PAS kinase is required for normal cellular energy balance

Nutrient Signaling-Dependent Quaternary Structure Remodeling Drives the Catalytic Activation of metazoan PASK

The Per-Arnt-Sim (PAS) domains are characterized by diverse sequences and feature tandemly arranged PAS and PAS-associated C-terminal (PAC) motifs that fold seamlessly to generate the metabolite-sensing PAS domain. Here, using evolutionary scale sequence, domain mapping, and deep learning-based protein structure analysis, we deconstructed the sequence-structure relationship to unearth a novel example of signal-regulated assembly of PAS and PAC subdomains in metazoan PAS domain-regulated kinase (PASK). By comparing protein sequence, domain architecture, and computational protein models between fish, bird, and mammalian PASK orthologs, we propose the existence of previously unrecognized third PAS domain of PASK (PAS-C) formed through long-range intramolecular interactions between the N-terminal PAS fold and the C-terminal PAC fold. We experimentally validated this novel structural design using residue-level cross-linking assays and showed that the PAS-C domain assembly is nutrient-responsive. Furthermore, by combining structural phylogeny approaches with residue-level cross-linking, we revealed that the PAS-C domain assembly links nutrient sensing with quaternary structure reorganization in PASK, stabilizing the kinase catalytic core of PASK. Thus, PAS-C domain assembly likely integrates environmental signals, thereby relaying sensory information for catalytic control of the PASK kinase domain. In conclusion, we theorize that during their horizontal transfer from bacteria to multicellular organisms, PAS domains gained the capacity to integrate environmental signals through dynamic modulation of PAS and PAC motif interaction, adding a new regulatory layer suited for multicellular systems. We propose that metazoan PAS domains are likely to be more dynamic in integrating sensory information than previously considered, and their structural assembly could be targeted by regulatory signals and exploited to develop therapeutic strategies.

Jasminoidin reduces ischemic stroke injury by regulating microglia polarization via PASK-EEF1A1 axis

Jasminoidin (JAS) can alleviate ischemic stroke (IS) injury, but its molecular mechanism remains undefined. The polarization of microglia affects IS process. This research is powered to probe whether the molecular mechanism of JAS for IS treatment is coupled with microglia polarization. IS modeling in mice was accomplished by middle cerebral artery occlusion (MCAO) and model mice were injected with 25 and 50 mg/mL JAS, followed by determination of infarct volume, brain water content, and histological changes in mouse brains. The microglia modeling was performed by 1-h oxygen-glucose deprivation and 24-h reoxygenation. Oxygen-glucose deprivation/reoxygenation (OGD/R)-induced microglia were treated with JAS and transfected with Per-Arnt-Sim kinase (PASK)-overexpressing plasmid, subsequent to which cell viability and lactate dehydrogenase (LDH) level were determined. The mRNA or protein expressions of examined genes in microglia and brain tissues were detected by quantitative real-time polymerase chain reaction or western blot. MCAO-induced massive infarction, edema, and injury in mouse brain tissues, upregulated interleukin-1 beta (IL-1β), FcγRIIB (CD32), tumor necrosis factor alpha (TNF-α), PASK, p-eukaryotic elongation factor 1A1 (EEF1A1), and p-EEF1A1/EEF1A1 levels, but downregulated mannose receptor 1 (CD206), arginase-1 (Arg-1) and interleukin-10 (IL-10), and EEF1A1 expressions, which was reversed by JAS. OGD/R treatment decreased microglial viability as well as expressions of CD206, Arg-1, IL-10, and EEF1A1, yet increased cytotoxicity and levels of IL-1β, CD32, TNF-α, PASK, p-EEF1A1, and p-EEF1A1/EEF1A1, which was reversed by JAS. PASK overexpression reversed the effects of JAS on microglia. JAS reduces IS injury by regulating microglia polarization via PASK-EEF1A1 axis.

SIKs Regulate HDAC7 Stabilization and Cytokine Recall in Late-Stage T Cell Effector Differentiation

Understanding the mechanisms underlying the acquisition and maintenance of effector function during T cell differentiation is important to unraveling how these processes can be dysregulated in the context of disease and manipulated for therapeutic intervention. In this study, we report the identification of a previously unappreciated regulator of murine T cell differentiation through the evaluation of a previously unreported activity of the kinase inhibitor, BioE-1197. Specifically, we demonstrate that liver kinase B1 (LKB1)-mediated activation of salt-inducible kinases epigenetically regulates cytokine recall potential in effector CD8+ and Th1 cells. Evaluation of this phenotype revealed that salt-inducible kinase-mediated phosphorylation-dependent stabilization of histone deacetylase 7 (HDAC7) occurred during late-stage effector differentiation. HDAC7 stabilization increased nuclear HDAC7 levels, which correlated with total and cytokine loci-specific reductions in the activating transcription mark histone 3 lysine 27 acetylation (H3K27Ac). Accordingly, HDAC7 stabilization diminished transcriptional induction of cytokine genes upon restimulation. Inhibition of this pathway during differentiation produced effector T cells epigenetically poised for enhanced cytokine recall. This work identifies a previously unrecognized target for enhancing effector T cell functionality.

Origin and functional diversification of PAS domain, a ubiquitous intracellular sensor

Signal perception is a key function in regulating biological activities and adapting to changing environments. Per-Arnt-Sim (PAS) domains are ubiquitous sensors found in diverse receptors in bacteria, archaea, and eukaryotes, but their origins, distribution across the tree of life, and extent of their functional diversity are not fully characterized. Here, we show that using sequence conservation and structural information, it is possible to propose specific and potential functions for a large portion of nearly 3 million PAS domains. Our analysis suggests that PAS domains originated in bacteria and were horizontally transferred to archaea and eukaryotes. We reveal that gas sensing via a heme cofactor evolved independently in several lineages, whereas redox and light sensing via flavin adenine dinucleotide and flavin mononucleotide cofactors have the same origin. The close relatedness of human PAS domains to those in bacteria provides an opportunity for drug design by exploring potential natural ligands and cofactors for bacterial homologs.

Metabolic "Sense Relay" in Stem Cells: A Short But Impactful Life of PAS Kinase Balancing Stem Cell Fates

Tissue regeneration is a complex molecular and biochemical symphony. Signaling pathways establish the rhythmic proliferation and differentiation cadence of participating cells to repair the damaged tissues and repopulate the tissue-resident stem cells. Sensory proteins form a critical bridge between the environment and cellular response machinery, enabling precise spatiotemporal control of stem cell fate. Of many sensory modules found in proteins from prokaryotes to mammals, Per-Arnt-Sim (PAS) domains are one of the most ancient and found in the most diverse physiological context. In metazoa, PAS domains are found in many transcription factors and ion channels; however, PAS domain-containing Kinase (PASK) is the only metazoan kinase where the PAS sensory domain is connected to a signaling kinase domain. PASK is predominantly expressed in undifferentiated, self-renewing embryonic and adult stem cells, and its expression is rapidly lost upon differentiation, resulting in its nearly complete absence from the adult mammalian tissues. Thus, PASK is expressed within a narrow but critical temporal window when stem cell fate is established. In this review, we discuss the emerging insight into the sensory and signaling functions of PASK as an integrator of metabolic and nutrient signaling information that serves to balance self-renewal and differentiation programs during mammalian tissue regeneration.

Adipose-Specific PPARα Knockout Mice Have Increased Lipogenesis by PASK-SREBP1 Signaling and a Polarity Shift to Inflammatory Macrophages in White Adipose Tissue

The nuclear receptor PPARα is associated with reducing adiposity, especially in the liver, where it transactivates genes for β-oxidation. Contrarily, the function of PPARα in extrahepatic tissues is less known. Therefore, we established the first adipose-specific PPARα knockout (PparaFatKO) mice to determine the signaling position of PPARα in adipose tissue expansion that occurs during the development of obesity. To assess the function of PPARα in adiposity, female and male mice were placed on a high-fat diet (HFD) or normal chow for 30 weeks. Only the male PparaFatKO animals had significantly more adiposity in the inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT) with HFD, compared to control littermates. No changes in adiposity were observed in female mice compared to control littermates. In the males, the loss of PPARα signaling in adipocytes caused significantly higher cholesterol esters, activation of the transcription factor sterol regulatory element-binding protein-1 (SREBP-1), and a shift in macrophage polarity from M2 to M1 macrophages. We found that the loss of adipocyte PPARα caused significantly higher expression of the Per-Arnt-Sim kinase (PASK), a kinase that activates SREBP-1. The hyperactivity of the PASK-SREBP-1 axis significantly increased the lipogenesis proteins fatty acid synthase (FAS) and stearoyl-Coenzyme A desaturase 1 (SCD1) and raised the expression of genes for cholesterol metabolism (Scarb1, Abcg1, and Abca1). The loss of adipocyte PPARα increased Nos2 in the males, an M1 macrophage marker indicating that the population of macrophages had changed to proinflammatory. Our results demonstrate the first adipose-specific actions for PPARα in protecting against lipogenesis, inflammation, and cholesterol ester accumulation that leads to adipocyte tissue expansion in obesity.

