The LKB1/AMPK polarity pathway

Bioinformatics analysis identifies potential m6A hub genes in the pathogenesis of intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) is a type of stroke associated with a high rate of disability and mortality. The role of N6-methyladenosine (m6A) in ICH remains unclear.

METHODS

Screening of m6A DEGs by differentially expressed genes (DEGs) analysis. m6A hub genes in ICH were identified by protein-protein interaction (PPI) networks. Pearson correlation tests were used to explore the relationship between m6A hub genes and DNA methylation. m6A hub genes were examined by ROC curves for their ability to predict ICH occurrence. Immune cell infiltration and m6A hub gene correlation in ICH were analysed using the CIBERSORT algorithm. Construction of ceRNA networks and enrichment analysis by GO/KEGG.

RESULTS

A total of 12 m6A regulatory enzymes were differentially expressed after ICH. the PPI network screened three m6A hub genes, including YTHDF2, FTO and HNRNPA2B1. A high expression of YTHDF2 was associated with DNA hypomethylation after ICH and could better predict the development of ICH. yTHDF2 was associated with high infiltration of M1 macrophages after ICH. A ceRNA network was constructed based on the m6A central gene with target genes enriched in transcriptional regulation and the LKB1 signalling pathway.

CONCLUSION

M6A modifications are involved in the progression of ICH. YTHDF2, an m6A key gene, may regulate ICH progression by promoting infiltration of M1 macrophages or through the ceRNA network.

Influence of chrysin on D-galactose induced-aging in mice: Up regulation of AMP kinase/liver kinase B1/peroxisome proliferator-activated receptor-γ coactivator 1-α signaling pathway

Adenosine monophosphate kinase/liver kinase B1/peroxisome proliferator-activated receptor-γ coactivator 1-α (AMPK/LKB1/PGC1α) pathway has a vital role in regulating age-related diseases. It controls neurogenesis, cell proliferation, axon outgrowth, and cellular energy homeostasis. AMPK pathway also regulates mitochondrial synthesis. The current study evaluated the effect of chrysin on D-galactose (D-gal) induced-aging, neuron degeneration, mitochondrial dysfunction, oxidative stress, and neuroinflammation in mice. The mice were allocated randomly into four groups (10 each group): Group 1: normal control group, Group 2: D-gal group, Groups 3 and 4: chrysin (125 and 250 mg/kg, respectively). Groups 2-4 were injected with D-gal (200 mg/kg/day; s.c) for 8 weeks to induce aging. Groups 3 and 4 were orally gavaged every day concurrent with D-gal. At the end of experiment, behavioral, brain biochemical and histopathological changes were monitored. Chrysin administration elevated discrimination ratio in object recognition, Y Maze percentage alternation, locomotor activity and brain contents of AMPK, LKB1, PGC1α, NAD (P)H quinone oxidoreductase 1 (NQO1), heme oxygenase 1 (HO-1), nerve growth factor (NGF) (neurotrophin-3; NT-3), and seretonin as well as reduced brain contents of tumor necrosis factor-alpha (TNF-α), nuclear factor kappa B (NF-κB), advanced glycation end products (AGEs) and glial fibrillary acidic protein (GFAP) compared to D-gal-treated mice. Chrysin also alleviated cerebral cortex and white matter neurons degeneration. Chrysin protects against neurodegeneration, improves mitochondrial autophagy and biogenesis as well as activates antioxidant genes expression. In addition, chrysin ameliorates neuroinflammation and stimulates the release of NGF and serotonin neurotransmitter. So, chrysin has a neuroprotective effect in D-gal induced-aging in mice.

AMPK targets a proto-oncogene TPD52 (isoform 3) expression and its interaction with LKB1 suppress AMPK-GSK3β signaling axis in prostate cancer

Tumor protein D52 (TPD52) is a proto-oncogene overexpressed in prostate cancer (PCa) due to gene amplification and it is involved in the cancer progression of many cancers including PCa. However, the molecular mechanisms underlying the role of TPD52 in cancer progression are still under investigation. In this study, we report that the activation of AMP-activated protein kinase (AMPK) by AICAR (5-Aminoimidazole-4-carboxamide ribonucleotide) inhibited the LNCaP and VCaP cells growth by silencing TPD52 expression. Activation of AMPK inhibited the proliferation and migration of LNCaP and VCaP cells. Interestingly, AICAR treatment to LNCaP and VCaP cells led to the downregulation of TPD52 via activation of GSK3β by a decrease of inactive phosphorylation at Ser9. Moreover, in AICAR treated LNCaP cells, inhibition of GSK3β by LiCl attenuated downregulation of TPD52 indicating that AICAR acts via GSK3β. Furthermore, we found that TPD52 interacts with serine/threonine kinase 11 or Liver kinase B1 (LKB1) a known tumor suppressor and an upstream kinase for AMPK. The molecular modeling and MD simulations indicates that the interaction between TPD52 and LKB1 leads to inhibition of the kinase activity of LKB1 as its auto-phosphorylation sites were masked in the complex. Consequently, TPD52-LKB1 interaction may lead to inactivation of AMPK. Moreover, overexpression of TPD52 is found to be responsible for the reduction of pLKB1 (Ser428) and pAMPK (Thr172). Therefore, TPD52 may be playing its oncogenic role via suppressing the AMPK activation. Altogether, our results revealed a new mechanism of PCa progression in which TPD52 overexpression inhibits AMPK activation by interacting with LKB1. These results support that the use of AMPK activators and/or small molecules that could disrupt the TPD52-LKB1 interaction might be useful to suppress PCa cell growth. TPD52 interacts LKB1 and interfere with activation of AMPK in PCa cells.

Identification of a novel mitochondria-localized LKB1 variant required for the regulation of the oxidative stress response

The tumor suppressor Liver Kinase B1 (LKB1) is a multifunctional serine/threonine protein kinase that regulates cell metabolism, polarity, and growth and is associated with Peutz-Jeghers Syndrome and cancer predisposition. The LKB1 gene comprises 10 exons and 9 introns. Three spliced LKB1 variants have been documented, and they reside mainly in the cytoplasm, although two possess a nuclear-localization sequence (NLS) and are able to shuttle into the nucleus. Here, we report the identification of a fourth and novel LKB1 isoform that is, interestingly, targeted to the mitochondria. We show that this mitochondria-localized LKB1 (mLKB1) is generated from alternative splicing in the 5' region of the transcript and translated from an alternative initiation codon encoded by a previously unknown exon 1b (131 bp) hidden within the long intron 1 of LKB1 gene. We found by replacing the N-terminal NLS of the canonical LKB1 isoform, the N-terminus of the alternatively spliced mLKB1 variant encodes a mitochondrial transit peptide that allows it to localize to the mitochondria. We further demonstrate that mLKB1 colocalizes histologically with mitochondria-resident ATP Synthase and NAD-dependent deacetylase sirtuin-3, mitochondrial (SIRT3) and that its expression is rapidly and transiently upregulated by oxidative stress. We conclude that this novel LKB1 isoform, mLKB1, plays a critical role in regulating mitochondrial metabolic activity and oxidative stress response.

