Laurent Bultot

Publications (4) View all

• Article: PFKFB3 activation in cancer cells by the p38/MK2 pathway in response to stress stimuli.

  Laura Novellasdemunt, Laurent Bultot, Anna Manzano, Francesc Ventura, Jose Luis Rosa, Didier Vertommen, Mark H Rider, Aurea Navarro-Sabate, Ramon Bartrons
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  ABSTRACT: PFK-2/FBPase-2 (6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase) catalyses the synthesis and degradation of Fru-2,6-P2 (fructose-2,6-bisphosphate), a key modulator of glycolysis and gluconeogenesis. The PFKFB3 gene is involved in cell proliferation owing to its role in carbohydrate metabolism. Here we analyze its mechanism of regulation as an immediately early gene controlled by stress stimuli that activate p38/MK2 pathway. We report that exposure of HeLa and T98G cells to different stress stimuli (NaCl, H2O2, UV radiation and anisomycin) leads to a rapid increase (15-30 minutes) in PFKFB3 mRNA levels. The use of specific inhibitors in combination with MK2-deficient cells implicate control by MK2 protein kinase. Transient transfection of HeLa cells with deleted gene promoter constructs allowed us to identify a Serum Response Element (SRE) to which Serum Response Factor (SRF) binds and thus transactivates PFKFB3 gene transcription. Direct Binding of phospho-SRF to the SRE sequence (-918 nt) was confirmed by ChIP (chromatin immunoprecipiation) assays. Moreover, PFKFB3 isoenzyme phosphorylation at Ser461 by MK2 increases PFK-2 activity. Together, the results suggest a multimodal mechanism of stress stimuli affecting PFKFB3 transcriptional regulation and kinase activation by protein phosphorylation, resulting in an increase in Fru-2,6-P2 concentration and stimulation of glycolysis in cancer cells.
  Biochemical Journal 04/2013; · 4.90 Impact Factor
• Article: AMP-activated protein kinase phosphorylates and inactivates liver glycogen synthase.

  Laurent Bultot, Bruno Guigas, Alexander Von Wilamowitz-Moellendorff, Liliane Maisin, Didier Vertommen, Nusrat Hussain, Monique Beullens, Joan J Guinovart, Marc Foretz, Benoît Viollet, Kei Sakamoto, Louis Hue, Mark H Rider
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  ABSTRACT: Recombinant muscle GYS1 (glycogen synthase 1) and recombinant liver GYS2 were phosphorylated by recombinant AMPK (AMP-activated protein kinase) in a time-dependent manner and to a similar stoichiometry. The phosphorylation site in GYS2 was identified as Ser7, which lies in a favourable consensus for phosphorylation by AMPK. Phosphorylation of GYS1 or GYS2 by AMPK led to enzyme inactivation by decreasing the affinity for both UDP-Glc (UDP-glucose) [assayed in the absence of Glc-6-P (glucose-6-phosphate)] and Glc-6-P (assayed at low UDP-Glc concentrations). Incubation of freshly isolated rat hepatocytes with the pharmacological AMPK activators AICA riboside (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside) or A769662 led to persistent GYS inactivation and Ser7 phosphorylation, whereas inactivation by glucagon treatment was transient. In hepatocytes from mice harbouring a liver-specific deletion of the AMPK catalytic α1/α2 subunits, GYS2 inactivation by AICA riboside and A769662 was blunted, whereas inactivation by glucagon was unaffected. The results suggest that GYS inactivation by AMPK activators in hepatocytes is due to GYS2 Ser7 phosphorylation.
  Biochemical Journal 01/2012; 443(1):193-203. · 4.90 Impact Factor
• Article: Characterization and quality control of antibodies used in ChIP assays.

  Géraldine Goens, Dorina Rusu, Laurent Bultot, Jean-Jacques Goval, Juana Magdalena
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  ABSTRACT: We present here the very robust characterization and quality control (QC) process that we have established for our polyclonal antibodies, which are mainly directed against targets relevant to the epigenetics field such as modified histones, modifying enzymes, and chromatin-interacting proteins. The final purpose of the characterization and QC is to label antibodies as chromatin immunoprecipitation (ChIP) grade. Indeed, the ChIP method is extensively used in epigenetics to study gene regulation and relies on the use of antibodies to select the protein of interest and then precipitate and identify the DNA associated to it. We have optimized in-house all protocols and reagents needed from the first to the last step of antibody characterization. First, following immunizations, the rabbit crude serum is tested for immune response. Whether or not the antibody is specific is determined in further characterizations. Then, only specific antibodies are tested in ChIP using an optimized method which is ideal for antibody screening. Once QC is established for one antibody, it is used to similarly characterize each antibody batch in order to supply researchers in a reproducible manner with validated antibodies. All in all, this demonstrates that we develop epigenetics research tools based on everyday's researcher's needs by providing batch-specific fully characterized ChIP-grade antibodies.
  Methods in molecular biology (Clifton, N.J.) 02/2009; 567:27-43.
• Article: Myosin light chains are not a physiological substrate of AMPK in the control of cell structure changes.

  Laurent Bultot, Sandrine Horman, Dietbert Neumann, Michael P Walsh, Louis Hue, Mark H Rider
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  ABSTRACT: The kinetics of myosin regulatory light chain (MLC) phosphorylation by recombinant AMP-activated protein kinase (AMPK) were compared with commercial AMPK from rat liver and smooth muscle myosin light chain kinase (smMLCK). With identical amounts of activity units, initial rates of phosphorylation of MLC were at least 100-fold less with recombinant AMPK compared to smMLCK, whereas with rat liver AMPK significant phosphorylation was seen. In Madin-Darby Canine Kidney cells, AMPK activation led to an increase in MLC phosphorylation, which was decreased by a Rho kinase inhibitor without affecting AMPK activation. Therefore, MLC phosphorylation during energy deprivation does not result from direct phosphorylation by AMPK.
  FEBS letters 01/2009; 583(1):25-8. · 3.54 Impact Factor