Preventing Oxidative Stress in the Liver: An Opportunity for GLP-1 and/or PASK

The liver’s high metabolic activity and detoxification functions generate reactive oxygen species, mainly through oxidative phosphorylation in the mitochondria of hepatocytes. In contrast, it also has a potent antioxidant mechanism for counterbalancing the oxidant’s effect and relieving oxidative stress. PAS kinase (PASK) is a serine/threonine kinase containing an N-terminal Per-Arnt-Sim (PAS) domain, able to detect redox state. During fasting/feeding changes, PASK regulates the expression and activation of critical liver proteins involved in carbohydrate and lipid metabolism and mitochondrial biogenesis. Interestingly, the functional inactivation of PASK prevents the development of a high-fat diet (HFD)-induced obesity and diabetes. In addition, PASK deficiency alters the activity of other nutrient sensors, such as the AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR). In addition to the expression and subcellular localization of nicotinamide-dependent histone deacetylases (SIRTs). This review focuses on the relationship between oxidative stress, PASK, and other nutrient sensors, updating the limited knowledge on the role of PASK in the antioxidant response. We also comment on glucagon-like peptide 1 (GLP-1) and its collaboration with PASK in preventing the damage associated with hepatic oxidative stress. The current knowledge would suggest that PASK inhibition and/or exendin-4 treatment, especially under fasting conditions, could ameliorate disorders associated with excess oxidative stress.

Storage and Utilization of Glycogen by Mouse Liver during Adaptation to Nutritional Changes Are GLP-1 and PASK Dependent

Glucagon-like peptide 1 (GLP-1) and PAS kinase (PASK) control glucose and energy homeostasis according to nutritional status. Thus, both glucose availability and GLP-1 lead to hepatic glycogen synthesis or degradation. We used a murine model to discover whether PASK mediates the effect of exendin-4 (GLP-1 analogue) in the adaptation of hepatic glycogen metabolism to nutritional status. The results indicate that both exendin-4 and fasting block the Pask expression, and PASK deficiency disrupts the physiological levels of blood GLP1 and the expression of hepatic GLP1 receptors after fasting. Under a non-fasted state, exendin-4 treatment blocks AKT activation, whereby Glucokinase and Sterol Regulatory Element-Binding Protein-1c (Srebp1c) expressions were inhibited. Furthermore, the expression of certain lipogenic genes was impaired, while increasing Glucose Transporter 2 (GLUT2) and Glycogen Synthase (GYS). Moreover, exendin-4 treatment under fasted conditions avoided Glucose 6-Phosphatase (G6pase) expression, while maintaining high GYS and its activation state. These results lead to an abnormal glycogen accumulation in the liver under fasting, both in PASK-deficient mice and in exendin-4 treated wild-type mice. In short, exendin-4 and PASK both regulate glucose transport and glycogen storage, and some of the exendin-4 effects could therefore be due to the blocking of the Pask expression.

Gut Microbiota Regulates the Interaction between Diet and Genetics to Influence Glucose Tolerance

Background: Metabolic phenotypes are the result of an intricate interplay between multiple factors, including diet, genotype, and the gut microbiome. Per-Arnt-Sim (PAS) kinase is a nutrient-sensing serine/threonine kinase, whose absence (PASK^-/-) protects against triglyceride accumulation, insulin resistance, and weight gain on a high-fat diet; conditions that are associated with dysbiosis of the gut microbiome. Methods: Herein, we report the metabolic effects of the interplay of diet (high fat high sugar, HFHS), genotype (PASK^-/-), and microbiome (16S sequencing). Results: Microbiome analysis identified a diet-induced, genotype-independent forked shift, with two discrete clusters of HFHS mice having increased beta and decreased alpha diversity. A "lower" cluster contained elevated levels of Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria and Defferibacteres, and was associated with increased weight gain, glucose intolerance, triglyceride accumulation, and decreased claudin-1 expression. Genotypic effects were observed within the clusters, lower cluster PASK^-/- mice displayed increased weight gain and decreased triglyceride accumulation, whereas upper PASK^-/- were resistant to decreased claudin-1. Conclusions: These results confirm previous reports that PAS kinase deficiency can protect mice against the deleterious effects of diet, and they suggest that microbiome imbalances can override protection. In addition, these results support a healthy diet for beneficial microbiome maintenance and suggest microbial culprits associated with metabolic disease.

Response to Oxidative Burst-Induced Hypoxia Is Associated With Macrophage Inflammatory Profiles as Revealed by Cellular Genome-Wide Association

Background

In mammalian species, hypoxia is a prominent feature of inflammation. The role of hypoxia in regulating macrophage responses via alteration in metabolic pathways is well established. Recently, oxidative burst-induced hypoxia has been shown in murine macrophages after phagocytosis. Despite the available detailed information on the regulation of macrophage function at transcriptomic and epigenomic levels, the association of genetic polymorphism and macrophage function has been less explored. Previously, we have shown that host genetics controls approximately 80% of the variation in an oxidative burst as measured by nitric oxide (NO^-). Further studies revealed two clusters of transcription factors (hypoxia-related and inflammatory-related) are under the genetic control that shapes macrophages’ pro-inflammatory characteristics.

Material and Methods

In the current study, the association between 43,066 autosomal Single Nucleic Polymorphism (SNPs) and the ability of MDMs in production of NO^- in response to E. coli was evaluated in 58 Holstein cows. The positional candidate genes near significant SNPs were selected to perform functional analysis. In addition, the interaction between the positional candidate genes and differentially expressed genes from our previous study was investigated.

Results

Sixty SNPs on 22 chromosomes of the bovine genome were found to be significantly associated with NO^- production of macrophages. The functional genomic analysis showed a significant interaction between positional candidate genes and mitochondria-related differentially expressed genes from the previous study. Further examination showed 7 SNPs located in the vicinity of genes with roles in response to hypoxia, shaping approximately 73% of the observed individual variation in NO^- production by MDM. Regarding the normoxic condition of macrophage culture in this study, it was hypothesized that oxidative burst is responsible for causing hypoxia at the cellular level.

Conclusion

The results suggest that the genetic polymorphism via regulation of response to hypoxia is a candidate step that perhaps shapes macrophage functional characteristics in the pathway of phagocytosis leading to oxidative burst, hypoxia, cellular response to hypoxia and finally the pro-inflammatory responses. Since all cells in one individual carry the same alleles, the effect of genetic predisposition of sensitivity to hypoxia will likely be notable on the clinical outcome to a broad range of host-pathogen interactions.

