mTORC1 enhancement of STIM1-mediated store-operated Ca2+ entry constrains tuberous sclerosis complex-related tumor development

Ang-1 and VEGF: central regulators of angiogenesis

Angiopoietin-1 (Ang-1) and Vascular Endothelial Growth Factor (VEGF) are central regulators of angiogenesis and are often inactivated in various cardiovascular diseases. VEGF forms complexes with ETS transcription factor family and exerts its action by downregulating multiple genes. Among the target genes of the VEGF-ETS complex, there are a significant number encoding key angiogenic regulators. Phosphorylation of the VEGF-ETS complex releases transcriptional repression on these angiogenic regulators, thereby promoting their expression. Ang-1 interacts with TEK, and this phosphorylation release can be modulated by the Ang-1-TEK signaling pathway. The Ang-1-TEK pathway participates in the transcriptional activation of VEGF genes. In summary, these elements constitute the Ang-1-TEK-VEGF signaling pathway. Additionally, Ang-1 is activated under hypoxic and inflammatory conditions, leading to an upregulation in the expression of TEK. Elevated TEK levels result in the formation of the VEGF-ETS complex, which, in turn, downregulates the expression of numerous angiogenic genes. Hence, the Ang-1-dependent transcriptional repression is indirect. Reduced expression of many target genes can lead to aberrant angiogenesis. A significant overlap exists between the target genes regulated by Ang-1-TEK-VEGF and those under the control of the Ang-1-TEK-TSP-1 signaling pathway. Mechanistically, this can be explained by the replacement of the VEGF-ETS complex with the TSP-1 transcriptional repression complex at the ETS sites on target gene promoters. Furthermore, VEGF possesses non-classical functions unrelated to ETS and DNA binding. Its supportive role in TSP-1 formation may be exerted through the VEGF-CRL5-VHL-HIF-1α-VH032-TGF-β-TSP-1 axis. This review assesses the regulatory mechanisms of the Ang-1-TEK-VEGF signaling pathway and explores its significant overlap with the Ang-1-TEK-TSP-1 signaling pathway.

The Mystery of EVP4593: Perspectives of the Quinazoline-Derived Compound in the Treatment of Huntington's Disease and Other Human Pathologies

Quinazoline derivatives have various pharmacological activities and are widely used in clinical practice. Here, we reviewed the proposed mechanisms of the physiological activity of the quinazoline derivative EVP4593 and perspectives for its clinical implication. We summarized the accumulated data about EVP4593 and focused on its activities in different models of Huntington's disease (HD), including patient-specific iPSCs-based neurons. To make a deeper insight into its neuroprotective role in HD treatment, we discussed the ability of EVP4593 to modulate calcium signaling and reduce the level of the huntingtin protein. Moreover, we described possible protective effects of EVP4593 in other pathologies, such as oncology, cardiovascular diseases and parasite invasion. We hope that comprehensive analyses of the molecular mechanisms of EVP4593 activity will allow for the expansion of the scope of the EVP4593 application.

CRACking the Molecular Regulatory Mechanism of SOCE during Platelet Activation in Thrombo-Occlusive Diseases

Thrombo-occlusive diseases such as myocardial infarction, ischemic stroke and deep vein thrombosis with subsequent pulmonary embolism still represent a major health burden worldwide. Besides the cells of the vasculature or other hematopoietic cells, platelets are primarily responsible for the development and progression of an occluding thrombus. The activation and function of platelets crucially depend on free cytosolic calcium (Ca2+) as second messenger, which modulates platelet secretion, aggregation and thrombus formation. Ca2+ is elevated upon platelet activation by release of Ca2+ from intracellular stores thus triggering of the subsequent store-operated Ca2+ entry (SOCE), which is facilitated by Ca2+ release-activated channels (CRACs). In general, CRACs are assembled by the pore-forming unit Orai in the plasma membrane and the Ca2+-sensing stromal interaction molecule (STIM) in the endoplasmic reticulum after the depletion of internal Ca2+ stores. In the last few years, there is a growing body of the literature demonstrating the importance of STIM and Orai-mediated mechanism in thrombo-occlusive disorders. Thus, this review provides an overview of the recent understanding of STIM and Orai signaling in platelet function and its implication in the development and progression of ischemic thrombo-occlusive disorders. Moreover, potential pharmacological implications of STIM and Orai signaling in platelets are anticipated and discussed in the end.

p53 transcriptionally regulates SQLE to repress cholesterol synthesis and tumor growth

Cholesterol is essential for membrane biogenesis, cell proliferation, and differentiation. The role of cholesterol in cancer development and the regulation of cholesterol synthesis are still under active investigation. Here we show that under normal-sterol conditions, p53 directly represses the expression of SQLE, a rate-limiting and the first oxygenation enzyme in cholesterol synthesis, in a SREBP2-independent manner. Through transcriptional downregulation of SQLE, p53 represses cholesterol production in vivo and in vitro, leading to tumor growth suppression. Inhibition of SQLE using small interfering RNA (siRNA) or terbinafine (a SQLE inhibitor) reverses the increased cell proliferation caused by p53 deficiency. Conversely, SQLE overexpression or cholesterol addition promotes cell proliferation, particularly in p53 wild-type cells. More importantly, pharmacological inhibition or shRNA-mediated silencing of SQLE restricts nonalcoholic fatty liver disease (NAFLD)-induced liver tumorigenesis in p53 knockout mice. Therefore, our findings reveal a role for p53 in regulating SQLE and cholesterol biosynthesis, and further demonstrate that downregulation of SQLE is critical for p53-mediated tumor suppression.

