AMP-activated protein kinase inhibits IGF-I signaling and protein synthesis in vascular smooth muscle cells via stimulation of insulin receptor substrate 1 S794 and tuberous sclerosis 2 S1345 phosphorylation

Metformin: A Dual-Role Player in Cancer Treatment and Prevention

Cancer continues to pose a significant global health challenge, as evidenced by the increasing incidence rates and high mortality rates, despite the advancements made in chemotherapy. The emergence of chemoresistance further complicates the effectiveness of treatment. However, there is growing interest in the potential of metformin, a commonly prescribed drug for type 2 diabetes mellitus (T2DM), as an adjuvant chemotherapy agent in cancer treatment. Although the precise mechanism of action of metformin in cancer therapy is not fully understood, it has been found to have pleiotropic effects, including the modulation of metabolic pathways, reduction in inflammation, and the regulation of cellular proliferation. This comprehensive review examines the anticancer properties of metformin, drawing insights from various studies conducted in vitro and in vivo, as well as from clinical trials and observational research. This review discusses the mechanisms of action involving both insulin-dependent and independent pathways, shedding light on the potential of metformin as a therapeutic agent for different types of cancer. Despite promising findings, there are challenges that need to be addressed, such as conflicting outcomes in clinical trials, considerations regarding dosing, and the development of resistance. These challenges highlight the importance of further research to fully harness the therapeutic potential of metformin in cancer treatment. The aims of this review are to provide a contemporary understanding of the role of metformin in cancer therapy and identify areas for future exploration in the pursuit of effective anticancer strategies.

Tuberous Sclerosis, Type II Diabetes Mellitus and the PI3K/AKT/mTOR Signaling Pathways-Case Report and Literature Review

Tuberous sclerosis complex (TSC) is a rare autosomal dominant neurocutaneous syndrome. It is manifested mainly in cutaneous lesions, epilepsy and the emergence of hamartomas in several tissues and organs. The disease sets in due to mutations in two tumor suppressor genes: TSC1 and TSC2. The authors present the case of a 33-year-old female patient registered with the Bihor County Regional Center of Medical Genetics (RCMG) since 2021 with a TSC diagnosis. She was diagnosed with epilepsy at eight months old. At 18 years old she was diagnosed with tuberous sclerosis and was referred to the neurology department. Since 2013 she has been registered with the department for diabetes and nutritional diseases with a type 2 diabetes mellitus (T2DM) diagnosis. The clinical examination revealed: growth delay, obesity, facial angiofibromas, sebaceous adenomas, depigmented macules, papillomatous tumorlets in the thorax (bilateral) and neck, periungual fibroma in both lower limbs, frequent convulsive seizures; on a biological level, high glycemia and glycated hemoglobin levels. Brain MRI displayed a distinctive TS aspect with five bilateral hamartomatous subependymal nodules associating cortical/subcortical tubers with the frontal, temporal and occipital distribution. Molecular diagnosis showed a pathogenic variant in the TSC1 gene, exon 13, c.1270A>T (p. Arg424*). Current treatment targets diabetes (Metformin, Gliclazide and the GLP-1 analog semaglutide) and epilepsy (Carbamazepine and Clonazepam). This case report presents a rare association between type 2 diabetes mellitus and Tuberous Sclerosis Complex. We suggest that the diabetes medication Metformin may have positive effects on both the progression of the tumor associated with TSC and the seizures specific to TSC and we assume that the association of TSC and T2DM in the presented cases is accidental, as there are no similar cases reported in the literature.

New insights on the cardiovascular effects of IGF-1

INTRODUCTION

Cardiovascular (CV) disorders are steadily increasing, making them the world's most prevalent health issue. New research highlights the importance of insulin-like growth factor 1 (IGF-1) for maintaining CV health.

METHODS

We searched PubMed and MEDLINE for English and non-English articles with English abstracts published between 1957 (when the first report on IGF-1 identification was published) and 2022. The top search terms were: IGF-1, cardiovascular disease, IGF-1 receptors, IGF-1 and microRNAs, therapeutic interventions with IGF-1, IGF-1 and diabetes, IGF-1 and cardiovascular disease. The search retrieved original peer-reviewed articles, which were further analyzed, focusing on the role of IGF-1 in pathophysiological conditions. We specifically focused on including the most recent findings published in the past five years.

RESULTS

IGF-1, an anabolic growth factor, regulates cell division, proliferation, and survival. In addition to its well-known growth-promoting and metabolic effects, there is mounting evidence that IGF-1 plays a specialized role in the complex activities that underpin CV function. IGF-1 promotes cardiac development and improves cardiac output, stroke volume, contractility, and ejection fraction. Furthermore, IGF-1 mediates many growth hormones (GH) actions. IGF-1 stimulates contractility and tissue remodeling in humans to improve heart function after myocardial infarction. IGF-1 also improves the lipid profile, lowers insulin levels, increases insulin sensitivity, and promotes glucose metabolism. These findings point to the intriguing medicinal potential of IGF-1. Human studies associate low serum levels of free or total IGF-1 with an increased risk of CV and cerebrovascular illness. Extensive human trials are being conducted to investigate the therapeutic efficacy and outcomes of IGF-1-related therapy.

DISCUSSION

We anticipate the development of novel IGF-1-related therapy with minimal side effects. This review discusses recent findings on the role of IGF-1 in the cardiovascular (CVD) system, including both normal and pathological conditions. We also discuss progress in therapeutic interventions aimed at targeting the IGF axis and provide insights into the epigenetic regulation of IGF-1 mediated by microRNAs.

The dynamics of mitochondrial-linked gene expression among tissues and life stages in two contrasting strains of laying hens

The cellular energy metabolism is one of the most conserved processes, as it is present in all living organisms. Mitochondria are providing the eukaryotic cell with energy and thus their genome and gene expression has been of broad interest for a long time. Mitochondrial gene expression changes under different conditions and is regulated by genes encoded in the nucleus of the cell. In this context, little is known about non-model organisms and we provide the first large-scaled gene expression analysis of mitochondrial-linked genes in laying hens. We analysed 28 mitochondrial and nuclear genes in 100 individuals in the context of five life-stages and strain differences among five tissues. Our study showed that mitochondrial gene expression increases during the productive life span, and reacts tissue and strain specific. In addition, the strains react different to potential increased oxidative stress, resulting from the increase in mitochondrial gene expression. The results suggest that the cellular energy metabolism as part of a complex regulatory system is strongly affected by the productive life span in laying hens and thus partly comparable to model organisms. This study provides a starting point for further analyses in this field on non-model organisms, especially in laying-hens.

Canagliflozin, a SGLT-2 inhibitor, relieves ER stress, modulates autophagy and induces apoptosis in irradiated HepG2 cells: Signal transduction between PI3K/AKT/GSK-3β/mTOR and Wnt/β-catenin pathways; in vitro

Background and Objectives

Metabolic shifting from mitochondrial respiration to glycolysis characterizes malignant cells from its normal counterparts and is attributed to overactivation of oncogenic signaling pathways. Hence, this study intended to investigate the influence of canagliflozin (CAN) and/or γ-irradiation (γ-IR) on HepG2 cell proliferation, crosstalk between phosphatidylinositol 3-kinases (PI3K)/AKT/glycogen synthase kinase-3-β (GSK3-β)/mTOR and Wnt/β-catenin signaling pathways, and their regulation of diverse processes, such as endoplasmic reticulum (ER) stress, autophagy, and apoptosis.

Materials and Methods

HepG2 cells were treated with different doses of CAN and then exposed to different doses of γ-IR to achieve optimization that was based on cytotoxicity and clonogenic assays, respectively. The effects of CAN and/or γ-IR on glycolytic metabolism, cellular bioenergetics, oxidative stress, ER stress and autophagy biomarkers, expression of PI3K/AKT/GSK3-β/mTOR and Wnt/β-Catenin signaling pathways, and apoptotic markers were monitored.

Results

CAN enhanced the antitumor potential of γ-IR as displayed by a significant inhibition of clonogenic survival in HepG2 cells via inhibition of glucose uptake, lactate release, and modulation of ER stress-mediated autophagy; switched it to apoptosis; as well as disabled signaling pathways which contribute to metabolic reprogramming and tumor progression induced by γ-IR that confer radioresistance and treatment failure.

Conclusion

Our study sheds light on the effective combination of CAN and γ-IR in hepatocellular carcinoma treatment and necessitates CAN treatment prior to γ-IR to overcome metabolic reprogramming-associated radioresistance and improve curative outcomes.