Validation of PAS Kinase, a Regulator of Hepatic Fatty Acid and Triglyceride Synthesis, as a Therapeutic Target for Nonalcoholic Steatohepatitis

Hyperactivation of sterol regulatory element binding protein 1c (SREBP‐1c), which transcriptionally induces expression of enzymes responsible for de novo lipogenesis and triglyceride (TG) formation, is implicated in nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) pathogenesis. Posttranslational SREBP‐1c maturation and activation is stimulated by the protein per–arnt–sim kinase (PASK). PASK‐knockout mice are phenotypically normal on a conventional diet but exhibit decreased hypertriglyceridemia, insulin resistance, and hepatic steatosis on a high‐fat diet. We investigated the effects of pharmacologic PASK inhibition using BioE‐1115, a selective and potent oral PASK inhibitor, in Zucker fatty (fa)/fa) rats, a genetic model of obesity, dyslipidemia, and insulin resistance, and in a dietary murine model of NAFLD/NASH. Female Zucker (fa/fa) rats and lean littermate (fa/+) controls received BioE‐1115 (3‐100 mg/kg/day) and/or omega‐3 fatty acids, and blood glucose, hemoglobin A1c, glucose tolerance, insulin, and serum TG were measured. C57BL/6J mice fed a high‐fat/high‐fructose diet (HF‐HFrD) were treated with BioE‐1115 (100 mg/kg/day) or vehicle. Body weight and fasting glucose were measured regularly; serum TG, body and organ weights, and liver TG and histology were assessed at sacrifice. Messenger RNA (mRNA) abundance of SREBP‐1c target genes was measured in both models. In Zucker rats, BioE‐1115 treatment produced significant dose‐dependent reductions in blood glucose, insulin, and TG (all greater than omega‐3 fatty acids) and dose dependently restored insulin sensitivity assessed by glucose tolerance testing. In HF‐HFrD mice, BioE‐1115 reduced body weight, liver weight, fasting blood glucose, serum TGs, hepatic TG, hepatic fibrosis, hepatocyte vacuolization, and bile duct hyperplasia. BioE‐1115 reduced SREBP‐1c target mRNA transcripts in both models. Conclusion: PASK inhibition mitigates many adverse metabolic consequences associated with an HF‐HFrD and reduces hepatic fat content and fibrosis. This suggests that inhibition of PASK is an attractive therapeutic strategy for NAFLD/NASH treatment.

PAS kinase deficiency reduces aging effects in mice

Several signaling pathways may be affected during aging. All are regulated by nutrient levels leading to a decline in mitochondrial function and autophagy and to an increase in oxidative stress. PAS Domain Kinase (PASK) is a nutrient and bioenergetic sensor. We have previously found that PASK plays a role in the control of hepatic metabolic balance and mitochondrial homeostasis. To investigate PASK’s role in hepatic oxidative stress during aging, we analyzed the mitochondrial function, glucose tolerance, insulin resistance, and lipid-related parameters in aged PASK-deficient mice. Hepatic Pask mRNA decreased in step with aging, being undetectable in aged wild-type (WT) mice. Aged PASK-deficient mice recorded lower levels of ROS/RNS compared to aged WT. The regulators of mitochondrial biogenesis, PGC1a, SIRT1 and NRF2, decreased in aged WT, while aged PASK-deficient mice recorded a higher expression of NRF2, GCLm and HO1 proteins and CS activity under fasted conditions. Additionally, aged PASK-deficient mice recorded an overexpression of the longevity gene FoxO3a, and maintained elevated PCNA protein, suggesting that hepatic cell repair mechanisms might be functional. PASK-deficient mice have better insulin sensitivity and no glucose intolerance, as confirmed by a normal HOMA-IR index. PASK may be a good target for reducing damage during aging.

PSK1 coordinates glucose metabolism and utilization and regulates energy-metabolism oscillation in Saccharomyces cerevisiae

Energy-metabolism oscillations (EMO) are ultradian biological rhythms observed in in aerobic chemostat cultures of Saccharomyces cerevisiae. EMO regulates energy metabolism such as glucose, carbohydrate storage, O₂ uptake, and CO₂ production. PSK1 is a nutrient responsive protein kinase involved in regulation of glucose metabolism, sensory response to light, oxygen, and redox state. The aim of this investigation was to assess the function of PSK1 in regulation of EMO. The mRNA levels of PSK1 fluctuated in concert with EMO, and deletion of PSK1 resulted in unstable EMO with disappearance of the fluctuations and reduced amplitude, compared with the wild type. Furthermore, the mutant PSK1Δ showed downregulation of the synthesis and breakdown of glycogen with resultant decrease in glucose concentrations. The redox state represented by NADH also decreased in PSK1Δ compared with the wild type. These data suggest that PSK1 plays an important role in the regulation of energy metabolism and stabilizes ultradian biological rhythms. These results enhance our understanding of the mechanisms of biorhythms in the budding yeast.

PAS Kinase: A Nutrient and Energy Sensor "Master Key" in the Response to Fasting/Feeding Conditions

The protein kinase with PAS domains (PASK) is a nutrient and energy sensor located in the cells of multiple organs. Many of the recent findings for understanding PASK functions in mammals have been reported in studies involving PASK-deficient mice. This minireview summarizes the PASK role in the control of fasting and feeding responses, focusing especially on the hypothalamus and liver. In 2013, PASK was identified in the hypothalamic areas involved in feeding behavior, and its expression was regulated under fasting/refeeding conditions. Furthermore, it plays a role in coordinating the activation/inactivation of the hypothalamic energy sensors AMPK and mTOR/S6K1 pathways in response to fasting. On the other hand, PASK deficiency prevents the development of obesity and non-alcoholic fatty liver in mice fed with a high-fat diet. This protection is explained by the re-establishment of several high-fat diet metabolic alterations produced in the expression of hepatic transcription factors and key enzymes that control the main metabolic pathways involved in maintaining metabolic homeostasis in fasting/feeding responses. This minireview covers the effects of PASK inactivation in the expression of certain transcription factors and target enzymes in several metabolic pathways under situations such as fasting and feeding with either a standard or a high-fat diet.

The metabolic sensor PASK is a histone 3 kinase that also regulates H3K4 methylation by associating with H3K4 MLL2 methyltransferase complex

The metabolic sensor Per-Arnt-Sim (Pas) domain-containing serine/threonine kinase (PASK) is expressed predominantly in the cytoplasm of different cell types, although a small percentage is also expressed in the nucleus. Herein, we show that the nuclear PASK associates with the mammalian H3K4 MLL2 methyltransferase complex and enhances H3K4 di- and tri-methylation. We also show that PASK is a histone kinase that phosphorylates H3 at T3, T6, S10 and T11. Taken together, these results suggest that PASK regulates two different H3 tail modifications involving H3K4 methylation and H3 phosphorylation. Using muscle satellite cell differentiation and functional analysis after loss or gain of Pask expression using the CRISPR/Cas9 system, we provide evidence that some of the regulatory functions of PASK during development and differentiation may occur through the regulation of these histone modifications.

The pan-PIM inhibitor INCB053914 displays potent synergy in combination with ruxolitinib in models of MPN

Aberrant JAK2 tyrosine kinase signaling drives the development of Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia, and primary myelofibrosis. However, JAK2 kinase inhibitors have failed to significantly reduce allele burden in MPN patients, underscoring the need for improved therapeutic strategies. Members of the PIM family of serine/threonine kinases promote cellular proliferation by regulating a variety of cellular processes, including protein synthesis and the balance of signaling that regulates apoptosis. Overexpression of PIM family members is oncogenic, exemplified by their ability to induce lymphomas in collaboration with c-Myc. Thus, PIM kinases are potential therapeutic targets for several malignancies such as solid tumors and blood cancers. We and others have shown that PIM inhibitors augment the efficacy of JAK2 inhibitors by using in vitro models of MPNs. Here we report that the recently developed pan-PIM inhibitor INCB053914 augments the efficacy of the US Food and Drug Administration-approved JAK1/2 inhibitor ruxolitinib in both in vitro and in vivo MPN models. INCB053914 synergizes with ruxolitinib to inhibit cell growth in JAK2-driven MPN models and induce apoptosis. Significantly, low nanomolar INCB053914 enhances the efficacy of ruxolitinib to inhibit the neoplastic growth of primary MPN patient cells, and INCB053914 antagonizes ruxolitinib persistent myeloproliferation in vivo. These findings support the notion that INCB053914, which is currently in clinical trials in patients with advanced hematologic malignancies, in combination with ruxolitinib may be effective in MPN patients, and they support the clinical testing of this combination in MPN patients.

