Differential effects of AMPK agonists on cell growth and metabolism

Mild Glucose Starvation Induces KDM2A-Mediated H3K36me2 Demethylation through AMPK To Reduce rRNA Transcription and Cell Proliferation

Environmental conditions control rRNA transcription. Previously, we found that serum and glucose deprivation induces KDM2A-mediated H3K36me2 demethylation in the rRNA gene (rDNA) promoter and reduces rRNA transcription in the human breast cancer cell line MCF-7. However, the molecular mechanism and biological significance are still unclear. In the present study, we found that glucose starvation alone induced the KDM2A-dependent reduction of rRNA transcription. The treatment of cells with 2-deoxy-d-glucose, an inhibitor of glycolysis, reduced rRNA transcription and H3K36me2 in the rDNA promoter, both of which were completely dependent on KDM2A in low concentrations of 2-deoxy-d-glucose, that is, mild starvation conditions. The mild starvation induced these KDM2A activities through AMP-activated kinase (AMPK) but did not affect another AMPK effector of rRNA transcription, TIF-IA. In the triple-negative breast cancer cell line MDA-MB-231, the mild starvation also reduced rRNA transcription in a KDM2A-dependent manner. We detected KDM2A in breast cancer tissues irrespective of their estrogen receptor, progesterone receptor, and HER2 status, including triple-negative cancer tissues. In both MCF-7 and MDA-MB-231 cells, mild starvation reduced cell proliferation, and KDM2A knockdown suppressed the reduction of cell proliferation. These results suggest that under mild glucose starvation AMPK induces KDM2A-dependent reduction of rRNA transcription to control cell proliferation.

Metformin repositioning as antitumoral agent: selective antiproliferative effects in human glioblastoma stem cells, via inhibition of CLIC1-mediated ion current

Epidemiological and preclinical studies propose that metformin, a first-line drug for type-2 diabetes, exerts direct antitumor activity. Although several clinical trials are ongoing, the molecular mechanisms of this effect are unknown.

Here we show that chloride intracellular channel-1 (CLIC1) is a direct target of metformin in human glioblastoma cells. Metformin exposure induces antiproliferative effects in cancer stem cell-enriched cultures, isolated from three individual WHO grade IV human glioblastomas. These effects phenocopy metformin-mediated inhibition of a chloride current specifically dependent on CLIC1 functional activity. CLIC1 ion channel is preferentially active during the G1-S transition via transient membrane insertion. Metformin inhibition of CLIC1 activity induces G1 arrest of glioblastoma stem cells. This effect was time-dependent, and prolonged treatments caused antiproliferative effects also for low, clinically significant, metformin concentrations. Furthermore, substitution of Arg29 in the putative CLIC1 pore region impairs metformin modulation of channel activity.

The lack of drugs affecting cancer stem cell viability is the main cause of therapy failure and tumor relapse. We identified CLIC1 not only as a modulator of cell cycle progression in human glioblastoma stem cells but also as the main target of metformin's antiproliferative activity, paving the way for novel and needed pharmacological approaches to glioblastoma treatment.

Disruption of Nucleotide Homeostasis by the Antiproliferative Drug 5-Aminoimidazole-4-carboxamide-1-β-d-ribofuranoside Monophosphate (AICAR)

5-Aminoimidazole-4-carboxamide-1-β-D-ribofuranoside monophosphate (AICAR) is a natural metabolite with potent anti-proliferative and low energy mimetic properties. At high concentration, AICAR is toxic for yeast and mammalian cells, but the molecular basis of this toxicity is poorly understood. Here, we report the identification of yeast purine salvage pathway mutants that are synthetically lethal with AICAR accumulation. Genetic suppression revealed that this synthetic lethality is in part due to low expression of adenine phosphoribosyl transferase under high AICAR conditions. In addition, metabolite profiling points to the AICAR/NTP balance as crucial for optimal utilization of glucose as a carbon source. Indeed, we found that AICAR toxicity in yeast and human cells is alleviated when glucose is replaced by an alternative carbon source. Together, our metabolic analyses unveil the AICAR/NTP balance as a major factor of AICAR antiproliferative effects.

