vitro and in vivo. In addition, we elucidate the mechanism of action by identifying the target gene of miR-26a. Both miR-26a and let-7a inhibited proliferation and invasiveness and halted the cell cycle at the G₁/G₀ phase in SKMEL-28 and WM1552C malignant melanoma cell lines. Moreover, miR-26a potently induced apoptosis and downregulated the expressions of microphthalmia-associated transcription factor (MITF) and MAP4K3 in both cell lines. The luciferase reporter assay demonstrated that miR-26a suppresses MITF expression by binding the 3′-UTR, suggesting that MITF is a bona fide target of miR-26a. SiRNA knockdown of the MITF gene confirmed that miR-26a reduced cell viability and induced apoptosis by regulating MITF. Using a murine model, we also found miR-26a significantly retarded the growth of melanoma tumors in vivo. In conclusion, miR-26a and let-7a suppressed the growth and invasiveness of melanoma cells, suggesting that miR-26a and let-7a may represent novel therapies for malignant melanoma.

A novel mechanism of mTORC1-mediated serine/glycine metabolism in osteosarcoma development

Osteosarcoma is the major malignant primary bone cancer in children and adolescents, which is highly aggressive with frequent acquisition of chemoresistance phenotypes. Although much progress has been made, mechanisms of osteosarcoma rapid growth and chemoresistance are still not well elucidated. Generally, alternated metabolic characterization has been proposed to be a hallmark of cancer, yet it is lack of a systematic characterization of cancer metabolic networks. In the present study, we aim to characterize osteosarcoma metabolism and key regulators to reveal mechanisms of how osteosarcoma grows and resists apoptosis under stress conditions. The results demonstrate that mTORC1 pathway is hyperactivated in clinical osteosarcoma samples. However, inhibition of mTORC1 may not be enough to induce significant death of osteosarcoma cells. Results of GC-TOFMS suggested that inhibition of mTORC1 reduce one-carbon amino acids, serine and glycine, in osteosarcoma cells. Moreover, mTORC1 regulates serine/glycine de novo synthesis via modulating glycolysis and serine/glycine synthesis gene expressions. Further, mTORC1/serine/glycine metabolic axis promotes osteosarcoma proliferation and antioxidant ability to environmental stress, which finally leads to cell survival. Our results identify a novel mechanism of mTORC1-mediated serine/glycine metabolism as a significant protective system in osteosarcoma cells.

Tyrosine kinase receptor EGFR regulates the switch in cancer cells between cell survival and cell death induced by autophagy in hypoxia

Autophagy is an intracellular lysosomal degradation pathway where its primary function is to allow cells to survive under stressful conditions. Autophagy is, however, a double-edge sword that can either promote cell survival or cell death. In cancer, hypoxic regions contribute to poor prognosis due to the ability of cancer cells to adapt to hypoxia in part through autophagy. In contrast, autophagy could contribute to hypoxia induced cell death in cancer cells. In this study, we showed that autophagy increased during hypoxia. At 4 h of hypoxia, autophagy promoted cell survival whereas, after 48 h of hypoxia, autophagy increased cell death. Furthermore, we found that the tyrosine phosphorylation of EGFR (epidermal growth factor receptor) decreased after 16 h in hypoxia. Furthermore, EGFR binding to BECN1 in hypoxia was significantly higher at 4 h compared to 72 h. Knocking down or inhibiting EGFR resulted in an increase in autophagy contributing to increased cell death under hypoxia. In contrast, when EGFR was reactivated by the addition of EGF, the level of autophagy was reduced which led to decreased cell death. Hypoxia led to autophagic degradation of the lipid raft protein CAV1 (caveolin 1) that is known to bind and activate EGFR in a ligand-independent manner during hypoxia. By knocking down CAV1, the amount of EGFR phosphorylation was decreased in hypoxia and amount of autophagy and cell death increased. This indicates that the activation of EGFR plays a critical role in the switch between cell survival and cell death induced by autophagy in hypoxia.

Protein Kinase A Activation Promotes Cancer Cell Resistance to Glucose Starvation and Anoikis

Cancer cells often rely on glycolysis to obtain energy and support anabolic growth. Several studies showed that glycolytic cells are susceptible to cell death when subjected to low glucose availability or to lack of glucose. However, some cancer cells, including glycolytic ones, can efficiently acquire higher tolerance to glucose depletion, leading to their survival and aggressiveness. Although increased resistance to glucose starvation has been shown to be a consequence of signaling pathways and compensatory metabolic routes activation, the full repertoire of the underlying molecular alterations remain elusive. Using omics and computational analyses, we found that cyclic adenosine monophosphate-Protein Kinase A (cAMP-PKA) axis activation is fundamental for cancer cell resistance to glucose starvation and anoikis. Notably, here we show that such a PKA-dependent survival is mediated by parallel activation of autophagy and glutamine utilization that in concert concur to attenuate the endoplasmic reticulum (ER) stress and to sustain cell anabolism. Indeed, the inhibition of PKA-mediated autophagy or glutamine metabolism increased the level of cell death, suggesting that the induction of autophagy and metabolic rewiring by PKA is important for cancer cellular survival under glucose starvation. Importantly, both processes actively participate to cancer cell survival mediated by suspension-activated PKA as well. In addition we identify also a PKA/Src mechanism capable to protect cancer cells from anoikis. Our results reveal for the first time the role of the versatile PKA in cancer cells survival under chronic glucose starvation and anoikis and may be a novel potential target for cancer treatment.