Discrepancy Between Low Levels of mTOR Activity and High Levels of P-S6 in Primary Central Nervous System Lymphoma May Be Explained by PAS Domain-Containing Serine/Threonine-Protein Kinase-Mediated Phosphorylation

The primary aim of this study was to determine mTOR-pathway activity in primary central nervous system lymphoma (PCNSL), which could be a potential target for therapy. After demonstrating that p-S6 positivity largely exceeded mTOR activity, we aimed to identify other pathways that may lead to S6 phosphorylation. We measured mTOR activity with immunohistochemistry for p-mTOR and its downstream effectors p(T389)-p70S6K1, p-S6, and p-4E-BP1 in 31 cases of PCNSL and 51 cases of systemic diffuse large B-cell lymphoma (DLBCL) and evaluated alternative S6 phosphorylation pathways with p-RSK, p(T229)-p70S6K1, and PASK antibodies. Finally, we examined the impact of PASK inhibition on S6 phosphorylation on BHD1 cell line. mTOR-pathway activity was significantly less frequent in PCNSL compared with DLBCL. p-S6 positivity was related to mTOR-pathway in DLBCL, but not in PCNSL. Among the other kinases potentially responsible for S6 phosphorylation, PASK proved to be positive in all cases of PCNSL and DLBCL. Inhibition of PASK resulted in reduced expression of p-S6 in BHD1-cells. This is the first study demonstrating an mTOR independent p-S6 activity in PCNSL and that PASK may contribute to the phosphorylation of S6. Our findings also suggest a potential role of PASK in the pathomechanism of PCNSL and in DLBCL.

The Regulation of Cbf1 by PAS Kinase Is a Pivotal Control Point for Lipogenesis vs. Respiration in Saccharomyces cerevisiae

PAS kinase 1 (Psk1) is a key regulator of respiration in Saccharomyces cerevisiae. Herein the molecular mechanisms of this regulation are explored through the characterization of its substrate, Centromere binding factor 1 (Cbf1). CBF1-deficient yeast displayed a significant decrease in cellular respiration, while PAS kinase-deficient yeast, or yeast harboring a Cbf1 phosphosite mutant (T211A) displayed a significant increase. Transmission electron micrographs showed an increased number of mitochondria in PAS kinase-deficient yeast consistent with the increase in respiration. Although the CBF1-deficient yeast did not appear to have an altered number of mitochondria, a mitochondrial proteomics study revealed significant differences in the mitochondrial composition of CBF1-deficient yeast including altered Atp3 levels, a subunit of the mitochondrial F₁-ATP synthase complex. Both beta-galactosidase reporter assays and western blot analysis confirmed direct transcriptional control of ATP3 by Cbf1. In addition, we confirmed the regulation of yeast lipid genes LAC1 and LAG1 by Cbf1. The human homolog of Cbf1, Upstream transcription factor 1 (USF1), is also known to be involved in lipid biogenesis. Herein, we provide the first evidence for a role of USF1 in respiration since it appeared to complement Cbf1in vivo as determined by respiration phenotypes. In addition, we confirmed USF1 as a substrate of human PAS kinase (hPASK) in vitro. Combined, our data supports a model in which Cbf1/USF1 functions to partition glucose toward respiration and away from lipid biogenesis, while PAS kinase inhibits respiration in part through the inhibition of Cbf1/USF1.

Per-Arnt-Sim Kinase (PASK) Deficiency Increases Cellular Respiration on a Standard Diet and Decreases Liver Triglyceride Accumulation on a Western High-Fat High-Sugar Diet

Diabetes and the related disease metabolic syndrome are epidemic in the United States, in part due to a shift in diet and decrease in physical exercise. PAS kinase is a sensory protein kinase associated with many of the phenotypes of these diseases, including hepatic triglyceride accumulation and metabolic dysregulation in male mice placed on a high-fat diet. Herein we provide the first characterization of the effects of western diet (high-fat high-sugar, HFHS) on Per-Arnt-Sim kinase mice (PASK^−/−) and the first characterization of both male and female PASK^−/− mice. Soleus muscle from the PASK^−/− male mice displayed a 2-fold higher oxidative phosphorylation capacity than wild type (WT) on the normal chow diet. PASK^−/− male mice were also resistant to hepatic triglyceride accumulation on the HFHS diet, displaying a 2.7-fold reduction in hepatic triglycerides compared to WT mice on the HFHS diet. These effects on male hepatic triglyceride were further explored through mass spectrometry-based lipidomics. The absence of PAS kinase was found to affect many of the 44 triglycerides analyzed, preventing hepatic triglyceride accumulation in response to the HFHS diet. In contrast, the female mice showed resistance to hepatic triglyceride accumulation on the HFHS diet regardless of genotype, suggesting the effects of PAS kinase may be masked.

Pas Kinase Deficiency Triggers Antioxidant Mechanisms in the Liver

Metabolic dysfunction in the liver is the cause of numerous pathologies, which are associated with an altered redox state. PASK (PAS Domain Kinase) is a nutrient and bioenergetic sensor. We contend that PASK could act as an oxidative stress sensor in liver and/or control the metabolic balance, playing a role in the mitochondrial homeostasis. Using PASK-deficient mice, we observed that PASK deficiency promotes antioxidant response mechanisms: a lower production of ROS/RNS under non-fasting conditions, overexpression of genes coding to ROS-detoxifying enzymes and mitochondrial fusion proteins (MnSod Gpx, Mfn1 and Opa1), coactivator Ppargc1a, transcription factors (Pparg and FoxO3a) and deacetylase Sirt1. Also, under fasting conditions, PASK deficiency induced the overexpression of Ppargc1a, Ppara, Pparg, FoxO3a and Nrf2 leading to the overexpression of genes coding to antioxidant enzymes such as MnSOD, Cu/ZnSOD, GPx, HO1 and GCLm. Additionally, inducing PINK1 involved in cell survival and mitophagy. These changes kept ROS steady levels and improved the regenerative state. We suggest a new role for PASK as a controller of oxidative stress and mitochondrial dynamics in the liver. In fact, antioxidant response is PASK dependent. PASK-targeting could therefore be a good way of reducing the oxidative stress in order to prevent or treat liver diseases.

PAS Kinase deficiency alters the glucokinase function and hepatic metabolism

The liver controls metabolic homeostasis in response to fasting and refeeding periods. Glucokinase (GCK) adjusts hepatic glucose phosphorylation to blood glucose levels, acting as a glucose sensor. Our objective was to determine whether PAS kinase (PASK), a nutrient sensor, could be affecting the expression or activity of liver GCK and the response to fasting and refeeding states of key hepatic metabolic pathways. PASK-deficient mice have impaired insulin signaling (AKT overactivation). Furthermore, PASK deficiency modified the expression of several transcription factors involved in the adjustment to fasting and refeeding. Foxo1 decreased under fasting conditions, while Ppara and Pparg were overexpressed in PASK-deficient mice. However, PEPCK protein levels were similar or higher, while the expression of Cpt1a decreased in PASK-deficient mice. By contrast, Lxra and Chrebp were overexpressed after refeeding, while the expression of Acc and Fas decreased in PASK-deficient mice. Likewise, with a decreased expression of Gck and increased nuclear location of the complex GCK-GCKR, GCK activity decreased in PASK-deficient mice. Therefore, PASK regulated some of the genes and proteins responsible for glucose sensing, such as glucokinase, and for insulin signalling, affecting glucose and lipid metabolism and consequently certain critical hepatic functions.

Genetic Architecture of Natural Variation Underlying Adult Foraging Behavior That Is Essential for Survival of Drosophila melanogaster

Foraging behavior is critical for the fitness of individuals. However, the genetic basis of variation in foraging behavior and the evolutionary forces underlying such natural variation have rarely been investigated. We developed a systematic approach to assay the variation in survival rate in a foraging environment for adult flies derived from a wild Drosophila melanogaster population. Despite being such an essential trait, there is substantial variation of foraging behavior among D. melanogaster strains. Importantly, we provided the first evaluation of the potential caveats of using inbred Drosophila strains to perform genome-wide association studies on life-history traits, and concluded that inbreeding depression is unlikely a major contributor for the observed large variation in adult foraging behavior. We found that adult foraging behavior has a strong genetic component and, unlike larval foraging behavior, depends on multiple loci. Identified candidate genes are enriched in those with high expression in adult heads and, demonstrated by expression knock down assay, are involved in maintaining normal functions of the nervous system. Our study not only identified candidate genes for foraging behavior that is relevant to individual fitness, but also shed light on the initial stage underlying the evolution of the behavior.

