Metabolic Reprogramming by the PI3K-Akt-mTOR Pathway in Cancer

miR-718 is involved in malignancy of papillary thyroid cancer through repression of PDPK1

BACKGROUND

MicroRNAs bind the 3' untranslated regions (3'-UTRs) of mRNAs and thereby regulate gene expression post-transcriptionally and play an important role in cancer delvelopment. In the present study, we have explored the role of miR-718 in papillary thyroid cancer cell malignancy.

MATERIALS/METHODS

Here we examined the miRNA expression in human papillary thyroid cancer by RT-PCR. Luciferase activity, RT-PCR and western blot assays were used to confirmed the target of miRNA. MTT, colony formation, transwell, glucose consumption and lactate production assays were performed to analyze papillary thyroid cancer cell function. Western blot for signaling proteins was used to reveal the mechanism.

RESULTS

We first determined that miR-718 mRNA expression levels in PTC samples were reduced. The 3'-UTR of 3-Phosphoinositide Dependent Protein Kinase 1 (PDPK1) was then identified as a target of miR-718. Luciferase assays showed that miR-718 does in fact bind the wild-type PDPK1 3'-UTR. We assessed the effects of miR-718 on p-Akt, Akt, p-mTOR and mTOR expression. We determined that miR-718 negatively regulates their levels, respectively, of Akt-mTOR pathway components. We then assessed the effects of miR-718 on PTC cell behavior. The results revealed that miR-718 negatively regulates PTC cell proliferation, migration, and invasion. In addition, miR-718 was found to inhibit cell glucose metabolism, likely through the Akt-mTOR pathway. Finally, PDPK1 could rescue PTC cell inhibition induced by miR-718.

CONCLUSIONS

The present study strongly suggests that miR-718 inhibits PTC cell proliferation, metastasis, and glucose metabolism by negatively regulating the Akt-mTOR signaling pathway.

Microenvironmental regulation of cancer cell metabolism: implications for experimental design and translational studies

Cancers have an altered metabolism, and there is interest in understanding precisely how oncogenic transformation alters cellular metabolism and how these metabolic alterations can translate into therapeutic opportunities. Researchers are developing increasingly powerful experimental techniques to study cellular metabolism, and these techniques have allowed for the analysis of cancer cell metabolism, both in tumors and in ex vivo cancer models. These analyses show that, while factors intrinsic to cancer cells such as oncogenic mutations, alter cellular metabolism, cell-extrinsic microenvironmental factors also substantially contribute to the metabolic phenotype of cancer cells. These findings highlight that microenvironmental factors within the tumor, such as nutrient availability, physical properties of the extracellular matrix, and interactions with stromal cells, can influence the metabolic phenotype of cancer cells and might ultimately dictate the response to metabolically targeted therapies. In an effort to better understand and target cancer metabolism, this Review focuses on the experimental evidence that microenvironmental factors regulate tumor metabolism, and on the implications of these findings for choosing appropriate model systems and experimental approaches.

Inhibition of protein arginine methyltransferase 5 enhances hepatic mitochondrial biogenesis

Protein arginine methyltransferase 5 (PRMT5) regulates gene expression either transcriptionally by symmetric dimethylation of arginine residues on histones H4R3, H3R8, and H2AR3 or at the posttranslational level by methylation of nonhistone target proteins. Although emerging evidence suggests that PRMT5 functions as an oncogene, its role in metabolic diseases is not well-defined. We investigated the role of PRMT5 in promoting high-fat-induced hepatic steatosis. A high-fat diet up-regulated PRMT5 levels in the liver but not in other metabolically relevant tissues such as skeletal muscle or white and brown adipose tissue. This was associated with repression of master transcription regulators involved in mitochondrial biogenesis. In contrast, lentiviral short hairpin RNA-mediated reduction of PRMT5 significantly decreased phosphatidylinositol 3-kinase/AKT signaling in mouse AML12 liver cells. PRMT5 knockdown or knockout decreased basal AKT phosphorylation but boosted the expression of peroxisome proliferator-activated receptor α (PPARα) and PGC-1α with a concomitant increase in mitochondrial biogenesis. Moreover, by overexpressing an exogenous WT or enzyme-dead mutant PRMT5 or by inhibiting PRMT5 enzymatic activity with a small-molecule inhibitor, we demonstrated that the enzymatic activity of PRMT5 is required for regulation of PPARα and PGC-1α expression and mitochondrial biogenesis. Our results suggest that targeting PRMT5 may have therapeutic potential for the treatment of fatty liver.