Liver Kinase B1 Functions as a Regulator for Neural Development and a Therapeutic Target for Neural Repair

The liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11) and Par-4 in C. elegans, has been identified as a master kinase of AMPKs and AMPK-related kinases. LKB1 plays a crucial role in cell growth, metabolism, polarity, and tumor suppression. By interacting with the downstream signals of SAD, NUAK, MARK, and other kinases, LKB1 is critical to regulating neuronal polarization and axon branching during development. It also regulates Schwann cell function and the myelination of peripheral axons. Regulating LKB1 activity has become an attractive strategy for repairing an injured nervous system. LKB1 upregulation enhances the regenerative capacity of adult CNS neurons and the recovery of locomotor function in adult rodents with CNS axon injury. Here, we update the major cellular and molecular mechanisms of LKB1 in regulating neuronal polarization and neural development, and the implications thereof for promoting neural repair, axon regeneration, and functional recovery in adult mammals.

Amycenone reduces excess body weight and attenuates hyperlipidaemia by inhibiting lipogenesis and promoting lipolysis and fatty acid β-oxidation in KK-Ay obese diabetic mice

Excess body weight and hyperlipidaemia cause severe health problems and have social implications. Amycenone is an active substance extracted from Yamabushitake mushrooms with no reports of its activity against excess body weight and hyperlipidaemia. This research clarifies the effects and mechanisms of action of amycenone on the inhibition of body weight excess and hyperlipidaemia attenuation using KK-A^y mice. Amycenone or water was administered to 8-week-old male KK-A^y mice by gavage for 8 weeks. Their body weight and food intake were recorded during the experiment. At the end of the experimental period, the mice were dissected, and blood samples, lipid metabolism-related organs and tissues were collected and stored for further analysis. Amycenone treatment suppressed body weight gain and improved serum levels of fasting blood glucose and non-esterified fatty acids. Additionally, serum and hepatic cholesterol and triacylglycerol levels were reduced after this treatment, whereas the phosphorylation levels of AMPK, PKA and HSL increased and the expression level of FAS decreased. The protein level of C/EBPβ and gene expression level of Cpt1 were higher in the perirenal adipose tissue of amycenone-treated KK-A^y mice. Furthermore, amycenone phosphorylated AMPK, PKA and ACC, and PPARγ expression was lower in the mesenteric adipose tissue. The phosphorylation levels of AMPK, LKB1, PKA and ACC were also induced, and FAS expression level was reduced in the liver of the amycenone-treated group. Amycenone could reduce excess body weight and attenuate hyperlipidaemia in KK-A^y mice by inhibiting lipogenesis and promoting lipolysis through lipid metabolism pathway stimulation and fatty acid β-oxidation acceleration.

Protein Kinase CK2 Is Upregulated by Calorie Restriction and Induces Autophagy

Calorie restriction (CR) and the activation of autophagy extend healthspan by delaying the onset of age-associated diseases in most living organisms. Because protein kinase CK2 (CK2) downregulation induces cellular senescence and nematode aging, we investigated CK2's role in CR and autophagy. This study indicated that CR upregulated CK2's expression, thereby causing SIRT1 and AMP-activated protein kinase (AMPK) activation. CK2α overexpression, including antisense inhibitors of miR-186, miR-216b, miR-337-3p, and miR-760, stimulated autophagy initiation and nucleation markers (increase in ATG5, ATG7, LC3BII, beclin-1, and Ulk1, and decrease in SQSTM1/p62). The SIRT1 deacetylase, AKT, mammalian target of rapamycin (mTOR), AMPK, and forkhead homeobox type O (FoxO) 3a were involved in CK2-mediated autophagy. The treatment with the AKT inhibitor triciribine, the AMPK activator AICAR, or the SIRT1 activator resveratrol rescued a reduction in the expression of lgg-1 (the Caenorhabditis elegans ortholog of LC3B), bec-1 (the C. elegans ortholog of beclin-1), and unc-51 (the C. elegans ortholog of Ulk1), mediated by kin-10 (the C. elegans ortholog of CK2β) knockdown in nematodes. Thus, this study indicated that CK2 acted as a positive regulator in CR and autophagy, thereby suggesting that these four miRs' antisense inhibitors can be used as CR mimetics or autophagy inducers.

Natural AMPK Activators in Cardiovascular Disease Prevention

Cardiovascular diseases (CVD), as a life-threatening global disease, is receiving worldwide attention. Seeking novel therapeutic strategies and agents is of utmost importance to curb CVD. AMP-activated protein kinase (AMPK) activators derived from natural products are promising agents for cardiovascular drug development owning to regulatory effects on physiological processes and diverse cardiometabolic disorders. In the past decade, different therapeutic agents from natural products and herbal medicines have been explored as good templates of AMPK activators. Hereby, we overviewed the role of AMPK signaling in the cardiovascular system, as well as evidence implicating AMPK activators as potential therapeutic tools. In the present review, efforts have been made to compile and update relevant information from both preclinical and clinical studies, which investigated the role of natural products as AMPK activators in cardiovascular therapeutics.

Glucose and Serum Deprivation Led to Altered Proliferation, Differentiation Potential and AMPK Activation in Stem Cells from Human Deciduous Tooth

Stem cell therapy is an evolving treatment strategy in regenerative medicine. Recent studies report stem cells from human exfoliated deciduous teeth could complement the traditional mesenchymal stem cell sources. Stem cells from human exfoliated deciduous teeth exhibit mesenchymal characteristics with multilineage differentiation potential. Mesenchymal stem cells are widely investigated for cell therapy and disease modeling. Although many research are being conducted to address the challenges of mesenchymal stem cell therapy in clinics, most of the studies are still in infancy. Host cell microenvironment is one of the major factors affecting the homing of transplanted stem cell and understanding the factors affecting the fate of stem cells of prime important. In this study we aimed to understand the effects of serum deprivation in stem cells derived from human deciduous tooth. Our study aimed to understand the morphological, transcriptional, cell cycle and stemness based changes of stem cells in nutrient deprived medium. Our results suggest that stem cells in nutrient deprived media undergo low proliferation, high apoptosis and changed the differentiation potential of the stem cells. Serum deprived mesenchymal stem cells exhibited enhanced chondrogenic differentiation potential and reduced osteogenic differentiation potential. Moreover, the activation of key metabolic sensor AMP-activated kinase (AMPK) leads to activation of transcription factors such as FOXO3, which leads to an S phase quiescence. Serum deprivation also enhanced the expression of stemness related genes Sox2 and c-Myc.