CHD1L prevents lipopolysaccharide-induced hepatocellular carcinomar cell death by activating hnRNP A2/B1-nmMYLK axis

Chromodomain helicase/ATPase DNA-binding protein 1-like gene (CHD1L) has been characterized to be a driver gene in hepatocellular carcinoma (HCC). However, the intrinsic connections between CHD1L and intestinal dysbacteriosis-related inflammation reaction in HCC progression remain incompletely understood. In this study, a specific correlation between CHD1L and nonmuscle isoform of myosin light chain kinase (nmMLCK/nmMYLK), a newly identified molecule associated NF-κB signaling transduction, was disclosed in HCC. CHD1L promotes nmMYLK expression and prevents lipopolysaccharide (LPS) induced tumor cell death. In vitro experiment demonstrated that overexpressed nmMYLK is essential for CHD1L to maintain HCC cell alive, while knocking down nmMYLK significantly attenuate the oncogenic roles of CHD1L. Mechanism analysis revealed that nmMYLK can prevent Caspase-8 from combining with MyD88, an important linker of TLRs signaling pathway, while, knocking down nmMYLK facilitate the MyD88 combines with Caspase-8 and lead to the proteolytic cascade of Caspase as well as the consequent cell apoptosis. Mechanism analysis showed that CHD1L promotes the nmMYLK expression potentially through upregulating the heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNP A2/B1) expression, which can bind to myosin light chain kinase (MYLK) pre-mRNA and lead to the regnant translation of nmMYLK. In summary, this work characterizes a previously unknown role of CHD1L in preventing LPS-induced tumor cell death through activating hnRNP A2/B1-nmMYLK axis. Further inhibition of CHD1L and its downstream signaling could be a novel promising strategy in HCC treatment.

Ablation of Collagen VI leads to the release of platelets with altered function

Megakaryocytes express collagen VI that regulates the release of functional platelets.

Collagen VI–null megakaryocytes and platelets display increased mTOR signaling and store-operated calcium entry.

Hemostatic abnormalities and impaired platelet function have been described in patients affected by connective tissue disorders. We observed a moderate bleeding tendency in patients affected by collagen VI–related disorders and investigated the defects in platelet functionality, whose mechanisms are unknown. We demonstrated that megakaryocytes express collagen VI that is involved in the regulation of functional platelet production. By exploiting a collagen VI–null mouse model (Col6a1^−/−), we found that collagen VI–null platelets display significantly increased susceptibility to activation and intracellular calcium signaling. Col6a1^−/− megakaryocytes and platelets showed increased expression of stromal interaction molecule 1 (STIM1) and ORAI1, the components of store-operated calcium entry (SOCE), and activation of the mammalian target of rapamycin (mTOR) signaling pathway. In vivo mTOR inhibition by rapamycin reduced STIM1 and ORAI1 expression and calcium flows, resulting in a normalization of platelet susceptibility to activation. These defects were cell autonomous, because transplantation of lineage-negative bone marrow cells from Col6a1^−/− mice into lethally irradiated wild-type animals showed the same alteration in SOCE and platelet activation seen in Col6a1^−/− mice. Peripheral blood platelets of patients affected by collagen VI–related diseases, Bethlem myopathy and Ullrich congenital muscular dystrophy, displayed increased expression of STIM1 and ORAI1 and were more prone to activation. Altogether, these data demonstrate the importance of collagen VI in the production of functional platelets by megakaryocytes in mouse models and in collagen VI–related diseases.

Aberrant mTOR/autophagy/Nurr1 signaling is critical for TSC-associated tumor development

Tuberous sclerosis complex (TSC), an inherited neurocutaneous disease, is caused by mutations in either the TSC1 or TSC2 gene. This genetic disorder is characterized by the growth of benign tumors in the brain, kidneys, and other organs. As a member of the orphan nuclear receptor family, nuclear receptor related 1 (Nurr1) plays a vital role in some neuropathological diseases and several types of benign or malignant tumors. Here, we explored the potential regulatory role of TSC1/2 signaling in Nurr1 and the effect of Nurr1 in TSC-related tumors. We found that Nurr1 expression was drastically decreased by the disruption of the TSC1/2 complex in Tsc2-null cells, genetically modified mouse models of TSC, cortical tubers of TSC patients, and kidney tumor tissue obtained from a TSC patient. Deficient TSC1/2 complex downregulated Nurr1 expression in an mTOR-dependent manner. Moreover, hyperactivation of mTOR reduced Nurr1 expression via suppression of autophagy. In addition, Nurr1 overexpression inhibited cell proliferation and suppressed cell cycle progression. Therefore, TSC/mTOR/autophagy/Nurr1 signaling is partially responsible for the tumorigenesis of TSC. Taken together, Nurr1 may be a novel therapeutic target for TSC-associated tumors, and Nurr1 agonists or reagents that induce Nurr1 expression may be used for the treatment of TSC.

Store-operated Ca2+ entry as a key oncogenic Ca2+ signaling driving tumor invasion-metastasis cascade and its translational potential

Tumor metastasis is the primary cause of treatment failure and cancer-related deaths. Store-operated Ca²⁺ entry (SOCE), which is mediated by stromal interaction molecules (STIM) and ORAI proteins, has been implicated in the tumor invasion-metastasis cascade. Epithelial-mesenchymal transition (EMT) is a cellular program that enables tumor cells to acquire the capacities needed for migration and invasion and the formation of distal metastases. Tumor-associated angiogenesis contributes to metastasis because aberrantly developed vessels offer a path for tumor cell dissemination as well as supply sufficient nutrients for the metastatic colony to develop into metastasis. Recently, increasing evidence has indicated that SOCE alterations actively participate in the multi-step process of tumor metastasis. In addition, the dysregulated expression of STIM/ORAI has been reported to be a predictor of poor prognosis. Herein, we review the latest advances about the critical role of SOCE in the tumor metastasis cascade and the underlying regulatory mechanisms. We emphasize the contributions of SOCE to the EMT program, tumor cell migration and invasion, and angiogenesis. We further discuss the possibility of modulating SOCE or intervening in the downstream signaling pathways as a feasible targeting therapy for cancer treatment.