Tumor heterogeneity exists in many human cancers, and it has been shown that it can play a role in tumor progression. Indeed, cell diversity may be critically important when tumors experience selective pressures, like nutrient deprivation, hypoxia, chemotherapy. PKA, through incompletely understood mechanisms, controls several cellular processes like cell growth, cell differentiation, cell metabolism, cell migration and, as more recently observed, also cancer progression. In this work, we show that activation of PKA induces the ability of a cancer cell sub-population to survive under strong stress conditions namely nutrient deprivation and cell detachment. Indeed, PKA activation in these cells results in autophagy induction, and at the same time, in activation of glutamine metabolism and Src kinase. Importantly, blocking directly the PKA pathway, as well as the autophagy, the glutamine metabolism or the Src pathway by inhibitory drugs, almost completely prevents cell growth of this sub-population of resistant cancer cells. These results suggest that drugs, targeting especially PKA pathway as well as downstream processes like autophagy, glutamine metabolism and Src signaling, may specifically inhibit cancer cells ability to survive under selective pressure favoring cancer resistance.

Autophagy regulation in the development and treatment of breast cancer

Autophagy is a major catabolic process in which intracellular membrane structures, protein complexes, and lysosomes are formed as lysoautophagosome to degrade and renew cytoplasmic components. Autophagy is physiologically a strategy and mechanism for cellular homeostasis as well as adaptation to stress, and thus alterations in the autophagy machinery may lead to diverse pathological conditions. The role of autophagy in cancer is complex, and the current literature reflects this as a 'double-edged sword'. Autophagy shows promise as a novel therapeutic target in various types of breast cancer, inhibiting or increasing treatment efficacy in a context- and cell-type-dependent manner. This review aims to summarize the recent advances in the understanding of the mechanisms by which key modulators of autophagy participate in cancer metastasis, highlight different autophagy-deficient murine models for breast cancer study, and provide further impetus for the modulation of autophagy in anticancer therapy.

Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved?

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

•

Oxidative stress is linked to overnutrition, obesity and associated diseases or cancer.

•

Reactive oxygen species (ROS) are crucially involved in modulation of signaling cascades.

•

NOX proteins and hypoxia contribute to formation of ROS under different nutrient regimes.

•

ROS are powerful post-transcriptional and epigenetic regulators.

•

Treatment of obesity with antioxidants requires more, larger, and better monitored clinical trials.

Anticipating mechanisms of resistance to PI3K inhibition in breast cancer: a challenge in the era of precision medicine

Frequent subversion of the PI3K (phosphoinositide 3-kinase) pathway during neoplastic transformation contributes to several hallmarks of cancer that result in a competitive advantage for cancer cells. Deregulation of this pathway can be the result of genomic alterations such as PIK3CA mutation, PTEN (phosphatase and tensin homologue deleted on chromosome 10) loss or the activation of upstream protein tyrosine kinases. Not surprisingly, the PI3K signalling pathway has become an attractive therapeutic target, and numerous inhibitors are in clinical trials. Unfortunately, current therapies for advanced cancers that target PI3K often lead to the development of resistance and relapse of the disease. It is therefore important to establish the molecular mechanisms of resistance to PI3K-targeted therapy. With the focus on breast cancer, in the present article, we summarize the different ways of targeting PI3K, review potential mechanisms of resistance to PI3K inhibition and discuss the rationale of combination treatments to reach a balance between efficacy and toxicity.

mTOR signaling in tumorigenesis

mTOR (the mechanistic target of rapamycin) is an atypical serine/threonine kinase involved in regulating major cellular functions including growth and proliferation. Deregulation of the mTOR signaling pathway is one of the most commonly observed pathological alterations in human cancers. To this end, oncogenic activation of the mTOR signaling pathway contributes to cancer cell growth, proliferation and survival, highlighting the potential for targeting the oncogenic mTOR pathway members as an effective anti-cancer strategy. In order to do so, a thorough understanding of the physiological roles of key mTOR signaling pathway components and upstream regulators would guide future targeted therapies. Thus, in this review, we summarize available genetic mouse models for mTORC1 and mTORC2 components, as well as characterized mTOR upstream regulators and downstream targets, and assign a potential oncogenic or tumor suppressive role for each evaluated molecule. Together, our work will not only facilitate the current understanding of mTOR biology and possible future research directions, but more importantly, provide a molecular basis for targeted therapies aiming at key oncogenic members along the mTOR signaling pathway.