Metformin: review of epidemiology and mechanisms of action in pancreatic cancer

Pancreatic ductal adenocarcinoma continues to be a lethal disease, for which efficient treatment options are very limited. Increasing efforts have been taken to understand how to prevent or intercept this disease at an early stage. There is convincing evidence from epidemiologic and preclinical studies that the antidiabetic drug metformin possesses beneficial effects in pancreatic cancer, including reducing the risk of developing the disease and improving survival in patients with early-stage disease. This review will summarize the current literature about the epidemiological data on metformin and pancreatic cancer as well as describe the preclinical evidence illustrating the anticancer effects of metformin in pancreatic cancer. Underlying mechanisms and targets of metformin will also be discussed. These include direct effects on transformed pancreatic epithelial cells and indirect, systemic effects on extra-pancreatic tissues.

Therapeutic effect of oxyberberine on obese non-alcoholic fatty liver disease rats

BACKGROUND

Berberine (BBR) has been widely used to treat non-alcoholic fatty liver disease (NAFLD). The metabolites of BBR were believed to contribute significantly to its pharmacological effects. Oxyberberine (OBB), a gut microbiota-mediated oxidative metabolite of BBR, has been firstly identified in our recent work.

PURPOSE

Here, we aimed to comparatively investigate the anti-NAFLD properties of OBB and BBR.

METHODS

The anti-NAFLD effect was evaluated in high-fat diet-induced obese NAFLD rats with biochemical/ELISA tests and histological staining. The related gene and protein expressions were detected by qRT-PCR and Western blotting respectively. Molecular docking and dynamic simulation were also performed to provide further insight.

RESULTS

Results indicated OBB remarkably and dose-dependently attenuated the clinical manifestations of NAFLD, which (100 mg/kg) achieved similar therapeutic effect to metformin (300 mg/kg) and was superior to BBR of the same dose. OBB significantly inhibited aberrant phosphorylation of IRS-1 and up-regulated the downstream protein expression and phosphorylation (PI3K, p-Akt/Akt and p-GSK-3β/GSK-3β) to improve hepatic insulin signal transduction. Meanwhile, OBB treatment remarkably alleviated inflammation via down-regulating the mRNA expression of MCP-1, Cd68, Nos2, Cd11c, while enhancing Arg1 mRNA expression in white adipose tissue. Moreover, OBB exhibited closer affinity with AMPK in silicon and superior hyperphosphorylation of AMPK in vivo, leading to increased ACC mRNA expression in liver and UCP-1 protein expression in adipose tissue.

CONCLUSION

Taken together, compared with BBR, OBB was more capable of maintaining lipid homeostasis between liver and WAT via attenuating hepatic insulin pathway and adipocyte inflammation, which was associated with its property of superior AMPK activator.

AMPK regulation of Raptor and TSC2 mediate metformin effects on transcriptional control of anabolism and inflammation

Here, Van Nostrand et al. investigated the mechanisms of action of the biguanide drug metformin by using a new Raptor^AA mouse model, in which AMPK phospho-serine sites Ser722 and Ser792 of RAPTOR were mutated to alanine. The hepatic transcriptional response in mice on a high-fat diet treated with metformin was largely ablated by AMPK deficiency under the conditions examined, indicating the essential role of this kinase and its targets in metformin action in vivo.

Despite being the frontline therapy for type 2 diabetes, the mechanisms of action of the biguanide drug metformin are still being discovered. In particular, the detailed molecular interplays between the AMPK and the mTORC1 pathway in the hepatic benefits of metformin are still ill defined. Metformin-dependent activation of AMPK classically inhibits mTORC1 via TSC/RHEB, but several lines of evidence suggest additional mechanisms at play in metformin inhibition of mTORC1. Here we investigated the role of direct AMPK-mediated serine phosphorylation of RAPTOR in a new Raptor^AA mouse model, in which AMPK phospho-serine sites Ser722 and Ser792 of RAPTOR were mutated to alanine. Metformin treatment of primary hepatocytes and intact murine liver requires AMPK regulation of both RAPTOR and TSC2 to fully inhibit mTORC1, and this regulation is critical for both the translational and transcriptional response to metformin. Transcriptionally, AMPK and mTORC1 were both important for regulation of anabolic metabolism and inflammatory programs triggered by metformin treatment. The hepatic transcriptional response in mice on high-fat diet treated with metformin was largely ablated by AMPK deficiency under the conditions examined, indicating the essential role of this kinase and its targets in metformin action in vivo.

AMPK controls the axonal regenerative ability of dorsal root ganglia sensory neurons after spinal cord injury

Regeneration after injury occurs in axons that lie in the peripheral nervous system but fails in the central nervous system, thereby limiting functional recovery. Differences in axonal signalling in response to injury that might underpin this differential regenerative ability are poorly characterized. Combining axoplasmic proteomics from peripheral sciatic or central projecting dorsal root ganglion (DRG) axons with cell body RNA-seq, we uncover injury-dependent signalling pathways that are uniquely represented in peripheral versus central projecting sciatic DRG axons. We identify AMPK as a crucial regulator of axonal regenerative signalling that is specifically downregulated in injured peripheral, but not central, axons. We find that AMPK in DRG interacts with the 26S proteasome and its CaMKIIα-dependent regulatory subunit PSMC5 to promote AMPKα proteasomal degradation following sciatic axotomy. Conditional deletion of AMPKα1 promotes multiple regenerative signalling pathways after central axonal injury and stimulates robust axonal growth across the spinal cord injury site, suggesting inhibition of AMPK as a therapeutic strategy to enhance regeneration following spinal cord injury.

Intermittent fasting promotes adult hippocampal neuronal differentiation by activating GSK-3β in 3xTg-AD mice

Moderate dietary restriction can ameliorate age-related chronic diseases such as Alzheimer's disease (AD) by increasing the expression of neurotrophic factors and promoting neurogenesis in the brain. Glycogen synthase kinase-3β (GSK-3β) signaling is essential for the coordination of progenitor cell proliferation and differentiation during brain development. The mechanisms by which GSK-3β is involved in dietary restriction-induced neurogenesis and cognitive improvement remain unclear. Six-month-old male 3xTg-AD and wild-type mice were fed on alternate days (intermittent fasting, IF) or ad libitum (AL) for 3 months. GSK-3β activity was regulated by bilaterally infusing lentiviral vectors carrying siRNA targeting GSK-3β into the dentate gyrus region of the hippocampus. Intermittent fasting promoted neuronal differentiation and maturation in the dentate gyrus and ameliorated recognized dysfunction in 3xTg-AD mice. These effects were reversed by siRNA targeting GSK-3β. After intermittent fasting, the insulin and protein kinase A signaling pathways were inhibited, while the adenosine monophosphate-activated protein kinase and brain-derived neurotrophic factor pathways were activated. These findings suggest that intermittent fasting can promote neuronal differentiation and maturation in the hippocampus by activating GSK-3β, thus improving learning and memory.

Metalloproteinase PAPP-A regulation of IGF-1 contributes to polycystic kidney disease pathogenesis

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic cause of end-stage renal disease (ESRD). The treatment options for ADPKD are limited. We observed an upregulation in several IGF-1 pathway genes in the kidney of Pkd1RC/RC mice, a model of ADPKD. Pregnancy-associated plasma protein A (PAPP-A), a metalloproteinase that cleaves inhibitory IGF binding proteins (IGFBPs), increasing the local bioactivity of IGF-1, was highly induced in the kidney of ADPKD mice. PAPP-A levels were high in cystic fluid and kidneys of humans with ADPKD. Our studies further showed that PAPP-A transcription in ADPKD was mainly regulated through the cAMP/CREB/CBP/p300 pathway. Pappa deficiency effectively inhibited the development of cysts in the Pkd1RC/RC mice. The role of PAPP-A in cystic disease appears to be regulation of the IGF-1 pathway and cellular proliferation in the kidney. Finally, preclinical studies demonstrated that treatment with a monoclonal antibody that blocks the proteolytic activity of PAPP-A against IGFBP4 ameliorated ADPKD cystic disease in vivo in Pkd1RC/RC mice and ex vivo in embryonic kidneys. These data indicated that the PAPP-A/IGF-1 pathway plays an important role in the growth and expansion of cysts in ADPKD. Our findings introduce a therapeutic strategy for ADPKD that involves the inhibition of PAPP-A.