Mechanism of the lifespan extension induced by submaximal SERCA inhibition in C. elegans

We have reported recently that submaximal inhibition of the Sarco Endoplasmic Reticulum Ca²⁺ ATPase (SERCA) produces an increase in the lifespan of C. elegans worms. We have explored here the mechanism of this increased survival by studying the effect of SERCA inhibition in several mutants of signaling pathways related to longevity. Our data show that the mechanism of the effect is unrelated with the insulin signaling pathway or the sirtuin activity, because SERCA inhibitors increased lifespan similarly in mutants of these pathways. However, the effect required functional mitochondria and both the AMP kinase and TOR pathways, as the SERCA inhibitors were ineffective in the corresponding mutants. The same effects were obtained after reducing SERCA expression with submaximal RNAi treatment. The SERCA inhibitors did not induce ER-stress at the concentrations used, and their effect was not modified by inactivation of the OP50 bacterial food. Altogether, our data suggest that the effect may be due to a reduced ER-mitochondria Ca²⁺ transfer acting via AMPK activation and mTOR inhibition to promote survival.

Study on the Treatment of Tuberous Sclerosis with Rapamycin Nanomicelles Based on Abdominal Ultrasound

In recent years, mTOR signaling pathway has been found to be the main bridge between TSC1/TSC2 gene mutation and tuberous sclerosis phenotype. Although mTOR inhibitors have been reported to treat tuberous sclerosis in foreign countries, there is still a lack of long-term follow-up results and clinical treatment experience in children. Therefore, research at home and abroad is actively focusing on the mTOR signaling pathway to further clarify the pathogenesis of the disease, and from a clinical point of view, to summarize the clinical data of more patients treated with mTOR inhibitors, to conduct a long-term follow-up and exploration of rapamycin treatment, and to summarize mature treatment experience. This is also the research hotspot of tuberous sclerosis. Based on the study of the treatment of tuberous sclerosis patients with rapamycin nanomicelles by abdominal ultrasound, the therapeutic effect and safety were compared and evaluated through the observation and description of the clinical seizure control and the recovery of EEG peak out of rhythm in children with tuberous sclerosis and infantile spasm.

Caloric Intake in Renal Patients: Repercussions on Mineral Metabolism

The aim of this paper is to review current knowledge about how calorie intake influences mineral metabolism focussing on four aspects of major interest for the renal patient: (a) phosphate (P) handling, (b) fibroblast growth factor 23 (FGF23) and calcitriol synthesis and secretion, (c) metabolic bone disease, and (d) vascular calcification (VC). Caloric intake has been shown to modulate P balance in experimental models: high caloric intake promotes P retention, while caloric restriction decreases plasma P concentrations. Synthesis and secretion of the phosphaturic hormone FGF23 is directly influenced by energy intake; a direct correlation between caloric intake and FGF23 plasma concentrations has been shown in animals and humans. Moreover, in vitro, energy availability has been demonstrated to regulate FGF23 synthesis through mechanisms in which the molecular target of rapamycin (mTOR) signalling pathway is involved. Plasma calcitriol concentrations are inversely proportional to caloric intake due to modulation by FGF23 of the enzymes implicated in vitamin D metabolism. The effect of caloric intake on bone is controversial. High caloric intake has been reported to increase bone mass, but the associated changes in adipokines and cytokines may as well be deleterious for bone. Low caloric intake tends to reduce bone mass but also may provide indirect (through modulation of inflammation and insulin regulation) beneficial effects on bone. Finally, while VC has been shown to be exacerbated by diets with high caloric content, the opposite has not been demonstrated with low calorie intake. In conclusion, although prospective studies in humans are needed, when planning caloric intake for a renal patient, it is important to take into consideration the associated changes in mineral metabolism.

Direct regulation of fibroblast growth factor 23 by energy intake through mTOR

To test the hypothesis that fibroblast growth factor 23 (FGF23) is directly regulated by energy intake, in vivo and in vitro experiments were conducted. Three groups of rats were fed diets with high (HC), normal (NC) and low (LC) caloric content that resulted in different energy intake. In vitro, UMR106 cells were incubated in high (HG, 4.5 g/l) or low glucose (LG, 1 g/l) medium. Additional treatments included phosphorus (P), mannitol, rapamycin and everolimus. Intestinal absorption of P and plasma P concentrations were similar in the three groups of rats. As compared with NC, plasma FGF23 concentrations were increased in HC and decreased in the LC group. A significant correlation between energy intake and plasma FGF23 concentrations was observed. In vitro, mRNA FGF23 was significantly higher in UMR106 cells cultured in HG than in LG. When exposed to high P, mRNA FGF23 increased but only when cells were cultured in HG. Cells incubated with HG and mechanistic target of rapamycin (mTOR) inhibitors expressed low mRNA FGF23, similar to the values obtained in LG. In conclusion, this study shows a direct regulation of FGF23 production by energy availability and demonstrates that the mTOR signaling pathway plays a central role in this regulatory system.

Upregulation of 6-phosphofructo-2-kinase (PFKFB3) by hyperactivated mammalian target of rapamycin complex 1 is critical for tumor growth in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterized by the benign tumor formation in multiple organs. The main etiology of TSC is the loss-of-function mutation of TSC1 or TSC2 gene, which leads to aberrant activation of mammalian target of rapamycin complex 1 (mTORC1). In this research, we found a significant increase of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) expression in Tsc1-/- and Tsc2-/- mouse embryonic fibroblasts (MEFs) compared with the control cells. Inhibition of mTORC1 led to a dramatic decrease of PFKFB3 expression, indicating PFKFB3 regulation by mTORC1. Moreover, suppression of mTORC1 inhibited the expression of PFKFB3 in rat uterine leiomyoma-derived Tsc2-null ELT3 cells and human tumor cells. Furthermore, we identified hypoxia-inducible factor 1α (HIF-1α) as a mediator transmitting the signal from mTORC1 to PFKFB3. Depletion of PFKFB3 inhibited proliferation and tumorigenicity of Tsc1- or Tsc2-deficient cells. In addition, combination of rapamycin with PFK15, a PFKFB3 inhibitor, exerts a stronger inhibitory effect on cell proliferation of Tsc1- or Tsc2-null MEFs than treatment with single drug. We conclude that loss of TSC1 or TSC2 led to upregulated expression of PFKFB3 through activation of mTORC1/HIF-1α signaling pathway and co-administration of rapamycin and PFK15 may be a promising strategy for the treatment of TSC tumors as well as other hyperactivated mTORC1-related tumors.

