Dimeric and tetrameric forms of muscle fructose-1,6-bisphosphatase play different roles in the cell

Abstract

Muscle fructose 1,6-bisphosphatase (FBP2), besides being a regulatory enzyme of glyconeogenesis also protects mitochondria against calcium stress and plays a key role in regulation of the cell cycle, promoting cardiomyocytes survival. However, in cancer cells, FBP2 acts as an anti-oncogenic/anti-proliferative protein. Here, we show that the physiological function of FBP2 depends both on its level of expression in a cell as well as its oligomerization state. Animal fructose-1,6-bisphosphatases are thought to function as tetramers. We present evidence that FBP2 exists in an equilibrium between tetramers and dimers. The dimeric form is fully active and insensitive to AMP, the main allosteric inhibitor of FBP2. Tetramerization induces the sensitivity of the protein to AMP, but it requires the presence of a hydrophobic central region in which leucine 190 plays a crucial role. Only the tetrameric form of FBP2 is retained in cardiomyocyte cell nucleus whereas only the dimeric form associates with mitochondria and protects them against stress stimuli, such as elevated calcium and H2O2 level. Remarkably, in hypoxic conditions, which are typical for many cancers, FBP2 ceases to interact with mitochondria and loses its pro-survival potential. Our results throw new light on the basis of the diverse role of FBP2 in cells.

The Reverse Warburg Effect Is Associated with Fbp2-Dependent Hif1α Regulation in Cancer Cells Stimulated by Fibroblasts

“…Fbp2 exists as a mixture of dimers and tetramers, and in a living cell, the oligomeric state of Fbp2, modulated by its allosteric inhibitors, affects the ability of the enzyme to interact with cellular components [20]. Moreover, in contrast to Fbp1, which is a planar tetramer, Fbp2, in its active tetrameric conformation, adopts a unique cruciform-like quaternary structure, in which completely new protein surfaces are exposed and become targets for interactions with various binding partners [20].…”

“…In the co-immunoprecipitation experiments, the recombinant Fbp2 and Hif1α (Abcam, ab154478) proteins and the Fbp1 isolated from bovine liver were used. The expression and purification of the recombinant human Fbp2 were carried out according to the method described previously [20] with the following modification: in order to obtain a higher yield of the protein, elution was performed twice using a 50 and 100 mM phosphate buffer. The purification of the Fbp1 from a mammalian liver was described previously [21], although here, the incubation with cellulose phosphate (Sigma-Aldrich, c2258) was performed at pH 7.1, and the pH of both the wash and the elution buffer was set to 7.0.…”

Mitochondrial calcium: Transport and modulation of cellular processes in homeostasis and cancer (Review)

“…Muscle FBP has two predominant oligomeric states that determine its subcellular localization. Only dimeric FBP interacts with mitochondria and protects them against stress stimuli (40). Therefore, as a survival mechanism associated with the elevation of calcium, cardiomyocytes promote the binding of FBP to mitochondria.…”

Expression of Fbp2, a Newly Discovered Constituent of Memory Formation Mechanisms, Is Regulated by Astrocyte–Neuron Crosstalk

“…In contrast to total cellular ROS, we observed a small but statistically significant (17%, p < 0.01; Figure S1) elevation of mitochondrial ROS production under the tested conditions. It is well documented that, in cardiomyocytes and neurons, Fbp2 binds to mitochondria and protects them against Ca 2+ -or ROS-induced excessive depolarization that can lead to swelling of the organelles [1,[4][5][6]. Thus, the observed increase in mitochondrial ROS production was not unexpected and reflected a weaker protection of mitochondria resulting from the lowered amount of Fbp2 protein in astrocytes.…”

“…Only the dimeric form of Fbp2 interacts with mitochondria, and only its tetrameric form is retained in the nucleus. The ratio of these oligomeric forms depends on the presence of physiological inhibitors of Fbp2 enzymatic activity-AMP and NAD + , which also tetramerize the protein [5].…”