Metformin Targets Glucose Metabolism in Triple Negative Breast Cancer

Metformin is the most widely administered anti-diabetic agent worldwide. In patients receiving metformin for metabolic syndrome or diabetes, it reduces the incidence and improves the survival of breast cancer (BC) patients. We have previously shown that metformin is particularly potent against triple negative breast cancer (TNBC), with a reduction of proliferation, oncogenicity and motility, inhibition of pro-oncogenic signaling pathways and induction of apoptosis. These BCs are well recognized to be highly dependent on glucose/glucosamine (metabolized through anaerobic glycolysis) and lipids, which are metabolized for the production of energy and cellular building blocks to sustain a high rate of proliferation. We have previously demonstrated that metformin inhibits lipid metabolism, specifically targeting fatty acid synthase (FASN), cholesterol biosynthesis and GM1 lipid rafts in TNBC. We also reported that glucose promotes phenotypic aggression and reduces metformin efficacy. We now show that metformin inhibits several key enzymes requisite to glucose metabolism in TNBC, providing additional insight into why metformin is especially toxic to this subtype of BC. Our data suggests that the use of metformin to target key metabolic defects in lipid and carbohydrate metabolism in cancer may be broadly applicable, especially against highly aggressive malignant cells.

Standing up to the cardiometabolic consequences of hematological cancers

Hematological cancer survivors are highly vulnerable to cardiometabolic complications impacting long-term health status, quality of life and survival. Elevated risk of diabetes and cardiovascular disease arises not only from the effects of the cancers themselves, but also from the toxic effects of cancer therapies, and deconditioning arising from reduced physical activity levels. Regular physical activity can circumvent or reverse adverse effects on the heart, skeletal muscle, vasculature and blood cells, through a combination of systemic and molecular mechanisms. We review the link between hematological cancers and cardiometabolic risk with a focus on adult survivors, including the contributing mechanisms and discuss the potential for physical activity interventions, which may act to oppose the negative effects of both physical deconditioning and therapies (conventional and targeted) on metabolic and growth signaling (kinase) pathways in the heart and beyond. In this context, we focus particularly on strategies targeting reducing and breaking up sedentary time and provide recommendations for future research.

Metabolic Determinants of Sensitivity to Phosphatidylinositol 3-Kinase Pathway Inhibitor in Small-Cell Lung Carcinoma

Comprehensive genomic analysis has revealed that the PI3K/AKT/mTOR pathway is a feasible therapeutic target in small-cell lung carcinoma (SCLC). However, biomarkers to identify patients likely to benefit from inhibitors of this pathway have not been identified. Here, we show that metabolic features determine sensitivity to the PI3K/mTOR dual inhibitor gedatolisib in SCLC cells. Substantial phosphatidyl lipid analysis revealed that a specific phosphatidylinositol (3,4,5)-trisphosphate (PIP₃) subspecies lipid product PIP₃ (38:4) is predictive in assessing sensitivity to PI3K/mTOR dual inhibitor. Notably, we found that higher amounts of purine-related aqueous metabolites such as hypoxanthine, which are characteristic of SCLC biology, lead to resistance to PI3K pathway inhibition. In addition, the levels of the mRNA encoding hypoxanthine phosphoribosyl transferase 1, a key component of the purine salvage pathway, differed significantly between SCLC cells sensitive or resistant to gedatolisib. Moreover, complementation with purine metabolites could reverse the vulnerability to targeting of the PI3K pathway in SCLC cells normally sensitive to gedatolisib. These results indicate that the resistance mechanism of PI3K pathway inhibitors is mediated by the activation of the purine salvage pathway, supplying purine resource to nucleotide biosynthesis. Metabolomics is a powerful approach for finding novel therapeutic biomarkers in SCLC treatment.Significance: These findings identify features that determine sensitivity of SCLC to PI3K pathway inhibition and support metabolomics as a tool for finding novel therapeutic biomarkers. Cancer Res; 78(9); 2179-90. ©2018 AACR.