STIM-Orai Channels and Reactive Oxygen Species in the Tumor Microenvironment

The tumor microenvironment (TME) is shaped by cancer and noncancerous cells, the extracellular matrix, soluble factors, and blood vessels. Interactions between the cells, matrix, soluble factors, and blood vessels generate this complex heterogeneous microenvironment. The TME may be metabolically beneficial or unbeneficial for tumor growth, it may favor or not favor a productive immune response against tumor cells, or it may even favor conditions suited to hijacking the immune system for benefitting tumor growth. Soluble factors relevant for TME include oxygen, reactive oxygen species (ROS), ATP, Ca2+, H⁺, growth factors, or cytokines. Ca2+ plays a prominent role in the TME because its concentration is directly linked to cancer cell proliferation, apoptosis, or migration but also to immune cell function. Stromal-interaction molecules (STIM)-activated Orai channels are major Ca2+ entry channels in cancer cells and immune cells, they are upregulated in many tumors, and they are strongly regulated by ROS. Thus, STIM and Orai are interesting candidates to regulate cancer cell fate in the TME. In this review, we summarize the current knowledge about the function of ROS and STIM/Orai in cancer cells; discuss their interdependencies; and propose new hypotheses how TME, ROS, and Orai channels influence each other.

Tsc1-dependent transcriptional programming of dendritic cell homeostasis and function

Dendritic cells (DCs) are pivotal to initiating adaptive immune response. Emerging evidence highlights important roles of tuberous sclerosis complex 1 (Tsc1) in DC development and activation. Our previous study also showed that Tsc1 expression in DCs was required to promote T-cell homeostasis and response partially through inhibiting mammalian target of rapamycin complex1 (mTORC1). However, the molecular mechanism of transcriptional regulation by which Tsc1 control DC homeostasis and function remains largely unknown. Here we globally identified the Tsc1-regulated genes by comparing the transcriptional profiling of Tsc1-deficient DCs with wild-type DCs. It showed that Tsc1 specifically regulated the expression of groups of gene sets critically involved in DC survival, proliferation, metabolism and antigen presentation. The impacts of Tsc1 on DC gene expression were partially dependent on inhibition of mTORC1 signal. Our study thus provides a comprehensive molecular basis for understanding how Tsc1 programs the homeostasis and function of DCs through transcriptional regulation.

Deficient TSC1/TSC2-complex suppression of SOX9-osteopontin-AKT signalling cascade constrains tumour growth in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder featured with multi-organ benign tumours. Disruption of TSC1/TSC2 complex suppression on mammalian/mechanistic target of rapamycin (mTOR) signalling causes TSC. Hyperactive mTOR-mediated negative feedback regulation of AKT partially contributes to the benign nature of TSC-associated tumours. In this study, we demonstrated that osteopontin (OPN) was dramatically reduced by loss of TSC1/TSC2 complex in Tsc2-null mouse embryonic fibroblasts (MEFs), rat uterine leiomyoma-derived Tsc2-deficient cells, genetically modified mouse TSC models, and clinical samples. TSC1/TSC2 complex upregulation of OPN expression is mediated by transcription factor SOX9 in an mTOR-independent manner. Moreover, ablation of OPN by deficient TSC1/TSC2 complex contributed to inactivation of AKT in TSC cells. Lastly, the abundance of OPN dictated the potency of cell proliferation and tumour development. Therefore, loss of TSC1/TSC2 complex led to mTOR-independent inhibition of AKT at least partially through downregulation of the SOX9-OPN signalling cascade. We suggest that the decreased SOX9-OPN-AKT signalling pathway safeguard against the development of malignant tumours in TSC patients.

Up-regulation of brain-expressed X-linked 2 is critical for hepatitis B virus X protein-induced hepatocellular carcinoma development

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Chronic hepatitis B virus (HBV) infection is a major cause for HCC. Hepatitis B virus X (HBx), one of four proteins encoded by HBV genome, plays a vital role in the pathogenesis of HBV-induced HCC. However, the molecular mechanisms of HBx-triggered HCC remain largely undetermined. Here we revealed that the expression of Brain-expressed X-linked 2 (BEX2) and Osteopontin (OPN) were elevated in liver tissues of HBV transgenic mice and human HCC specimens. Moreover, a positive correlation between BEX2 and OPN was exhibited in samples from HCC patients with HBV infection. The protein levels of BEX2 and OPN were both higher in HBV-positive HCC specimens compared to that of HBV-negative HCC specimens. HBx potentiated OPN expression through up-regulation of BEX2. Importantly, the depletion of BEX2 suppressed tumorigenic potential of HCC cells with highly expressed HBx. We demonstrated the important role of BEX2 in HCC pathogenesis, and BEX2 may be a novel therapeutic target for HCC patients with HBV infection. The newly identified HBx/BEX2/OPN signaling cassette is implicated in the pathogenesis of HBV-induced HCC.

