Editors' ChoiceCancer Metabolism

GTP sensor is a lipid kinase

Sci. Signal.  26 Jan 2016:
Vol. 9, Issue 412, pp. ec15
DOI: 10.1126/scisignal.aaf3049

Changes in concentrations of vital molecules that store and transfer energy in a cell, such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), affect cellular homeostasis and can lead to pathological conditions. For example, during protein synthesis two GTP molecules are used for every amino acid incorporated into the polypeptide chain and therefore active and rapidly proliferating cells, such as cancer cells, need a large amount of GTP. Sumita et al. performed mass spectrometry analysis of proteins from cell lysates that bound to GTP-conjugated agarose beads and identified phoshatidylinositol 5-phosphate 4-kinase β (PI5P4Kβ) as a GTP-binding partner. Nuclear magnetic resonance spectrometry confirmed the binding of recombinant PI5P4Kβ to GTP and in vitro analysis indicated that PI5P4Kβ hydrolyzed GTP. In vitro kinase assays revealed that PI5P4Kβ used GTP as the phosphate donor to phosphorylate its substrate phosphatidylinositol 5-phosphate [PI(5)P]. Furthermore, compared with other isoforms of PI5P4K, which exhibited low KM for GTP and thus were fully activated at all physiological concentrations of this metabolite, PI5P4Kβ had a high KM for GTP, which enabled the kinase activity to change in response to physiological changes in GTP concentration. Crystal structure analysis of PI5P4Kβ identified Thr201 and Phe205 as critical residues for GTP binding. PI5P4KβF205L mutant protein exhibited both reduced hydrolysis of GTP and kinase activity compared with wild-type. Disrupting GTP synthesis in mouse embryonic fibroblasts (MEFs) overexpressing wild-type PI5P4Kβ resulted in increased concentrations of PI(5)P, whereas the amount of PI(5)P was unaffected in MEFs that overexpressed PI5P4KβF205L. MEFs expressing PI5P4KβF205L grown in soft agar to mimic nutrient deprivation experienced by cancer cells produced significantly fewer colonies than MEFs expressing PI5P4Kβ. Immunocompromised mice developed tumors when MEFs expressing PI5P4Kβ were injected subcutaneously, whereas injection of MEFs expressing PI5P4KβF205L did not. Thus, this study suggested that PI5P4Kβ senses GTP concentration, PI(5)P may function as a second messenger in this response, and this may serve as a key metabolic regulatory event enabling cancer.

K. Sumita, Y.-H. Lo, K. Takeuchi, M. Senda, S. Kofuji, Y. Ikeda, J. Terakawa, M. Sasaki, H. Yoshino, N. Majd, Y. Zheng, E. R. Kahoud, T. Yokota, B. M. Emerling, J. M. Asara, T. Ishida, J. W. Locasale, T. Daikoku, D. Anastasiou, T. Senda, A. T. Sasaki, The lipid kinase PI5P4Kβ is an intracellular GTP sensor for metabolism and tumorigenesis. Mol. Cell. 61, 187–198 (2016). [PubMed]