Signaling Network of Forkhead Family of Transcription Factors (FOXO) in Dietary Restriction

Dietary restriction (DR), which is defined as a reduction of particular or total nutrient intake without causing malnutrition, has been proved to be a robust way to extend both lifespan and health-span in various species from yeast to mammal. However, the molecular mechanisms by which DR confers benefits on longevity were not yet fully elucidated. The forkhead box O transcription factors (FOXOs), identified as downstream regulators of the insulin/IGF-1 signaling pathway, control the expression of many genes regulating crucial biological processes such as metabolic homeostasis, redox balance, stress response and cell viability and proliferation. The activity of FOXOs is also mediated by AMP-activated protein kinase (AMPK), sirtuins and the mammalian target of rapamycin (mTOR). Therefore, the FOXO-related pathways form a complex network critical for coordinating a response to environmental fluctuations in order to maintain cellular homeostasis and to support physiological aging. In this review, we will focus on the role of FOXOs in different DR interventions. As different DR regimens or calorie (energy) restriction mimetics (CRMs) can elicit both distinct and overlapped DR-related signaling pathways, the benefits of DR may be maximized by combining diverse forms of interventions. In addition, a better understanding of the precise role of FOXOs in different mechanistic aspects of DR response would provide clear cellular and molecular insights on DR-induced increase of lifespan and health-span.

The Upstream Pathway of mTOR-Mediated Autophagy in Liver Diseases

Autophagy, originally found in liver experiments, is a cellular process that degrades damaged organelle or protein aggregation. This process frees cells from various stress states is a cell survival mechanism under stress stimulation. It is now known that dysregulation of autophagy can cause many liver diseases. Therefore, how to properly regulate autophagy is the key to the treatment of liver injury. mechanistic target of rapamycin (mTOR)is the core hub regulating autophagy, which is subject to different upstream signaling pathways to regulate autophagy. This review summarizes three upstream pathways of mTOR: the phosphoinositide 3-kinase (PI3K)/protein kinase (AKT) signaling pathway, the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway, and the rat sarcoma (Ras)/rapidly accelerated fibrosarcoma (Raf)/mitogen-extracellular activated protein kinase kinase (MEK)/ extracellular-signal-regulated kinase (ERK) signaling pathway, specifically explored their role in liver fibrosis, hepatitis B, non-alcoholic fatty liver, liver cancer, hepatic ischemia reperfusion and other liver diseases through the regulation of mTOR-mediated autophagy. Moreover, we also analyzed the crosstalk between these three pathways, aiming to find new targets for the treatment of human liver disease based on autophagy.

Central role of Yes-associated protein and WW-domain-containing transcriptional co-activator with PDZ-binding motif in pancreatic cancer development

Pancreatic ductal adenocarcinoma (PDAC) remains a deadly disease with no efficacious treatment options. PDAC incidence is projected to increase, which may be caused at least partially by the obesity epidemic. Significantly enhanced efforts to prevent or intercept this cancer are clearly warranted. Oncogenic KRAS mutations are recognized initiating events in PDAC development, however, they are not entirely sufficient for the development of fully invasive PDAC. Additional genetic alterations and/or environmental, nutritional, and metabolic signals, as present in obesity, type-2 diabetes mellitus, and inflammation, are required for full PDAC formation. We hypothesize that oncogenic KRAS increases the intensity and duration of the growth-promoting signaling network. Recent exciting studies from different laboratories indicate that the activity of the transcriptional co-activators Yes-associated protein (YAP) and WW-domain-containing transcriptional co-activator with PDZ-binding motif (TAZ) play a critical role in the promotion and maintenance of PDAC operating as key downstream target of KRAS signaling. While initially thought to be primarily an effector of the tumor-suppressive Hippo pathway, more recent studies revealed that YAP/TAZ subcellular localization and co-transcriptional activity is regulated by multiple upstream signals. Overall, YAP has emerged as a central node of transcriptional convergence in growth-promoting signaling in PDAC cells. Indeed, YAP expression is an independent unfavorable prognostic marker for overall survival of PDAC. In what follows, we will review studies implicating YAP/TAZ in pancreatic cancer development and consider different approaches to target these transcriptional regulators.

Toxin-induced hormesis may restrain aging

Mild environmental stress might have beneficial effects in aging by activating maintenance and repair processes in cells and organs. These beneficial stress effects fit to the concept of hormesis. Prominent stressors acting in a hormetic way are physical exercises, fasting, cold and heat. This review will introduce some toxins, which have been found to induce hormetic responses in animal models of aging research. To highlight the molecular signature of these hormetic effects we will depict signaling pathways affected by low doses of toxins on cellular and organismic level. As prominent examples for signaling pathways involved in both aging processes as well as toxin responses, PI3K/Akt/mTOR- and AMPK-signal transduction will be described in more detail. Due to the striking overlap of signaling pathways mediating toxin induced responses and aging processes we propose considering the ability of low doses of toxins to slow down the rate of aging.

The journey of metformin from glycaemic control to mTOR inhibition and the suppression of tumour growth

Our knowledge of the effect of metformin on human health is increasing. In addition to its ability to improve the control of hyperglycaemia, metformin has been shown to reduce the burden o,f ageing via effects on damaged DNA and the process of apoptosis. Studies have shown that metformin may reduce the risk of cardiovascular disease through influences on body weight, blood pressure, cholesterol levels and the progression of atherosclerosis. Studies also suggest that metformin may be beneficial for neuro-psychiatric disorders, cognitive impairment and in reducing the risk of dementia, erectile dysfunction and Duchenne muscular dystrophy. In vivo and in vitro studies have shown that metformin has anti-cancer properties, and population studies have suggested that metformin may reduce the risk of cancer or improve cancer prognosis. It is thought that it exerts its anti-cancer effect through the inhibition of the mammalian target of rapamycin (mTOR) signalling pathway. Because of its effect on the mTOR pathway, there may be a role for metformin in slowing or reversing growth of life-threatening hamartomas in tuberous sclerosis complex.

Metformin as a Therapeutic Target in Endometrial Cancers

Endometrial cancer is the most common gynecologic malignancy in developed countries. Its increasing incidence is thought to be related in part to the rise of metabolic syndrome, which has been shown to be a risk factor for the development of hyperestrogenic and hyperinsulinemic states. This has consequently lead to an increase in other hormone-responsive cancers as well e.g., breast and ovarian cancer. The correlation between obesity, hyperglycemia, and endometrial cancer has highlighted the important role of metabolism in cancer establishment and persistence. Tumor-mediated reprogramming of the microenvironment and macroenvironment can range from induction of cytokines and growth factors to stimulation of surrounding stromal cells to produce energy-rich catabolites, fueling the growth, and survival of cancer cells. Such mechanisms raise the prospect of the metabolic microenvironment itself as a viable target for treatment of malignancies. Metformin is a biguanide drug that is a first-line treatment for type 2 diabetes that has beneficial effects on various markers of the metabolic syndrome. Many studies suggest that metformin shows potential as an adjuvant treatment for uterine and other cancers. Here, we review the evidence for metformin as a treatment for cancers of the endometrium. We discuss the available clinical data and the molecular mechanisms by which it may exert its effects, with a focus on how it may alter the tumor microenvironment. The pleiotropic effects of metformin on cellular energy production and usage as well as intercellular and hormone-based interactions make it a promising candidate for reprogramming of the cancer ecosystem. This, along with other treatments aimed at targeting tumor metabolic pathways, may lead to novel treatment strategies for endometrial cancer.

KRAS, YAP, and obesity in pancreatic cancer: A signaling network with multiple loops

Pancreatic ductal adenocarcinoma (PDAC) continues to be a lethal disease with no efficacious treatment modalities. The incidence of PDAC is expected to increase, at least partially because of the obesity epidemic. Increased efforts to prevent or intercept this disease are clearly needed. Mutations in KRAS are initiating events in pancreatic carcinogenesis supported by genetically engineered mouse models of the disease. However, oncogenic KRAS is not entirely sufficient for the development of fully invasive PDAC. Additional genetic mutations and/or environmental, nutritional, and metabolic stressors, e.g. inflammation and obesity, are required for efficient PDAC formation with activation of KRAS downstream effectors. Multiple factors "upstream" of KRAS associated with obesity, including insulin resistance, inflammation, changes in gut microbiota and GI peptides, can enhance/modulate downstream signals. Multiple signaling networks and feedback loops "downstream" of KRAS have been described that respond to obesogenic diets. We propose that KRAS mutations potentiate a signaling network that is promoted by environmental factors. Specifically, we envisage that KRAS mutations increase the intensity and duration of the growth-promoting signaling network. As the transcriptional activator YAP plays a critical role in the network, we conclude that the rationale for targeting the network (at different points), e.g. with FDA approved drugs such as statins and metformin, is therefore compelling.

