DIF-1 inhibits growth and metastasis of triple-negative breast cancer through AMPK-mediated inhibition of the mTORC1-S6K signaling pathway

Mammalian target of differentiation-inducing factor-1 is mitochondrial malate dehydrogenase for activation of AMP-activated protein kinase and induction of mitochondrial fission

AIMS

Differentiation-inducing factor-1 (DIF-1) is a polyketide produced by Dictyostelium discoideum that inhibits growth and migration, while promoting the differentiation of Dictyostelium stalk cells through unknown mechanisms. DIF-1 localizes in stalk mitochondria. In addition to its effect on Dictyostelium, DIF-1 also inhibits growth and migration, and induces mitochondrial fission followed by mitophagy in mammalian cells, at least in part by activating AMP-activated protein kinase (AMPK). In a previous study, we found that DIF-1 binds to mitochondrial malate dehydrogenase (MDH2) and inhibits its activity in HeLa cells. In the present study, we investigated whether MDH2 serves as a pharmacological target of DIF-1 in mammalian cells.

MAIN METHODS

To examine the enzymatic activity of MDH, mitochondrial morphology, and molecular mechanisms of DIF-1 action, we conducted an MDH reverse reaction assay, immunofluorescence staining, western blotting, and RNA interference using mammalian cells such as human umbilical vein endothelial cells, human cervical cancer cells, mouse endothelial cells, and mouse breast cancer cells.

KEY FINDINGS

DIF-1 inhibited mitochondrial but not cytoplasmic MDH activity. Similar to DIF-1, LW6, an authentic MDH2 inhibitor, induced phosphorylation of AMPK, resulting in the phosphorylation of acetyl-CoA carboxylase (ACC) and the dephosphorylation of p70 S6 kinase with approximately the same potency. DIF-1 and LW6 induced mitochondrial fission. Furthermore, MDH2 knockdown using siRNA reproduced the DIF-1 action on the AMPK signaling and mitochondrial morphology. Conversely, an AMPK inhibitor prevented DIF-1-induced mitochondrial fission.

SIGNIFICANCE

We propose that MDH2 is a mammalian target of DIF-1 for the activation of AMPK and induction of mitochondrial fission.

DT-13 inhibits the proliferation of pancreatic cancer by inducing apoptosis via AMPK-mTOR signaling

BACKGROUND/OBJECTIVE

DT-13, the principal active component of Mysidium shortscapes from the Liliaceae family, has garnered substantial interest in cancer therapy owing to its potential anticancer properties. This study investigated the effects of DT-13 on the proliferation and apoptosis of human pancreatic cancer cell lines and aimed to elucidate the underlying mechanisms.

METHODS

PANC1 and CFPAC1 cells were exposed to DT-13 and their proliferation was assessed using RTCA and clone formation assays. Apoptotic protein expression was analyzed by western blotting, and apoptotic cells were identified by flow cytometry. RNA was extracted from DT-13 treated and untreated PANC1 cells for RNA sequencing. Differentially expressed genes were identified and subjected to GO bioprocess, KEGG pathway analysis, and western blotting. Finally, to evaluate tumor growth, CFPAC1 cells were subcutaneously injected into BALB/c nude mice.

RESULTS

DT-13 inhibited proliferation and induced apoptosis of PANC1 and CFPAC1 cells by activating the AMPK/mTOR pathway and suppressing p70 S6K. Moreover, DT-13 hindered the growth of CFPAC1 xenograft tumors in nude mice.

CONCLUSIONS

DT-13 effectively inhibited the growth of human pancreatic cancer cells.

Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake via Direct Inhibition of Mitochondrial Malate Dehydrogenase in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1), found in Dictyostelium discoideum, has antiproliferative and glucose-uptake-promoting activities in mammalian cells. DIF-1 is a potential lead for the development of antitumor and/or antiobesity/antidiabetes drugs, but the mechanisms underlying its actions have not been fully elucidated. In this study, we searched for target molecules of DIF-1 that mediate the actions of DIF-1 in mammalian cells by identifying DIF-1-binding proteins in human cervical cancer HeLa cells and mouse 3T3-L1 fibroblast cells using affinity chromatography and liquid chromatography-tandem mass spectrometry and found mitochondrial malate dehydrogenase (MDH2) to be a DIF-1-binding protein in both cell lines. Since DIF-1 has been shown to directly inhibit MDH2 activity, we compared the effects of DIF-1 and the MDH2 inhibitor LW6 on the growth of HeLa and 3T3-L1 cells and on glucose uptake in confluent 3T3-L1 cells in vitro. In both HeLa and 3T3-L1 cells, DIF-1 at 10-40 μM dose-dependently suppressed growth, whereas LW6 at 20 μM, but not at 2-10 μM, significantly suppressed growth in these cells. In confluent 3T3-L1 cells, DIF-1 at 10-40 μM significantly promoted glucose uptake, with the strongest effect at 20 μM DIF-1, whereas LW6 at 2-20 μM significantly promoted glucose uptake, with the strongest effect at 10 μM LW6. Western blot analyses showed that LW6 (10 μM) and DIF-1 (20 μM) phosphorylated and, thus, activated AMP kinase in 3T3-L1 cells. Our results suggest that MDH2 inhibition can suppress cell growth and promote glucose uptake in the cells, but appears to promote glucose uptake more strongly than it suppresses cell growth. Thus, DIF-1 may promote glucose uptake, at least in part, via direct inhibition of MDH2 and a subsequent activation of AMP kinase in 3T3-L1 cells.

Differentiation-inducing factor-1 reduces lipopolysaccharide-induced vascular cell adhesion molecule-1 by suppressing mTORC1-S6K signaling in vascular endothelial cells

AIMS

Differentiation-inducing factor-1 (DIF-1), a compound in Dictyostelium discoideum, exhibits anti-cancer effects by inhibiting cell proliferation and motility of various mammalian cancer cells in vitro and in vivo. In addition, DIF-1 suppresses lung colony formation in a mouse model, thus impeding cancer metastasis. However, the precise mechanism underlying its anti-metastatic effect remains unclear. In the present study, we aim to elucidate this mechanism by investigating the adhesion of circulating tumor cells to blood vessels using in vitro and in vivo systems.

MAIN METHODS

Melanoma cells (1.0 × 105 cells) were injected into the tail vein of 8-week-old male C57BL/6 mice after administration of DIF-1 (300 mg/kg per day) and/or lipopolysaccharide (LPS: 2.5 mg/kg per day). To investigate cell adhesion and molecular mechanisms, cell adhesion assay, western blotting, immunofluorescence staining, and flow cytometry were performed.

KEY FINDINGS

Intragastric administration of DIF-1 suppressed lung colony formation. DIF-1 also substantially inhibited the adhesion of cancer cells to human umbilical vein endothelial cells. Notably, DIF-1 did not affect the expression level of adhesion-related proteins in cancer cells, but it did decrease the expression of vascular cell adhesion molecule-1 (VCAM-1) in human umbilical vein endothelial cells by suppressing its mRNA-to-protein translation through inhibition of mTORC1-p70 S6 kinase signaling.

SIGNIFICANCE

DIF-1 reduced tumor cell adhesion to blood vessels by inhibiting mTORC1-S6K signaling and decreasing the expression of adhesion molecule VCAM-1 on vascular endothelial cells. These findings highlight the potential of DIF-1 as a promising compound for the development of anti-cancer drugs with anti-metastatic properties.

Pharmacological Evidence That Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake Partly via an Increase in Intracellular cAMP Content in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1) isolated from the cellular slime mold Dictyostelium discoideum can inhibit mammalian calmodulin-dependent cAMP/cGMP phosphodiesterase (PDE1) in vitro. DIF-1 also promotes glucose uptake, at least in part, via a mitochondria- and AMPK-dependent pathway in mouse 3T3-L1 fibroblast cells, but the mechanism underlying this effect has not been fully elucidated. In this study, we investigated the effects of DIF-1 on intracellular cAMP and cGMP levels, as well as the effects that DIF-1 and several compounds that increase cAMP and cGMP levels have on glucose uptake in confluent 3T3-L1 cells. DIF-1 at 20 μM (a concentration that promotes glucose uptake) increased the level of intracellular cAMP by about 20% but did not affect the level of intracellular cGMP. Neither the PDE1 inhibitor 8-methoxymethyl-3-isobutyl-1-methylxanthine at 10-200 μM nor the broad-range PDE inhibitor 3-isobutyl-1-methylxanthine at 40-400 μM had any marked effects on glucose uptake. The membrane-permeable cAMP analog 8-bromo-cAMP at 200-1000 μM significantly promoted glucose uptake (by 20-25%), whereas the membrane-permeable cGMP analog 8-bromo-cGMP at 3-100 μM did not affect glucose uptake. The adenylate cyclase activator forskolin at 1-10 μM promoted glucose uptake by 20-30%. Thus, DIF-1 may promote glucose uptake by 3T3-L1 cells, at least in part, via an increase in intracellular cAMP level.