Hyperactivated mTORC1 downregulation of FOXO3a/PDGFRα/AKT cascade restrains tuberous sclerosis complex-associated tumor development

Hyperactivation of mammalian target of rapamycin complex 1 (mTORC1), caused by loss-of-function mutations in either the TSC1 or TSC2 gene, leads to the development of tuberous sclerosis complex (TSC), a benign tumor syndrome with multiple affected organs. mTORC1-mediated inhibition of AKT constrains the tumor progression of TSC, but the exact mechanisms remain unclear. Herein we showed that loss of TSC1 or TSC2 downregulation of platelet-derived growth factor receptor α (PDGFRα) expression was mediated by mTORC1. Moreover, mTORC1 inhibited PDGFRα expression via suppression of forkhead box O3a (FOXO3a)-mediated PDGFRα gene transcription. In addition, ectopic expression of PDGFRα promoted AKT activation and enhanced proliferation and tumorigenic capacity of Tsc1- or Tsc2-null mouse embryonic fibroblasts (MEFs), and vice versa. Most importantly, rapamycin in combination with AG1295, a PDGFR inhibitor, significantly inhibited growth of TSC1/TSC2 complex-deficient cells in vitro and in vivo. Therefore, downregulated FOXO3a/PDGFRα/AKT pathway exerts a protective effect against hyperactivated mTORC1-induced tumorigenesis caused by loss of TSC1/TSC2 complex, and the combination of rapamycin and AG1295 may be a new effective strategy for TSC-associated tumors treatment.

Anti-proliferative Effects of Nucleotides on Gastric Cancer via a Novel P2Y6/SOCE/Ca2+/β-catenin Pathway

Although purinegic signaling is important in regulating gastric physiological functions, it is currently unknown for its role in gastric cancer (GC). We demonstrate for the first time that the expression of P2Y6 receptors was markedly down-regulated in human GC cells and primary GC tissues compared to normal tissues, while the expression of P2Y2 and P2Y4 receptors was up-regulated in GC cells. Moreover, the expression levels of P2Y6 receptors in GC tissues were correlated to tumor size, differentiation, metastasis to lymph nodes, and the survival rate of the patients with GC. Ncleotides activated P2Y6 receptors to raise cytosolic Ca²⁺ concentrations in GC cells through store-operated calcium entry (SOCE), and then mediated Ca²⁺-dependent inhibition of β-catenin and proliferation, eventually leading to GC suppression. Furthermore, UTP particularly blocked the G1/S transition of GC cells but did not induce apoptosis. Collectively, we conclude that nucleotides activate P2Y6 receptors to suppress GC growth through a novel SOCE/Ca²⁺/β-catenin-mediated anti-proliferation of GC cells, which is different from the canonical SOCE/Ca²⁺-induced apoptosis in other tumors.

Negative regulation of Smad1 pathway and collagen IV expression by store-operated Ca2+ entry in glomerular mesangial cells

Collagen IV (Col IV) is a major component of expanded glomerular extracellular matrix in diabetic nephropathy and Smad1 is a key molecule regulating Col IV expression in mesangial cells (MCs). The present study was conducted to determine if Smad1 pathway and Col IV protein abundance were regulated by store-operated Ca²⁺ entry (SOCE). In cultured human MCs, pharmacological inhibition of SOCE significantly increased the total amount of Smad1 protein. Activation of SOCE blunted high-glucose-increased Smad1 protein content. Treatment of human MCs with ANG II at 1 µM for 15 min, high glucose for 3 days, or TGF-β1 at 5 ng/ml for 30 min increased the level of phosphorylated Smad1. However, the phosphorylation of Smad1 by those stimuli was significantly attenuated by activation of SOCE. Knocking down Smad1 reduced, but expressing Smad1 increased, the amount of Col IV protein. Furthermore, activation of SOCE significantly attenuated high-glucose-induced Col IV protein production, and blockade of SOCE substantially increased the abundance of Col IV. To further verify those in vitro findings, we downregulated SOCE specifically in MCs in mice using small-interfering RNA (siRNA) against Orai1 (the channel protein mediating SOCE) delivered by the targeted nanoparticle delivery system. Immunohistochemical examinations showed that expression of both Smad1 and Col IV proteins was significantly greater in the glomeruli with positively transfected Orai1 siRNA compared with the glomeruli from the mice without Orai1 siRNA treatment. Taken together, our results indicate that SOCE negatively regulates the Smad1 signaling pathway and inhibits Col IV protein production in MCs.

mTOR promotes pituitary tumor development through activation of PTTG1

As one of the most common intracranial tumors, pituitary tumor is associated with high morbidity. Effective therapy is currently not available for some pituitary tumors due to the largely undefined pathological processes of pituitary tumorigenesis. In this study, hyperactivation of mammalian/mechanistic target of rapamycin (mTOR) signaling was observed in estrogen-induced rat pituitary tumor and mTOR inhibitor rapamycin blocked the tumor development. Pituitary knockout of either mTOR signaling pathway negative regulator Tsc1 or Pten caused mouse pituitary prolactinoma, which was abolished by rapamycin treatment. Mechanistically, the expression of pituitary tumor transforming gene 1 (PTTG1) was upregulated in an mTOR complex 1-dependent manner. Overexpressed PTTG1 was crucial in hyperactive mTOR-mediated tumorigenesis. mTOR-PTTG1 signaling axis may be targeted for the treatment of tumors with mTOR hyperactivation.

Store-operated calcium entry and diabetic complications

Store-operated Ca(2+) entry (SOCE) is mediated by the store-operated Ca(2+) channel (SOC) that opens upon depletion of internal Ca(2+) stores following activation of G protein-coupled receptors or receptor tyrosine kinases. Over the past two decades, the physiological and pathological relevance of SOCE has been extensively studied. Recently, accumulating evidence suggests associations of altered SOCE with diabetic complications. This review focuses on the implication of SOCE as it pertains to various complications resulting from diabetes. We summarize recent findings by us and others on the involvement of abnormal SOCE in the development of diabetic complications, such as diabetic nephropathy and diabetic vasculopathy. The underlying mechanisms that mediate the diabetes-associated alterations of SOCE are also discussed. The SOCE pathway may be considered as a potential therapeutic target for diabetes-associated diseases.

mTORC1 Up-Regulates GP73 to Promote Proliferation and Migration of Hepatocellular Carcinoma Cells and Growth of Xenograft Tumors in Mice

BACKGROUND & AIMS

Levels of the Golgi protein 73 (GP73) increase during development of hepatocellular carcinoma (HCC); GP73 is a serum marker for HCC. However, little is known about the mechanisms or effects of GP73 during hepatic carcinogenesis.

