Glutaredoxin 1 controls monocyte reprogramming during nutrient stress and protects mice against obesity and atherosclerosis in a sex-specific manner.

High-calorie diet-induced nutrient stress promotes thiol oxidative stress and the reprogramming of blood monocytes, giving rise to dysregulated, obesogenic, proatherogenic monocyte-derived macrophages. We report that in chow-fed, reproductively senescent female mice but not in age-matched male mice, deficiency in the thiol transferase glutaredoxin 1 (Grx1) promotes dysregulated macrophage phenotypes as well as rapid weight gain and atherogenesis. Grx1 deficiency derepresses distinct expression patterns of reactive oxygen species and reactive nitrogen species generators in male versus female macrophages, poising female but not male macrophages for increased peroxynitrate production. Hematopoietic Grx1 deficiency recapitulates this sexual dimorphism in high-calorie diet-fed LDLR-/- mice, whereas macrophage-restricted overexpression of Grx1 eliminates the sex differences unmasked by high-calorie diet-feeding and protects both males and females against atherogenesis. We conclude that loss of monocytic Grx1 activity disrupts the immunometabolic balance in mice and derepresses sexually dimorphic oxidative stress responses in macrophages. This mechanism may contribute to the sex differences reported in cardiovascular disease and obesity in humans.

Ursolic Acid and Related Analogues: Triterpenoids with Broad Health Benefits.

Ursolic acid (UA) is a well-studied natural pentacyclic triterpenoid found in herbs, fruit and a number of traditional Chinese medicinal plants. UA has a broad range of biological activities and numerous potential health benefits. In this review, we summarize the current data on the bioavailability and pharmacokinetics of UA and review the literature on the biological activities of UA and its closest analogues in the context of inflammation, metabolic diseases, including liver and kidney diseases, obesity and diabetes, cardiovascular diseases, cancer, and neurological disorders. We end with a brief overview of UA's main analogues with a special focus on a newly discovered naturally occurring analogue with intriguing biological properties and potential health benefits, 23-hydroxy ursolic acid.

Dyslipidemic Diet-Induced Monocyte "Priming" and Dysfunction in Non-Human Primates Is Triggered by Elevated Plasma Cholesterol and Accompanied by Altered Histone Acetylation.

Monocytes and the recruitment of monocyte-derived macrophages into sites of inflammation play a key role in atherogenesis and other chronic inflammatory diseases linked to cardiometabolic syndrome and obesity. Previous studies from our group have shown that metabolic stress promotes monocyte priming, i.e., enhanced adhesion and accelerated chemotaxis of monocytes in response to chemokines, both in vitro and in dyslipidemic LDLR-/- mice. We also showed that metabolic stress-induced monocyte dysfunction is, at least to a large extent caused by the S-glutathionylation, inactivation, and subsequent degradation of mitogen-activated protein kinase phosphatase 1. Here, we analyzed the effects of a Western-style, dyslipidemic diet (DD), which was composed of high levels of saturated fat, cholesterol, and simple sugars, on monocyte (dys)function in non-human primates (NHPs). We found that similar to mice, a DD enhances monocyte chemotaxis in NHP within 4 weeks, occurring concordantly with the onset of hypercholesterolemia but prior to changes in triglycerides, blood glucose, monocytosis, or changes in monocyte subset composition. In addition, we identified transitory decreases in the acetylation of histone H3 at the lysine residues 18 and 23 in metabolically primed monocytes, and we found that monocyte priming was correlated with the acetylation of histone H3 at lysine 27 after an 8-week DD regimen. Our data show that metabolic stress promotes monocyte priming and hyper-chemotactic responses in NHP. The histone modifications accompanying monocyte priming in primates suggest a reprogramming of the epigenetic landscape, which may lead to dysregulated responses and functionalities in macrophages derived from primed monocytes that are recruited to sites of inflammation.

Characterization of Macrophage Polarization States Using Combined Measurement of 2-Deoxyglucose and Glutamine Accumulation: Implications for Imaging of Atherosclerosis.