HER3/Akt/mTOR pathway is a key therapeutic target for the reduction of triple‑negative breast cancer metastasis via the inhibition of CXCR4 expression

Triple‑negative breast cancer (TNBC), a highly metastatic subtype of breast cancer, and it has the worst prognosis among all subtypes of breast cancer. However, no effective systematic therapy is currently available for TNBC metastasis. Therefore, novel therapies targeting the key molecular mechanisms involved in TNBC metastasis are required. The present study examined whether the expression levels of human epidermal growth factor receptor 3 (HER3) were associated with the metastatic phenotype of TNBC, and evaluated the potential of HER3 as a therapeutic target in vitro and in vivo. A new highly metastatic 4T1 TNBC cell line, termed 4T1‑L8, was established. The protein expression levels in 4T1‑L8 cells were measured using luminex magnetic bead assays and western blot analysis. The HER3 expression levels and distant metastasis‑free survival (DMFS) in TNBC were analyzed using Kaplan‑Meier Plotter. Transwell migration and invasion assays were performed to detect migration and invasion. The anti‑metastatic effects were determined in an experimental mouse model of metastasis. The results revealed that the increased expression of the HER3/Akt/mTOR pathway was associated with a greater level of cell migration, invasion and metastasis of TNBC cells. In addition, it was found that high expression levels of HER3 were associated with a poor DMFS. The inhibition of the HER3/Akt/mammalian target of rapamycin (mTOR) pathway decreased the migration, invasion and metastasis of TNBC cells by decreasing the expression of C‑X‑C chemokine receptor type 4 (CXCR4). Furthermore, treatment of metastatic TNBC cells with everolimus inhibited their migration, invasion and metastasis by decreasing CXCR4 expression. Thus, targeting the HER3/Akt/mTOR pathway opens up a new avenue for the development of therapeutics against TNBC metastasis; in addition, everolimus may prove to be an effective therapeutic agent for the suppression of TNBC metastasis.

Promising small molecule anti-fibrotic agents: Newly developed or repositioned drugs targeting myofibroblast transdifferentiation

Fibrosis occurs in all organs and tissues except the brain, and its progression leads to dysfunction of affected organs. Fibrosis-induced organ dysfunction results from the loss of elasticity, strength, and functionality of tissues due to the extracellular matrix secreted by myofibroblasts that express smooth muscle-type actin as a marker. Myofibroblasts, which play a major role in fibrosis, were once thought to originate exclusively from activated fibroblasts; however, it is now clear that myofibroblasts are diverse in origin, from epithelial cells, endothelial cells, adipocytes, macrophages, and other cells. Fibrosis of vital organs, such as the heart, lungs, kidneys, and liver, is a serious chronic disease that ultimately leads to death. Currently, anti-cancer drugs have made remarkable progress, as evidenced by the development of many molecular-targeted drugs, and are making a significant contribution to improving the prognosis of cancer treatment. However, the development of anti-fibrotic agents, which also play an important role in prognosis, has lagged. In this review, the current knowledge regarding myofibroblasts is summarized, with particular attention given to their origin and transdifferentiation signaling pathways (e.g., TGF-β, Wnt/β-catenin, YAP/TAZ and AMPK signaling pathways). The development of new small molecule anti-fibrotic agents and the repositioning of existing drugs targeting myofibroblast transdifferentiation are discussed.