L-citrulline inhibits body weight gain and hepatic fat accumulation by improving lipid metabolism in a rat nonalcoholic fatty liver disease model

BACKGROUND

Body weight gain is a social issue all over the world. When body weight increased, hepatic fat accumulation also increased and it causes fatty liver disease. Therefore, developing a new treatment method and elucidating its mechanism is necessary. L-citrulline (L-Cit) is a free amino acid found mainly in watermelon. No reports regarding its effects on the improvement of hepatic steatosis and fibrogenesis are currently available. The aim of this study was to clarify the effect and the mechanism of L-Cit on inhibition of body weight gain and hepatic fat accumulation in high-fat and high-cholesterol fed SHRSP5/Dmcr rats.

METHODS

L-Cit or water (controls) was administered to six-week-old male SHRSP5/Dmcr rats by gavage for nine weeks. We recorded the level of body weight and food intake while performing the administration and sacrificed rats. After that, the blood and lipid metabolism-related organs and tissues were collected and analyzed.

RESULTS

L-Cit treatment reduced body weight gain and hepatic TC and TG levels, and serum levels of AST and ALT. L-Cit enhanced AMPK, LKB1, PKA, and hormone-sensitive lipase (HSL) protein phosphorylation levels in the epididymal fat. L-Cit treatment improved steatosis as revealed by HE staining of liver tissues and enhanced AMPK and LKB1 phosphorylation levels. Moreover, activation of Sirt1 was higher, while the liver fatty acid synthase (FAS) level was lower. Azan staining of liver sections revealed a reduction in fibrogenesis following L-Cit treatment. Further, the liver levels of TGF-β, Smad2/3, and α-SMA, fibrogenesis-related proteins and genes, were lower in the L-Cit-treated group.

CONCLUSIONS

From the results of analysis of the epididymal fat and the liver, L-Cit inhibits body weight gain and hepatic fat accumulation by activating lipid metabolism and promoting fatty acid β-oxidation in SHRSP5/Dmcr rats.

Mammalian cold-inducible RNA-binding protein facilitates wound healing through activation of AMP-activated protein kinase

The skin is usually maintained within a temperature range that induces cold-inducible RNA-binding protein (Cirp). To determine whether Cirp plays a role in barrier function of the skin, we analyzed the skin wound healing in cirp-knockout (KO) mice. They exhibited delayed wound healing compared with wild-type littermates in the absence as well as presence of skin contraction. Dermal fibroblasts and keratinocytes from cirp-KO mice migrated slower than those from wild-type mice. When expression of Cirp was downregulated in cultured cells, migration rate was decreased. Cirp bound liver-kinase-B1 (LKB1) in the nucleus and was suggested to enhance its translocation to the cytoplasm, resulting in enhanced phosphorylation of AMP-activated protein kinase (AMPK) and cell motility. Stimulation of AMPK ameliorated the delayed wound healing in cirp-KO mice. These findings suggest that Cirp facilitates skin wound healing by enhancing cell migration via AMPK, indicating roles for Cirp in linking skin temperature with metabolism and defense mechanism.

Quantitative In Vivo Proteomics of Metformin Response in Liver Reveals AMPK-Dependent and -Independent Signaling Networks

Metformin is the front-line treatment for type 2 diabetes worldwide. It acts via effects on glucose and lipid metabolism in metabolic tissues, leading to enhanced insulin sensitivity. Despite significant effort, the molecular basis for metformin response remains poorly understood, with a limited number of specific biochemical pathways studied to date. To broaden our understanding of hepatic metformin response, we combine phospho-protein enrichment in tissue from genetically engineered mice with a quantitative proteomics platform to enable the discovery and quantification of basophilic kinase substrates in vivo. We define proteins whose binding to 14-3-3 are acutely regulated by metformin treatment and/or loss of the serine/threonine kinase, LKB1. Inducible binding of 250 proteins following metformin treatment is observed, 44% of which proteins bind in a manner requiring LKB1. Beyond AMPK, metformin activates protein kinase D and MAPKAPK2 in an LKB1-independent manner, revealing additional kinases that may mediate aspects of metformin response. Deeper analysis uncovered substrates of AMPK in endocytosis and calcium homeostasis.

Extracellular AMP Suppresses Endotoxemia-Induced Inflammation by Alleviating Neutrophil Activation

Intracellular adenosine monophosphate (AMP) is indispensable for cellular metabolic processes, and it is interconverted to ADP and/or ATP or activates AMP-activated protein kinase (AMPK). However, the specific biological function of extracellular AMP has not been identified. We evaluated the effect of extracellular AMP using in vivo and in vitro models of endotoxemia. We found that AMP inhibited inflammation and neutrophil activation in lipopolysaccharide (LPS)-induced endotoxemic mice. The effects of extracellular AMP were abolished by an adenosine 1 receptor (A1R) antagonist but were not influenced by inhibiting the conversion of AMP to adenosine (ADO), indicating that AMP inhibited inflammation by directly activating A1R. In addition, in vitro experiments using LPS-stimulated mouse neutrophils showed that AMP inhibited LPS-induced reactive oxygen species (ROS) production, degranulation, and cytokine production, while the effects were reversed by an A1R antagonist. Further research showed that AMP regulated LPS-stimulated neutrophil functions by inhibiting the p38 MAPK pathway. These findings were also confirmed in primary neutrophils derived from healthy human blood. Moreover, we collected serum samples from septic patients. We found that AMP levels were increased compared with those of healthy volunteers and that AMP levels were negatively correlated with disease severity. Together, these data provide evidence that extracellular AMP acts on A1R to suppress endotoxemia-induced inflammation by inhibiting neutrophil overactivation and that the p38 MAPK signaling pathway is involved.