OBJECTIVE: Despite the early promising results of 18F-fluorodeoxyglucose positron emission tomography for assessment of vessel wall inflammation, its accuracy in prospective identification of vulnerable plaques has remained limited. Additionally, previous studies have indicated that 18F-fluorodeoxyglucose uptake alone may not allow for accurate identification of specific macrophage activation states. We aimed to determine whether combined measurement of glucose and glutamine accumulation-the 2 most important bioenergetic substrates for macrophages-improves the distinction of macrophage inflammatory states and can be utilized to image atherosclerosis. APPROACH AND RESULTS: Murine peritoneal macrophages (MΦ) were activated ex vivo into proinflammatory states with either lipopolysaccharide (MΦLPS) or interferon-γ+tumor necrosis factor-α (MΦIFN-γ+TNF-α). An alternative polarization phenotype was induced with interleukin-4 (MΦIL-4). The pronounced increase in 2-deoxyglucose uptake distinguishes MΦLPS from MΦIFN-γ+TNF-α, MΦIL-4, and unstimulated macrophages (MΦ0). Despite having comparable levels of 2-deoxyglucose accumulation, MΦIL-4 can be distinguished from both MΦIFN-γ+TNF-α and MΦ0 based on the enhanced glutamine accumulation, which was associated with increased expression of a glutamine transporter, Slc1a5. Ex vivo autoradiography experiments demonstrated distinct and heterogenous patterns of 18F-fluorodeoxyglucose and 14C-glutamine accumulation in atherosclerotic lesions of low-density lipoprotein receptor-null mice fed a high-fat diet. CONCLUSIONS: Combined assessment of glutamine and 2-deoxyglucose accumulation improves the ex vivo identification of macrophage activation states. Combined ex vivo metabolic imaging demonstrates heterogenous and distinct patterns of substrate accumulation in atherosclerotic lesions. Further studies are required to define the in vivo significance of glutamine uptake in atherosclerosis and its potential application in identification of vulnerable plaques.

Differential Regulation of Macrophage Glucose Metabolism by Macrophage Colony-stimulating Factor and Granulocyte-Macrophage Colony-stimulating Factor: Implications for 18F FDG PET Imaging of Vessel Wall Inflammation.

Purpose To determine the divergence of immunometabolic phenotypes of macrophages stimulated with macrophage colony-stimulating factor (M-CSF) and granulocyte-M-CSF (GM-CSF) and its implications for fluorine 18 (18F) fluorodeoxyglucose (FDG) imaging of atherosclerosis. Materials and Methods This study was approved by the animal care committee. Uptake of 2-deoxyglucose and various indexes of oxidative and glycolytic metabolism were evaluated in nonactivated murine peritoneal macrophages (MΦ0) and macrophages stimulated with M-CSF (MΦM-CSF) or GM-CSF (MΦGM-CSF). Intracellular glucose flux was measured by using stable isotope tracing of glycolytic and tricyclic acid intermediary metabolites. 18F-FDG uptake was evaluated in murine atherosclerotic aortas after stimulation with M-CSF or GM-CSF by using quantitative autoradiography. Results Despite inducing distinct activation states, GM-CSF and M-CSF stimulated progressive but similar levels of increased 2-deoxyglucose uptake in macrophages that reached up to sixfold compared with MΦ0. The expression of glucose transporters, oxidative metabolism, and mitochondrial biogenesis were induced to similar levels in MΦM-CSF and MΦGM-CSF. Unexpectedly, there was a 1.7-fold increase in extracellular acidification rate, a 1.4-fold increase in lactate production, and overexpression of several critical glycolytic enzymes in MΦM-CSF compared with MΦGM-CSF with associated increased glucose flux through glycolytic pathway. Quantitative autoradiography demonstrated a 1.6-fold induction of 18F-FDG uptake in murine atherosclerotic plaques by both M-CSF and GM-CSF. Conclusion The proinflammatory and inflammation-resolving activation states of macrophages induced by GM-CSF and M-CSF in either cell culture or atherosclerotic plaques may not be distinguishable by the assessment of glucose uptake. © RSNA, 2016 Online supplemental material is available for this article.

Protein Thiol Redox Signaling in Monocytes and Macrophages.