AMP-Activated Protein Kinase: An Ubiquitous Signaling Pathway With Key Roles in the Cardiovascular System

The AMP-activated protein kinase (AMPK) is a key regulator of cellular and whole-body energy homeostasis, which acts to restore energy homoeostasis whenever cellular energy charge is depleted. Over the last 2 decades, it has become apparent that AMPK regulates several other cellular functions and has specific roles in cardiovascular tissues, acting to regulate cardiac metabolism and contractile function, as well as promoting anticontractile, anti-inflammatory, and antiatherogenic actions in blood vessels. In this review, we discuss the role of AMPK in the cardiovascular system, including the molecular basis of mutations in AMPK that alter cardiac physiology and the proposed mechanisms by which AMPK regulates vascular function under physiological and pathophysiological conditions.

ROS signaling under metabolic stress: cross-talk between AMPK and AKT pathway

Cancer cells are frequently confronted with metabolic stress in tumor microenvironments due to their rapid growth and limited nutrient supply. Metabolic stress induces cell death through ROS-induced apoptosis. However, cancer cells can adapt to it by altering the metabolic pathways. AMPK and AKT are two primary effectors in response to metabolic stress: AMPK acts as an energy-sensing factor which rewires metabolism and maintains redox balance. AKT broadly promotes energy production in the nutrient abundance milieu, but the role of AKT under metabolic stress is in dispute. Recent studies show that AMPK and AKT display antagonistic roles under metabolic stress. Metabolic stress-induced ROS signaling lies in the hub between metabolic reprogramming and redox homeostasis. Here, we highlight the cross-talk between AMPK and AKT and their regulation on ROS production and elimination, which summarizes the mechanism of cancer cell adaptability under ROS stress and suggests potential options for cancer therapeutics.

ROS signaling under metabolic stress: cross-talk between AMPK and AKT pathway

Cancer cells are frequently confronted with metabolic stress in tumor microenvironments due to their rapid growth and limited nutrient supply. Metabolic stress induces cell death through ROS-induced apoptosis. However, cancer cells can adapt to it by altering the metabolic pathways. AMPK and AKT are two primary effectors in response to metabolic stress: AMPK acts as an energy-sensing factor which rewires metabolism and maintains redox balance. AKT broadly promotes energy production in the nutrient abundance milieu, but the role of AKT under metabolic stress is in dispute. Recent studies show that AMPK and AKT display antagonistic roles under metabolic stress. Metabolic stress-induced ROS signaling lies in the hub between metabolic reprogramming and redox homeostasis. Here, we highlight the cross-talk between AMPK and AKT and their regulation on ROS production and elimination, which summarizes the mechanism of cancer cell adaptability under ROS stress and suggests potential options for cancer therapeutics.

Metformin targets multiple signaling pathways in cancer

Metformin, an inexpensive and well-tolerated oral agent commonly used in the first-line treatment of type 2 diabetes, has become the focus of intense research as a candidate anticancer agent. Here, we discuss the potential of metformin in cancer therapeutics, particularly its functions in multiple signaling pathways, including AMP-activated protein kinase, mammalian target of rapamycin, insulin-like growth factor, c-Jun N-terminal kinase/mitogen-activated protein kinase (p38 MAPK), human epidermal growth factor receptor-2, and nuclear factor kappaB pathways. In addition, cutting-edge targeting of cancer stem cells by metformin is summarized.

Role of the PI3K-Akt Signaling Pathway in the Pathogenesis of Polycystic Ovary Syndrome

This review aimed to focus on the recent progress of the understanding of the role of phosphatidylinositol 3-kinase (PI3K) in polycystic ovary syndrome (PCOS). In recent years, it has been increasingly recognized that PI3K plays an important role in PCOS whose pathogenesis is unclear. However, research continues into revealing the details of how PI3Ks are involved in developing PCOS. Previous studies have shown that activation of the PI3K-protein kinase B (Akt) signaling pathway has important effects on insulin resistance and endometrial cancer. Knowledge of the action of PI3K in PCOS might provide valuable information to further validate the pathogenesis of PCOS and suggest new methods of treatment.

The role of sex steroid hormones in the pathophysiology and treatment of sarcopenia

Sex steroids influence the maintenance and growth of muscles. Decline in androgens, estrogens and progesterone by aging leads to the loss of muscular function and mass, sarcopenia. These steroid hormones can interact with different signaling pathways through their receptors. To date, sex steroid hormone receptors and their exact roles are not completely defined in skeletal and smooth muscles. Although numerous studies focused on the effects of sex steroid hormones on different types of cells, still many unexplained molecular mechanisms in both skeletal and smooth muscle cells remain to be investigated. In this paper, many different molecular mechanisms that are activated or inhibited by sex steroids and those that influence the growth, proliferation, and differentiation of skeletal and smooth muscle cells are reviewed. Also, the similarities of cellular and molecular pathways of androgens, estrogens and progesterone in both skeletal and smooth muscle cells are highlighted. The reviewed signaling pathways and participating molecules can be targeted in the future development of novel therapeutics.

Metformin Enhances the Therapy Effects of Anti-IGF-1R mAb Figitumumab to NSCLC

The insulin-like growth factor (IGF) signaling system plays a critical role in tumorigenesis, highlighting the potential of targeting IGF-1R as an anti-cancer therapy. Although multiple anti-IGF-1R monoclonal antibody (mAb) drugs have been developed, challenges remain in the validation of the therapeutic effects and understanding the molecular mechanism of these mAbs. Herein, we conducted a study to validate the effect of Figitumumab (CP), an anti-IGF-1R mAb, in a panel of non-small cell lung cancer (NSCLC) cell lines. We found all tested cell lines were sensitive to CP, and CP could block IGF-1R and the downstream PI3K/AKT pathway activation. Unexpectedly, we found CP could activate ERK signaling pathway in IGF-1R kinase independent manner, which we further verified was mainly mediated by β-arrestin2. We also investigated the anti-tumor effect of metformin alone as well as its combination with CP to target NSCLC. Metformin could target IGF-1R signaling pathway by attenuating PI3K/AKT and MEK/ERK signaling pathways and down-regulating IGF-1R. Finally, we found that combining metformin with CP could further induce IGF-1R down-regulation and was more effective to target NSCLC cells. Our data suggests the combining of metformin with CP has additive therapeutic value against NSCLC.

Age-related changes in AMPK activation: Role for AMPK phosphatases and inhibitory phosphorylation by upstream signaling pathways

AMP-activated protein kinase (AMPK) is a fundamental regulator of energy metabolism, stress resistance, and cellular proteostasis. AMPK signaling controls an integrated signaling network which is involved in the regulation of healthspan and lifespan e.g. via FoxO, mTOR/ULK1, CRCT-1/CREB, and SIRT1 signaling pathways. Several studies have demonstrated that the activation capacity of AMPK signaling declines with aging, which impairs the maintenance of efficient cellular homeostasis and enhances the aging process. However, it seems that the aging process affects AMPK activation in a context-dependent manner since occasionally, it can also augment AMPK activation, possibly attributable to the type of insult and tissue homeostasis. Three protein phosphatases, PP1, PP2A, and PP2C, inhibit AMPK activation by dephosphorylating the Thr172 residue of AMPKα, required for AMPK activation. In addition, several upstream signaling pathways can phosphorylate Ser/Thr residues in the β/γ interaction domain of the AMPKα subunit that subsequently blocks the activation of AMPK. These inhibitory pathways include the insulin/AKT, cyclic AMP/PKA, and RAS/MEK/ERK pathways. We will examine the evidence whether the efficiency of AMPK responsiveness declines during the aging process. Next, we will review the mechanisms involved in curtailing the activation of AMPK. Finally, we will elucidate the potential age-related changes in the inhibitory regulation of AMPK signaling that might be a part of the aging process.

Berberine improves mesenteric artery insulin sensitivity through up-regulating insulin receptor-mediated signalling in diabetic rats

BACKGROUND AND PURPOSE

Berberine, a small molecule derived from Coptidis rhizome, has been found to be potent at lowering blood glucose and regulating lipid metabolism. Recent clinical studies have shown that berberine reduces blood pressure and increases systemic insulin sensitivity in patients with metabolic syndrome; however, the underlying mechanism is still unclear. Here, we investigated the mechanism by which berberine improves vascular insulin sensitivity in diabetic rats.