Is 5´-AMP-Activated Protein Kinase Both Jekyll and Hyde in Bladder Cancer?

The 5´-AMP-activated protein kinase (AMPK) is a key regulator of cellular metabolism and energy homeostasis in mammalian tissues. Metabolic adaptation is a critical step in ensuring cell survival during metabolic stress. Because of its critical role in the regulation of glucose homeostasis and carbohydrate, lipid, and protein metabolism, AMPK is involved in many human diseases, including cancers. Although AMPK signaling was originally characterized as a tumor-suppressive signaling pathway, several lines of evidence suggest that AMPK plays a much broader role and cannot simply be defined as either an oncogenic regulator or tumor suppressor. Notably, several recent studies demonstrated that the antitumorigenic effects of many indirect AMPK activators, such as metformin, do not depend on AMPK. Conversely, activation of AMPK induces the progression of cancers, emphasizing its oncogenic effect. Bladder cancer can be divided into two groups: non–muscle-invasive bladder cancer (NMIBC) and muscle-invasive bladder cancer (MIBC). The molecular mechanisms underlying these two types of cancer are distinct: NMIBC is associated with activation of the Ras pathway, whereas MIBC is characterized by loss of major tumor suppressors. Importantly, both pathways are connected to the mammalian target of rapamycin (mTOR) pathway. In addition, our recent metabolomic findings suggest that β-oxidation of fatty acids is an important factor in the development of bladder cancer. Both mTOR and β-oxidation are tightly associated with the AMPK pathway. Here, I summarize and discuss the recent findings on the two distinct roles of AMPK in cancer, as well as the relationship between bladder cancer and AMPK.

Phenformin Induces Cell Cycle Change, Apoptosis, and Mesenchymal-Epithelial Transition and Regulates the AMPK/mTOR/p70s6k and MAPK/ERK Pathways in Breast Cancer Cells

Breast cancer remains a world-wide challenge, and additional anti-cancer therapies are still urgently needed. Emerging evidence has demonstrated the potent anti-tumor effect of biguanides, among which phenformin was reported to potentially be a more active anti-cancer agent than metformin. However, little attention has been given to the role of phenformin in breast cancer. In this study, we reveal the role of phenformin in cell death of the MCF7, ZR-75-1, MDA-MB-231 and SUM1315 breast cancer cell lines. The respective IC₅₀ values of phenformin in MCF7, ZR-75-1, MDA-MB-231 and SUM1315 cells were 1.184±0.045 mM, 0.665±0.007 mM, 2.347±0.010 mM and 1.885±0.015 mM (mean± standard error). Phenformin induced cell cycle change and apoptosis in breast cancer cells via the AMPK/mTOR/p70s6k and MAPK/ERK pathways. Interestingly, phenformin induced MET (mesenchymal-epithelial transition) and decreased the migration rate in breast cancer cell lines. Furthermore, our results suggest that phenformin inhibits breast cancer cell metastasis after intracardiac injection into nude mice. Taken together, our study further confirms the potential benefit of phenformin in breast cancer treatment and provides novel mechanistic insight into its anti-cancer activity in breast cancer.

AMP-Activated Protein Kinase Regulates the Cell Surface Proteome and Integrin Membrane Traffic