Metabolomic Profiling Reveals Cellular Reprogramming of B-Cell Lymphoma by a Lysine Deacetylase Inhibitor through the Choline Pathway

Despite the proven clinical antineoplastic activity of histone deacetylase inhibitors (HDACI), their effect has been reported to be lower than expected in B-cell lymphomas. Traditionally considered as “epigenetic drugs”, HDACI modify the acetylation status of an extensive proteome, acting as general lysine deacetylase inhibitors (KDACI), and thus potentially impacting various branches of cellular metabolism. Here, we demonstrate through metabolomic profiling of patient plasma and cell lines that the KDACI panobinostat alters lipid metabolism and downstream survival signaling in diffuse large B-cell lymphomas (DLBCL). Specifically, panobinostat induces metabolic adaptations resulting in newly acquired dependency on the choline pathway and activation of PI3K signaling. This metabolic reprogramming decreased the antineoplastic effect of panobinostat. Conversely, inhibition of these metabolic adaptations resulted in superior anti-lymphoma effect as demonstrated by the combination of panobinostat with a choline pathway inhibitor. In conclusion, our study demonstrates the power of metabolomics in identifying unknown effects of KDACI, and emphasizes the need for a better understanding of these drugs in order to achieve successful clinical implementation.

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Lysine deacetylase inhibitor (KDACI) treatment alters choline metabolism in B-cell lymphoma patients.

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KDACI-treated lymphoma cells acquire PI3K pathway dependency via increased choline kinase A (CHKA) activity.

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Targeting the acquired choline dependency improves the anti-lymphoma effect of KDACI.

Pera et al. explored the effects of the lysine deacetylase inhibitor panobinostat in the metabolism of patients with lymphoma. They demonstrated that panobinostat alters choline metabolism leading to PI3K pathway activation. Their findings revealed the mechanism behind the anti-lymphoma activity of dual lysine deacetylase/PI3K inhibitors, and uncovered a novel therapeutic strategy based on targeting choline pathway following panobinostat treatment.

Antitumor T-cell Reconditioning: Improving Metabolic Fitness for Optimal Cancer Immunotherapy

With the rapid rise of immunotherapy for cancer treatment, attention has focused on gaining a better understanding of T-cell biology in the tumor microenvironment. Elucidating the factors underlying changes in their function will allow for the development of new therapeutic strategies that could expand the patient population benefiting from immunotherapy, as well as circumvent therapy resistance. Cancers go beyond avoiding immune recognition and inducing T-cell dysfunction through coinhibitory molecules. Recent work has demonstrated that the tumor microenvironment elicits metabolic changes in T cells that dampen their ability to respond and that manipulating these metabolic changes can strengthen an antitumor immune response. Here we review the metabolic status of various types of T cells, the energetic state of the tumor microenvironment, and proposed modalities for improvement of immunotherapy through metabolic remodeling. Clin Cancer Res; 24(11); 2473-81. ©2018 AACR.

Non-coding RNAs in the reprogramming of glucose metabolism in cancer

Proliferating cancer cells reprogram their metabolic circuitry to thrive in an environment deficient in nutrients and oxygen. Cancer cells exhibit a higher rate of glucose metabolism than normal somatic cells, which is achieved by switching from oxidative phosphorylation to aerobic glycolysis to meet the energy and metabolites demands of tumour progression. This phenomenon, which is known as the Warburg effect, has generated renewed interest in the process of glucose metabolism reprogramming in cancer cells. Several regulatory pathways along with glycolytic enzymes are responsible for the emergence of glycolytic dependence. Non-coding (nc)RNAs are a class of functional RNA molecules that are not translated into proteins but regulate target gene expression. NcRNAs have been shown to be involved in various biological processes, including glucose metabolism. In this review, we describe the regulatory role of ncRNAs-specifically, microRNAs and long ncRNAs-in the glycolytic switch and propose that ncRNA-based therapeutics can be used to inhibit the process of glucose metabolism reprogramming in cancer cells.

Cancer chemoprevention and therapy using chinese herbal medicine

Traditional Chinese medicine (TCM) plays an indispensable role in cancer prevention and treatment. Chinese herbal medicine (CHM) is a key component of TCM and has been practiced for thousands of years. A number of naturally occurring products from Chinese herbs extracts exhibit strong inhibitory properties against carcinogenesis, including CHM single-herb extracts, CHM-derived active components, and CHM formulas (the polyherbal combinations), which regulate JAK/STAT, MAPK, and NF-ҡB pathways. The present review aims to report the cancer-preventive effect of CHM with evidence from cell-line, animal, epidemiological, and clinical experiments. We also present several issues that have yet to be resolved. In the future, cancer prevention by CHM will face unprecedented opportunities and challenges.

