Regulation of Akt ignal transduction by glucose metabolism

Aerobic glycolysis is carried out at an inordinately high rate in cancer cells, a phenomenon known as the Warburg effect. While the relevance of this effect is unclear, it is partly driven by upregulation of the glycolytic enzyme 6‐phosphofructo‐2‐kinase/fructose‐2,6‐biphosphatase 3 (PFKFB3). Intriguingly, the expression of PFKFB3 in adipocytes is extremely high compared to most other tissues. I observed an insulin-dependent induction of aerobic glycolysis in adipocytes through lactate production and hypothesised that this phenomenon is critical for adipocytes to enter the anabolic state. I therefore examined the effect of perturbing PFKFB3 activity on glucose metabolism and insulin signalling. The PFKFB3 inhibitor 3PO decreased insulin-stimulated glucose uptake, GLUT4 translocation and lactate production in adipocytes. These data suggest that glycolysis controls insulin-stimulated glucose entry into adipocytes. Because this process relies on activation of the Ser/Thr kinase Akt, I examined the effects of 3PO on Akt signaling and found that insulin-dependent phosphorylation of Akt, an index of its activation, was inhibited by 3PO in 3T3-L1 adipocytes. I next examined the consequences of heterologous overexpression of PFKFB3 in a cell line, HEK-293, that express minimal levels of this enzyme. PFKFB3 overexpression increased insulin-stimulated Akt phosphorylation and activity by ~2 fold. Given the role of PFKFB3 in glycolysis, these data suggested a role for glucose metabolism in the regulation of Akt. A possible role for the metabolic pathways linked to glycolysis, hexosamine biosynthetic pathway (HBP) and the pentose phosphate pathway (PPP), was investigated using specific inhibitors. These studies indicated that the PPP was required for full activation of Akt, but inhibition of PPP was accompanied by inhibition of glycolysis. Moreover, Increasing lactate production by overexpression of GLUT4 in adipocytes or inhibition of mitochondrial metabolism was accompanied by increased insulin-stimulated Akt activation. Inhibition of glycolysis by inhibiting the plasma membrane lactate transporter, on the other hand, blocked insulin-stimulated Akt activation. These studies reveal an unexpected role of glucose metabolism as a regulator of Akt signaling. This has potential implications for both cancer, where Akt activity may be driven by over stimulation of glycolysis, and diabetes where impaired glucose uptake may compromise Akt activity.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2014

Author dc:creator

• Trefely, Sophie

• Glycolysis
• PFKFB3
• Akt
• Warburg effect
• Insulin
• Adipocyte
• Metabolism

Statement dc:rights

• open access
• CC BY-NC-ND 3.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by-nc-nd/3.0/au/

Language dc:language

EN

Identifier

https://doi.org/10.26190/unsworks/2708

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/54272