SIGNIFICANCE: Monocyte and macrophage dysfunction plays a critical role in a wide range of inflammatory disease processes, including obesity, impaired wound healing diabetic complications, and atherosclerosis. Emerging evidence suggests that the earliest events in monocyte or macrophage dysregulation include elevated reactive oxygen species production, thiol modifications, and disruption of redox-sensitive signaling pathways. This review focuses on the current state of research in thiol redox signaling in monocytes and macrophages, including (i) the molecular mechanisms by which reversible protein-S-glutathionylation occurs, (ii) the identification of bona fide S-glutathionylated proteins that occur under physiological conditions, and (iii) how disruptions of thiol redox signaling affect monocyte and macrophage functions and contribute to atherosclerosis. Recent Advances: Recent advances in redox biochemistry and biology as well as redox proteomic techniques have led to the identification of many new thiol redox-regulated proteins and pathways. In addition, major advances have been made in expanding the list of S-glutathionylated proteins and assessing the role that protein-S-glutathionylation and S-glutathionylation-regulating enzymes play in monocyte and macrophage functions, including monocyte transmigration, macrophage polarization, foam cell formation, and macrophage cell death. CRITICAL ISSUES: Protein-S-glutathionylation/deglutathionylation in monocytes and macrophages has emerged as a new and important signaling paradigm, which provides a molecular basis for the well-established relationship between metabolic disorders, oxidative stress, and cardiovascular diseases. FUTURE DIRECTIONS: The identification of specific S-glutathionylated proteins as well as the mechanisms that control this post-translational protein modification in monocytes and macrophages will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis and other metabolic diseases. Antioxid. Redox Signal. 25, 816-835.

Protein S-Glutathionylation Mediates Macrophage Responses to Metabolic Cues from the Extracellular Environment.

AIMS: Protein S-glutathionylation, the formation of a mixed disulfide between glutathione and protein thiols, is an oxidative modification that has emerged as a new signaling paradigm, potentially linking oxidative stress to chronic inflammation associated with heart disease, diabetes, cancer, lung disease, and aging. Using a novel, highly sensitive, and selective proteomic approach to identify S-glutathionylated proteins, we tested the hypothesis that monocytes and macrophages sense changes in their microenvironment and respond to metabolic stress by altering their protein thiol S-glutathionylation status. RESULTS: We identified over 130 S-glutathionylated proteins, which were associated with a variety of cellular functions, including metabolism, transcription and translation, protein folding, free radical scavenging, cell motility, and cell death. Over 90% of S-glutathionylated proteins identified in metabolically stressed THP-1 monocytes were also found in hydrogen peroxide (H2O2)-treated cells, suggesting that H2O2 mediates metabolic stress-induced protein S-glutathionylation in monocytes and macrophages. We validated our findings in mouse peritoneal macrophages isolated from both healthy and dyslipidemic atherosclerotic mice and found that 52% of the S-glutathionylated proteins found in THP-1 monocytes were also identified in vivo. Changes in macrophage protein S-glutathionylation induced by dyslipidemia were sexually dimorphic. INNOVATION: We provide a novel mechanistic link between metabolic (and thiol oxidative) stress, macrophage dysfunction, and chronic inflammatory diseases associated with metabolic disorders. CONCLUSION: Our data support the concept that changes in the extracellular metabolic microenvironment induce S-glutathionylation of proteins central to macrophage metabolism and a wide array of cellular signaling pathways and functions, which in turn initiate and promote functional and phenotypic changes in macrophages. Antioxid. Redox Signal. 25, 836-851.

Anti-cancer Parasporin Toxins are Associated with Different Environments: Discovery of Two Novel Parasporin 5-like Genes.

Cry toxins are primarily a family of insecticidal toxins produced by the bacterium Bacillus thuringiensis (Bt). However, some Cry toxins, called parasporins (PSs), are non-insecticidal and have been shown to differentially kill human cancer cells. Based on amino acid homology, there are currently six different classes of parasporins (PS1-6). It is not known what role parasporins play in nature, nor if certain PSs are associated with Bt found in particular environments. Herein, we present ten parasporin-containing isolates of Bt from the Caribbean island of Trinidad. Genes coding for PS1 and PS6 were found in isolates associated mainly with artificial aquatic environments (e.g., barrels with rain water), while Bt possessing two novel PS5-like genes (ps5-1 and ps5-2), were isolated from manure collected directly from the rectum of cattle. The amino acid sequences inferred from the two PS5-like genes were 51 % homologous to each other, while being only 41 or 45 % similar to PS5Aa1/Cry64Aa, the only reported member of the parasporin five class. The low level of amino acid homology between the two PS5-like genes and PS5Aa1 indicate that the two PS5-like genes may represent a new class of parasporins, or greatly expand the level of diversity within the current parasporin 5 class.