Oncogenic PI3K promotes methionine dependency in breast cancer cells through the cystine-glutamate antiporter xCT

The precursor homocysteine is metabolized either through the methionine cycle to produce methionine or through the transsulfuration pathway to synthesize cysteine. Alternatively, cysteine can be obtained through uptake of its oxidized form, cystine. Many cancer cells exhibit methionine dependency such that their proliferation is impaired in growth media in which methionine is replaced by homocysteine. We showed that oncogenic PIK3CA and decreased expression of SLC7A11, a gene that encodes a cystine transporter also known as xCT, correlated with increased methionine dependency in breast cancer cells. Oncogenic PIK3CA was sufficient to confer methionine dependency to mammary epithelial cells, partly by decreasing cystine uptake through the transcriptional and posttranslational inhibition of xCT. Manipulation of xCT activity altered the proliferation of breast cancer cells in methionine-deficient, homocysteine-containing media, suggesting that it functionally contributed to methionine dependency. We propose that concurrent with decreased cystine uptake through xCT, PIK3CA mutant cells use homocysteine through the transsulfuration pathway to synthesize cysteine. Consequently, less homocysteine is available to produce methionine, contributing to methionine dependency. These results indicate that oncogenic PIK3CA alters methionine and cysteine utilization, partly by inhibiting xCT to contribute to the methionine dependency phenotype in breast cancer cells.

Varying the ratio of Lys:Met while maintaining the ratios of Thr:Phe, Lys:Thr, Lys:His, and Lys:Val alters mammary cellular metabolites, mammalian target of rapamycin signaling, and gene transcription

Amino acids are not only precursors for but also signaling molecules regulating protein synthesis. Regulation of protein synthesis via AA occurs at least in part by alterations in the phosphorylation status of mammalian target of rapamycin (mTOR) pathway proteins. Although the ideal profile of Lys:Met to promote milk protein synthesis during established lactation in dairy cows has been proposed to be 3:1, aside from being the most-limiting AA for milk protein synthesis, the role of Met in other key biologic pathways such as methylation is not well characterized in the bovine. The objective of this study was to determine the influence of increasing supplemental Met, based on the ideal 3:1 ratio of Lys to Met, on intracellular metabolism related to protein synthesis and mTOR pathway phosphorylation status. MAC-T cells, an immortalized bovine mammary epithelial cell line, were incubated (n = 5 replicates/treatment) for 12 h with 3 incremental doses of Met while holding Lys concentration constant to achieve the following: Lys:Met 2.9:1 (ideal AA ratio; IPAA), Lys:Met 2.5:1 (LM2.5), and Lys:Met 2.0:1 (LM2.0). The ratios of Thr:Phe (1.05:1), Lys:Thr (1.8:1), Lys:His (2.38:1), and Lys:Val (1.23:1) were the same across the 3 treatments. Applying gas chromatography-mass spectrometry metabolomics revealed distinct clusters of differentially concentrated metabolites in response to Lys:Met. Lower Phe, branched-chain AA, and putrescine concentrations were observed with LM2.5 compared with IPAA. Apart from greater intracellular Met concentrations, further elevations in Met level (LM2.0) led to greater intracellular concentrations of nonessential AA (Pro, Glu, Gln, and Gly) compared with IPAA and greater essential AA (EAA; Met, Ile, and Leu) and nonessential AA (Pro, Gly, Ala, Gln, and Glu) compared with LM2.5. However, compared with IPAA, mRNA expression of β-casein and AA transporters (SLC7A5, SLC36A1, SLC38A2, SLC38A9, and SLC43A1) and mTOR phosphorylation were lower in response to LM2.5 and LM2.0. Overall, the results of this study provide evidence that increasing Met while Lys and the ratios of Phe, Thr, His, and Val relative to Lys were held constant could increase the concentration and utilization of intracellular EAA, in particular branched-chain AA, potentially through improving the activity of AA transporters partly controlled by mTOR signaling. Because EAA likely are metabolized by other tissues upon absorption, a question for future in vivo studies is whether formulating diets for optimal ratios of EAA in the metabolizable protein is sufficient to provide the desired levels of these AA to the mammary cells.