The LKB1-SIK Pathway Controls Dendrite Self-Avoidance in Purkinje Cells

Strictly controlled dendrite patterning underlies precise neural connection. Dendrite self-avoidance is a crucial system preventing self-crossing and clumping of dendrites. Although many cell-surface molecules that regulate self-avoidance have been identified, the signaling pathway that orchestrates it remains poorly understood, particularly in mammals. Here, we demonstrate that the LKB1-SIK kinase pathway plays a pivotal role in the self-avoidance of Purkinje cell (PC) dendrites by ensuring dendritic localization of Robo2, a regulator of self-avoidance. LKB1 is activated in developing PCs, and PC-specific deletion of LKB1 severely disrupts the self-avoidance of PC dendrites without affecting gross morphology. SIK1 and SIK2, downstream kinases of LKB1, mediate LKB1-dependent dendrite self-avoidance. Furthermore, loss of LKB1 leads to significantly decreased Robo2 levels in the dendrite but not in the cell body. Finally, restoration of dendritic Robo2 level via overexpression largely rescues the self-avoidance defect in LKB1-deficient PCs. These findings reveal an LKB1-pathway-mediated developmental program that establishes dendrite self-avoidance.

Molecular characteristics of AMPK and its role in regulating the phagocytosis of oyster hemocytes

Phagocytosis is one of the fundamental cellular immune defense parameter that helps in the elimination of the invading pathogens in both vertebrates and invertebrates, which require plenty of energy for functioning. In the present study, we identified the critical energy regulator AMP-activated protein kinase (AMPK) in Crassostrea hongkongensis which is composed of three subunits, named ChAMPK-α, ChAMPK-β, and ChAMPK-γ, and then analyzed the function of AMPK in regulating hemocyte phagocytosis. All the three ChAMPK subunits mRNA were detected to be expressed at various embryological stages, and also constitutively expressed in multiple tissues with high expression in gill and mantle. The phylogenetic tree showed that the three subunits of AMPK were correspondingly clustered with its orthologue branches. Furthermore Western Blot analysis revealed that the AMPK pharmacological inhibitors Compound C could effectively down-regulate the Thr¹⁷² phosphorylation level of AMPK-α, and the hemocyte phagocytosis was inhibited by Compound C (CC), which indicate its existence in the oyster. Our results showed that treatment of AMPK inhibitors significantly attenuated the capacity of hemocytes phagocytosis. Moreover, Compound C could also change the organization of actin cytoskeleton in the oyster hemocytes, demonstrating the crucial role of AMPK signaling in control of phagocytosis.

Cordycepin inhibits lipopolysaccharide-induced cell migration and invasion in human colorectal carcinoma HCT-116 cells through down-regulation of prostaglandin E2 receptor EP4

Prostaglandin E₂ (PGE₂), a major product of cyclooxygenase-2 (COX-2), plays an important role in the carcinogenesis of many solid tumors, including colorectal cancer. Because PGE₂ functions by signaling through PGE₂ receptors (EPs), which regulate tumor cell growth, invasion, and migration, there has been a growing amount of interest in the therapeutic potential of targeting EPs. In the present study, we investigated the role of EP4 on the effectiveness of cordycepin in inhibiting the migration and invasion of HCT116 human colorectal carcinoma cells. Our data indicate that cordycepin suppressed lipopolysaccharide (LPS)-enhanced cell migration and invasion through the inactivation of matrix metalloproteinase (MMP)-9 as well as the down-regulation of COX-2 expression and PGE₂ production. These events were shown to be associated with the inactivation of EP4 and activation of AMP-activated protein kinase (AMPK). Moreover, the EP4 antagonist AH23848 prevented LPS-induced MMP-9 expression and cell invasion in HCT116 cells. However, the AMPK inhibitor, compound C, as well as AMPK knockdown via siRNA, attenuated the cordycepin-induced inhibition of EP4 expression. Cordycepin treatment also reduced the activation of CREB. These findings indicate that cordycepin suppresses the migration and invasion of HCT116 cells through modulating EP4 expression and the AMPK-CREB signaling pathway. Therefore, cordycepin has the potential to serve as a potent anti-cancer agent in therapeutic strategies against colorectal cancer metastasis.

Hyaluronidase2 (Hyal2) modulates low shear stress-induced glycocalyx impairment via the LKB1/AMPK/NADPH oxidase-dependent pathway

The endothelium glycocalyx layer (ECL), presents on the apical surface of endothelial cells, creates a barrier between circulating blood and the vessel wall. Low shear stress (LSS) may accelerate the degradation of the glycocalyx via hyaluronidase2 (Hyal2) and then alter the cell polarity. Yet the liver kinase B1 (LKB1) signaling pathway plays an important role in regulating cell polarity. However, the relationship between LKB1 and glycocalyx during LSS is not clear. In the current study, we demonstrate that LSS attenuates LKB1 and AMP-activated protein kinase activation as well as activated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (p47^phox ) and Hyal2 in the human umbilical vein endothelial cell (HUVEC). Pretreatment with 5-Aminoimidazole-4-carboxamide1-β-D-ribofuranoside (AICAR), or diphenyleneiodonium (DPI chloride) and transfection with LKB1 overexpression vector and p47^phox small interfering RNA downregulated LSS-induced Hyal2 activation. By coimmunoprecipitation, we discovered the existence of p47^phox /Hyal2 complex. LSS induced the dissociation of p47^phox /Hyal2 complex, which was inhibited by LKB1 overexpression and AICAR. Furthermore, knockdown of Hyal2 performed a positive feedback on LKB1 activity. In addition, we also show that LSS enhanced LKB1 translocation from the cytosol to the nucleus. Taken together, these data indicate that Hyal2 regulates LSS-induced injury of the glycocalyx via LKB1/AMPK/NADPH oxidase signaling cascades.

A comparison of LKB1/AMPK/mTOR metabolic axis response to global ischaemia in brain, heart, liver and kidney in a rat model of cardiac arrest

BACKGROUND

Cellular energy failure in high metabolic rate organs is one of the underlying causes for many disorders such as neurodegenerative diseases, cardiomyopathies, liver and renal failures. In the past decade, numerous studies have discovered the cellular axis of LKB1/AMPK/mTOR as an essential modulator of cell homeostasis in response to energy stress. Through regulating adaptive mechanisms, this axis adjusts the energy availability to its demand by a systematized control on metabolism. Energy stress, however, could be sensed at different levels in various tissues, leading to applying different strategies in response to hypoxic insults.

METHODS

Here the immediate strategies of high metabolic rate organs to time-dependent short episodes of ischaemia were studied by using a rat model (n = 6/group) of cardiac arrest (CA) (15 and 30 s, 1, 2, 4 and 8 min CA). Using western blot analysis, we examined the responses of LKB1/AMPK/mTOR pathway in brain, heart, liver and kidney from 15 s up to 8 min of global ischaemia. The ratio of ADP/ATP was assessed in all ischemic and control groups, using ApoSENSOR bioluminescent assay kit.