EXPERIMENTAL APPROACH

Diabetes was induced in male Sprague–Dawley rats by feeding a high-fat diet and administration of a low dose of streptozotocin. These diabetic rats were treated with berberine (200 mg·kg(−1)·day(−1), gavage) for 4 weeks. Vascular dilation was determined in isolated mesenteric artery rings. Effects of berberine on insulin signalling were also studied in human artery endothelial cells cultured in high glucose (25 mmol·L(−1)) and palmitate (500 μmol·L(−1)).

KEY RESULTS

Berberine treatment for 4 weeks significantly restored the impaired ACh- and insulin-induced vasodilatation of mesenteric arteries from diabetic rats. In isolated mesenteric artery rings, berberine (2.5–10 μmol·L(−1)) elicited dose-dependent vasodilatation and significantly enhanced insulin-induced vasodilatation. Mechanistically, berberine up-regulated phosphorylation of the insulin receptor and its downstream signalling molecules AMPK, Akt and eNOS, and increased cell viability and autophagy in cultured endothelial cells. Moreover, down-regulating insulin receptors with specific siRNA significantly attenuated berberine-induced phosphorylation of AMPK.

CONCLUSIONS AND IMPLICATIONS

Berberine improves diabetic vascular insulin sensitivity and mesenteric vasodilatation by up-regulating insulin receptor-mediated signalling in diabetic rats. These findings suggest berberine has potential as a preventive or adjunctive treatment of diabetic vascular complications.

LINKED ARTICLES

This article is part of a themed section on Chinese Innovation in Cardiovascular Drug Discovery. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-23.

Berberine improves mesenteric artery insulin sensitivity through up-regulating insulin receptor-mediated signalling in diabetic rats

BACKGROUND AND PURPOSE

Berberine, a small molecule derived from Coptidis rhizome, has been found to be potent at lowering blood glucose and regulating lipid metabolism. Recent clinical studies have shown that berberine reduces blood pressure and increases systemic insulin sensitivity in patients with metabolic syndrome; however, the underlying mechanism is still unclear. Here, we investigated the mechanism by which berberine improves vascular insulin sensitivity in diabetic rats.

EXPERIMENTAL APPROACH

Diabetes was induced in male Sprague–Dawley rats by feeding a high-fat diet and administration of a low dose of streptozotocin. These diabetic rats were treated with berberine (200 mg·kg(−1)·day(−1), gavage) for 4 weeks. Vascular dilation was determined in isolated mesenteric artery rings. Effects of berberine on insulin signalling were also studied in human artery endothelial cells cultured in high glucose (25 mmol·L(−1)) and palmitate (500 μmol·L(−1)).

KEY RESULTS

Berberine treatment for 4 weeks significantly restored the impaired ACh- and insulin-induced vasodilatation of mesenteric arteries from diabetic rats. In isolated mesenteric artery rings, berberine (2.5–10 μmol·L(−1)) elicited dose-dependent vasodilatation and significantly enhanced insulin-induced vasodilatation. Mechanistically, berberine up-regulated phosphorylation of the insulin receptor and its downstream signalling molecules AMPK, Akt and eNOS, and increased cell viability and autophagy in cultured endothelial cells. Moreover, down-regulating insulin receptors with specific siRNA significantly attenuated berberine-induced phosphorylation of AMPK.

CONCLUSIONS AND IMPLICATIONS

Berberine improves diabetic vascular insulin sensitivity and mesenteric vasodilatation by up-regulating insulin receptor-mediated signalling in diabetic rats. These findings suggest berberine has potential as a preventive or adjunctive treatment of diabetic vascular complications.

LINKED ARTICLES

This article is part of a themed section on Chinese Innovation in Cardiovascular Drug Discovery. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-23.

IGF-I and IGFBP-2 Stimulate AMPK Activation and Autophagy, Which Are Required for Osteoblast Differentiation

IGF-I/insulin-like growth factor binding protein 2 (IGFBP-2) coordinately stimulate osteoblast differentiation but the mechanisms by which they function have not been determined. AMP-activated protein kinase (AMPK) is induced during differentiation and AMPK knockout mice have reduced bone mass. IGF-I modulates AMPK in other cell types; therefore, these studies determined whether IGF-I/IGFBP-2 stimulate AMPK activation and the mechanism by which AMPK modulates differentiation. Calvarial osteoblasts and MC-3T3 cells expressed activated AMPK early in differentiation and AMPK inhibitors attenuated differentiation. However, expression of constitutively activated AMPK inhibited differentiation. To resolve this discrepancy we analyzed the time course of AMPK induction. AMPK activation was required early in differentiation (day 3-6) but down-regulation of AMPK after day 9 was also necessary. IGF-I/IGFBP-2 induced AMPK through their respective receptors and blocking-receptor activation blocked AMPK induction. To determine the mechanism by which AMPK functioned we analyzed components of the autophagosome. Activated AMPK stimulated ULK-1 S555 phosphorylation as well as beclin-1 and microtubule-associated protein 1A/1B light-chain phosphatidylethanolamine conjugate (LC3II) induction. Inhibition of AMPK attenuated these changes and direct inhibition of autophagy inhibited differentiation. Conversely, expression of activated AMPK was associated with persistence of these changes beyond day 9 and inhibited differentiation. Blocking AMPK activation after day 9 down-regulated these autophagosome components and rescued differentiation. This allowed induction of mechanistic target of rapamycin and AKT, which suppressed autophagy. The results show that early induction of AMPK in response to IGF-I/IGFBP-2 followed by suppression is required for osteoblast differentiation. AMPK functions through stimulation of autophagy. The findings suggest that these early catabolic changes are important for determining the energy source for osteoblast respiration and down-regulation of these components may be required for induction of glycolysis, which is required during the final anabolic stages of differentiation.

Insulin Receptor Substrate 1, the Hub Linking Follicle-stimulating Hormone to Phosphatidylinositol 3-Kinase Activation

The ubiquitous phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates many cellular functions. However, the mechanism by which G protein-coupled receptors (GPCRs) signal to activate PI3K is poorly understood. We have used ovarian granulosa cells as a model to investigate this pathway, based on evidence that the GPCR agonist follicle-stimulating hormone (FSH) promotes the protein kinase A (PKA)-dependent phosphorylation of insulin receptor substrate 1 (IRS1) on tyrosine residues that activate PI3K. We report that in the absence of FSH, granulosa cells secrete a subthreshold concentration of insulin-like growth factor-1 (IGF-1) that primes the IGF-1 receptor (IGF-1R) but fails to promote tyrosine phosphorylation of IRS1. FSH via PKA acts to sensitize IRS1 to the tyrosine kinase activity of the IGF-1R by activating protein phosphatase 1 (PP1) to promote dephosphorylation of inhibitory Ser/Thr residues on IRS1, including Ser(789). Knockdown of PP1β blocks the ability of FSH to activate PI3K in the presence of endogenous IGF-1. Activation of PI3K thus requires both PKA-mediated relief of IRS1 inhibition and IGF-1R-dependent tyrosine phosphorylation of IRS1. Treatment with FSH and increasing concentrations of exogenous IGF-1 triggers synergistic IRS1 tyrosine phosphorylation at PI3K-activating residues that persists downstream through protein kinase B (AKT) and FOXO1 (forkhead box protein O1) to drive synergistic expression of genes that underlies follicle maturation. Based on the ability of GPCR agonists to synergize with IGFs to enhance gene expression in other cell types, PP1 activation to relieve IRS1 inhibition may be a more general mechanism by which GPCRs act with the IGF-1R to activate PI3K/AKT.