Kernel differential subgraph reveals dynamic changes in biomolecular networks

Many major diseases, including various types of cancer, are increasingly threatening human health. However, the mechanisms of the dynamic processes underlying these diseases remain ambiguous. From the holistic perspective of systems science, complex biological networks can reveal biological phenomena. Changes among networks in different states influence the direction of living organisms. The identification of the kernel differential subgraph (KDS) that leads to drastic changes is critical. The existing studies contribute to the identification of a KDS in networks with the same nodes; however, networks in different states involve the disappearance of some nodes or the appearance of some new nodes. In this paper, we propose a new topology-based KDS (TKDS) method to explore the core module from gene regulatory networks with different nodes in this process. For the common nodes, the TKDS method considers the differential value (D-value) of the topological change. For the different nodes, TKDS identifies the most similar gene pairs and computes the D-value. Hence, TKDS discovers the essential KDS, which considers the relationships between the same nodes as well as different nodes. After applying this method to non-small cell lung cancer (NSCLC), we identified 30 genes that are most likely related to NSCLC and extracted the KDSs in both the cancer and normal states. Two significance functional modules were revealed, and gene ontology (GO) analyses and literature mining indicated that the KDSs are essential to the processes in NSCLC. In addition, compared with existing methods, TKDS provides a unique perspective in identifying particular genes and KDSs related to NSCLC. Moreover, TKDS has the potential to predict other critical disease-related genes and modules.

Reprograming of Glucose Metabolism by Zerumbone Suppresses Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the most prevalent and highly aggressive liver malignancy with limited therapeutic options. Here, the therapeutic potential of zerumbone, a sesquiterpene derived from the ginger plant Zingiber zerumbet, against HCC was explored. Zerumbone inhibited proliferation and clonogenic survival of HCC cells in a dose-dependent manner by arresting cells at the G₂-M phase and inducing apoptosis. To elucidate the underlying molecular mechanisms, a phosphokinase array was performed that showed significant inhibition of the PI3K/AKT/mTOR and STAT3 signaling pathways in zerumbone-treated HCC cells. Gene expression profiling using microarray and analysis of microarray data by Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA) revealed that zerumbone treatment resulted in significant deregulation of genes regulating apoptosis, cell cycle, and metabolism. Indeed, tracing glucose metabolic pathways by growing HCC cells with ¹³C₆-glucose and measuring extracellular and intracellular metabolites by 2D nuclear magnetic resonance (NMR) spectroscopy showed a reduction in glucose consumption and reduced lactate production, suggesting glycolytic inhibition. In addition, zerumbone impeded shunting of glucose-6-phosphate through the pentose phosphate pathway, thereby forcing tumor cells to undergo cell-cycle arrest and apoptosis. Importantly, zerumbone treatment suppressed subcutaneous and orthotopic growth and lung metastasis of HCC xenografts in immunocompromised mice. In conclusion, these findings reveal a novel and potentially effective therapeutic strategy for HCC using a natural product that targets cancer cell metabolism.Implications: Dietary compounds, like zerumbone, that impact cell cycle, apoptosis, and metabolic processes may have therapeutic benefits for HCC patients. Mol Cancer Res; 16(2); 256-68. ©2017 AACR.

Small molecule inhibitor regorafenib inhibits RET signaling in neuroblastoma cells and effectively suppresses tumor growth in vivo

Neuroblastoma (NB), the most common extracranial pediatric solid tumor, continues to cause significant cancer-related morbidity and mortality in children. Dysregulation of oncogenic receptor tyrosine kinases (RTKs) has been shown to contribute to tumorigenesis in various human cancers and targeting these RTKs has had therapeutic benefit. RET is an RTK which is commonly expressed in NB, and high expression of RET correlates with poor outcomes in patients with NB. Herein we report that RET is required for NB cell proliferation and that the small molecule inhibitor regorafenib (BAY 73-4506) blocks glial cell derived neurotrophic factor (GDNF)-induced RET signaling in NB cells and inhibits NB growth both in vitro and in vivo. We found that regorafenib significantly inhibited cell proliferation and colony formation ability of NB cells. Moreover, regorafenib suppressed tumor growth in both an orthotopic xenograft NB mouse model and a TH-MYCN transgenic NB mouse model. Finally, regorafenib markedly improved the overall survival of TH-MYCN transgenic tumor-bearing mice. In summary, our study suggests that RET is a potential therapeutic target in NB, and that using a novel RET inhibitor, like regorafenib, should be investigated as a therapeutic treatment option for children with NB.