RESULTS

Brain, followed by kidney showed the early dephosphorylation response in AMPK (Thr172) and LKB1 (Ser431); in the absence of ATP decline (ADP/ATP elevation). Dephosphorylation of AMPK was followed by rephosphorylation and hyperphosphorylation, which was associated with a significant ATP decline. While heart's activity of AMPK and LKB1 remained at the same level during short episodes of ischaemia, liver's LKB1 was dephosphorylated after 2 min. AMPK response to ischaemia in liver was mainly based on an early alternative and a late constant hyperphosphorylation. No significant changes was observed in mTOR activity in all groups.

CONCLUSION

Together our results suggest that early AMPK dephosphorylation followed by late hyperphosphorylation is the strategy of brain and kidney in response to ischaemia. While the liver seemed to get benefit of its AMPK system in early ischameia, possibly to stabilize ATP, the level of LKB1/AMPK activity in heart remained unchanged in short ischaemic episodes up to 8 min. Further researches must be conducted to elucidate the molecular mechanism underlying LKB1/AMPK response to oxygen supply.

Glycolysis regulates pollen tube polarity via Rho GTPase signaling

As a universal energy generation pathway utilizing carbon metabolism, glycolysis plays an important housekeeping role in all organisms. Pollen tubes expand rapidly via a mechanism of polarized growth, known as tip growth, to deliver sperm for fertilization. Here, we report a novel and surprising role of glycolysis in the regulation of growth polarity in Arabidopsis pollen tubes via impingement of Rho GTPase-dependent signaling. We identified a cytosolic phosphoglycerate kinase (pgkc-1) mutant with accelerated pollen germination and compromised pollen tube growth polarity. pgkc-1 mutation greatly diminished apical exocytic vesicular distribution of REN1 RopGAP (Rop GTPase activating protein), leading to ROP1 hyper-activation at the apical plasma membrane. Consequently, pgkc-1 pollen tubes contained higher amounts of exocytic vesicles and actin microfilaments in the apical region, and showed reduced sensitivity to Brefeldin A and Latrunculin B, respectively. While inhibition of mitochondrial respiration could not explain the pgkc-1 phenotype, the glycolytic activity is indeed required for PGKc function in pollen tubes. Moreover, the pgkc-1 pollen tube phenotype was mimicked by the inhibition of another glycolytic enzyme. These findings highlight an unconventional regulatory function for a housekeeping metabolic pathway in the spatial control of a fundamental cellular process.

Glycolysis, which breaks down glucose to produce energy, has long been considered a “housekeeping” pathway in living cells, i.e., it helps maintain basic cellular functions. Here, we found that the glycolysis pathway plays an unconventional regulatory role in cell polarity, i.e., the intrinsic asymmetry in the shape, structure, and organization of cellular components. Mutation in the gene encoding the glycolytic enzyme cytosolic phosphoglycerate kinase (PGKc) leads to swollen and shorter pollen tubes in Arabidopsis thaliana, which is associated with the over-activation of Rho GTPase—a master regulator of cell polarity. Our results suggest that this phenomenon is caused by a specific regulatory role of cytosolic glycolysis rather than the global energy supply or moonlighting functions of glycolytic enzymes that modulate pollen tube growth polarity. Our findings shed light on the diverse biological roles of glycolysis in plants beyond simple “housekeeping” functions.

Decreased expression of LKB1 predicts poor prognosis in pancreatic neuroendocrine tumor patients undergoing curative resection

Background

Liver kinase B1 (LKB1) is a key regulatory protein of cellular metabolism, proliferation, and polarity. The present study aimed to characterize the expression pattern of LKB1 in pancreatic neuroendocrine tumors (pNETs) and evaluate the relationship between LKB1 expression and prognosis in pNETs.

Patients and methods

We retrospectively analyzed the pathologic and clinical data of 71 pNET patients who underwent curative surgical resection in Guangdong General Hospital. LKB1 mRNA and protein levels in tumor tissues and paired nontumor tissues were evaluated in 24 patients by quantitative real-time reverse-transcription polymerase chain reaction and Western blot, respectively. Immunohistochemical expression of LKB1 in tumor tissues was detected in all of the 71 patients, and the immunohistochemical expression level was re-coded in two classes (high versus low/negative) and correlated with clinicopathological parameters and survival outcomes. The association between LKB1 expression and clinicopathological characters was evaluated by chi-square test and Student’s t-test. Kaplan–Meier curves and log-rank test were used to analyze the survival outcomes, including overall survival (OS) and disease-free survival (DFS).

Results

Compared to adjacent normal tissues, LKB1 mRNA level and protein expression level in tumor tissues were both increased. The immunostaining of LKB1 was mainly found within the cytoplasm. Overall, 52 of 71 (73.2%) cases were positive for LKB1 protein, which showed either a diffuse staining pattern or a partial staining pattern. Decreased LKB1 expression was correlated with older age (P=0.042), increased Ki-67 index (P=0.004), increased mitotic count (P=0.001), and advanced histologic grade (P=0.001). Moreover, patients with low/negative LKB1 expression had shorter OS and DFS than those with high expression.

Conclusion

Our results suggested that LKB1 expression could be a useful prognostic marker for recurrence and survival in pNET patients who had received curative resection.

Two-cell embryos are more sensitive than blastocysts to AMPK-dependent suppression of anabolism and stemness by commonly used fertility drugs, a diet supplement, and stress

PURPOSE

This study tests whether metformin or diet supplement BR-DIM-induced AMP-activated protein kinase (AMPK) mediated effects on development are more pronounced in blastocysts or 2-cell mouse embryos.

METHODS

Culture mouse zygotes to two-cell embryos and test effects after 0.5-1 h AMPK agonists' (e.g., Met, BR-DIM) exposure on AMPK-dependent ACCser79P phosphorylation and/or Oct4 by immunofluorescence. Culture morulae to blastocysts and test for increased ACCser79P, decreased Oct4 and for AMPK dependence by coculture with AMPK inhibitor compound C (CC). Test whether Met or BR-DIM decrease growth rates of morulae cultured to blastocyst by counting cells.