Pioglitazone, a PPARγ agonist, attenuates PDGF-induced vascular smooth muscle cell proliferation through AMPK-dependent and AMPK-independent inhibition of mTOR/p70S6K and ERK signaling

Pioglitazone (PIO), a PPARγ agonist that improves glycemic control in type 2 diabetes through its insulin-sensitizing action, has been shown to exhibit beneficial effects in the vessel wall. For instance, it inhibits vascular smooth muscle cell (VSMC) proliferation, a major event in atherosclerosis and restenosis after angioplasty. Although PPARγ-dependent and PPARγ-independent mechanisms have been attributed to its vasoprotective effects, the signaling events associated with PIO action in VSMCs are not fully understood. To date, the likely intermediary role of AMP-activated protein kinase (AMPK) toward PIO inhibition of VSMC proliferation has not been examined. Using human aortic VSMCs, the present study demonstrates that PIO activates AMPK in a sustained manner thereby contributing in part to inhibition of key proliferative signaling events. In particular, PIO at 30μM concentration activates AMPK to induce raptor phosphorylation, which diminishes PDGF-induced mTOR activity as evidenced by decreased phosphorylation of p70S6K, 4E-BP1, and S6 and increased accumulation of p27(kip1), a cell cycle inhibitor. In addition, PIO inhibits the basal phosphorylation of ERK in VSMCs. Downregulation of endogenous AMPK by target-specific siRNA reveals an AMPK-independent effect for PIO inhibition of ERK, which contributes in part to diminutions in cyclin D1 expression and Rb phosphorylation and the suppression of VSMC proliferation. Furthermore, AMPK-dependent inhibition of mTOR/p70S6K and AMPK-independent inhibition of ERK signaling occur regardless of PPARγ expression/activation in VSMCs as evidenced by gene silencing and pharmacological inhibition of PPARγ. Strategies that utilize nanoparticle-mediated PIO delivery at the lesion site may limit restenosis after angioplasty without inducing PPARγ-mediated systemic adverse effects.

Effects of sex steroids on bones and muscles: Similarities, parallels, and putative interactions in health and disease

Estrogens and androgens influence the growth and maintenance of bones and muscles and are responsible for their sexual dimorphism. A decline in their circulating levels leads to loss of mass and functional integrity in both tissues. In the article, we highlight the similarities of the molecular and cellular mechanisms of action of sex steroids in the two tissues; the commonality of a critical role of mechanical forces on tissue mass and function; emerging evidence for an interplay between mechanical forces and hormonal and growth factor signals in both bones and muscles; as well as the current state of evidence for or against a cross-talk between muscles and bone. In addition, we review evidence for the parallels in the development of osteoporosis and sarcopenia with advancing age and the potential common mechanisms responsible for the age-dependent involution of these two tissues. Lastly, we discuss the striking difference in the availability of several drug therapies for the prevention and treatment of osteoporosis, as compared to none for sarcopenia. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Lewis lung carcinoma regulation of mechanical stretch-induced protein synthesis in cultured myotubes

Mechanical stretch can activate muscle and myotube protein synthesis through mammalian target of rapamycin complex 1 (mTORC1) signaling. While it has been established that tumor-derived cachectic factors can induce myotube wasting, the effect of this catabolic environment on myotube mechanical signaling has not been determined. We investigated whether media containing cachectic factors derived from Lewis lung carcinoma (LLC) can regulate the stretch induction of myotube protein synthesis. C2C12 myotubes preincubated in control or LLC-derived media were chronically stretched. Protein synthesis regulation by anabolic and catabolic signaling was then examined. In the control condition, stretch increased mTORC1 activity and protein synthesis. The LLC treatment decreased basal mTORC1 activity and protein synthesis and attenuated the stretch induction of protein synthesis. LLC media increased STAT3 and AMP-activated protein kinase phosphorylation in myotubes, independent of stretch. Both stretch and LLC independently increased ERK1/2, p38, and NF-κB phosphorylation. In LLC-treated myotubes, the inhibition of ERK1/2 and p38 rescued the stretch induction of protein synthesis. Interestingly, either leukemia inhibitory factor or glycoprotein 130 antibody administration caused further inhibition of mTORC1 signaling and protein synthesis in stretched myotubes. AMP-activated protein kinase inhibition increased basal mTORC1 signaling activity and protein synthesis in LLC-treated myotubes, but did not restore the stretch induction of protein synthesis. These results demonstrate that LLC-derived cachectic factors can dissociate stretch-induced signaling from protein synthesis through ERK1/2 and p38 signaling, and that glycoprotein 130 signaling is associated with the basal stretch response in myotubes.

Dose-Dependent AMPK-Dependent and Independent Mechanisms of Berberine and Metformin Inhibition of mTORC1, ERK, DNA Synthesis and Proliferation in Pancreatic Cancer Cells

Natural products represent a rich reservoir of potential small chemical molecules exhibiting anti-proliferative and chemopreventive properties. Here, we show that treatment of pancreatic ductal adenocarcinoma (PDAC) cells (PANC-1, MiaPaCa-2) with the isoquinoline alkaloid berberine (0.3-6 µM) inhibited DNA synthesis and proliferation of these cells and delay the progression of their cell cycle in G1. Berberine treatment also reduced (by 70%) the growth of MiaPaCa-2 cell growth when implanted into the flanks of nu/nu mice. Mechanistic studies revealed that berberine decreased mitochondrial membrane potential and intracellular ATP levels and induced potent AMPK activation, as shown by phosphorylation of AMPK α subunit at Thr-172 and acetyl-CoA carboxylase (ACC) at Ser79. Furthermore, berberine dose-dependently inhibited mTORC1 (phosphorylation of S6K at Thr389 and S6 at Ser240/244) and ERK activation in PDAC cells stimulated by insulin and neurotensin or fetal bovine serum. Knockdown of α1 and α2 catalytic subunit expression of AMPK reversed the inhibitory effect produced by treatment with low concentrations of berberine on mTORC1, ERK and DNA synthesis in PDAC cells. However, at higher concentrations, berberine inhibited mitogenic signaling (mTORC1 and ERK) and DNA synthesis through an AMPK-independent mechanism. Similar results were obtained with metformin used at doses that induced either modest or pronounced reductions in intracellular ATP levels, which were virtually identical to the decreases in ATP levels obtained in response to berberine. We propose that berberine and metformin inhibit mitogenic signaling in PDAC cells through dose-dependent AMPK-dependent and independent pathways.

Effects of VBMDMP on the reversal of cisplatin resistance in human lung cancer A549/DDP cells

Tumor drug resistance is a major obstacle to cancer chemotherapy. We previously constructed a fusion protein based on two tumstatin-derived sequences named recombinant VBMDM (rVBMDMP). We preliminarily confirmed its inhibition of HUVEC and colon cancer cell growth. The present study further systematically observed the inhibitory effect of rVBMDMP on lung cancer cell growth and analyzed a possible mechanism to provide a theoretical basis for the development of new antitumor protein drugs. The effect of rVBMDMP on human lung adenocarcinoma (A549) and cisplatin-resistant human lung adenocarcinoma (A549/DDP) cell proliferation was evaluated by MTS assay. Hoechst 33342 staining performed together with fluorescence microscopy and immunoblot analysis were used to examine the effects of rVBMDMP on the apoptosis of A549/DDP cells. A protein phosphorylation chip was used to identify changes in rVBMDMP-induced signaling protein phosphorylation. Changes in the phosphatidylinositol 3 kinase (PI3K)/Akt signal transduction pathway and expression of multidrug resistance protein (MRP-2)-related molecules following rVBMDMP treatment in A549/DDP cells were evaluated by western blot analysis. A lung cancer xenograft model was used to evaluate the reversal effect of rVBMDMP on drug-resistance of A549/DDP cell tumors to cisplatin in vivo. The results demonstrated that rVBMDMP increased the phosphorylation of 79 signaling proteins, including focal adhesion kinase (FAK), caspase-6, Fas, FasL and FAF1 and downregulated 30 signaling proteins, including integrin αV, integrin β3, PI3K/Akt, NF-κB and MRP-2 compared with the controls. rVBMDMP also increased the sensitivity of A549 and A549/DDP cells to cisplatin and directly induced apoptosis, which may be related to MRP-2 and Bcl-2 downregulation. The effects of growth inhibition and apoptosis induction of rVBMDMP on A549/DDP cells may be related to the inhibition of integrin αVβ3 and PI3K/Akt protein phosphorylation. Finally, we observed an increase in cancer cell sensitivity to cisplatin by rVBMDMP using the A549/DDP cell xenograft model in nude mice. Our study suggests that rVBMDMP may be an effective potential chemotherapy sensitizer and may be a viable drug candidate in anticancer therapies.