The PI3K Pathway in Human Disease

Phosphoinositide 3-kinase (PI3K) activity is stimulated by diverse oncogenes and growth factor receptors, and elevated PI3K signaling is considered a hallmark of cancer. Many PI3K pathway-targeted therapies have been tested in oncology trials, resulting in regulatory approval of one isoform-selective inhibitor (idelalisib) for treatment of certain blood cancers and a variety of other agents at different stages of development. In parallel to PI3K research by cancer biologists, investigations in other fields have uncovered exciting and often unpredicted roles for PI3K catalytic and regulatory subunits in normal cell function and in disease. Many of these functions impinge upon oncology by influencing the efficacy and toxicity of PI3K-targeted therapies. Here we provide a perspective on the roles of class I PI3Ks in the regulation of cellular metabolism and in immune system functions, two topics closely intertwined with cancer biology. We also discuss recent progress developing PI3K-targeted therapies for treatment of cancer and other diseases.

Deletion of HNF1α in hepatocytes results in fatty liver-related hepatocellular carcinoma in mice

Hepatocyte nuclear factor 1α (HNF1α) is a liver-enriched transcription factor that is critical for the maintenance of hepatocyte function. Our previous studies have demonstrated the therapeutic effects of HNF1α on hepatic fibrosis and hepatocellular carcinoma (HCC) in animals. In this study, we created hepatocyte-specific Hnf1α knockout mice using the Cre-loxP recombination system. The knockout mice display increased fatty acid synthesis in the liver. Moreover, these mice spontaneously develop HCC through fatty liver without cirrhosis. Inflammatory cytokines, such as tumor necrosis factor α and IL-6, are upregulated and accompanied by increased phosphorylation of Akt, p-65 and STAT3 in the livers of HNF1α knockout mice. Our findings suggest that HNF1α plays a crucial role in hepatocyte lipid metabolism and hepatocarcinogenesis.

HIF-2α regulates non-canonical glutamine metabolism via activation of PI3K/mTORC2 pathway in human pancreatic ductal adenocarcinoma

Hypoxia‐inducible factor‐2α (HIF‐2α) plays an important role in increasing cancer progression and distant metastasis in a variety of tumour types. We aimed to investigate its biological function and clinical significance in human pancreatic ductal adenocarcinoma (PDAC). A total of 283 paired PDAC tissues and adjacent normal tissues were collected from patients who underwent surgery or biopsy at Sun Yat‐sen Memorial Hospital between February 2004 and October 2016. In this study, we noted that HIF‐2α expression was significantly up‐regulated in PDAC, positively associated with disease stage, lymph‐node metastasis and patient survival, and identified as an independent prognostic factor of PDAC patients. We demonstrated that HIF‐2α silencing could reduce proliferation, migration and invasion of PDAC cells in vitro. The similar effect on growth was demonstrated in vivo. Furthermore, we noted that knock‐down of HIF‐2α significantly decreased the expression of glutamate oxaloacetate transaminase 1 (GOT1). Importantly, we confirmed that the PI3K/mTORC2 pathway promoted GOT1 expression by targeting HIF‐2α. Our study validated HIF‐2α was an important factor in PDAC progression and poor prognosis and may promote non‐canonical glutamine metabolism via activation of PI3K/mTORC2 pathway. Targeting HIF‐2α represents a novel prognostic biomarker and therapeutic target for patients with PDAC.