RESULT(S)

Aspirin, metformin, and hyperosmotic sorbitol increased pACC ser79P ~ 20-fold, and BR-DIM caused a ~ 30-fold increase over two-cell embryos cultured for 1 h in KSOMaa but only 3- to 6-fold increase in blastocysts. We previously showed that these stimuli decreased Oct4 40-85% in two-cell embryos that was ~ 60-90% reversible by coculture with AMPK inhibitor CC. However, Oct4 decreased only 30-50% in blastocysts, although reversibility of loss by CC was similar at both embryo stages. Met and BR-DIM previously caused a near-complete cell proliferation arrest in two-cell embryos and here Met caused lower CC-reversible growth decrease and AMPK-independent BR-DIM-induced blastocyst growth decrease.

CONCLUSION

Inducing drug or diet supplements decreased anabolism, growth, and stemness have a greater impact on AMPK-dependent processes in two-cell embryos compared to blastocysts.

AMPK negatively regulates tensin-dependent integrin activity

Georgiadou et al. show that the major metabolic sensor AMPK regulates integrin activity and integrin-dependent processes in fibroblasts by modulating tensin levels. Loss of AMPK up-regulates tensin expression, triggering enhanced integrin activity in fibrillar adhesions, fibronectin remodeling, and traction stress.

Tight regulation of integrin activity is paramount for dynamic cellular functions such as cell matrix adhesion and mechanotransduction. Integrin activation is achieved through intracellular interactions at the integrin cytoplasmic tails and through integrin–ligand binding. In this study, we identify the metabolic sensor AMP-activated protein kinase (AMPK) as a β1-integrin inhibitor in fibroblasts. Loss of AMPK promotes β1-integrin activity, the formation of centrally located active β1-integrin– and tensin-rich mature fibrillar adhesions, and cell spreading. Moreover, in the absence of AMPK, cells generate more mechanical stress and increase fibronectin fibrillogenesis. Mechanistically, we show that AMPK negatively regulates the expression of the integrin-binding proteins tensin1 and tensin3. Transient expression of tensins increases β1-integrin activity, whereas tensin silencing reduces integrin activity in fibroblasts lacking AMPK. Accordingly, tensin silencing in AMPK-depleted fibroblasts impedes enhanced cell spreading, traction stress, and fibronectin fiber formation. Collectively, we show that the loss of AMPK up-regulates tensins, which bind β1-integrins, supporting their activity and promoting fibrillar adhesion formation and integrin-dependent processes.

AMP-activated protein kinase fortifies epithelial tight junctions during energetic stress via its effector GIV/Girdin

Loss of epithelial polarity impacts organ development and function; it is also oncogenic. AMPK, a key sensor of metabolic stress stabilizes cell-cell junctions and maintains epithelial polarity; its activation by Metformin protects the epithelial barrier against stress and suppresses tumorigenesis. How AMPK protects the epithelium remains unknown. Here, we identify GIV/Girdin as a novel effector of AMPK, whose phosphorylation at a single site is both necessary and sufficient for strengthening mammalian epithelial tight junctions and preserving cell polarity and barrier function in the face of energetic stress. Expression of an oncogenic mutant of GIV (cataloged in TCGA) that cannot be phosphorylated by AMPK increased anchorage-independent growth of tumor cells and helped these cells to evade the tumor-suppressive action of Metformin. This work defines a fundamental homeostatic mechanism by which the AMPK-GIV axis reinforces cell junctions against stress-induced collapse and also provides mechanistic insight into the tumor-suppressive action of Metformin.

LKB1 and Notch Pathways Interact and Control Biliary Morphogenesis

Background

LKB1 is an evolutionary conserved kinase implicated in a wide range of cellular functions including inhibition of cell proliferation, regulation of cell polarity and metabolism. When Lkb1 is inactivated in the liver, glucose homeostasis is perturbed, cellular polarity is affected and cholestasis develops. Cholestasis occurs as a result from deficient bile duct development, yet how LKB1 impacts on biliary morphogenesis is unknown.

Methodology/Principal Findings

We characterized the phenotype of mice in which deletion of the Lkb1 gene has been specifically targeted to the hepatoblasts. Our results confirmed that lack of LKB1 in the liver results in bile duct paucity leading to cholestasis. Immunostaining analysis at a prenatal stage showed that LKB1 is not required for differentiation of hepatoblasts to cholangiocyte precursors but promotes maturation of the primitive ductal structures to mature bile ducts. This phenotype is similar to that obtained upon inactivation of Notch signaling in the liver. We tested the hypothesis of a functional overlap between the LKB1 and Notch pathways by gene expression profiling of livers deficient in Lkb1 or in the Notch mediator RbpJκ and identified a mutual cross-talk between LKB1 and Notch signaling. In vitro experiments confirmed that Notch activity was deficient upon LKB1 loss.

Conclusion

LKB1 and Notch share a common genetic program in the liver, and regulate bile duct morphogenesis.

Low LKB1 Expression Results in Unfavorable Prognosis in Prostate Cancer Patients

Background

The present study aimed to compare the expression of liver kinase B1 (LKB1) in prostate cancer (PCa) tissues and the paired adjacent tissues, then to evaluate the statistical relationship between LKB1 expression and prognosis of PCa patients.

Material/Methods

The relative expression of LKB1 at mRNA level was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of LKB1 at protein level was measured by immunohistochemistry (IHC) method. The relationship between LKB1 expression and clinicopathologic characteristics was estimated by chi-square test. Kaplan-Meier method was used to analyze the overall survival of PCa patients with different LKB1 expression. Cox regression analysis was performed to estimate the significance of LKB1 expression and clinicopathologic characteristics in the prognosis of PCa patients.

Results

The relative expression of LKB1 at mRNA level was significantly lower in PCa tissues than in the normal tissues (P<0.001). The LKB1 expression was proved to be affected by clinical stage (P=0.019) and PSA concentration (P=0.031) of PCa patients. Moreover, patients with negative LKB1 expression had shorter survival than those with positive expression. Cox regression analysis confirmed that LKB1 could be regarded as a prognostic biomarker for PCa patients (P=0.001, HR=3.981, 95% CI=1.698–9.336).

Conclusions

The expression of LKB1 was lower in PCa tissues and might be a predictor for the prognosis of PCa patients.

Ignoring matrix boundaries when the LKB1 master kinase is gone

Gradients of soluble attractants as well as extracellular matrix (ECM) proteins serve as cues for directional cell movement. Such "chemotaxis" and "haptotaxis" steers migration of cells during embryonic development, wound healing, and immune responses. In this issue, Chan et al. (2014. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201404067) show that the tumor suppressor LKB1 controls haptotaxis through the microtubule affinity-regulating kinase (MARK) family, one of the many substrates of the LKB1 master kinase. In the absence of this pathway, melanoma cells migrate irrespective of ECM gradients, which may explain the increased metastatic spread observed in LKB1-deficient tumors.