Effects of Hyaluronan on Breast Cancer Aggressiveness

The expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) in breast cancer cells is critical for determining tumor aggressiveness and targeting therapies. The presence of such receptors allows for the use of antagonists that effectively reduce breast cancer growth and dissemination. However, the absence of such receptors in triple-negative breast cancer (TNBC) reduces the possibility of targeted therapy, making these tumors very aggressive with a poor outcome. Cancers are not solely composed of tumor cells, but also include several types of infiltrating cells, such as fibroblasts, macrophages, and other immune cells that have critical functions in regulating cancer cell behaviors. In addition to these cells, the extracellular matrix (ECM) has become an important player in many aspects of breast cancer biology, including cell growth, motility, metabolism, and chemoresistance. Hyaluronan (HA) is a key ECM component that promotes cell proliferation and migration in several malignancies. Notably, HA accumulation in the tumor stroma is a negative prognostic factor in breast cancer. HA metabolism depends on the fine balance between HA synthesis by HA synthases and degradation yielded by hyaluronidases. All the different cell types present in the tumor can release HA in the ECM, and in this review, we will describe the role of HA and HA metabolism in different breast cancer subtypes.

Dictyostelium Differentiation-inducing Factor Derivatives Reduce the Glycosylation of PD-L1 in MDA-MB-231 Human Breast Cancer Cells

Objectives

Triple-negative breast cancer (TNBC) is a metastatic and intractable cancer with limited treatment options. Refractory cancer cells often express the immune checkpoint molecules programmed death-ligand 1 (PD-L1) and PD-L2, which inhibit the anticancer effects of T cells. Differentiation-inducing factors, originally found in Dictyostelium discoideum, and their derivatives possess strong antiproliferative activity, at least in part by reducing cyclin D1 expression in various cancer cells, but their effects on PD-L1/PD-L2 have not been examined. In this study, we investigate the effects of six DIF compounds (DIFs) on the expression of PD-L1/PD-L2 and cyclin D1/D3 in MDA-MB-231 cells, a model TNBC cell line.

Methods

MDA-MB-231 cells were incubated for 5 or 15 h with or without DIFs, and the mRNA expression of cyclin D1, PD-L1, and PD-L2 were assessed by quantitative polymerase chain reaction (qPCR). Whereas, MDA-MD-231 cells were incubated for 12 or 24 h with or without DIFs, and the protein expression of cyclins D1 and D3, PD-L1, and PD-L2 were assessed by Western blotting.

Results

As expected, some DIFs strongly reduced cyclin D1/D3 protein expression in MDA-MB-231 cells. Contrary to our expectation, DIFs had little effect on PD-L1 mRNA expression or increased it transiently. However, some DIFs partially reduced glycosylated PD-L1 and increased non-glycosylated PD-L1 in MDA-MB-231 cells. The level of PD-L2 was very low in these cells.

Conclusions

Since PD-L1 glycosylation plays an important role in preventing T cells from attacking cancer cells, such DIFs may promote T cell attack on cancer cells in vivo.

DIF-1 exhibits anticancer activity in breast cancer via inhibition of CXCLs/CXCR2 axis-mediated communication between cancer-associated fibroblasts and cancer cells

The tumor microenvironment (TME), largely composed of tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs), plays a key role in cancer progression. A small molecule, differentiation-inducing factor-1 (DIF-1) secreted by Dictyostelium discoideum, is known to exhibit anticancer activity; however, its effect on the TME remains unknown. In this study, we investigated the effect of DIF-1 on the TME using mouse triple-negative breast cancer 4T1-GFP cells, mouse macrophage RAW 264.7 cells, and mouse primary dermal fibroblasts (DFBs). Polarization of 4T1 cell-conditioned medium-induced macrophage into TAMs was not affected by DIF-1. In contrast, DIF-1 decreased 4T1 cell co-culturing-induced C-X-C motif chemokine ligand 1 (CXCL1), CXCL5, and CXCL7 expression in DFBs and suppressed DFB differentiation into CAF-like cells. Additionally, DIF-1 inhibited C-X-C motif chemokine receptor 2 (CXCR2) expression in 4T1 cells. Immunohistochemical analyses of tumor tissue samples excised from breast cancer-bearing mice showed that DIF-1 did not affect the number of CD206-positive TAMs; however, it decreased the number of α-smooth muscle actin-positive CAFs and CXCR2 expression. These results indicated that the anticancer effect of DIF-1 was partially attributed to the inhibition of CXCLs/CXCR2 axis-mediated communication between breast cancer cells and CAFs.