Design, synthesis and biological evaluation of novel pyrenyl derivatives as anticancer agents.

Polycyclic aromatic hydrocarbons are widespread in nature with a toxicity range from non-toxic to extremely toxic. A series of pyrenyl derivatives has been synthesized following a four-step strategy where the pyrene nucleus is attached with a basic heterocyclic moiety through a carbon linker. Virtual screening of the physicochemical properties and druggability has been carried out. The cytotoxicity of the compounds (1-8) have been evaluated in vitro against a small panel of human cancer cell lines which includes two liver cancer (HepG2 and Hepa 1-6), two colon cancer (HT-29 and Caco-2) and one each for cervical (HeLa) and breast (MCF-7) cancer cell lines. The IC50 data indicate that compound 6 and 8 are the most effective cytotoxic agents in the present set of pyrenyl derivatives, suggesting that having a 4-carbon linker is more effective than a 5-carbon linker and the presence of amide carbonyl groups in the linker severely reduces the efficacy of the compound. The compounds showed selectivity toward cancer cells at lower doses (<5 µM) when compared with the normal hepatocytes. The mechanism of action supports the cell death through apoptosis in a caspase-independent manner without cleavage of poly (ADP-ribose) polymerase (PARP), even though the compounds cause plasma membrane morphological changes. The compounds, whether highly cytotoxic or mildly cytotoxic, localize to the membrane of cells. The compounds with either a piperidine ring (6) or an N-methyl piperazine (8) in the side chain were both capable of circumventing the drug resistance in SKOV3-MDR1-M6/6 ovarian cancer cells overexpressing P-glycoprotein. Qualitative structure-activity relationship has also been studied.

Nedd8 regulates inflammasome-dependent caspase-1 activation.

Caspase-1 is activated by the inflammasome complex to process cytokines like interleukin-1ß (IL-1ß). Pro-caspase-1 consists of three domains, CARD, p20, and p10. Association of pro-caspase-1 with the inflammasome results in initiation of its autocatalytic activity, culminating in self-cleavage that generates catalytically active subunits (p10 and p20). In the current study, we show that Nedd8 is required for efficient self-cleavage of pro-caspase-1 to generate its catalytically active subunits. Nedd8 silencing or treating cells with the neddylation inhibitor MLN4924 led to diminished caspase-1 processing and reduced IL-1ß maturation following inflammasome activation. Coimmunoprecipitation and mass spectrometric analysis of 293 cells overexpressing pro-caspase-1 (and CARD) and Nedd8 suggested possible neddylation of caspase-1 CARD. Following inflammasome activation in primary macrophages, we observed colocalization of endogenous Nedd8 with caspase-1. Similarly, interaction of endogenous Nedd8 with caspase-1 CARD was detected in inflammasome-activated macrophages. Furthermore, enhanced autocatalytic activity of pro-caspase-1 was observed following Nedd8 overexpression in 293 cells, and such activity in inflammasome-activated macrophages was drastically diminished upon treatment of cells with MLN4924. Thus, our studies demonstrate a role of Nedd8 in regulating caspase-1 activation following inflammasome activation, presumably via augmenting autoprocessing/cleavage of pro-caspase-1 into its corresponding catalytically active subunits.

Bismuth nitrate-induced novel nitration of estradiol: an entry to new anticancer agents.

Direct nitration of estradiol was carried out using metal nitrates on solid surfaces under mild condition, and a combination of bismuth nitrate pentahydrate impregnated KSF clay was found to be the best reagent to synthesize 2- and 4-nitroestradiol effectively. Furthermore, various basic side chains were introduced, through O-linker at C-3, to these nitroestradiols. The ability of these derivatives to cause cytotoxicity in Estrogen Receptor (ER)-positive and ER-negative breast cancer cell lines, as well as cancer cell lines of other origins, was examined. Qualitative structure activity relationship (SAR) has also been studied. We found that a basic side chain containing either a piperidine or morpholine ring, when conjugated to 2-nitroestradiol, was particularly effective at causing cytotoxicity in each of the cancer cell lines examined. Surprisingly, this effective cytotoxicity was even seen in ER-negative breast cancer cells.

