Is Akt the “Warburg kinase”?—Akt-energy metabolism interactions and oncogenesis

The “Warburg kinase” is Akt, right? Akt connections with energy metabolism and oncogenesis

• R. Brooks Robeya, b, c, 1
• Nissim Hayd, 2
• White River Junction VA Medical Center’s Research and Development Service
• b Department of Medicine, United States, Dartmouth Medical School
• c Department of Physiology, Dartmouth Medical School, United States
• d University of Illinois at Chicago’s Biochemistry and Molecular Genetics Department
• Online as of December 14, 2008.
• Link: http://www.sciencedirect.com/science/article/pii/S1044579X08001053
• Abstract

One of the most frequently activated protein kinases in human cancer is the serine/threonine kinase Akt, also known as protein kinase B (PKB). In fact, this crucial kinase is ultimately activated by the majority of cancers, if not all of them. As a result, Akt activation is a characteristic of the majority of cancer cells, and this prevalence presumably indicates significant involvement in tumor formation and/or development. Similar to this, it is believed that cancer cells have certain metabolic characteristics due to their hypermetabolic state and greater reliance on “aerobic glycolysis,” as first documented by Otto Warburg and colleagues. In this study, we discuss the particular ways in which Akt activation affects the distinguishing metabolic characteristics of cancer cells, such as the so-called “Warburg effect.”

Keywords

• Energy metabolism;
• Glycolysis;
• Oxygen consumption;
• Oxidative phosphorylation;
• Cancer

Figures and tables from this article:

Figure 1 shows the relationship between cell proliferation, cell survival, and Akt-mediated cellular energy metabolism. Akt enhances cellular ATP production by speeding up both glycolytic and oxidative metabolism after being activated by PI3K, PDK1, and mTORC2. By promoting metabolic coupling between glycolysis and oxidative phosphorylation, mitochondrial hexokinase (mtHK; i.e., HKI and HKII) interaction with VDAC and mitochondria, as well as by as-yet-unknown methods, Akt may boost oxidative phosphorylation. Akt improves cell viability by promoting mtHK interaction with mitochondria. Furthermore, Akt increases glycolytic flow via a variety of ways. First, it boosts the production of glucose transporters (GLUT1, GLUT2, and GLUT4) and, in some situations, promotes translocation to the plasma membrane to improve glucose (Glc) uptake. Second, increased glycolytic flux may be favored kinetically by improved coupling between oxidative phosphorylation and glycolysis. Third, overactive Akt stimulates mTORC1, which in turn enhances the accumulation of HIF1 under normoxic conditions and raises the abundance of GLUT1, HKII, and lactate dehydrogenase (LDH). Improved glucose-6-phosphate (Glc-6-P) availability for use in glycolysis and the pentose phosphate pathway is the result of increased Glc transport and phosphorylation capacity (PPP). Fourth, fructose-2,6-bisphosphate, a byproduct of phosphorylating and activating phosphofructokinase-2 (PFK2), allosterically activates phosphofructokinase-1 (PFK1) (Fru-2,6-P2). The ATP-citrate lyase (ACL), which is directly phosphorylated and activated by Akt, uses citrate produced in the mitochondrial TCA cycle that is exported to the cytoplasm to produce acetyl-coA. The TCA cycle flux may be aided by Akt by enhancing citrate consumption, which also contributes to the production of precursors for the synthesis of lipids in the production of new membranes. Finally, mTORC1 activation requires full AMPK function, which is maintained by Akt-increased cellular ATP levels. mTORC1 is the most significant Akt downstream effector, and it plays a significant role in how Akt affects cell growth, proliferation, and susceptibility to oncogenic transformation.