Expression of the F-type 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA during liver regeneration

A combined proteomic and metabolomic analyses of the priming phase during rat liver regeneration

By comparing differentially abundant proteins and metabolites, the protein expression, metabolic changes and metabolic regulation mechanisms during the priming phase of liver regeneration (LR) were investigated. We combined proteomic analysis via isobaric tags for relative and absolute quantification (iTRAQ) with metabolomic analysis via nontargeted liquid chromatography-mass spectrometry (LC-MS). LC-MS was used to examine 29 energy metabolites expression alterations in targeted metabolomics. A total number of 441 differentially expressed proteins and 65 metabolites were identified. PSMB10, PSMB5, RCG_63409, PSME4 and PSMB7 were key node proteins, these proteins are involved in the proteasome pathway. The most strongly enriched transcription factor motif was TP63. These results point out a critical role of the proteasome pathway (defense mechanisms) and of TP63 (metabolic regulator) as the key transcription factor during the priming phase of LR. Metabolomic and metabolite analysis showed that profiling indicates upregulation of arginine biosynthesis and glycolysis as the main ATP-delivering pathway. Integrative proteomic and metabolomic analysis showed that biomolecular changes were primarily related to the neurological disease, cell death and survival and cell morphology. What's more, neurotransmitters may play an important role in the regulation of LR.

Increase in Fru-2,6-P(2) levels results in altered cell division in Schizosaccharomyces pombe

Mitogenic response to growth factors is concomitant with the modulation they exert on the levels of Fructose 2,6-bisphosphate (Fru-2,6-P2), an essential activator of the glycolytic flux. In mammalian cells, decreased Fru-2,6-P2 concentration causes cell cycle delay, whereas high levels of Fru-2,6-P2 sensitize cells to apoptosis. In order to analyze the cell cycle consequences due to changes in Fru-2,6-P2 levels, the bisphosphatase-dead mutant (H258A) of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase enzyme was over-expressed in Schizosaccharomyces pombe cells and the variation in cell phenotype was studied. The results obtained demonstrate that the increase in Fru-2,6-P2 levels results in a defective division of S. pombe, as revealed by an altered multisepted phenotype. The H258A-expressing cells showed impairment of cytokinesis, but normal nuclear division. In order to identify cellular mediators responsible for this effect, we transformed different S. pombe strains and observed that the cytokinetic defect was absent in cells defective for Wee1 kinase function. Therefore, in S. pombe, Wee1 integrates the metabolic signal emerging from changes in Fru-2,6-P2 content, thus coupling metabolism with cell proliferation. As the key regulators of the cell cycle checkpoints are conserved throughout evolution, these results may help to understand the experimental evidences obtained by manipulation of Fru-2,6-P2 levels in mammalian cells.

6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase: head-to-head with a bifunctional enzyme that controls glycolysis

Fru-2,6-P2 (fructose 2,6-bisphosphate) is a signal molecule that controls glycolysis. Since its discovery more than 20 years ago, inroads have been made towards the understanding of the structure-function relationships in PFK-2 (6-phosphofructo-2-kinase)/FBPase-2 (fructose-2,6-bisphosphatase), the homodimeric bifunctional enzyme that catalyses the synthesis and degradation of Fru-2,6-P2. The FBPase-2 domain of the enzyme subunit bears sequence, mechanistic and structural similarity to the histidine phosphatase family of enzymes. The PFK-2 domain was originally thought to resemble bacterial PFK-1 (6-phosphofructo-1-kinase), but this proved not to be correct. Molecular modelling of the PFK-2 domain revealed that, instead, it has the same fold as adenylate kinase. This was confirmed by X-ray crystallography. A PFK-2/FBPase-2 sequence in the genome of one prokaryote, the proteobacterium Desulfovibrio desulfuricans, could be the result of horizontal gene transfer from a eukaryote distantly related to all other organisms, possibly a protist. This, together with the presence of PFK-2/FBPase-2 genes in trypanosomatids (albeit with possibly only one of the domains active), indicates that fusion of genes initially coding for separate PFK-2 and FBPase-2 domains might have occurred early in evolution. In the enzyme homodimer, the PFK-2 domains come together in a head-to-head like fashion, whereas the FBPase-2 domains can function as monomers. There are four PFK-2/FBPase-2 isoenzymes in mammals, each coded by a different gene that expresses several isoforms of each isoenzyme. In these genes, regulatory sequences have been identified which account for their long-term control by hormones and tissue-specific transcription factors. One of these, HNF-6 (hepatocyte nuclear factor-6), was discovered in this way. As to short-term control, the liver isoenzyme is phosphorylated at the N-terminus, adjacent to the PFK-2 domain, by PKA (cAMP-dependent protein kinase), leading to PFK-2 inactivation and FBPase-2 activation. In contrast, the heart isoenzyme is phosphorylated at the C-terminus by several protein kinases in different signalling pathways, resulting in PFK-2 activation.