A novel Bacillus thuringiensis Cry-like protein from a rare filamentous strain promotes crystal localization within the exosporium.

Mutation of a novel cry-like gene (cry256) from Bacillus thuringiensis resulted in a protein crystal, normally located within the spore's exosporium, being found predominately outside the exosporium. The cry256 gene codes for a 3-domain Cry-like protein that does not correspond to any of the known Cry protein holotypes.

Inhibition of neddylation represses lipopolysaccharide-induced proinflammatory cytokine production in macrophage cells.

Cullin-RING E3 ligases (CRLs) are a class of ubiquitin ligases that control the proteasomal degradation of numerous target proteins, including IκB, and the activity of these CRLs are positively regulated by conjugation of a Nedd8 polypeptide onto Cullin proteins in a process called neddylation. CRL-mediated degradation of IκB, which normally interacts with and retains NF-κB in the cytoplasm, permits nuclear translocation and transactivation of the NF-κB transcription factor. Neddylation occurs through a multistep enzymatic process involving Nedd8 activating enzymes, and recent studies have shown that the pharmacological agent, MLN4924, can potently inhibit Nedd8 activating enzymes, thereby preventing neddylation of Cullin proteins and preventing the degradation of CRL target proteins. In macrophages, regulation of NF-κB signaling functions as a primary pathway by which infectious agents such as lipopolysaccharides (LPSs) cause the up-regulation of proinflammatory cytokines. Here we have analyzed the effects of MLN4924, and compared the effects of MLN4924 with a known anti-inflammatory agent (dexamethasone), on certain proinflammatory cytokines (TNF-α and IL-6) and the NF-κB signaling pathway in LPS-stimulated macrophages. We also used siRNA to block neddylation to assess the role of this molecular process during LPS-induced cytokine responsiveness. Our results demonstrate that blocking neddylation, either pharmacologically or using siRNA, abrogates the increase in certain proinflammatory cytokines secreted from macrophages in response to LPS. In addition, we have shown that MLN4924 and dexamethasone inhibit LPS-induced cytokine up-regulation at the transcriptional level, albeit through different molecular mechanisms. Thus, neddylation represents a novel molecular process in macrophages that can be targeted to prevent and/or treat the LPS-induced up-regulation of proinflammatory cytokines and the disease processes associated with their up-regulation.

Polycyclic aromatic compounds as anticancer agents: Evaluation of synthesis and in vitro cytotoxicity.

Polycyclic aromatic hydrocarbons (PAHs) are considered to be significant environmental carcinogens. Additionally, various planar ring systems are capable of intercalating with DNA, leading to a number of drugs that possess chemotherapeutic activity. In this study, three new polyaromatic compounds with a side chain were synthesized, and spectroscopic as well as elemental analyses were performed. The addition of the long chains to either chrysene or pyrene caused a red-shift in the spectral emission when compared to the corresponding polycyclic aromatic hydrocarbons itself. Furthermore, the cytotoxicity of the three novel polyaromatic compounds was evaluated in vitro in a panel of cultured mammalian cell lines. The pyrenyl ether demonstrated better cytotoxicity compared to cisplatin against colon (HT-29) as well as cervical (HeLa) cancer cell lines. In conclusion, three new compounds were synthesized and investigated in this study. This novel method is likely to play a role in other areas of research.

Ultrasound-assisted bismuth nitrate-induced green synthesis of novel pyrrole derivatives and their biological evaluation as anticancer agents.