METHODS

GP73 was overexpressed from a retroviral vector in HepG2 cells, which were analyzed in proliferation and migration assays. Xenograft tumors were grown from these cells in nude mice. The effects of monoclonal antibodies against GP73 were studied in mice and cell lines. GP73(-/-), GP73(+/-), and GP73(+/+) mice were given injections of diethylnitrosamine to induce liver injury. Levels of GP73 were reduced in MHCC97H, HCCLM3, and HepG2.215 cell lines using small hairpin RNAs; xenograft tumors were grown in mice from MHCC97H-small hairpin GP73 or MHCC97H-vector cells. We used microarray analysis to compare expression patterns between GP73-knockdown and control MHCC97H cells. We studied the effects of the mechanistic target of rapamycin (mTOR) inhibitor rapamycin on GP73 expression in different cancer cell lines and on growth of tumors in mice. Levels of GP73 and activated mTOR were quantified in human HCC tissues.

RESULTS

Xenograft tumors grown from HepG2 cells that expressed GP73 formed more rapidly and more metastases than control HepG2 cells in mice. A monoclonal antibody against GP73 reduced proliferation of HepG2 cells and growth of xenograft tumors in mice. GP73(-/-) mice had less liver damage after administration of diethylnitrosamine than GP73(+/-) or GP73(+/+) mice. In phosphatase and tensin homolog-null mouse embryonic fibroblasts with constitutively activated mTOR, GP73 was up-regulated compared with control mouse embryonic fibroblasts; this increase was reversed after incubation with rapamycin. Expression of GP73 also was reduced in HCC and other cancer cell lines incubated with rapamycin. mTORC1 appeared to regulate expression of GP73 in cell lines. Activated mTOR correlated with the level of GP73 in human HCC tissues. Injection of rapamycin slowed the growth of xenograft tumors from MHCC97H-vector cells, compared with MHCC97H-short hairpin GP73 cells.

CONCLUSIONS

Increased expression of GP73 promotes proliferation and migration of HCC cell lines and growth of xenograft tumors in mice. mTORC1 regulates the expression of GP73, so GP73 up-regulation can be blocked with rapamycin. mTOR inhibitors or other reagents that reduce the level or activity of GP73 might be developed for the treatment of HCC.

Brain-expressed X-linked 2 Is Pivotal for Hyperactive Mechanistic Target of Rapamycin (mTOR)-mediated Tumorigenesis

Frequent alteration of upstream proto-oncogenes and tumor suppressor genes activates mechanistic target of rapamycin (mTOR) and causes cancer. However, the downstream effectors of mTOR remain largely elusive. Here we report that brain-expressed X-linked 2 (BEX2) is a novel downstream effector of mTOR. Elevated BEX2 in Tsc2(-/-) mouse embryonic fibroblasts, Pten(-/-) mouse embryonic fibroblasts, Tsc2-deficient rat uterine leiomyoma cells, and brains of neuronal specific Tsc1 knock-out mice were abolished by mTOR inhibitor rapamycin. Furthermore, BEX2 was also increased in the liver of a hepatic specific Pten knock-out mouse and the kidneys of Tsc2 heterozygous deletion mice, and a patient with tuberous sclerosis complex (TSC). mTOR up-regulation of BEX2 was mediated in parallel by both STAT3 and NF-κB. BEX2 was involved in mTOR up-regulation of VEGF production and angiogenesis. Depletion of BEX2 blunted the tumorigenesis of cells with activated mTOR. Therefore, enhanced STAT3/NF-κB-BEX2-VEGF signaling pathway contributes to hyperactive mTOR-induced tumorigenesis. BEX2 may be targeted for the treatment of the cancers with aberrantly activated mTOR signaling pathway.

STIM1 accelerates cell senescence in a remodeled microenvironment but enhances the epithelial-to-mesenchymal transition in prostate cancer

The importance of store-operated Ca²⁺ entry (SOCE) and the role of its key molecular regulators, STIM1 and ORAI1, in the development of cancer are emerging. Here, we report an unexpected dual function of SOCE in prostate cancer progression by revealing a decrease in the expression of STIM1 in human hyperplasia and tumor tissues of high histological grade and by demonstrating that STIM1 and ORAI1 inhibit cell growth by arresting the G0/G1 phase and enhancing cell senescence in human prostate cancer cells. In addition, STIM1 and ORAI1 inhibited NF-κB signaling and remodeled the tumor microenvironment by reducing the formation of M2 phenotype macrophages, possibly creating an unfavorable tumor microenvironment and inhibiting cancer development. However, STIM1 also promoted cell migration and the epithelial-to-mesenchymal transition by activating TGF-β, Snail and Wnt/β-Catenin pathways. Thus, our study revealed novel regulatory effects and the mechanisms by which STIM1 affects cell senescence, tumor migration and the tumor microenvironment, revealing that STIM1 has multiple functions in prostate cancer cells.