Pask integrates hormonal signaling with histone modification via Wdr5 phosphorylation to drive myogenesis

PAS domain containing protein kinase (Pask) is an evolutionarily conserved protein kinase implicated in energy homeostasis and metabolic regulation across eukaryotic species. We now describe an unexpected role of Pask in promoting the differentiation of myogenic progenitor cells, embryonic stem cells and adipogenic progenitor cells. This function of Pask is dependent upon its ability to phosphorylate Wdr5, a member of several protein complexes including those that catalyze histone H3 Lysine 4 trimethylation (H3K4me3) during transcriptional activation. Our findings suggest that, during myoblast differentiation, Pask stimulates the conversion of repressive H3K4me1 to activating H3K4me3 marks on the promoter of the differentiation gene myogenin (Myog) via Wdr5 phosphorylation. This enhances accessibility of the MyoD transcription factor and enables transcriptional activation of the Myog promoter to initiate muscle differentiation. Thus, as an upstream kinase of Wdr5, Pask integrates signaling cues with the transcriptional network to regulate the differentiation of progenitor cells.

DOI:http://dx.doi.org/10.7554/eLife.17985.001

Cell type-specific deletion in mice reveals roles for PAS kinase in insulin and glucagon production

AIMS/HYPOTHESIS

Per-Arnt-Sim kinase (PASK) is a nutrient-regulated domain-containing protein kinase previously implicated in the control of insulin gene expression and glucagon secretion. Here, we explore the roles of PASK in the control of islet hormone release, by generating mice with selective deletion of the Pask gene in pancreatic beta or alpha cells.

METHODS

Floxed alleles of Pask were produced by homologous recombination and animals bred with mice bearing beta (Ins1 (Cre); PaskBKO) or alpha (Ppg (Cre) [also known as Gcg]; PaskAKO) cell-selective Cre recombinase alleles. Glucose homeostasis and hormone secretion in vivo and in vitro, gene expression and islet cell mass were measured using standard techniques.

RESULTS

Ins1 (Cre)-based recombination led to efficient beta cell-targeted deletion of Pask. Beta cell mass was reduced by 36.5% (p < 0.05) compared with controls in PaskBKO mice, as well as in global Pask-null mice (38%, p < 0.05). PaskBKO mice displayed normal body weight and fasting glycaemia, but slightly impaired glucose tolerance, and beta cell proliferation, after maintenance on a high-fat diet. Whilst glucose tolerance was unaffected in PaskAKO mice, glucose infusion rates were increased, and glucagon secretion tended to be lower, during hypoglycaemic clamps. Although alpha cell mass was increased (21.9%, p < 0.05), glucagon release at low glucose was impaired (p < 0.05) in PaskAKO islets.

CONCLUSIONS/INTERPRETATION

The findings demonstrate cell-autonomous roles for PASK in the control of pancreatic endocrine hormone secretion. Differences between the glycaemic phenotype of global vs cell type-specific null mice suggest important roles for tissue interactions in the control of glycaemia by PASK.

AMPK in Yeast: The SNF1 (Sucrose Non-fermenting 1) Protein Kinase Complex

In yeast, SNF1 protein kinase is the orthologue of mammalian AMPK complex. It is a trimeric complex composed of Snf1 protein kinase (orthologue of AMPKα catalytic subunit), Snf4 (orthologue of AMPKγ regulatory subunit), and a member of the Gal83/Sip1/Sip2 family of proteins (orthologues of AMPKβ subunit) that act as scaffolds and also regulate the subcellular localization of the complex. In this chapter, we review the recent literature on the characteristics of SNF1 complex subunits, the structure and regulation of the activity of the SNF1 complex, its role at the level of transcriptional regulation of relevant target genes and also at the level of posttranslational modification of targeted substrates. We also review the crosstalk of SNF1 complex activity with other key protein kinase pathways such as cAMP-PKA, TORC1, and PAS kinase.

Nuciferine downregulates Per-Arnt-Sim kinase expression during its alleviation of lipogenesis and inflammation on oleic acid-induced hepatic steatosis in HepG2 cells

Non-alcoholic fatty liver disease (NAFLD) is a prevalent liver disease associated with lipotoxicity, lipid peroxidation, oxidative stress, and inflammation. Nuciferine, an active ingredient extracted from the natural lotus leaf, has been reported to be effective for the prevention and treatment of NAFLD. Per-Arnt-Sim kinase (PASK) is a nutrient responsive protein kinase that regulates lipid and glucose metabolism, mitochondrial respiration, and gene expression. The aim of the present study was to investigate the protective effect of nuciferine against NAFLD and its inhibitory effect on PASK, exploring the possible underlying mechanism of nuciferine-mediated inhibition on NAFLD. Relevant biochemical parameters (lipid accumulation, extent of oxidative stress and release of inflammation cytokines) in oleic acid (OA)-induced HepG₂ cells that mimicked steatosis in vitro were measured and compared with the control. It was found that nuciferine and silenced-PASK (siRNA PASK) both inhibited triglyceride (TG) accumulation and was effective in decreasing fatty acid (FFAs). The content of total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) were increased respectively by nuciferine and siRNA PASK without increase in glutathione (GSH). Malondialdehyde (MDA) was decreased respectively by nuciferine and siRNA PASK. In addition, nuciferine decreased TNF-a, IL-6 and IL-8 as well as the siRNA PASK group. IL-10 was increased by nuciferine and siRNA PASK respectively. Further investigation revealed that nuciferine and siRNA PASK could respectively regulate the expression of target genes involved in lipogenesis and inflammation, suggesting that nuciferine may be a potential therapeutic treatment for NAFLD. Furthermore, the modulated effect of nuciferine on (OA)-induced HepG₂ cells lipogenesis and inflammation, which was accompanied with PASK inhibition, was also consistent with siRNA PASK, implying that PASK might play a role in nuciferine-mediated regulation on NAFLD.

Per-Arnt-Sim Kinase (PASK): An Emerging Regulator of Mammalian Glucose and Lipid Metabolism

Per-Arnt-Sim Kinase (PASK) is an evolutionarily-conserved nutrient-responsive protein kinase that regulates lipid and glucose metabolism, mitochondrial respiration, phosphorylation, and gene expression. Recent data suggests that mammalian PAS kinase is involved in glucose metabolism and acts on pancreatic islet α/β cells and glycogen synthase (GS), affecting insulin secretion and blood glucose levels. In addition, PASK knockout mice (PASK-/-) are protected from obesity, liver triglyceride accumulation, and insulin resistance when fed a high-fat diet, implying that PASK may be a new target for metabolic syndrome (MetS) treatment as well as the cellular nutrients and energy sensors—adenosine monophosphate (AMP)-activated protein kinase (AMPK) and the targets of rapamycin (m-TOR). In this review, we will briefly summarize the regulation of PASK on mammalian glucose and lipid metabolism and its possible mechanism, and further explore the potential targets for MetS therapy.

Targeting SREBPs for treatment of the metabolic syndrome

Over the past few decades, mortality resulting from cardiovascular disease (CVD) steadily decreased in western countries; however, in recent years, the decline has become offset by the increase in obesity. Obesity is strongly associated with the metabolic syndrome and its atherogenic dyslipidemia resulting from insulin resistance. While lifestyle treatment would be effective, drugs targeting individual risk factors are often required. Such treatment may result in polypharmacy. Novel approaches are directed towards the treatment of several risk factors with one drug. Studies in animal models and humans suggest a central role for sterol regulatory-element binding proteins (SREBPs) in the pathophysiology of the metabolic syndrome. Four recent studies targeting the maturation or transcriptional activities of SREBPs provide proof of concept for the efficacy of SREBP inhibition in this syndrome.