The cell surface proteome controls numerous cellular functions including cell migration and adhesion, intercellular communication and nutrient uptake. Cell surface proteins are controlled by acute changes in protein abundance at the plasma membrane through regulation of endocytosis and recycling (endomembrane traffic). Many cellular signals regulate endomembrane traffic, including metabolic signaling; however, the extent to which the cell surface proteome is controlled by acute regulation of endomembrane traffic under various conditions remains incompletely understood. AMP-activated protein kinase (AMPK) is a key metabolic sensor that is activated upon reduced cellular energy availability. AMPK activation alters the endomembrane traffic of a few specific proteins, as part of an adaptive response to increase energy intake and reduce energy expenditure. How increased AMPK activity during energy stress may globally regulate the cell surface proteome is not well understood. To study how AMPK may regulate the cell surface proteome, we used cell-impermeable biotinylation to selectively purify cell surface proteins under various conditions. Using ESI-MS/MS, we found that acute (90 min) treatment with the AMPK activator A-769662 elicits broad control of the cell surface abundance of diverse proteins. In particular, A-769662 treatment depleted from the cell surface proteins with functions in cell migration and adhesion. To complement our mass spectrometry results, we used other methods to show that A-769662 treatment results in impaired cell migration. Further, A-769662 treatment reduced the cell surface abundance of β1-integrin, a key cell migration protein, and AMPK gene silencing prevented this effect. While the control of the cell surface abundance of various proteins by A-769662 treatment was broad, it was also selective, as this treatment did not change the cell surface abundance of the transferrin receptor. Hence, the cell surface proteome is subject to acute regulation by treatment with A-769662, at least some of which is mediated by the metabolic sensor AMPK.

Special Conference on Tumor Immunology and Immunotherapy: A New Chapter

The overall objective of the fifth American Association for Cancer Research Special Conference, "Tumor Immunology and Immunotherapy: A New Chapter," organized by the Cancer Immunology Working Group, was to highlight multidisciplinary approaches of immunotherapy and mechanisms related to the ability of immunotherapy to fight established tumors. With the FDA approval of sipuleucel-T, ipilimumab (anti-CTLA-4; Bristol-Myers Squibb), and the two anti-PD-1 antibodies, pembrolizumab (formerly MK-3475 or lambrolizumab; Merck) and nivolumab (Bristol-Myers Squibb), immunotherapy has become a mainstream treatment option for some cancers. Many of the data presented at the conference and reviewed in this article showcase the progress made in determining the mechanistic reasons for the success of some treatments and the mechanisms associated with tolerance within the tumor microenvironment, both of which are potential targets for immunotherapy. In addition to combination and multimodal therapies, improvements in existing therapies will be needed to overcome the numerous ways that tumor-specific tolerance thwarts the immune system. This conference built upon the success of the 2012 conference and focused on seven progressing and/or emerging areas-new combination therapies, combination therapies and vaccine improvement, mechanisms of antibody therapy, factors in the tumor microenvironment affecting the immune response, the microbiomes effect on cancer and immunotherapy, metabolism in immunotherapy, and adoptive T-cell therapy. Cancer Immunol Res; 3(6); 1-8. ©2015 AACR.

Dissecting the Dual Role of AMPK in Cancer: From Experimental to Human Studies

The precise role of 5'AMP-activated kinase (AMPK) in cancer and its potential as a therapeutic target is controversial. Although it is well established that activation of this energy sensor inhibits the main anabolic processes that sustain cancer cell proliferation and growth, AMPK activation can confer on cancer cells the plasticity to survive under metabolic stress such as hypoxia and glucose deprivation, which are commonly observed in fast growing tumors. Thus, AMPK is referred to as both a "conditional" tumor suppressor and "contextual" oncogene. To add a further layer of complexity, AMPK activation in human cancer tissues and its correlation with tumor aggressiveness and progression appears to vary in different contexts. The current review discusses the different faces of this metabolic regulator, the therapeutic implications of its modulation, and provides an overview of the most relevant data available on AMPK activation and AMPK-activating drugs in human studies.

Fatty acid metabolism in the regulation of T cell function

The specific regulation of cellular metabolic processes is of major importance for directing immune cell differentiation and function. We review recent evidence indicating that changes in basic cellular lipid metabolism have critical effects on T cell proliferation and cell fate decisions. While induction of de novo fatty acid (FA) synthesis is essential for activation-induced proliferation and differentiation of effector T cells, FA catabolism via β-oxidation is important for the development of CD8(+) T cell memory as well as for the differentiation of CD4(+) regulatory T cells. We consider the influence of lipid metabolism and metabolic intermediates on the regulation of signaling and transcriptional pathways via post-translational modifications, and discuss how an improved understanding of FA metabolism may reveal strategies for manipulating immune responses towards therapeutic outcomes.