A series of novel N-substituted pyrrole derivatives have been designed and synthesized following ultrasound-assisted and bismuth nitrate-catalyzed eco-friendly route. This reaction has also provided a general method to prepare diverse varieties of N-substituted pyrroles with less nucleophilic polyaromatic amines. Based on (1)H NMR spectroscopy, a plausible mechanistic pathway has been advanced. Cytotoxicity of some selected N-substituted pyrrole derivatives has been evaluated in vitro in a panel of mammalian cancer cell lines which includes liver cancer cell lines (HepG2 and Hepa1-6), colon cancer cell lines (HT-29 and Caco-2), a cervical cancer cell line (HeLa) and NIH3T3 cells. Two compounds, 5-(1H-pyrrol-1-yl)-1,10-phenanthroline (9) and 1-(phenanthren-2-yl)-1H-pyrrole (10) have shown good cytotoxicity against some cancer cell lines. Furthermore, these compounds have exhibited cytotoxic specificity against liver cancer cell lines in vitro when compared with normal cultured primary hepatocytes.

Parasporins from a Caribbean Island: evidence for a globally dispersed Bacillus thuringiensis strain.

Parasporins represent a new functional class of Cry (crystal protein) toxins produced by the bacterium Bacillus thuringiensis (Bt). Unlike Cry toxins that demonstrate activity mainly against some insect cells, parasporins are characterized as being non-hemolytic, yet capable of preferentially killing some human cancer cells. Globally, six different parasporin types, PS1-PS6, based on protein sequence homology, have been identified in only four countries (Japan, Vietnam, India, and Canada). Herein we report the results of a screening study of 160 Bt isolates collected from the Caribbean island of Trinidad. One isolate (strain 64-1-94) was shown to kill human cancer cells and to contain one ps6 and two ps1 parasporin genes. The two ps1 genes were located approximately 6 kb apart from each other, sharing a similar spatial arrangement, and high sequence homology, with two plasmid-located ps1 genes, ps1Aa6 and ps1Ad1, recently isolated from a Japanese strain. Evidence is also presented that a parasporin gene reported previously for a Canadian strain, ps1Aa2, is most likely derived from a recombination event between these same two genes found in the Trinidadian and Japanese strains. Notably, all three strains share a ps6 parasporin gene, presumably located on a separate plasmid. These data suggest that the global population of ps1 genes may be have originated from a single pair of parasporin genes. Given the large geographical distance between the collection sites, which are located on both continental land masses and islands at sea, ps1 genes are able to retain a remarkable level of homology not easily explained.

AMPK-mediated phosphorylation of murine p27 at T197 promotes binding of 14-3-3 proteins and increases p27 stability.

The tuberous sclerosis complex 2 (Tsc2) gene product, tuberin, acts as a negative regulator of mTOR signaling, and loss of tuberin function leads to tumors of the brain, skin, kidney, heart, and lungs. Previous studies have shown that loss of tuberin function affects the stability and subcellular localization of the cyclin-dependent kinase inhibitor (CKI) p27, although the mechanism(s) by which tuberin modulates p27 stability has/have not been elucidated. Previous studies have also shown that AMP-activated protein kinase (AMPK), which functions in an energy-sensing pathway in the cell, becomes activated in the absence of tuberin. Here we show that in Tsc2-null tumors and cell lines, AMPK activation correlates with an increase in p27 levels, and inhibition of AMPK signaling decreases p27 levels in these cells. In addition, activation of AMPK led to phosphorylation of p27 at the conserved terminal threonine residue of murine p27 (T197) in both in vitro kinase assays and in cells. Phosphorylation of p27 at T197 led to increased interaction between p27 and 14-3-3 proteins and increased the protein stability of p27. Furthermore, activation of AMPK signaling promoted the interaction between p27 and 14-3-3 proteins and increased the stability of the p27 protein in a manner that was dependent on T197. These data identify a conserved mechanism for the regulation of p27 stability via phosphorylation at the terminal threonine (mT197/hT198) and binding of 14-3-3 proteins, which when AMPK is activated results in stabilization of the p27 protein.

Cytoplasmic sequestration of p27 via AKT phosphorylation in renal cell carcinoma.