Sufentanil combined with parecoxib sodium inhibits proliferation and metastasis of HER2-positive breast cancer cells and regulates epithelial-mesenchymal transition

BACKGROUND

Sufentanil combined with parecoxib sodium is a commonly used postoperative medication for cancer patients. However, the effects of this combination therapy on human epidermal growth factor receptor-2 (HER2)-positive breast cancer cells have still remained elusive. This study aimed to investigate the effects and potential mechanisms of sufentanil combined with parecoxib sodium on HER2-positive breast cancer cells.

METHODS

The cell counting kit-8 (CCK-8), colony formation, flow cytometry, scratch, transwell invasion, and angiogenesis assays were used to assess the proliferation, cell cycling, migration, invasion, and angiogenesis of HER2-positive breast cancer BT474 cells. Western blot assay was employed for detecting the expression levels of proteins involved in the cell cycle, migration, invasion, angiogenesis, and epithelial-mesenchymal transition (EMT). The in vivo effects of tumor growth and metastasis were examined by establishing an orthotopic transplantation mouse model of HER2-positive breast cancer (MMTV-PyMT).

RESULTS

Functional assays indicated that sufentanil combined with parecoxib sodium induced blockade of HER2-positive breast cancer BT474 cells in the G1 phase of the cell cycle and inhibited cell proliferation, migration, angiogenesis, and invasion in vitro. Western blot assay revealed that sufentanil combined with parecoxib sodium downregulated the expression levels of cyclin D1, matrix metalloproteinase-9 (MMP-9), cyclooxygenase-2 (COX-2), vascular endothelial growth factor A (VEGFA), and EMT-related proteins (N-cadherin, Vimentin, and Snail), while up-regulated the expression level of E-cadherin in BT474 cells. In addition, it was found that sufentanil combined with parecoxib sodium inhibited tumor growth and metastasis in the orthotopic transplantation mouse model of HER2-positive breast cancer.

CONCLUSION

Sufentanil combined with parecoxib sodium inhibited HER2-positive breast cancer progression, including cell proliferation, cell cycle, migration, invasion, and angiogenesis, and regulated EMT.

Disorders of cancer metabolism: The therapeutic potential of cannabinoids

Abnormal energy metabolism, as one of the important hallmarks of cancer, was induced by multiple carcinogenic factors and tumor-specific microenvironments. It comprises aerobic glycolysis, de novo lipid biosynthesis, and glutamine-dependent anaplerosis. Considering that metabolic reprogramming provides various nutrients for tumor survival and development, it has been considered a potential target for cancer therapy. Cannabinoids have been shown to exhibit a variety of anticancer activities by unclear mechanisms. This paper first reviews the recent progress of related signaling pathways (reactive oxygen species (ROS), AMP-activated protein kinase (AMPK), mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinase (PI3K), hypoxia-inducible factor-1alpha (HIF-1α), and p53) mediating the reprogramming of cancer metabolism (including glucose metabolism, lipid metabolism, and amino acid metabolism). Then we comprehensively explore the latest discoveries and possible mechanisms of the anticancer effects of cannabinoids through the regulation of the above-mentioned related signaling pathways, to provide new targets and insights for cancer prevention and treatment.

Nanomaterial-assisted CRISPR gene-engineering - A hallmark for triple-negative breast cancer therapeutics advancement

Triple-negative breast cancer (TNBC) is the most violent class of tumor and accounts for 20–24% of total breast carcinoma, in which frequently rare mutation occurs in high frequency. The poor prognosis, recurrence, and metastasis in the brain, heart, liver and lungs decline the lifespan of patients by about 21 months, emphasizing the need for advanced treatment. Recently, the adaptive immunity mechanism of archaea and bacteria, called clustered regularly interspaced short palindromic repeats (CRISPR) combined with nanotechnology, has been utilized as a potent gene manipulating tool with an extensive clinical application in cancer genomics due to its easeful usage and cost-effectiveness. However, CRISPR/Cas are arguably the efficient technology that can be made efficient via organic material-assisted approaches. Despite the efficacy of the CRISPR/Cas@nano complex, problems regarding successful delivery, biodegradability, and toxicity remain to render its medical implications. Therefore, this review is different in focus from past reviews by (i) detailing all possible genetic mechanisms of TNBC occurrence; (ii) available treatments and gene therapies for TNBC; (iii) overview of the delivery system and utilization of CRISPR-nano complex in TNBC, and (iv) recent advances and related toxicity of CRISPR-nano complex towards clinical trials for TNBC.