STIM and Orai proteins as novel targets for cancer therapy. A Review in the Theme: Cell and Molecular Processes in Cancer Metastasis

Calcium (Ca(2+)) regulates a plethora of cellular functions including hallmarks of cancer development such as cell cycle progression and cellular migration. Receptor-regulated calcium rise in nonexcitable cells occurs through store-dependent as well as store-independent Ca(2+) entry pathways. Stromal interaction molecules (STIM) and Orai proteins have been identified as critical constituents of both these Ca(2+) influx pathways. STIMs and Orais have emerged as targets for cancer therapeutics as their altered expression and function have been shown to contribute to tumorigenesis. Recent data demonstrate that they play a vital role in development and metastasis of a variety of tumor types including breast, prostate, cervical, colorectal, brain, and skin tumors. In this review, we will retrospect the data supporting a key role for STIM1, STIM2, Orai1, and Orai3 proteins in tumorigenesis and discuss the potential of targeting these proteins for cancer therapy.

Enhanced Orai1 and STIM1 expression as well as store operated Ca2+ entry in therapy resistant ovary carcinoma cells

Mechanisms underlying therapy resistance of tumor cells include protein kinase Akt. Putative Akt targets include store-operated Ca²⁺-entry (SOCE) accomplished by pore forming ion channel unit Orai1 and its regulator STIM1. We explored whether therapy resistant (A2780cis) differ from therapy sensitive (A2780) ovary carcinoma cells in Akt, Orai1, and STIM1 expression, Ca²⁺-signaling and cell survival following cisplatin (100μM) treatment. Transcript levels were quantified with RT-PCR, protein abundance with Western blotting, cytosolic Ca²⁺-activity ([Ca²⁺]i) with Fura-2-fluorescence, SOCE from increase of [Ca²⁺]i following Ca²⁺-readdition after Ca²⁺-store depletion, and apoptosis utilizing flow cytometry. Transcript levels of Orai1 and STIM1, protein expression of Orai1, STIM1, and phosphorylated Akt, as well as SOCE were significantly higher in A2780cis than A2780 cells. SOCE was decreased by Akt inhibitor III (SH-6, 10μM) in A2780cis but not A2780 cells and decreased in both cell lines by Orai1 inhibitor 2-aminoethoxydiphenyl borate (2-ABP, 50μM). Phosphatidylserine exposure and late apoptosis following cisplatin treatment were significantly lower in A2780cis than A2780 cells, a difference virtually abolished by SH-6 or 2-ABP. In conclusion, Orai1/STIM1 expression and function are increased in therapy resistant ovary carcinoma cells, a property at least in part due to enhanced Akt activity and contributing to therapy resistance in those cells.

Resveratrol activates autophagic cell death in prostate cancer cells via downregulation of STIM1 and the mTOR pathway

Resveratrol (RSV), a natural polyphenol, has been suggested to induce cell cycle arrest and activate apoptosis-mediated cell death in several cancer cells, including prostate cancer. However, several molecular mechanisms have been proposed on its chemopreventive action, the precise mechanisms by which RSV exerts its anti-proliferative effect in androgen-independent prostate cancer cells remain questionable. In the present study, we show that RSV activates autophagic cell death in PC3 and DU145 cells, which was dependent on stromal interaction molecule 1 (STIM1) expression. RSV treatment decreases STIM1 expression in a time-dependent manner and attenuates STIM1 association with TRPC1 and Orai1. Furthermore, RSV treatment also decreases ER calcium storage and store operated calcium entry (SOCE), which induces endoplasmic reticulum (ER) stress, thereby, activating AMPK and inhibiting the AKT/mTOR pathway. Similarly, inhibition of SOCE by SKF-96365 decreases the survival and proliferation of PC3 and DU145 cells and inhibits AKT/mTOR pathway and induces autophagic cell death. Importantly, SOCE inhibition and subsequent autophagic cell death caused by RSV was reversed by STIM1 overexpression. STIM1 overexpression restored SOCE, prevents the loss of mTOR phosphorylation and decreased the expression of CHOP and LC3A in PC3 cells. Taken together, for the first time, our results revealed that RSV induces autophagy-mediated cell death in PC3 and DU145 cells through regulation of SOCE mechanisms, including downregulating STIM1 expression and trigger ER stress by depleting ER calcium pool.

Store-Operated Ca2+ Channels in Mesangial Cells Inhibit Matrix Protein Expression

Accumulation of extracellular matrix derived from glomerular mesangial cells is an early feature of diabetic nephropathy. Ca(2+) signals mediated by store-operated Ca(2+) channels regulate protein production in a variety of cell types. The aim of this study was to determine the effect of store-operated Ca(2+) channels in mesangial cells on extracellular matrix protein expression. In cultured human mesangial cells, activation of store-operated Ca(2+) channels by thapsigargin significantly decreased fibronectin protein expression and collagen IV mRNA expression in a dose-dependent manner. Conversely, inhibition of the channels by 2-aminoethyl diphenylborinate significantly increased the expression of fibronectin and collagen IV. Similarly, overexpression of stromal interacting molecule 1 reduced, but knockdown of calcium release-activated calcium channel protein 1 (Orai1) increased fibronectin protein expression. Furthermore, 2-aminoethyl diphenylborinate significantly augmented angiotensin II-induced fibronectin protein expression, whereas thapsigargin abrogated high glucose- and TGF-β1-stimulated matrix protein expression. In vivo knockdown of Orai1 in mesangial cells of mice using a targeted nanoparticle siRNA delivery system resulted in increased expression of glomerular fibronectin and collagen IV, and mice showed significant mesangial expansion compared with controls. Similarly, in vivo knockdown of stromal interacting molecule 1 in mesangial cells by recombinant adeno-associated virus-encoded shRNA markedly increased collagen IV protein expression in renal cortex and caused mesangial expansion in rats. These results suggest that store-operated Ca(2+) channels in mesangial cells negatively regulate extracellular matrix protein expression in the kidney, which may serve as an endogenous renoprotective mechanism in diabetes.

