The role of PAS kinase in PASsing the glucose signal

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.

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.

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.

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.

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 AGC Kinase SsAgc1 Regulates Sporisorium scitamineum Mating/Filamentation and Pathogenicity

The AGC signaling pathway represents a conserved distinct signaling pathway in regulation of fungal differentiation and virulence, while it has not been identified or characterized in the sugarcane smut fungus Sporisorium scitamineum. In this study, we identified a PAS domain-containing AGC kinase, SsAgc1, in S. scitamineum. Functional analysis revealed that SsAgc1 plays a regulatory role on the fungal dimorphic switch.

Sporisorium scitamineum is the fungal pathogen causing severe sugarcane smut disease that leads to massive economic losses globally. S. scitamineum invades host cane by dikaryotic hyphae, formed after sexual mating of two haploid sporidia of opposite mating type. Therefore, mating/filamentation is critical for S. scitamineum pathogenicity, while its molecular mechanisms remain largely unknown. The AGC (cyclic AMP [cAMP]-dependent protein kinase 1 [protein kinase A {PKA}], cGMP-dependent protein kinase [PKG], and protein kinase C [PKC]) kinase family is a group of serine/threonine (Ser/Thr) protein kinases conserved among eukaryotic genomes, serving a variety of physiological functions, including cell growth, metabolism, differentiation, and cell death. In this study, we identified an AGC kinase, named SsAgc1 (for S. scitamineum Agc1), and characterized its function by reverse genetics. Our results showed that SsAgc1 is critical for S. scitamineum mating/filamentation and pathogenicity, and oxidative stress tolerance under some circumstances. Transcriptional profiling revealed that the SsAgc1 signaling pathway may control expression of the genes governing fungal mating/filamentation and tryptophan metabolism, especially for tryptophol production. We showed that tryptophan and tryptophol could at least partially restore ssagc1Δ mating/filamentation. Overall, our work revealed a signaling pathway mediated by AGC protein kinases to regulate fungal mating/filamentation, possibly through sensing and responding to tryptophol as signal molecules.

IMPORTANCE The AGC signaling pathway represents a conserved distinct signaling pathway in regulation of fungal differentiation and virulence, while it has not been identified or characterized in the sugarcane smut fungus Sporisorium scitamineum. In this study, we identified a PAS domain-containing AGC kinase, SsAgc1, in S. scitamineum. Functional analysis revealed that SsAgc1 plays a regulatory role on the fungal dimorphic switch.

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.

Structure and function of Per-ARNT-Sim domains and their possible role in the life-cycle biology of Trypanosoma cruzi

Per-ARNT-Sim (PAS) domains of proteins play important roles as modules for signalling and cellular regulation processes in widely diverse organisms such as Archaea, Bacteria, protists, plants, yeasts, insects and vertebrates. These domains are present in many proteins where they are used as sensors of stimuli and modules for protein interactions. Characteristically, they can bind a broad spectrum of molecules. Such binding causes the domain to trigger a specific cellular response or to make the protein containing the domain susceptible to responding to additional physical or chemical signals. Different PAS proteins have the ability to sense redox potential, light, oxygen, energy levels, carboxylic acids, fatty acids and several other stimuli. Such proteins have been found to be involved in cellular processes such as development, virulence, sporulation, adaptation to hypoxia, circadian cycle, metabolism and gene regulation and expression. Our analysis of the genome of different kinetoplastid species revealed the presence of PAS domains also in different predicted kinases from these protists. Open-reading frames coding for these PAS-kinases are unusually large. In addition, the products of these genes appear to contain in their structure combinations of domains uncommon in other eukaryotes. The physiological significance of PAS domains in these parasites, specifically in Trypanosoma cruzi, is discussed.

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.

All-encomPASsing regulation of β-cells: PAS domain proteins in β-cell dysfunction and diabetes

As a sensory micro-organ, pancreatic β-cells continually respond to nutritional signals and neuroendocrine input from other glucoregulatory organs. This sensory ability is essential for normal β-cell function and systemic glucose homeostasis. Period circadian protein (Per)-aryl hydrocarbon receptor nuclear translocator protein (Arnt)-single-minded protein (Sim) (PAS) domain proteins have a conserved role as sensory proteins, critical in adaptation to changes in voltage, oxygen potential, and xenobiotics. Within β-cells, PAS domain proteins such as hypoxia inducible factor 1α (Hif1α), Arnt, PAS kinase, Bmal1, and Clock respond to disparate stimuli, but act in concert to maintain proper β-cell function. Elucidating the function of these factors in islets offers a unique insight into the sensing capacity of β-cells, the consequences of impaired sensory function, and the potential to develop novel therapeutic targets for preserving β-cell function in diabetes.

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.

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.

Energy metabolism regulates clathrin adaptors at the trans-Golgi network and endosomes

Glucose is a master regulator of cell behavior in the yeast Saccharomyces cerevisiae. It acts as both a metabolic substrate and a potent regulator of intracellular signaling cascades. Glucose starvation induces the transient delocalization and then partial relocalization of clathrin adaptors at the trans-Golgi network and endosomes. Although these localization responses are known to depend on the protein kinase A (PKA) signaling pathway, the molecular mechanism of this regulation is unknown. Here we demonstrate that PKA and the AMP-regulated kinase regulate adaptor localization through changes in energy metabolism. We show that genetic and chemical manipulation of intracellular ATP levels cause corresponding changes in adaptor localization. In permeabilized cells, exogenous ATP is sufficient to induce adaptor localization. Furthermore, we reveal distinct energy-dependent steps in adaptor localization: a step that requires the ADP-ribosylation factor ARF, an ATP-dependent step that requires the phosphatidyl-inositol-4 kinase Pik1, and third ATP-dependent step for which we provide evidence but for which the mechanism is unknown. We propose that these energy-dependent mechanisms precisely synchronize membrane traffic with overall proliferation rates and contribute a crucial aspect of energy conservation during acute glucose starvation.