PAS kinase is activated by direct SNF1-dependent phosphorylation and mediates inhibition of TORC1 through the phosphorylation and activation of Pbp1

We describe the interplay between three sensory protein kinases in yeast: AMP-regulated kinase (AMPK, or SNF1 in yeast), PAS kinase 1 (Psk1 in yeast), and the target of rapamycin complex 1 (TORC1). This signaling cascade occurs through the SNF1-dependent phosphorylation and activation of Psk1, which phosphorylates and activates poly(A)- binding protein binding protein 1 (Pbp1), which then inhibits TORC1 through sequestration at stress granules. The SNF1-dependent phosphorylation of Psk1 appears to be direct, in that Snf1 is necessary and sufficient for Psk1 activation by alternate carbon sources, is required for altered Psk1 protein mobility, is able to phosphorylate Psk1 in vitro, and binds Psk1 via its substrate-targeting subunit Gal83. Evidence for the direct phosphorylation and activation of Pbp1 by Psk1 is also provided by in vitro and in vivo kinase assays, including the reduction of Pbp1 localization at distinct cytoplasmic foci and subsequent rescue of TORC1 inhibition in PAS kinase-deficient yeast. In support of this signaling cascade, Snf1-deficient cells display increased TORC1 activity, whereas cells containing hyperactive Snf1 display a PAS kinase-dependent decrease in TORC1 activity. This interplay between yeast SNF1, Psk1, and TORC1 allows for proper glucose allocation during nutrient depletion, reducing cell growth and proliferation when energy is low.

Chromosomal instability causes sensitivity to metabolic stress

Chromosomal INstability (CIN), a hallmark of cancer, refers to cells with an increased rate of gain or loss of whole chromosomes or chromosome parts. CIN is linked to the progression of tumors with poor clinical outcomes such as drug resistance. CIN can give tumors the diversity to resist therapy, but it comes at the cost of significant stress to tumor cells. To tolerate this, cancer cells must modify their energy use to provide adaptation against genetic changes as well as to promote their survival and growth. In this study, we have demonstrated that CIN induction causes sensitivity to metabolic stress. We show that mild metabolic disruption that does not affect normal cells, can lead to high levels of oxidative stress and subsequent cell death in CIN cells because they are already managing elevated stress levels. Altered metabolism is a differential characteristic of cancer cells, so our identification of key regulators that can exploit these changes to cause cell death may provide cancer-specific potential drug targets, especially for advanced cancers that exhibit CIN.

PAS kinase drives lipogenesis through SREBP-1 maturation

Elevated hepatic synthesis of fatty acids and triglycerides, driven by hyperactivation of the SREBP-1c transcription factor, has been implicated as a causal feature of metabolic syndrome. SREBP-1c activation requires the proteolytic maturation of the endoplasmic-reticulum-bound precursor to the active, nuclear transcription factor, which is stimulated by feeding and insulin signaling. Here, we show that feeding and insulin stimulate the hepatic expression of PASK. We also demonstrate, using genetic and pharmacological approaches, that PASK is required for the proteolytic maturation of SREBP-1c in cultured cells and in the mouse and rat liver. Inhibition of PASK improves lipid and glucose metabolism in dietary animal models of obesity and dyslipidemia. Administration of a PASK inhibitor decreases hepatic expression of lipogenic SREBP-1c target genes, decreases serum triglycerides, and partially reverses insulin resistance. While the signaling network that controls SREBP-1c activation is complex, we propose that PASK is an important component with therapeutic potential.

A comprehensive protein-protein interactome for yeast PAS kinase 1 reveals direct inhibition of respiration through the phosphorylation of Cbf1

PAS kinase is a conserved sensory protein kinase required for glucose homeostasis. The interactome for yeast PAS kinase 1 (Psk1) is identified, revealing 93 binding partners. Evidence is provided for in vivo phosphorylation of Cbf1 and subsequent inhibition of respiration, supporting a role for Psk1 in partitioning glucose for cell growth.

Per-Arnt-Sim (PAS) kinase is a sensory protein kinase required for glucose homeostasis in yeast, mice, and humans, yet little is known about the molecular mechanisms of its function. Using both yeast two-hybrid and copurification approaches, we identified the protein–protein interactome for yeast PAS kinase 1 (Psk1), revealing 93 novel putative protein binding partners. Several of the Psk1 binding partners expand the role of PAS kinase in glucose homeostasis, including new pathways involved in mitochondrial metabolism. In addition, the interactome suggests novel roles for PAS kinase in cell growth (gene/protein expression, replication/cell division, and protein modification and degradation), vacuole function, and stress tolerance. In vitro kinase studies using a subset of 25 of these binding partners identified Mot3, Zds1, Utr1, and Cbf1 as substrates. Further evidence is provided for the in vivo phosphorylation of Cbf1 at T211/T212 and for the subsequent inhibition of respiration. This respiratory role of PAS kinase is consistent with the reported hypermetabolism of PAS kinase–deficient mice, identifying a possible molecular mechanism and solidifying the evolutionary importance of PAS kinase in the regulation of glucose homeostasis.

PAS kinase is a nutrient and energy sensor in hypothalamic areas required for the normal function of AMPK and mTOR/S6K1

The complications caused by overweight, obesity and type 2 diabetes are one of the main problems that increase morbidity and mortality in developed countries. Hypothalamic metabolic sensors play an important role in the control of feeding and energy homeostasis. PAS kinase (PASK) is a nutrient sensor proposed as a regulator of glucose metabolism and cellular energy. The role of PASK might be similar to other known metabolic sensors, such as AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR). PASK-deficient mice resist diet-induced obesity. We have recently reported that AMPK and mTOR/S6K1 pathways are regulated in the ventromedial and lateral hypothalamus in response to nutritional states, being modulated by anorexigenic glucagon-like peptide-1 (GLP-1)/exendin-4 in lean and obese rats. We identified PASK in hypothalamic areas, and its expression was regulated under fasting/re-feeding conditions and modulated by exendin-4. Furthermore, PASK-deficient mice have an impaired activation response of AMPK and mTOR/S6K1 pathways. Thus, hypothalamic AMPK and S6K1 were highly activated under fasted/re-fed conditions. Additionally, in this study, we have observed that the exendin-4 regulatory effect in the activity of metabolic sensors was lost in PASK-deficient mice, and the anorexigenic properties of exendin-4 were significantly reduced, suggesting that PASK could be a mediator in the GLP-1 signalling pathway. Our data indicated that the PASK function could be critical for preserving the nutrient effect on AMPK and mTOR/S6K1 pathways and maintain the regulatory role of exendin-4 in food intake. Some of the antidiabetogenic effects of exendin-4 might be modulated through these processes.

PAS kinase: a nutrient sensing regulator of glucose homeostasis

Per-Arnt-Sim (PAS) kinase (PASK, PASKIN, and PSK) is a member of the group of nutrient sensing protein kinases. These protein kinases sense the energy or nutrient status of the cell and regulate cellular metabolism appropriately. PAS kinase responds to glucose availability and regulates glucose homeostasis in yeast, mice, and man. Despite this pivotal role, the molecular mechanisms of PAS kinase regulation and function are largely unknown. This review focuses on what is known about PAS kinase, including its conservation from yeast to man, identified substrates, associated phenotypes and role in metabolic disease.

Per-Arnt-Sim kinase regulates pancreatic duodenal homeobox-1 protein stability via phosphorylation of glycogen synthase kinase 3β in pancreatic β-cells

In pancreatic β-cells, glucose induces the binding of the transcription factor pancreatic duodenal homeobox-1 (PDX-1) to the insulin gene promoter to activate insulin gene transcription. At low glucose levels, glycogen synthase kinase 3β (GSK3β) is known to phosphorylate PDX-1 on C-terminal serine residues, which triggers PDX-1 proteasomal degradation. We previously showed that the serine/threonine Per-Arnt-Sim domain-containing kinase (PASK) regulates insulin gene transcription via PDX-1. However, the mechanisms underlying this regulation are unknown. In this study, we aimed to identify the role of PASK in the regulation of PDX-1 phosphorylation, protein expression, and stability in insulin-secreting cells and isolated rodent islets of Langerhans. We observed that glucose induces a decrease in overall PDX-1 serine phosphorylation and that overexpression of WT PASK mimics this effect. In vitro, PASK directly phosphorylates GSK3β on its inactivating phosphorylation site Ser(9). Overexpression of a kinase-dead (KD), dominant negative version of PASK blocks glucose-induced Ser(9) phosphorylation of GSK3β. Accordingly, GSK3β Ser(9) phosphorylation is reduced in islets from pask-null mice. Overexpression of WT PASK or KD GSK3β protects PDX-1 from degradation and results in increased PDX-1 protein abundance. Conversely, overexpression of KD PASK blocks glucose-induction of PDX-1 protein. We conclude that PASK phosphorylates and inactivates GSK3β, thereby preventing PDX-1 serine phosphorylation and alleviating GSK3β-mediated PDX-1 protein degradation in pancreatic β-cells.