Loss of LKB1 disrupts breast epithelial cell polarity and promotes breast cancer metastasis and invasion

Background

LKB1, also known as STK11, is a master kinase that serves as an energy metabolic sensor and is involved in cell polarity regulation. Recent studies have indicated that LKB1 is related to breast tumorigenesis and breast cancer progression. However, little work has been done on the roles of LKB1 in cell polarity and epithelial-mesenchymal transition in breast cancer. In this study, we tried to prove that loss of LKB1 disrupts breast epithelial cell polarity and causes tumor metastasis and invasion.

Methods

The relationships of LKB1 expression to clinic-pathological parameters and epithelial markers E-cadherin and high-molecular-weight -cytokeratin (HMW-CK) were investigated in 80 clinical breast cancer tissue samples and their paired normal control breast tissue samples by using immunohistochemistry. Then, the LKB1 expressions in metastatic and non-metastatic breast cancer cell lines were compared. The roles of LKB1 in cell polarity and epithelial-mesenchymal transition in breast cancer were determined by using immunofluorescence, western blot assay, and cell migration and invasive assays. Finally, the non-transformed human breast cell line MCF-10A was cultured in three dimensions to further reveal the role of LKB1 in breast epithelial cell polarity maintenance.

Results

Histopathological analysis showed that LKB1 expression level was significantly negatively correlated with breast cancer TNM stage, and positively correlated with ER/PR status and expression levels of E-cadherin and HMW-CK. Immunofluorescence staining showed that LKB1 was co-localized with E-cadherin at adheren junctions. In vitro analysis revealed that loss of LKB1 expression enhanced migration, invasion and the acquisition of mesenchymal phenotype, while LKB1 overexpression in MDA-MB-435 s cells, which have a low basal level of LKB1 expression, promoted the acquisition of epithelial phenotype. Finally, it was found for the first time that endogenous LKB1 knockdown resulted in abnormal cell polarity in acini formed by non-transformed breast epithelial cells grown in 3D culture.

Conclusion

Our data indicated that low expression of LKB1 was significantly associated with established markers of unfavorable breast cancer prognosis, such as loss of ER/PR, E-cadherin and HMW-CK. Knockdown of endogenous LKB1 gave rise to dysregulation of cell polarity and invasive phenotype of breast cancer cells.

Connecting metabolism to intestinal barrier function: The role of leptin

Structure and function of the intestinal epithelial barrier (IEB) are dependent upon the integrity of junctional protein structures sealing the apical surface between epithelial cells. Tight junctions (TJ) and the surrounding apical F-actin cytoskeleton are involved in the regulation of paracellular permeability. The regulation of actin cytoskeleton organization by RhoA/Rho-kinase (ROCK) pathway plays an important role in TJ assembly and function. There is mounting evidence that the adipocyte-derived hormone leptin exerts pleiotropic effects on the intestinal epithelium including nutrient absorption, epithelial growth, inflammation and injury. Leptin activates multiple cell signaling pathways in intestinal epithelial cells (IEC) that can explain these pleiotropic effects. However, these pathways are also involved in the primary role of leptin that is the regulation of energy and glucose metabolism homeostasis. In this commentary, we examine how the interplay between leptin signaling pathways that regulate cell metabolism could impact upon IEB function.

LKB1 and AMPK regulate synaptic remodeling in old age

Age-related decreases in neural function result in part from alterations in synapses. To identify molecular defects that lead to such changes, we focused on the outer retina, in which synapses are markedly altered in old rodents and humans. We found that the serine/threonine kinase LKB1 and one of its substrates, AMPK, regulate this process. In old mice, synaptic remodeling was accompanied by specific decreases in the levels of total LKB1 and active (phosphorylated) AMPK. In the absence of either kinase, young adult mice developed retinal defects similar to those that occurred in old wild-type animals. LKB1 and AMPK function in rod photoreceptors where their loss leads to aberrant axonal retraction, the extension of postsynaptic dendrites and the formation of ectopic synapses. Conversely, increasing AMPK activity genetically or pharmacologically attenuates and may reverse age-related synaptic alterations. Together, these results identify molecular determinants of age-related synaptic remodeling and suggest strategies for attenuating these changes.

STRAD pseudokinases regulate axogenesis and LKB1 stability

Background

Neuronal polarization is an essential step of morphogenesis and connectivity in the developing brain. The serine/threonine kinase LKB1 is a key regulator of cell polarity, metabolism, tumorigenesis, and is required for axon formation. It is allosterically regulated by two related and evolutionarily conserved pseudokinases, STe20-Related ADapters (STRADs) α and β. The roles of STRADα and STRADβ in the developing nervous system are not fully defined, nor is it known whether they serve distinct functions.

Results

We find that STRADα is highly spliced and appears to be the primal STRAD paralog. We report that each STRAD is sufficient for axogenesis and promoting cell survival in the developing cortex. We also reveal a reciprocal protein-stabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization.

Conclusions

We demonstrate a novel role for STRADβ in axogenesis and also show for the first time in vivo that STRADα, but not STRADβ, is responsible for LKB1 protein stability.

Cellular polarity in aging: role of redox regulation and nutrition

Cellular polarity concerns the spatial asymmetric organization of cellular components and structures. Such organization is important not only for biological behavior at the individual cell level, but also for the 3D organization of tissues and organs in living organisms. Processes like cell migration and motility, asymmetric inheritance, and spatial organization of daughter cells in tissues are all dependent of cell polarity. Many of these processes are compromised during aging and cellular senescence. For example, permeability epithelium barriers are leakier during aging; elderly people have impaired vascular function and increased frequency of cancer, and asymmetrical inheritance is compromised in senescent cells, including stem cells. Here, we review the cellular regulation of polarity, as well as the signaling mechanisms and respective redox regulation of the pathways involved in defining cellular polarity. Emphasis will be put on the role of cytoskeleton and the AMP-activated protein kinase pathway. We also discuss how nutrients can affect polarity-dependent processes, both by direct exposure of the gastrointestinal epithelium to nutrients and by indirect effects elicited by the metabolism of nutrients, such as activation of antioxidant response and phase-II detoxification enzymes through the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In summary, cellular polarity emerges as a key process whose redox deregulation is hypothesized to have a central role in aging and cellular senescence.

