The PAS-domain kinase PASKIN: a new sensor in energy homeostasis

Abstract.: The PAS domain kinase PASKIN, also termed PAS kinase or PASK, is an evolutionarily conserved potential sensor kinase related to the heme-based oxygen sensors of nitrogen-fixing bacteria. In yeast, the two PASKIN homologs link energy flux and protein synthesis following specific stress conditions. In mammals, PASKIN may regulate glycogen synthesis and protein translation. Paskin knock-out mice do not show any phenotype under standard animal husbandry conditions. Interestingly, these mice seem to be protected from the symptoms of the metabolic syndrome when fed a high-fat diet. Energy turnover might be increased in specific PASKIN-deficient cell types under distinct environmental conditions. According to the current model, binding of a putative ligand to the PAS domain disinhibits the kinase domain and activates PASKIN auto- and target phosphorylation. Future research needs to be conducted to elucidate the nature of the putative ligand and the molecular mechanisms of downstream signalling by PASKI

The PAS-domain kinase PASKIN: a new sensor in energy homeostasis

The PAS domain kinase PASKIN, also termed PAS kinase or PASK, is an evolutionarily conserved potential sensor kinase related to the heme-based oxygen sensors of nitrogen-fixing bacteria. In yeast, the two PASKIN homologs link energy flux and protein synthesis following specific stress conditions. In mammals, PASKIN may regulate glycogen synthesis and protein translation. Paskin knock-out mice do not show any phenotype under standard animal husbandry conditions. Interestingly, these mice seem to be protected from the symptoms of the metabolic syndrome when fed a high-fat diet. Energy turnover might be increased in specific PASKIN-deficient cell types under distinct environmental conditions. According to the current model, binding of a putative ligand to the PAS domain disinhibits the kinase domain and activates PASKIN auto- and target phosphorylation. Future research needs to be conducted to elucidate the nature of the putative ligand and the molecular mechanisms of downstream signalling by PASKIN

Glucose-stimulated insulin production in mice deficient for the PAS kinase PASKIN.

The Per-ARNT-Sim (PAS) domain serine/threonine kinase PASKIN, or PAS kinase, links energy flux and protein synthesis in yeast and regulates glycogen synthase in mammals. A recent report suggested that PASKIN mRNA, protein, and kinase activity are increased in pancreatic islet beta-cells under hyperglycemic conditions and that PASKIN is necessary for insulin gene expression. We previously generated Paskin knockout mice by targeted replacement of the kinase domain with the beta-geo fusion gene encoding beta-galactosidase reporter activity. Here we show that no 5-bromo-4-chloro-3-indolyl-ss-d-galactopyranoside (X-gal) staining was observed in islet beta-cells derived from Paskin knockout mice, irrespective of the ambient glucose concentration, whereas adenoviral expression of the lacZ gene in beta-cells showed strong X-gal staining. No induction of PASKIN mRNA could be detected in insulinoma cell lines or in islet beta-cells. Increasing glucose concentrations resulted in PASKIN-independent induction of insulin mRNA levels and insulin release. PASKIN mRNA levels were high in testes but undetectable in pancreas and in islet beta-cells. Finally, blood glucose levels and glucose tolerance after intraperitoneal glucose injection were indistinguishable between Paskin wild-type and knockout mice. These results suggest that Paskin gene expression is not induced by glucose in pancreatic beta-cells and that glucose-stimulated insulin production is independent of PASKIN

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

Substrate preference and phosphatidylinositol monophosphate inhibition of the catalytic domain of the PAS kinase PASKIN

The 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. Up to date, only synthetic but no endogenous PASKIN ligands have been reported. Here, we identified a number of novel PASKIN kinase targets, including ribosomal protein S6. Together with our previous identification of eukaryotic translation elongation factor eEF1A1, this suggests a role for PASKIN in the regulation of mammalian protein translation. While searching for endogenous PASKIN ligands, we found that various phospholipids can bind PASKIN and stimulate its autophosphorylation. Interestingly, strongest binding and autophosphorylation was achieved with monophosphorylated phosphatidylinositols. However, stimulated PASKIN autophosphorylation did not correlate with ribosomal protein S6 and eEF1A1 target phosphorylation. Whereas autophosphorylation was enhanced by monophosphorylated phosphatidylinositols, di- and triphosphorylated phosphatidylinositols inhibited autophosphorylation. In contrast, target phosphorylation was always inhibited, with highest efficiency of di- and tri-phosphorylated phosphatidylinositols. Since phosphatidylinositol monophosphates were found to interact with the kinase rather than with the PAS domain, these data suggest a multi-ligand regulation of PASKIN activity, including a still unknown PAS domain binding/activating ligand and kinase domain binding modulatory phosphatidylinositol phosphates

The development of inductive reasoning under consideration of the effect due to test speededness

Measures of inductive reasoning are frequently used as proxy of a child’s cognitive develop-ment. Unfortunately, a reasoning scale might be affected by speededness introduced by li-mited testing time. As a result, the scale might be heterogeneous and its correlation with age is hard to interpret. Here we investigated the development of inductive reasoning when a possible bias by the effect of speededness is controlled for. In 250 children, ranging in age from 8;0 to 12;8 years, inductive reasoning assessed with the Culture Fair Test 20-R (CFT 20-R) increased with age. The effect of speededness was identified in all four CFT 20-R sub-test and was also related to age indicating increasing processing speed with higher age. After controlling for the effect of speededness, the relation between age and inductive rea-soning was still observed but substantially decreased. Consequences of these results for the description of inductive reasoning data obtained with time-limited tests and for develop-mental studies on the interplay between age, inductive reasoning and speed of information processing are discussed.scussed

Ventilatory responses to acute and chronic hypoxia are altered in female but not male Paskin-deficient mice

Proteins harboring a Per-Arnt-Sim (PAS) domain are versatile and allow archaea, bacteria and plants to sense oxygen partial pressure as well as light intensity and redox potential. A PAS domain associated with a histidine kinase domain is found in FixL, the oxygen sensor molecule of Rhizobium species. Considering the PAS fold PASKIN is the mammalian homolog of FixL, but its function is far from being understood. Using whole body plethysmography we evaluated the ventilatory response to acute and chronic hypoxia of homozygous deficient male and female PASKIN mice (Paskin-/-). While only slight ventilatory differences were found in males, female Paskin-/- mice increased ventilatory response to acute hypoxia. Unexpectedly, females had an impaired ability to reach ventilatory acclimatization in response to chronic hypoxia. Central control of ventilation occurs in the brainstem respiratory centers and is modulated by catecholamines via tyrosine hydroxylase (TH) activity. We observed that TH activity was altered in male and female Paskin-/- mice. Peripheral chemoreceptor effects on ventilation were evaluated by exposing animals to hyperoxia (Dejours test) and domperidone, a peripheral ventilatory stimulant drug directly affecting the carotid sinus nerve discharge. Male and female Paskin-/- had normal peripheral chemosensory (carotid bodies) responses. In summary, our observations suggest that PASKIN is involved in the central control of hypoxic ventilation, modulating ventilation in a gender-dependent manner