Autophagy regulated by the HIF/REDD1/mTORC1 signaling is progressively increased during erythroid differentiation under hypoxia

For hematopoietic stem and progenitor cells (HSPCs), hypoxia is a specific microenvironment known as the hypoxic niche. How hypoxia regulates erythroid differentiation of HSPCs remains unclear. In this study, we show that hypoxia evidently accelerates erythroid differentiation, and autophagy plays a pivotal role in this process. We further determine that mTORC1 signaling is suppressed by hypoxia to relieve its inhibition of autophagy, and with the process of erythroid differentiation, mTORC1 activity gradually decreases and autophagy activity increases accordingly. Moreover, we provide evidence that the HIF-1 target gene REDD1 is upregulated to suppress mTORC1 signaling and enhance autophagy, thereby promoting erythroid differentiation under hypoxia. Together, our study identifies that the enhanced autophagy by hypoxia favors erythroid maturation and elucidates a new regulatory pattern whereby autophagy is progressively increased during erythroid differentiation, which is driven by the HIF-1/REDD1/mTORC1 signaling in a hypoxic niche.

Targeting Breast Cancer and Their Stem Cell Population through AMPK Activation: Novel Insights

Despite some significant advancements, breast cancer has become the most prevalent cancer in the world. One of the main reasons for failure in treatment and metastasis has been attributed to the presence of cancer initiating cells-cancer stem cells. Consequently, research is now being focussed on targeting cancer cells along with their stem cell population. Non-oncology drugs are gaining increasing attention for their potent anticancer activities. Metformin, a drug commonly used to treat type 2 diabetes, is the best example in this regard. It exerts its therapeutic action by activating 5' adenosine monophosphate-activated protein kinase (AMPK). Activated AMPK subsequently phosphorylates and targets several cellular pathways involved in cell growth and proliferation and the maintenance of stem-like properties of cancer stem cells. Therefore, AMPK is emerging as a target of choice for developing effective anticancer drugs. Vanadium compounds are well-known PTP inhibitors and AMPK activators. They find extensive applications in treatment of diabetes and obesity via PTP1B inhibition and AMPK-mediated inhibition of adipogenesis. However, their role in targeting cancer stem cells has not been explored yet. This review is an attempt to establish the applications of insulin mimetic vanadium compounds for the treatment of breast cancer by AMPK activation and PTP1B inhibition pathways.

Possible Involvement of the Nutrient and Energy Sensors mTORC1 and AMPK in Cell Fate Diversification in a Non-Metazoan Organism

mTORC1 and AMPK are mutually antagonistic sensors of nutrient and energy status that have been implicated in many human diseases including cancer, Alzheimer’s disease, obesity and type 2 diabetes. Starved cells of the social amoeba Dictyostelium discoideum aggregate and eventually form fruiting bodies consisting of stalk cells and spores. We focus on how this bifurcation of cell fate is achieved. During growth mTORC1 is highly active and AMPK relatively inactive. Upon starvation, AMPK is activated and mTORC1 inhibited; cell division is arrested and autophagy induced. After aggregation, a minority of the cells (prestalk cells) continue to express much the same set of developmental genes as during aggregation, but the majority (prespore cells) switch to the prespore program. We describe evidence suggesting that overexpressing AMPK increases the proportion of prestalk cells, as does inhibiting mTORC1. Furthermore, stimulating the acidification of intracellular acidic compartments likewise increases the proportion of prestalk cells, while inhibiting acidification favors the spore pathway. We conclude that the choice between the prestalk and the prespore pathways of cell differentiation may depend on the relative strength of the activities of AMPK and mTORC1, and that these may be controlled by the acidity of intracellular acidic compartments/lysosomes (pHv), cells with low pHv compartments having high AMPK activity/low mTORC1 activity, and those with high pHv compartments having high mTORC1/low AMPK activity. Increased insight into the regulation and downstream consequences of this switch should increase our understanding of its potential role in human diseases, and indicate possible therapeutic interventions.