PAS kinase as a nutrient sensor in neuroblastoma and hypothalamic cells required for the normal expression and activity of other cellular nutrient and energy sensors

PAS kinase (PASK) is a nutrient sensor that is highly conserved throughout evolution. PASK-deficient mice reveal a metabolic phenotype similar to that described in S6 kinase-1 S6K1-deficient mice that are protected against obesity. Hypothalamic metabolic sensors, such as AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR), play an important role in feeding behavior, the homeostasis of body weight, and energy balance. These sensors respond to changes in nutrient levels in the hypothalamic areas involved in feeding behavior and in neuroblastoma N2A cells, and we have recently reported that those effects are modulated by the anorexigenic peptide glucagon-like peptide-1 (GLP-1). Here, we identified PASK in both N2A cells and rat VMH and LH areas and found that its expression is regulated by glucose and GLP-1. High levels of glucose decreased Pask gene expression. Furthermore, PASK-silenced N2A cells record an impaired response by the AMPK and mTOR/S6K1 pathways to changes in glucose levels. Likewise, GLP-1 effect on the activity of AMPK, S6K1, and other intermediaries of both pathways and the regulatory role at the level of gene expression were also blocked in PASK-silenced cells. The absence of response to low glucose concentrations in PASK-silenced cells correlates with increased ATP content, low expression of mRNA coding for AMPK upstream kinase LKB1, and enhanced activation of S6K1. Our findings indicate that, at least in N2A cells, PASK is a key kinase in GLP-1 actions and exerts a coordinated response with the other metabolic sensors, suggesting that PASK might play an important role in feeding behavior.

Interleukin-1β regulates fat-liver crosstalk in obesity by auto-paracrine modulation of adipose tissue inflammation and expandability

The inflammasome has been recently implicated in obesity-associated dys-metabolism. However, of its products, the specific role of IL-1β was clinically demonstrated to mediate only the pancreatic beta-cell demise, and in mice mainly the intra-hepatic manifestations of obesity. Yet, it remains largely unknown if IL-1β, a cytokine believed to mainly function locally, could regulate dysfunctional inter-organ crosstalk in obesity. Here we show that High-fat-fed (HFF) mice exhibited a preferential increase of IL-1β in portal compared to systemic blood. Moreover, portally-drained mesenteric fat transplantation from IL-1βKO donors resulted in lower pyruvate-glucose flux compared to mice receiving wild-type (WT) transplant. These results raised a putative endocrine function for visceral fat-derived IL-1β in regulating hepatic gluconeogenic flux. IL-1βKO mice on HFF exhibited only a minor or no increase in adipose expression of pro-inflammatory genes (including macrophage M1 markers), Mac2-positive crown-like structures and CD11b-F4/80-double-positive macrophages, all of which were markedly increased in WT-HFF mice. Further consistent with autocrine/paracrine functions of IL-1β within adipose tissue, adipose tissue macrophage lipid content was increased in WT-HFF mice, but significantly less in IL-1βKO mice. Ex-vivo, adipose explants co-cultured with primary hepatocytes from WT or IL-1-receptor (IL-1RI)-KO mice suggested only a minor direct effect of adipose-derived IL-1β on hepatocyte insulin resistance. Importantly, although IL-1βKOs gained weight similarly to WT-HFF, they had larger fat depots with similar degree of adipocyte hypertrophy. Furthermore, adipogenesis genes and markers (pparg, cepba, fabp4, glut4) that were decreased by HFF in WT, were paradoxically elevated in IL-1βKO-HFF mice. These local alterations in adipose tissue inflammation and expansion correlated with a lower liver size, less hepatic steatosis, and preserved insulin sensitivity. Collectively, we demonstrate that by promoting adipose inflammation and limiting fat tissue expandability, IL-1β supports ectopic fat accumulation in hepatocytes and adipose-tissue macrophages, contributing to impaired fat-liver crosstalk in nutritional obesity.

Science Signaling Podcast: 31 January 2012

Signaling through PAS kinases bypasses the pro-growth requirement of Tor2 in yeast.

PAS kinase promotes cell survival and growth through activation of Rho1

In Saccharomyces cerevisiae, phosphorylation of Ugp1 by either of the yeast PASK family protein kinases (yPASK), Psk1 or Psk2, directs this metabolic enzyme to deliver glucose to the periphery for synthesis of the cell wall. However, we isolated PSK1 and PSK2 in a high-copy suppressor screen of a temperature-sensitive mutant of target of rapamycin 2 (TOR2). Posttranslational activation of yPASK, either by cell integrity stress or by growth on nonfermentative carbon sources, also suppressed the growth defect resulting from tor2 mutation. Although suppression of the tor2 mutant growth phenotype by activation of the kinase activity of yPASK required phosphorylation of the metabolic enzyme Ugp1 on serine 11, this resulted in the formation of a complex that induced Rho1 activation, rather than required the glucose partitioning function of Ugp1. In addition to phosphorylated Ugp1, this complex contained Rom2, a Rho1 guanine nucleotide exchange factor, and Ssd1, an mRNA-binding protein. Activation of yPASK-dependent Ugp1 phosphorylation, therefore, enables two processes that are required for cell growth and stress resistance: synthesis of the cell wall through partitioning glucose to the periphery and the formation of the signaling complex with Rom2 and Ssd1 to promote Rho1-dependent polarized cell growth. This complex may integrate metabolic and signaling responses required for cell growth and survival in suboptimal conditions.

PAS kinase: integrating nutrient sensing with nutrient partitioning

Recent data suggests that PAS kinase acts as a signal integrator to adjust metabolic behavior in response to nutrient conditions. Specifically, PAS kinase controls the partitioning of nutrient resources between the myriad of possible fates. In this capacity, PAS kinase elicits a pro-growth program, which includes both signaling and metabolic control, both in yeast and in mammals. We propose that, like other kinases possessing these properties-AMPK and TOR, PAS kinase might be target for therapy of diabetes, obesity and cancer.

Human mutation within Per-Arnt-Sim (PAS) domain-containing protein kinase (PASK) causes basal insulin hypersecretion

PAS kinase (PASK) is a glucose-regulated protein kinase involved in the control of pancreatic islet hormone release and insulin sensitivity. We aimed here to identify mutations in the PASK gene that may be associated with young-onset diabetes in humans. We screened 18 diabetic probands with unelucidated maturity-onset diabetes of the young (MODY). We identified two rare nonsynonymous mutations in the PASK gene (p.L1051V and p.G1117E), each of which was found in a single MODY family. Wild type or mutant PASKs were expressed in HEK 293 cells. Kinase activity of the affinity-purified proteins was assayed as autophosphorylation at amino acid Thr307 or against an Ugp1p-derived peptide. Whereas the PASK p.G1117E mutant displayed a ∼25% increase with respect to wild type PASK in the extent of autophosphorylation, and a ∼2-fold increase in kinase activity toward exogenous substrates, the activity of the p.L1051V mutant was unchanged. Amino acid Gly1117 is located in an α helical region opposing the active site of PASK and may elicit either: (a) a conformational change that increases catalytic efficiency or (b) a diminished inhibitory interaction with the PAS domain. Mouse islets were therefore infected with adenoviruses expressing wild type or mutant PASK and the regulation of insulin secretion was examined. PASK p.G1117E-infected islets displayed a 4-fold decrease in glucose-stimulated (16.7 versus 3 mM) insulin secretion, chiefly reflecting a 4.5-fold increase in insulin release at low glucose. In summary, we have characterized a rare mutation (p.G1117E) in the PASK gene from a young-onset diabetes family, which modulates glucose-stimulated insulin secretion.

Gene expression profiling in the Cynomolgus macaque Macaca fascicularis shows variation within the normal birth range

Background

Although an adverse early-life environment has been linked to an increased risk of developing the metabolic syndrome, the molecular mechanisms underlying altered disease susceptibility as well as their relevance to humans are largely unknown. Importantly, emerging evidence suggests that these effects operate within the normal range of birth weights and involve mechanisms of developmental palsticity rather than pathology.