Phosphorylation of serine 399 in LKB1 protein short form by protein kinase Cζ is required for its nucleocytoplasmic transport and consequent AMP-activated protein kinase (AMPK) activation

Two splice variants of LKB1 exist: LKB1 long form (LKB1(L)) and LKB1 short form (LKB1(S)). In a previous study, we demonstrated that phosphorylation of Ser-428/431 (in LKB1(L)) by protein kinase Cζ (PKCζ) was essential for LKB1-mediated activation of AMP-activated protein kinase (AMPK) in response to oxidants or metformin. Paradoxically, LKB1S also activates AMPK although it lacks Ser-428/431. Thus, we hypothesized that LKB1(S) contained additional phosphorylation sites important in AMPK activation. Truncation analysis and site-directed mutagenesis were used to identify putative PKCζ phosphorylation sites in LKB1(S). Substitution of Ser-399 to alanine did not alter the activity of LKB1(S), but abolished peroxynitrite- and metformin-induced activation of AMPK. Furthermore, the phosphomimetic mutation (S399D) increased the phosphorylation of AMPK and its downstream target phospho-acetyl-coenzyme A carboxylase (ACC). PKCζ-dependent phosphorylation of Ser-399 triggered nucleocytoplasmic translocation of LKB1(S) in response to metformin or peroxynitrite treatment. This effect was ablated by pharmacological and genetic inhibition of PKCζ, by inhibition of CRM1 activity and by substituting Ser-399 with alanine (S399A). Overexpression of PKCζ up-regulated metformin-mediated phosphorylation of both AMPK (Thr-172) and ACC (Ser-79), but the effect was ablated in the S399A mutant. We conclude that, similar to Ser-428/431 (in LKB1(L)), Ser-399 (in LKB1(S)) is a PKCζ-dependent phosphorylation site essential for nucleocytoplasmic export of LKB1(S) and consequent AMPK activation.

Cell confinement controls centrosome positioning and lumen initiation during epithelial morphogenesis

Epithelial organ morphogenesis involves sequential acquisition of apicobasal polarity by epithelial cells and development of a functional lumen. In vivo, cells perceive signals from components of the extracellular matrix (ECM), such as laminin and collagens, as well as sense physical conditions, such as matrix stiffness and cell confinement. Alteration of the mechanical properties of the ECM has been shown to promote cell migration and invasion in cancer cells, but the effects on epithelial morphogenesis have not been characterized. We analyzed the effects of cell confinement on lumen morphogenesis using a novel, micropatterned, three-dimensional (3D) Madin-Darby canine kidney cell culture method. We show that cell confinement, by controlling cell spreading, limits peripheral actin contractility and promotes centrosome positioning and lumen initiation after the first cell division. In addition, peripheral actin contractility is mediated by master kinase Par-4/LKB1 via the RhoA-Rho kinase-myosin II pathway, and inhibition of this pathway restores lumen initiation in minimally confined cells. We conclude that cell confinement controls nuclear-centrosomal orientation and lumen initiation during 3D epithelial morphogenesis.

LKB1 and AMP-activated protein kinase: regulators of cell polarity

Adenosine monophosphate-activated protein kinase (AMPK), a metabolic protein kinase, and its upstream kinase LKB1 play crucial roles in the establishment and maintenance of cell polarity. Although the shapes of polarized cells display extraordinary diversity, the key molecules involved in cell polarity are relatively well conserved. Here, we review the mechanisms and factors responsible for organizing cell polarity and the role of LKB1 and AMPK in cell polarity.

Epithelial cell polarity, stem cells and cancer

After years of extensive scientific discovery much has been learned about the networks that regulate epithelial homeostasis. Loss of expression or functional activity of cell adhesion and cell polarity proteins (including the PAR, crumbs (CRB) and scribble (SCRIB) complexes) is intricately related to advanced stages of tumour progression and invasiveness. But the key roles of these proteins in crosstalk with the Hippo and liver kinase B1 (LKB1)-AMPK pathways and in epithelial function and proliferation indicate that they may also be associated with the early stages of tumorigenesis. For example, deregulation of adhesion and polarity proteins can cause misoriented cell divisions and increased self-renewal of adult epithelial stem cells. In this Review, we highlight some advances in the understanding of how loss of epithelial cell polarity contributes to tumorigenesis.

The AMPK signalling pathway coordinates cell growth, autophagy and metabolism

One of the central regulators of cellular and organismal metabolism in eukaryotes is AMP-activated protein kinase (AMPK), which is activated when intracellular ATP production decreases. AMPK has critical roles in regulating growth and reprogramming metabolism, and has recently been connected to cellular processes such as autophagy and cell polarity. Here we review a number of recent breakthroughs in the mechanistic understanding of AMPK function, focusing on a number of newly identified downstream effectors of AMPK.

NUAK2: an emerging acral melanoma oncogene

Recent technological advances in cancer genomics make it possible to dissect complicated genomic aberrations of melanomas. In particular, several specific genomic aberrations including 11q13 amplification and KIT aberrations have been identified in acral melanomas. We recently identified NUAK2 at 1q32 as a promising oncogene in acral melanomas and reported its significant roles in tumorigenesis in melanoma cells using both in vitro and in vivo analyses. NUAK2 as a member of the AMPK family has several intriguing aspects both as an oncogene and as a tumor suppressor gene. Here we review genomic aberrations of melanomas focusing on acral melanomas to emphasize the possible roles of NUAK2 in tumorigenesis in general and suggest that NUAK2 has pivotal roles in acral melanomagenesis.

Insights from model organisms on the functions of the tumor suppressor protein LKB1: zebrafish chips in

The tumor suppressor LKB1 has emerged as a critical regulator of cell polarity and energy-metabolism. Studies in diverse model organisms continue to unravel the pathways downstream of LKB1; the emerging picture is that the outcomes of LKB1 signaling are mediated by a plethora of tissue-specific and context-dependent effectors.

Epithelial cell polarity: a major gatekeeper against cancer?

The correct establishment and maintenance of cell polarity are crucial for normal cell physiology and tissue homeostasis. Conversely, loss of cell polarity, tissue disorganisation and excessive cell growth are hallmarks of cancer. In this review, we focus on identifying the stages of tumoural development that are affected by the loss or deregulation of epithelial cell polarity. Asymmetric division has recently emerged as a major regulatory mechanism that controls stem cell numbers and differentiation. Links between cell polarity and asymmetric cell division in the context of cancer will be examined. Apical–basal polarity and cell–cell adhesion are tightly interconnected. Hence, how loss of cell polarity in epithelial cells may promote epithelial mesenchymal transition and metastasis will also be discussed. Altogether, we present the argument that loss of epithelial cell polarity may have an important role in both the initiation of tumourigenesis and in later stages of tumour development, favouring the progression of tumours from benign to malignancy.