PDK4 protein promotes tumorigenesis through activation of cAMP-response element-binding protein (CREB)-Ras homolog enriched in brain (RHEB)-mTORC1 signaling cascade

Mechanistic target of rapamycin (mTOR) integrates multiple extracellular and intracellular signals to regulate cell growth and survival. Hyperactivation of mTOR has been observed in various cancers. Regulation of mTOR activity is thus of importance in physiological processes and tumor development. Here, we present pyruvate dehydrogenase kinase 4 (PDK4) as a novel regulator of mTORC1 signaling. mTORC1 activity was augmented with PDK4 overexpression and reduced by PDK4 suppression in various cell lines. Furthermore, PDK4 bound to cAMP-response element-binding protein (CREB) and prevented its degradation. The enhanced CREB consequently transactivated the expression of Ras homolog enriched in brain (RHEB), a direct key activator of mTORC1, independent of AMP-activated protein kinase or tuberous sclerosis complex protein 2. PDK4 potentiated the mTORC1 effectors hypoxia-inducible factor 1α and pyruvate kinase isozymes M2 and promoted aerobic glycolysis (Warburg effect). Knockdown of PDK4 suppressed the tumor development of cancer cells with activated mTORC1. The abundance of PDK4 dictated the responsiveness of cells to the mTOR inhibitor, rapamycin. Combinatory suppression of mTOR and PDK4 exerted synergistic inhibition on cancer cell proliferation. Therefore, PDK4 promotes tumorigenesis through activation of the CREB-RHEB-mTORC1 signaling cascade.

Orai1 and STIM1 are critical for cell migration and proliferation of clear cell renal cell carcinoma

The intracellular Ca(2+) regulation has been implicated in tumorigenesis and tumor progression. Notably, store-operated Ca(2+) entry (SOCE) is a major Ca(2+) entry mechanism in non-excitable cells, being involved in cell proliferation and migration in several types of cancer. However, the expression and biological role of SOCE have not been investigated in clear cell renal cell carcinoma (ccRCC). Here, we demonstrate that Orai1 and STIM1, not Orai3, are crucial components of SOCE in the progression of ccRCC. The expression levels of Orai1 in tumor tissues were significantly higher than those in the adjacent normal parenchymal tissues. In addition, native SOCE was blunted by inhibiting SOCE or by silencing Orai1 and STIM1. Pharmacological blockade or knockdown of Orai1 or STIM1 also significantly inhibited RCC cell migration and proliferative capability. Taken together, Orai1 is highly expressed in ccRCC tissues illuminating that Orai1-mediated SOCE may play an important role in ccRCC development. Indeed, Orai1 and STIM1 constitute a native SOCE pathway in ccRCC by promoting cell proliferation and migration.

High glucose and diabetes enhanced store-operated Ca(2+) entry and increased expression of its signaling proteins in mesangial cells

The present study was conducted to determine whether and how store-operated Ca(2+) entry (SOCE) in glomerular mesangial cells (MCs) was altered by high glucose (HG) and diabetes. Human MCs were treated with either normal glucose or HG for different time periods. Cyclopiazonic acid-induced SOCE was significantly greater in the MCs with 7-day HG treatment and the response was completely abolished by GSK-7975A, a selective inhibitor of store-operated Ca(2+) channels. Similarly, the inositol 1,4,5-trisphosphate-induced store-operated Ca(2+) currents were significantly enhanced in the MCs treated with HG for 7 days, and the enhanced response was abolished by both GSK-7975A and La(3+). In contrast, receptor-operated Ca(2+) entry in MCs was significantly reduced by HG treatment. Western blotting showed that HG increased the expression levels of STIM1 and Orai1 in cultured MCs. A significant HG effect occurred at a concentration as low as 10 mM, but required a minimum of 7 days. The HG effect in cultured MCs was recapitulated in renal glomeruli/cortex of both type I and II diabetic rats. Furthermore, quantitative real-time RT-PCR revealed that a 6-day HG treatment significantly increased the mRNA expression level of STIM1. However, the expressions of STIM2 and Orai1 transcripts were not affected by HG. Taken together, these results suggest that HG/diabetes enhanced SOCE in MCs by increasing STIM1/Orai1 protein expressions. HG upregulates STIM1 by promoting its transcription but increases Orai1 protein through a posttranscriptional mechanism.

MTOR inhibition attenuates DNA damage and apoptosis through autophagy-mediated suppression of CREB1

Hyperactivation of mechanistic target of rapamycin (MTOR) is a common feature of human cancers, and MTOR inhibitors, such as rapamycin, are thus becoming therapeutics in targeting certain cancers. However, rapamycin has also been found to compromise the efficacy of chemotherapeutics to cells with hyperactive MTOR. Here, we show that loss of TSC2 or PTEN enhanced etoposide-induced DNA damage and apoptosis, which was blunted by suppression of MTOR with either rapamycin or RNA interference. cAMP response element-binding protein 1 (CREB1), a nuclear transcription factor that regulates genes involved in survival and death, was positively regulated by MTOR in mouse embryonic fibroblasts (MEFs) and cancer cell lines. Silencing Creb1 expression with siRNA protected MTOR-hyperactive cells from DNA damage-induced apoptosis. Furthermore, loss of TSC2 or PTEN impaired either etoposide or nutrient starvation-induced autophagy, which in turn, leads to CREB1 hyperactivation. We further elucidated an inverse correlation between autophagy activity and CREB1 activity in the kidney tumor tissue obtained from a TSC patient and the mouse livers with hepatocyte-specific knockout of PTEN. CREB1 induced DNA damage and subsequent apoptosis in response to etoposide in autophagy-defective cells. Reactivation of CREB1 or inhibition of autophagy not only improved the efficacy of rapamycin but also alleviated MTOR inhibition-mediated chemoresistance. Therefore, autophagy suppression of CREB1 may underlie the MTOR inhibition-mediated chemoresistance. We suggest that inhibition of MTOR in combination with CREB1 activation may be used in the treatment of cancer caused by an abnormal PI3K-PTEN-AKT-TSC1/2-MTOR signaling pathway. CREB1 activators should potentiate the efficacy of chemotherapeutics in treatment of these cancers.