Control of B lymphocyte development and functions by the mTOR signaling pathways

Mechanistic target of rapamycin (mTOR) is a serine/threonine kinase originally discovered as the molecular target of the immunosuppressant rapamycin. mTOR forms two compositionally and functionally distinct complexes, mTORC1 and mTORC2, which are crucial for coordinating nutrient, energy, oxygen, and growth factor availability with cellular growth, proliferation, and survival. Recent studies have identified critical, non-redundant roles for mTORC1 and mTORC2 in controlling B cell development, differentiation, and functions, and have highlighted emerging roles of the Folliculin-Fnip protein complex in regulating mTOR and B cell development. In this review, we summarize the basic mechanisms of mTOR signaling; describe what is known about the roles of mTORC1, mTORC2, and the Folliculin/Fnip1 pathway in B cell development and functions; and briefly outline current clinical approaches for targeting mTOR in B cell neoplasms. We conclude by highlighting a few salient questions and future perspectives regarding mTOR in B lineage cells.

Curcumin inhibits urothelial tumor development by suppressing IGF2 and IGF2-mediated PI3K/AKT/mTOR signaling pathway

We have previously reported that curcumin inhibits urothelial tumor development in a rat bladder carcinogenesis model. In this study, we report that curcumin inhibits urothelial tumor development by suppressing IGF2 and IGF2-mediated PI3K/AKT/mTOR signaling pathway. Curcumin inhibits IGF2 expression at the transcriptional level and decreases the phosphorylation levels of IGF1R and IRS-1 in bladder cancer cells and N-methyl-N-nitrosourea (MNU)-induced urothelial tumor tissue. Ectopic expression of IGF2 and IGF1R, but not IGF1, in bladder cancer cells restored this process, suggesting that IGF2 is a target of curcumin. Moreover, introduction of constitutively active AKT1 abolished the inhibitory effect of curcumin on cell proliferation, migration, and restored the phosphorylation levels of 4E-BP1 and S6K1, suggesting that curcumin functions via suppressing IGF2-mediated AKT/mTOR signaling pathway. In summary, our results reveal that suppressing IGF2 and IGF2-mediated PI3K/AKT/mTOR signaling pathway is one of the mechanisms of action of curcumin. Our findings suggest a new therapeutic strategy against human bladder cancer caused by aberrant activation of IGF2, which are useful for translational application of curcumin.

PI3K signaling in cancer: beyond AKT

The phosphoinositide 3-kinase (PI3K) signaling pathway is one of the most frequently altered pathways in human cancer and has a critical role in driving tumor initiation and progression. Although PI3K and its lipid product phosphatidylinositol-3,4,5-trisphosphate (PIP₃) have been shown to activate multiple downstream signaling proteins, the vast majority of studies have focused on the protein kinase AKT as the dominant effector of PI3K signaling. However, recent studies have demonstrated many contexts under which other PIP₃-dependent signaling proteins critically contribute to cancer progression, illustrating the importance of understanding AKT-independent signaling downstream of PI3K. Here, we highlight three PI3K-dependent, but AKT-independent, signaling branches that have recently been shown to have important roles in promoting phenotypes associated with malignancy. First, the PDK1-mTORC2-SGK axis can substitute for AKT in survival, migration, and growth signaling and has emerged as a major mechanism of resistance to PI3K and AKT inhibitors. Second, Rac signaling mediates the reorganization of the actin cytoskeleton to regulate cancer cell migration, invasion, and metabolism. Finally, the TEC family kinase BTK has a critical role in B cell function and malignancy and represents a recent example of an effective therapeutic target in cancer. These mechanisms highlight how understanding PI3K-dependent, but AKT-independent, signaling mechanisms that drive cancer progression will be crucial for the development of novel and more effective approaches for targeting the PI3K pathway for therapeutic benefit in cancer.

Impact of Metabolism on T-Cell Differentiation and Function and Cross Talk with Tumor Microenvironment

The immune system and metabolism are highly integrated and multilevel interactions between metabolic system and T lymphocyte signaling and fate exist. Accumulating evidence indicates that the regulation of nutrient uptake and utilization in T cells is critically important for the control of their differentiation and manipulating metabolic pathways in these cells can shape their function and survival. This review will discuss some potential cell metabolism pathways involved in shaping T lymphocyte function and differentiation. It will also describe show subsets of T cells have specific metabolic requirements and signaling pathways that contribute to their respective function. Examples showing the apparent similarity between cancer cell metabolism and T cells during activation are illustrated and finally some mechanisms being used by tumor microenvironment to orchestrate T-cell metabolic dysregulation and the subsequent emergence of immune suppression are discussed. We believe that targeting T-cell metabolism may provide an additional opportunity to manipulate T-cell function in the development of novel therapeutics.