PURPOSE: p27 localization and expression has prognostic and predictive value in cancer. Little is known regarding expression patterns of p27 in renal cell carcinoma (RCC) or how p27 participates in disease progression or response to therapy. EXPERIMENTAL DESIGN: RCC-derived cell lines, primary tumors, and normal renal epithelial cells were analyzed for p27 expression, phosphorylation (T157 of the NLS), and subcellular localization. RCC-derived cell lines were treated with phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors and effects on p27 localization were assessed. The potential contribution of cytoplasmic p27 to resistance to apoptosis was also evaluated. RESULTS: p27 was elevated in tumors compared with matched controls, and cytoplasmic mislocalization of p27 was associated with increasing tumor grade. Cytoplasmic localization of p27 correlated with phosphorylation at T157, an AKT phosphorylation site in the p27 NLS. In RCC cell lines, activated PI3K/AKT signaling was accompanied by mislocalization of p27. AKT activation and phosphorylation of p27 was associated with resistance to apoptosis, and small interfering RNA knockdown of p27 or relocalization to the nucleus increased apoptosis in RCC cells. Treatment with the PI3K inhibitors LY294002 or wortmannin resulted in nuclear relocalization of p27, whereas mTOR inhibition by rapamycin did not. CONCLUSIONS: In RCC, p27 is phosphorylated at T157 of the NLS, with increasing tumor grade associated with cytoplasmic p27. PI3K inhibition (which reduces AKT activity) reduces T157 phosphorylation and induces nuclear relocalization of p27, whereas mTOR inhibition does not. Clinical testing of these findings may provide a rational approach for use of mTOR and PI3K/AKT pathway inhibitors in patients with RCC.

AMP-activated protein kinase signaling results in cytoplasmic sequestration of p27.

Tuberin, the Tsc2 gene product, integrates the phosphatidylinositol 3-kinase/mitogen-activated protein kinase (mitogenic) and LKB1/AMP-activated protein kinase (AMPK; energy) signaling pathways, and previous independent studies have shown that loss of tuberin is associated with elevated AMPK signaling and altered p27 function. In Tsc2-null tumors and tumor-derived cells from Eker rats, we observed elevated AMPK signaling and concordant cytoplasmic mislocalization of p27. Cytoplasmic localization of p27 in Tsc2-null cells was reversible pharmacologically using inhibitors of the LKB1/AMPK pathway, and localization of p27 to the cytoplasm could be induced directly by activating AMPK physiologically (glucose deprivation) or genetically (constitutively active AMPK) in Tsc2-proficient cells. Furthermore, AMPK phosphorylated p27 in vitro on at least three sites including T170 near the nuclear localization signal, and T170 was shown to determine p27 localization in response to AMPK signaling. p27 functions in the nucleus to suppress cyclin-dependent kinase-2 (Cdk2) activity and has been reported to mediate an antiapoptotic function when localized to the cytoplasm. We found that cells with elevated AMPK signaling and cytoplasmic p27 localization exhibited elevated Cdk2 activity, which could be suppressed by inhibiting AMPK signaling. In addition, cells with elevated AMPK signaling and cytoplasmic p27 localization were resistant to apoptosis, which could be overcome by inhibition of AMPK signaling and relocalization of p27 to the nucleus. These data show that AMPK signaling determines the subcellular localization of p27, and identifies loss of integration of pathways controlling energy balance, the cell cycle, and apoptosis due to aberrant AMPK and p27 function as a feature of cells that have lost the Tsc2 tumor suppressor gene.

Activity of TSC2 is inhibited by AKT-mediated phosphorylation and membrane partitioning.

Loss of tuberin, the product of TSC2 gene, increases mammalian target of rapamycin (mTOR) signaling, promoting cell growth and tumor development. However, in cells expressing tuberin, it is not known how repression of mTOR signaling is relieved to activate this pathway in response to growth factors and how hamartin participates in this process. We show that hamartin colocalizes with hypophosphorylated tuberin at the membrane, where tuberin exerts its GTPase-activating protein (GAP) activity to repress Rheb signaling. In response to growth signals, tuberin is phosphorylated by AKT and translocates to the cytosol, relieving Rheb repression. Phosphorylation of tuberin at serines 939 and 981 does not alter its intrinsic GAP activity toward Rheb but partitions tuberin to the cytosol, where it is bound by 14-3-3 proteins. Thus, tuberin bound by 14-3-3 in response to AKT phosphorylation is sequestered away from its membrane-bound activation partner (hamartin) and its target GTPase (Rheb) to relieve the growth inhibitory effects of this tumor suppressor.