Method

To explore this further, we utilised a non-human primate model Macaca fascicularis (Cynomolgus macaque) which shares with humans the same progressive history of the metabolic syndrome. Using microarray we compared tissues from neonates in the average birth weight (50-75^th centile) to those of lower birth weight (5-25^th centile) and studied the effect of different growth trajectories within the normal range on gene expression levels in the umbilical cord, neonatal liver and skeletal muscle.

Results

We identified 1973 genes which were differentially expressed in the three tissue types between average and low birth weight animals (P < 0.05). Gene ontology analysis identified that these genes were involved in metabolic processes including cellular lipid metabolism, cellular biosynthesis, cellular macromolecule synthesis, cellular nitrogen metabolism, cellular carbohydrate metabolism, cellular catabolism, nucleotide and nucleic acid metabolism, regulation of molecular functions, biological adhesion and development.

Conclusion

These differences in gene expression levels between animals in the upper and lower percentiles of the normal birth weight range may point towards early life metabolic adaptations that in later life result in differences in disease risk.

Substrate preference and phosphatidylinositol monophosphate inhibition of the catalytic domain of the Per-Arnt-Sim domain kinase PASKIN

The Per-Arnt-Sim (PAS) domain serine/threonine kinase PASKIN, or PAS kinase, links energy flux and protein synthesis in yeast, regulates glycogen synthesis and protein translation in mammals, and might be involved in insulin regulation in the pancreas. According to the current model, binding of a putative ligand to the PAS domain disinhibits the kinase domain, leading to PASKIN autophosphorylation and increased kinase activity. To date, only synthetic but no endogenous PASKIN ligands have been reported. In the present study, we identified a number of novel PASKIN kinase targets, including ribosomal protein S6. Together with our previous identification of eukaryotic elongation factor 1A1, this suggests a role for PASKIN in the regulation of mammalian protein translation. When searching for endogenous PASKIN ligands, we found that various phospholipids can bind PASKIN and stimulate its autophosphorylation. Interestingly, the strongest binding and autophosphorylation was achieved with monophosphorylated phosphatidylinositols. However, stimulated PASKIN autophosphorylation did not correlate with ribosomal protein S6 and eukaryotic elongation factor 1A1 target phosphorylation. Although autophosphorylation was enhanced by monophosphorylated phosphatidylinositols, di- and tri-phosphorylated phosphatidylinositols inhibited autophosphorylation. By contrast, target phosphorylation was always inhibited, with the highest efficiency for di- and tri-phosphorylated phosphatidylinositols. Because phosphatidylinositol monophosphates were found to interact with the kinase rather than with the PAS domain, these data suggest a multiligand regulation of PASKIN activity, including a still unknown PAS domain binding/activating ligand and kinase domain binding modulatory phosphatidylinositol phosphates.

Per-arnt-sim (PAS) domain kinase (PASK) as a regulator of glucagon secretion

The physiological and pathophysiological regulation of glucagon secretion from pancreatic alpha cells remains a hotly debated topic. The mechanism(s) contributing to the glucose sensitivity of glucagon release and its impaired regulation in diabetes remain unclear. A paper in the current issue of Diabetologia by da Silva Xavier and colleagues (doi: 10.1007/s00125-010-2010-7 ) provides intriguing new insight into a metabolic sensing pathway mediated by the per-arnt-sim (PAS) domain kinase (PASK) that may contribute to both the paracrine and the intrinsic glucose regulation of alpha cells. Importantly, the authors show that PASK is decreased in islets from patients with type 2 diabetes, providing a potential mechanism for impaired suppression of glucagon by hyperglycaemia in this disease. Much work remains to be done to determine the exact role and mechanism of PASK in alpha and beta cells. Nevertheless, the present work introduces a new player in the metabolic regulation of glucagon secretion.

Per-arnt-sim (PAS) domain-containing protein kinase is downregulated in human islets in type 2 diabetes and regulates glucagon secretion

AIMS/HYPOTHESIS

We assessed whether per-arnt-sim (PAS) domain-containing protein kinase (PASK) is involved in the regulation of glucagon secretion.

METHODS

mRNA levels were measured in islets by quantitative PCR and in pancreatic beta cells obtained by laser capture microdissection. Glucose tolerance, plasma hormone levels and islet hormone secretion were analysed in C57BL/6 Pask homozygote knockout mice (Pask-/-) and control littermates. Alpha-TC1-9 cells, human islets or cultured E13.5 rat pancreatic epithelia were transduced with anti-Pask or control small interfering RNAs, or with adenoviruses encoding enhanced green fluorescent protein or PASK.

RESULTS

PASK expression was significantly lower in islets from human type 2 diabetic than control participants. PASK mRNA was present in alpha and beta cells from mouse islets. In Pask-/- mice, fasted blood glucose and plasma glucagon levels were 25 ± 5% and 50 ± 8% (mean ± SE) higher, respectively, than in control mice. At inhibitory glucose concentrations (10 mmol/l), islets from Pask-/- mice secreted 2.04 ± 0.2-fold (p < 0.01) more glucagon and 2.63 ± 0.3-fold (p < 0.01) less insulin than wild-type islets. Glucose failed to inhibit glucagon secretion from PASK-depleted alpha-TC1-9 cells, whereas PASK overexpression inhibited glucagon secretion from these cells and human islets. Extracellular insulin (20 nmol/l) inhibited glucagon secretion from control and PASK-deficient alpha-TC1-9 cells. PASK-depleted alpha-TC1-9 cells and pancreatic embryonic explants displayed increased expression of the preproglucagon (Gcg) and AMP-activated protein kinase (AMPK)-alpha2 (Prkaa2) genes, implying a possible role for AMPK-alpha2 downstream of PASK in the control of glucagon gene expression and release.

CONCLUSIONS/INTERPRETATION

PASK is involved in the regulation of glucagon secretion by glucose and may be a useful target for the treatment of type 2 diabetes.

PSK2 coordinates glucose metabolism and utilization to maintain ultradian clock-coupled respiratory oscillation in Saccharomyces cerevisiae yeast

Ultradian clock-coupled respiratory oscillation (UCRO) in an aerobic continuous culture of Saccharomyces cerevisiae S288C is principally regulated by control of certain redox reactions of energy metabolism. It is also modulated by the metabolism of storage carbohydrates during adaptation to environmental change. However, the mechanism of cell sensing and response to environmental nutrients in UCRO is unknown. The purpose of the present study was to determine the role of PSK2 kinase in UCRO in yeast. S. cerevisiae in culture showed oscillation in PSK2 mRNA levels with a definite phase relationship to the respiratory oscillation. Furthermore, inactivation of Psk2 by gene disruption severely affected UCRO and its decline to undetectable levels within 2days. In addition, the extracellular and intracellular glucose concentrations of PSK2 deletion mutants in culture were higher and lower, respectively, than those of the wild type. PSK2 mutant cells showed no alteration in redox state. Furthermore, the levels of storage carbohydrates such as glycogen and trehalose fluctuated in PSK2 mutants with attenuated amplitudes comparable to those in the wild type. The results indicated that PSK2 kinase is important for the uptake of glucose and regulation of storage-carbohydrate synthesis and hence the maintenance of an unperturbed continuously oscillating state.

Structural bases of PAS domain-regulated kinase (PASK) activation in the absence of activation loop phosphorylation

Per-Arnt-Sim (PAS) domain-containing protein kinase (PASK) is an evolutionary conserved protein kinase that coordinates cellular metabolism with metabolic demand in yeast and mammals. The molecular mechanisms underlying PASK regulation, however, remain unknown. Herein, we describe a crystal structure of the kinase domain of human PASK, which provides insights into the regulatory mechanisms governing catalysis. We show that the kinase domain adopts an active conformation and has catalytic activity in vivo and in vitro in the absence of activation loop phosphorylation. Using site-directed mutagenesis and structural comparison with active and inactive kinases, we identified several key structural features in PASK that enable activation loop phosphorylation-independent activity. Finally, we used combinatorial peptide library screening to determine that PASK prefers basic residues at the P-3 and P-5 positions in substrate peptides. Our results describe the key features of the PASK structure and how those features are important for PASK activity and substrate selection.