The double-edged sword of AMPK signaling in cancer and its therapeutic implications

5'-AMP-activated protein kinase (AMPK) plays a pivotal role in maintaining energy and redox homeostasis under various metabolic stress conditions. Metabolic adaptation, which can be triggered by the activation of AMPK during metabolic stress, is the critical process for cell survival through the maintenance of ATP and NADPH levels. The importance of such regulation of fundamental process poses the AMPK signaling pathway in one of the most attractive therapeutic targets in many pathologies such as diabetes and cancer. In cancer, however, accumulating data suggest that the role of AMPK would not be simply defined as anti- or pro-tumorigenic, but it seems to have two faces like a double-edged sword. Importantly, recent studies showed that the anti-tumorigenic effects of many 'indirect' AMPK activators such as anti-diabetic biguanides are not dependent on AMPK; rather the activation of AMPK induces the resistance to their cytotoxic effects, emphasizing the pro-tumorigenic effect of AMPK. In this review, we summarize and discuss recent findings suggesting the two faces of AMPK in cancer, and discuss how we can exploit this unique feature of AMPK for novel therapeutic intervention.

AMPK/mTOR-mediated inhibition of survivin partly contributes to metformin-induced apoptosis in human gastric cancer cell

Recent studies demonstrated that metformin exerts anti-neoplastic effect in a spectrum of malignancies. However, the mechanism whereby metformin affects various cancers, including gastric cancer, is poorly elucidated. Considering apoptosis plays critical role in tumorigenesis, we, in the present study, investigated the in vitro apoptotic effect of metformin on human gastric cancer cell and the underlying mechanism. Three differently-differentiated gastric cancer cell lines, MKN-28, SGC-7901 and BGC-823, along with one noncancerous gastric cell line GES-1 were used. We found that metformin treatment selectively induces apoptosis in the 3 cancer cell lines, but not the noncancerous one, as confirmed by flow cytometry, Caspase-Glo assay and western blotting against PARP and cleaved caspase 3. Moreover, the apoptotic effect of metformin seems to correlate negatively with the differentiation degree of gastric cancer. Metformin-induced apoptosis may be partially mediated through inhibition of anti-apoptotic survivin. Additionally, AMPK and mTOR, 2 important regulatory molecules responsible for metformin action, were investigated for their possible involvements in metformin-induced apoptosis of gastric cancer cell. AMPK knockdown by siRNA restores metformin-inhibited survivin expression and partially abolishes metformin-induced apoptosis. Similarly, forced overexpression of mTOR downstream effector p70S6K1 relieves metformin-induced inhibition of survivin and partly attenuates metformin-induced apoptosis. More importantly, survivin overexpression alleviates metformin-induced apoptosis. Xenograft nude mouse experiment also confirmed that AMPK/mTOR-mediated decrease of suvivin is in vivo implicated in metformin-induced apoptosis. Taken together, these evidences suggest that AMPK/mTOR-mediated inhibition of survivin may partly contribute to metformin-induced apoptosis of gastric cancer cell.

The role of Fatty Acid oxidation in the metabolic reprograming of activated t-cells

Activation represents a significant bioenergetic challenge for T-cells, which must undergo metabolic reprogramming to keep pace with increased energetic demands. This review focuses on the role of fatty acid metabolism, both in vitro and in vivo, following T-cell activation. Based upon previous studies in the literature, as well as accumulating evidence in allogeneic cells, I propose a multi-step model of in vivo metabolic reprogramming. In this model, a primary determinant of metabolic phenotype is the ubiquity and duration of antigen exposure. The implications of this model, as well as the future challenges and opportunities in studying T-cell metabolism, will be discussed.