Suppression of feedback loops mediated by PI3K/mTOR induces multiple overactivation of compensatory pathways: an unintended consequence leading to drug resistance

The development of drug resistance by cancer cells is recognized as a major cause for drug failure and disease progression. The PI3K/AKT/mTOR pathway is aberrantly stimulated in many cancer cells and thus it has emerged as a target for therapy. However, mTORC1 and S6K also mediate potent negative feedback loops that attenuate signaling via insulin/insulin growth factor receptor and other tyrosine kinase receptors. Suppression of these feedback loops causes overactivation of upstream pathways, including PI3K, AKT, and ERK that potentially oppose the antiproliferative effects of mTOR inhibitors and lead to drug resistance. A corollary of this concept is that release of negative feedback loops and consequent compensatory overactivation of promitogenic pathways in response to signal inhibitors can circumvent the mitogenic block imposed by targeting only one pathway. Consequently, the elucidation of the negative feedback loops that regulate the outputs of signaling networks has emerged as an area of fundamental importance for the rational design of effective anticancer combinations of inhibitors. Here, we review pathways that undergo compensatory overactivation in response to inhibitors that suppress feedback inhibition of upstream signaling and underscore the importance of unintended pathway activation in the development of drug resistance to clinically relevant inhibitors of mTOR, AKT, PI3K, or PI3K/mTOR.

Mechanistic target of rapamycin (mTOR): a point of convergence in the action of insulin/IGF-1 and G protein-coupled receptor agonists in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC), the most common form of pancreatic cancer, is one of the most lethal human diseases. PDAC is now the fourth leading cause of cancer mortality in both men and women and deaths due to PDAC are projected to increase dramatically. Novel targets and agents for chemoprevention are urgently needed and will most likely arise from a more detailed understanding of the signaling mechanisms that stimulate the promotion and progression of sub-malignant cells into pancreatic cancer cells and from the identification of modifiable risk factors for PDAC. Many epidemiological studies have linked obesity and long-standing type 2 diabetes mellitus (T2DM) with increased risk and worse clinical outcomes for developing PDAC. These diet-related metabolic disorders are multifaceted but characterized by peripheral insulin resistance, compensatory overproduction of insulin and increased bioavailability of insulin-like growth factor-1 (IGF-1). Mounting evidence indicates that the insulin/IGF-1 receptor system plays a critical role in PDAC development and multiple studies support the notion that crosstalk between the insulin receptor and heptahelical G protein-coupled receptor (GPCR) signaling systems is an important element in the biological responses elicited by these signaling systems, including cell proliferation. This article highlights the central role of the mechanistic target of rapamycin (mTOR) in mediating crosstalk between insulin/IGF-1 and GPCR signaling in pancreatic cancer cells and proposes strategies, including the use of metformin, to target this signaling system in PDAC cells.

Metformin exaggerates phenylephrine-induced AMPK phosphorylation independent of CaMKKβ and attenuates contractile response in endothelium-denuded rat aorta

Metformin, a widely prescribed antidiabetic drug, has been shown to reduce the risk of cardiovascular disease, including hypertension. Its beneficial effect toward improved vasodilation results from its ability to activate AMPK and enhance nitric oxide formation in the endothelium. To date, metformin regulation of AMPK has not been fully studied in intact arterial smooth muscle, especially during contraction evoked by G protein-coupled receptor (GPCR) agonists. In the present study, ex vivo incubation of endothelium-denuded rat aortic rings with 3mM metformin for 2h resulted in significant accumulation of metformin (∼ 600 pmoles/mg tissue), as revealed by LC-MS/MS MRM analysis. However, metformin did not show significant increase in AMPK phosphorylation under these conditions. Exposure of aortic rings to a GPCR agonist (e.g., phenylephrine) resulted in enhanced AMPK phosphorylation by ∼ 2.5-fold. Importantly, in metformin-treated aortic rings, phenylephrine challenge showed an exaggerated increase in AMPK phosphorylation by ∼ 9.7-fold, which was associated with an increase in AMP/ATP ratio. Pretreatment with compound C (AMPK inhibitor) prevented AMPK phosphorylation induced by phenylephrine alone and also that induced by phenylephrine after metformin treatment. However, pretreatment with STO-609 (CaMKKβ inhibitor) diminished AMPK phosphorylation induced by phenylephrine alone but not that induced by phenylephrine after metformin treatment. Furthermore, attenuation of phenylephrine-induced contraction (observed after metformin treatment) was prevented by AMPK inhibition but not by CaMKKβ inhibition. Together, these findings suggest that, upon endothelial damage in the vessel wall, metformin uptake by the underlying vascular smooth muscle would accentuate AMPK phosphorylation by GPCR agonists independent of CaMKKβ to promote vasorelaxation.

Alteration of splice site selection in the LMNA gene and inhibition of progerin production via AMPK activation

Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare genetic condition characterized by an accelerated aging phenotype and an average life span of 13years. Patients typically exhibit extensive pathophysiological vascular alterations, eventually resulting in death from stroke or myocardial infarction. A silent point mutation at position 1824 (C1824T) of the LMNA gene, generating a truncated form of lamin A (progerin), has been shown to be the cause of most cases of HGPS. Interestingly, this mutation induces the use of an internal 5' cryptic splice site within exon 11 of the LMNA pre-mRNA, leading to the generation of progerin via aberrant alternative splicing. The serine-arginine rich splicing factor 1 (SRSF1 or ASF/SF2) has been shown to function as an oncoprotein and is upregulated in many cancers and other age-related disorders. Indeed, SRSF1 inhibition results in a splicing ratio in the LMNA pre-mRNA favoring lamin A production over that of progerin. It is our hypothesis that activation of AMP-activated protein kinase (AMPK), a master regulator of cellular metabolism, may lead to a reduction in SRSF1 and thus a decrease in the use of the LMNA 5' cryptic splice site in exon 11 through upregulation of p32, a splicing factor-associated protein and putative mitochondrial chaperone that has been shown to inhibit SRSF1 and enhance mitochondrial DNA (mtDNA) replication and oxidative phosphorylation. AMPK activation by currently available compounds such as metformin, resveratrol, and berberine may thus have wide-ranging implications for disorders associated with increased production and accumulation of progerin.

Dietary antiaging phytochemicals and mechanisms associated with prolonged survival

Aging is well-known an inevitable process that is influenced by genetic, lifestyle and environmental factors. However, the exact mechanisms underlying the aging process are not well understood. Increasing evidence shows that aging is highly associated with chronic increase in reactive oxygen species (ROS), accumulation of a low-grade proinflammatory phenotype and reduction in age-related autophagy, suggesting that these factors may play important roles in promoting aging. Indeed, reduction of ROS and low-grade inflammation and promotion of autophagy by calorie restriction or other dietary manipulation can extend lifespan in a wide spectrum of model organisms. Interestingly, recent studies show that some food-derived small molecules, also called phytochemicals, can extend lifespan in various animal species. In this paper, we review several recently identified potential antiaging phytochemicals that have been studied in cells, animals and humans and further highlight the cellular and molecular mechanisms underlying the antiaging actions by these molecules.

Metformin--mode of action and clinical implications for diabetes and cancer

Metformin has been the mainstay of therapy for diabetes mellitus for many years; however, the mechanistic aspects of metformin action remained ill-defined. Recent advances revealed that this drug, in addition to its glucose-lowering action, might be promising for specifically targeting metabolic differences between normal and abnormal metabolic signalling. The knowledge gained from dissecting the principal mechanisms by which metformin works can help us to develop novel treatments. The centre of metformin's mechanism of action is the alteration of the energy metabolism of the cell. Metformin exerts its prevailing, glucose-lowering effect by inhibiting hepatic gluconeogenesis and opposing the action of glucagon. The inhibition of mitochondrial complex I results in defective cAMP and protein kinase A signalling in response to glucagon. Stimulation of 5'-AMP-activated protein kinase, although dispensable for the glucose-lowering effect of metformin, confers insulin sensitivity, mainly by modulating lipid metabolism. Metformin might influence tumourigenesis, both indirectly, through the systemic reduction of insulin levels, and directly, via the induction of energetic stress; however, these effects require further investigation. Here, we discuss the updated understanding of the antigluconeogenic action of metformin in the liver and the implications of the discoveries of metformin targets for the treatment of diabetes mellitus and cancer.

Metabolic roles of AMPK and metformin in cancer cells

Metformin is one of the most widely used anti-diabetic agents in the world, and a growing body of evidence suggests that it may also be effective as an anti-cancer drug. Observational studies have shown that metformin reduces cancer incidence and cancer-related mortality in multiple types of cancer. These results have drawn attention to the mechanisms underlying metformin's anti-cancer effects, which may include triggering of the AMP-activated protein kinase (AMPK) pathway, resulting in vulnerability to an energy crisis (leading to cell death under conditions of nutrient deprivation) and a reduction in circulating insulin/IGF-1 levels. Clinical trials are currently underway to determine the benefits, appropriate dosage, and tolerability of metformin in the context of cancer therapy. This review highlights fundamental aspects of the molecular mechanisms underlying metformin's anti-cancer effects, describes the epidemiological evidence and ongoing clinical challenges, and proposes directions for future translational research.

