title: Molecular association of glucose-6-phosphate isomerase and pyruvate kinase M2 with glyceraldehyde-3-phosphate dehydrogenase in cancer cells.
abstract: BACKGROUND
  For a long time cancer cells are known for increased uptake of glucose and its metabolization through glycolysis. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key regulatory enzyme of this pathway and can produce ATP through oxidative level of phosphorylation. Previously, we reported that GAPDH purified from a variety of malignant tissues, but not from normal tissues, was strongly inactivated by a normal metabolite, methylglyoxal (MG). Molecular mechanism behind MG mediated GAPDH inhibition in cancer cells is not well understood.
  
  
  METHODS
  GAPDH was purified from Ehrlich ascites carcinoma (EAC) cells based on its enzymatic activity. GAPDH associated proteins in EAC cells and 3-methylcholanthrene (3MC) induced mouse tumor tissue were detected by mass spectrometry analysis and immunoprecipitation (IP) experiment, respectively. Interacting domains of GAPDH and its associated proteins were assessed by in silico molecular docking analysis. Mechanism of MG mediated GAPDH inactivation in cancer cells was evaluated by measuring enzyme activity, Circular dichroism (CD) spectroscopy, IP and mass spectrometry analyses.
  
  
  RESULTS
  Here, we report that GAPDH is associated with glucose-6-phosphate isomerase (GPI) and pyruvate kinase M2 (PKM2) in Ehrlich ascites carcinoma (EAC) cells and also in 3-methylcholanthrene (3MC) induced mouse tumor tissue. Molecular docking analyses suggest C-terminal domain preference for the interaction between GAPDH and GPI. However, both C and N termini of PKM2 might be interacting with the C terminal domain of GAPDH. Expression of both PKM2 and GPI is increased in 3MC induced tumor compared with the normal tissue. In presence of 1 mM MG, association of GAPDH with PKM2 or GPI is not perturbed, but the enzymatic activity of GAPDH is reduced to 26.8 ± 5 % in 3MC induced tumor and 57.8 ± 2.3 % in EAC cells. Treatment of MG to purified GAPDH complex leads to glycation at R399 residue of PKM2 only, and changes the secondary structure of the protein complex.
  
  
  CONCLUSIONS
  PKM2 may regulate the enzymatic activity of GAPDH. Increased enzymatic activity of GAPDH in tumor cells may be attributed to its association with PKM2 and GPI. Association of GAPDH with PKM2 and GPI could be a signature for cancer cells. Glycation at R399 of PKM2 and changes in the secondary structure of GAPDH complex could be one of the mechanisms by which GAPDH activity is inhibited in tumor cells by MG.
authors.affiliation: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Kolkata, 700032, India.
authors.forename: Mahua R
authors.initials: MR
authors.lastname: Das
authors.affiliation: Cancer Biology and Inflammatory Disorder Division, Indian Institute of Chemical Biology, Kolkata, 700032, India.
authors.forename: Arup K
authors.initials: AK
authors.lastname: Bag
authors.affiliation: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Kolkata, 700032, India.
authors.forename: Shekhar
authors.initials: S
authors.lastname: Saha
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, 77843-3474, USA.
authors.forename: Alok
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Kolkata, 700032, India.
authors.forename: Sumit K
authors.initials: SK
authors.lastname: Dey
authors.affiliation: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Kolkata, 700032, India.
authors.forename: Provas
authors.initials: P
authors.lastname: Das
authors.affiliation: Cancer Biology and Inflammatory Disorder Division, Indian Institute of Chemical Biology, Kolkata, 700032, India.
authors.forename: Chitra
authors.initials: C
authors.lastname: Mandal
authors.affiliation: 13 Regent Estate, Kolkata, 700 092, India.
authors.forename: Subhankar
authors.initials: S
authors.lastname: Ray
authors.affiliation: Structural Biology and Bioinformatics Division, Indian Institute of Chemical Biology, Jadavpur, Kolkata, 700 032, India.
authors.forename: Saikat
authors.initials: S
authors.lastname: Chakrabarti
authors.affiliation: Department of Biophysics, Bose Institute, Kolkata, India. manjuray@mail.jcbose.ac.in.
authors.forename: Manju
authors.initials: M
authors.lastname: Ray
authors.affiliation: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Kolkata, 700032, India. bcssj@iacs.res.in.
authors.forename: Siddhartha S
authors.initials: SS
authors.lastname: Jana
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression; D005956:Glucose-6-Phosphate Isomerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013058:Mass Spectrometry; D051379:Mice; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011765:Pyruvaldehyde / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D011765:Pyruvaldehyde; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D011770:Pyruvate Kinase; D005956:Glucose-6-Phosphate Isomerase