Metformin-mediated growth inhibition involves suppression of the IGF-I receptor signalling pathway in human pancreatic cancer cells

Background

Epidemiological studies have shown direct associations between type 2 diabetes and obesity, both conditions associated with hyperglycaemia and hyperinsulinemia, and the risk of pancreatic cancer. Up to 80% of pancreatic cancer patients present with either new-onset type 2 diabetes or impaired glucose tolerance at the time of diagnosis. Recent population studies indicate that the incidence of pancreatic cancer is reduced among diabetics taking metformin. In this study, the effects of exposure of pancreatic cancer cells to high glucose levels on their growth and response to metformin were investigated.

Methods

The human pancreatic cancer cell lines AsPC-1, BxPC-3, PANC-1 and MIAPaCa-2 were grown in normal (5 mM) or high (25 mM) glucose conditions, with or without metformin. The influence by metformin on proliferation, apoptosis and the AMPK and IGF-IR signalling pathways were evaluated in vitro.

Results

Metformin significantly reduced the proliferation of pancreatic cancer cells under normal glucose conditions. Hyperglycaemia however, protected against the metformin-induced growth inhibition. The anti-proliferative actions of metformin were associated with an activation of AMP-activated protein kinase AMPK^Thr172 together with an inhibition of the insulin/insulin-like growth factor-I (IGF-I) receptor activation and downstream signalling mediators IRS-1 and phosphorylated Akt. Furthermore, exposure to metformin during normal glucose conditions led to increased apoptosis as measured by poly(ADP-ribose) polymerase (PARP) cleavage. In contrast, exposure to high glucose levels promoted a more robust IGF-I response and Akt activation which correlated to stimulated AMPK^Ser485 phosphorylation and impaired AMPK^Thr172 phosphorylation, resulting in reduced anti-proliferative and apoptotic effects by metformin.

Conclusion

Our results indicate that metformin has direct anti-tumour activities in pancreatic cancer cells involving AMPK^Thr172 activation and suppression of the insulin/IGF signalling pathways. However, hyperglycaemic conditions enhance the insulin/IGF-I responses resulting in an altered AMPK activation profile and prevent metformin from fully switching off the growth promoting signals in pancreatic cancer cells.

Different patterns of Akt and ERK feedback activation in response to rapamycin, active-site mTOR inhibitors and metformin in pancreatic cancer cells

The mTOR pathway is aberrantly stimulated in many cancer cells, including pancreatic ductal adenocarcinoma (PDAC), and thus it is a potential target for therapy. However, the mTORC1/S6K axis also mediates negative feedback loops that attenuate signaling via insulin/IGF receptor and other tyrosine kinase receptors. Suppression of these feed-back loops unleashes over-activation of upstream pathways that potentially counterbalance the antiproliferative effects of mTOR inhibitors. Here, we demonstrate that treatment of PANC-1 or MiaPaCa-2 pancreatic cancer cells with either rapamycin or active-site mTOR inhibitors suppressed S6K and S6 phosphorylation induced by insulin and the GPCR agonist neurotensin. Rapamycin caused a striking increase in Akt phosphorylation at Ser(473) while the active-site inhibitors of mTOR (KU63794 and PP242) completely abrogated Akt phosphorylation at this site. Conversely, active-site inhibitors of mTOR cause a marked increase in ERK activation whereas rapamycin did not have any stimulatory effect on ERK activation. The results imply that first and second generation of mTOR inhibitors promote over-activation of different pro-oncogenic pathways in PDAC cells, suggesting that suppression of feed-back loops should be a major consideration in the use of these inhibitors for PDAC therapy. In contrast, metformin abolished mTORC1 activation without over-stimulating Akt phosphorylation on Ser(473) and prevented mitogen-stimulated ERK activation in PDAC cells. Metformin induced a more pronounced inhibition of proliferation than either KU63794 or rapamycin while, the active-site mTOR inhibitor was more effective than rapamycin. Thus, the effects of metformin on Akt and ERK activation are strikingly different from allosteric or active-site mTOR inhibitors in PDAC cells, though all these agents potently inhibited the mTORC1/S6K axis.

Stimulatory effect of insulin on theca-interstitial cell proliferation and cell cycle regulatory proteins through MTORC1 dependent pathway

The present study examined the effect of insulin-mediated activation of the mammalian target of rapamycin complex 1 (MTORC1) signaling network on the proliferation of primary culture of theca-interstitial (T-I) cells. Our results show that insulin treatment increased proliferation of the T-I cells through the MTORC1-dependent signaling pathway by increasing cell cycle regulatory proteins. Inhibition of ERK1/2 signaling caused partial reduction of insulin-induced phosphorylation of RPS6KB1 and RPS6 whereas inhibition of PI3-kinase signaling completely blocked the insulin response. Pharmacological inhibition of MTORC1 with rapamycin abrogated the insulin-induced phosphorylation of EIF4EBP1, RPS6KB1 and its downstream effector, RPS6. These results were further confirmed by demonstrating that knockdown of Mtor using siRNA reduced the insulin-stimulated MTORC1 signaling. Furthermore, insulin-stimulated T-I cell proliferation and the expression of cell cycle regulatory proteins CDK4, CCND3 and PCNA were also blocked by rapamycin. Taken together, the present studies show that insulin stimulates cell proliferation and cell cycle regulatory proteins in T-I cells via activation of the MTORC1 signaling pathway.

Overexpression of AMP-activated protein kinase or protein kinase D prevents lipid-induced insulin resistance in cardiomyocytes

During lipid oversupply, the heart becomes insulin resistant, as exemplified by defective insulin-stimulated glucose uptake, and will develop diastolic dysfunction. In the healthy heart, not only insulin, but also increased contractile activity stimulates glucose uptake. Upon increased contraction both AMP-activated protein kinase (AMPK) and protein kinase D (PKD) are activated, and mediate the stimulation of glucose uptake into cardiomyocytes. Therefore, each of these kinases is a potential therapeutic target in the diabetic heart because they may serve to bypass defective insulin-stimulated glucose uptake. To test the preventive potential of these kinases against loss of insulin-stimulated glucose uptake, AMPK or PKD were adenovirally overexpressed in primary cultures of insulin resistant cardiomyocytes for assaying substrate uptake, insulin responsiveness and lipid accumulation. To induce insulin resistance and lipid loading, rat primary cardiomyocytes were cultured in the presence of high insulin (100 nM; HI) or high palmitate (palmitate/BSA: 3/1; HP). HI and HP each reduced insulin responsiveness, and increased basal palmitate uptake and lipid storage. Overexpression of each of the kinases prevented loss of insulin-stimulated glucose uptake. Overexpression of AMPK also prevented loss of insulin signaling in HI- and HP-cultured cardiomyocytes, but did not prevent lipid accumulation. In contrast, overexpression of PKD prevented lipid accumulation, but not loss of insulin signaling in HI- and HP-cultured cardiomyocytes. In conclusion, AMPK and PKD prevent loss of insulin-stimulated glucose uptake into cardiomyocytes cultured under insulin resistance-inducing conditions through different mechanisms. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

Targeting metabolism for cancer treatment and prevention: metformin, an old drug with multi-faceted effects

Understanding the complexity of cancer and of the underlying regulatory networks provides a new paradigm that tackles cancer development and treatment through a system biology approach, contemporarily acting on various intersecting pathways. Cancer cell metabolism is an old pathogenetic issue that has recently gained new interest as target for therapeutic approaches. More than 70 years ago, Warburg discovered that malignant cells generally have altered metabolism with high rates of glucose uptake and increased glycolysis, even under aerobic condition. Observational studies have provided evidence that impaired metabolism, obesity, hyperglycemia and hyperinsulinemia may have a role in cancer development, progression and prognosis, and actually diabetic and obese patients have increased cancer risk. On the other hand, caloric restriction has been shown to prolong life span and reduce cancer incidence in several animal models, having an impact on different metabolic pathways. Metformin, an antidiabetic drug widely used for over 40 years, mimics caloric restriction acting on cell metabolism at multiple levels, reducing all energy-consuming processes in the cells, including cell proliferation. By overviewing molecular mechanisms of action, epidemiological evidences, experimental data in tumor models and early clinical study results, this review provides information supporting the promising use of metformin in cancer prevention and treatment.