The interplay between metabolic pathways and cell signaling networks that contribute to the ?metabolic reprogramming? in cancer cells remains largely unknown. The oxidative pentose phosphate pathway (oxiPPP) plays a crucial role in the metabolic coordination of glycolysis, biosynthesis and redox homeostasis in cells by producing precursors for nucleotide and lipid biosynthesis, as well as antioxidant NADPH that quenches the reactive oxygen species (ROS) produced during rapid proliferation of cancer cells. There are three key enzymes along the oxiPPP. The first enzyme glucose-6-phosphate dehydrogenase (G6PD) converts glycolytic intermediate glucose-6-phosphate (G6P) to 6-phosphogluconolactone (6PGL) and produces NADPH. The second enzyme 6-phosphogluconolactonase (PGLS) converts 6PGL to 6-phosphogluconate (6PG). The third enzyme 6-phosphogluconate dehydrogenase (6PGD) converts 6PG to ribulose-5-phosphate (Ru-5-P) and also produces NADPH. We recently reported that 6PGD is commonly activated by lysine acetylation in cancer cells and activates lipogenesis through controlling its product Ru-5-P, which inhibits the LKB1-AMPK pathway by disrupting the active LKB1 complex (Shan et al., 2014 Mol Cell; Lin et al., 2015, Nat Cell Biol.). Interestingly, we found that knockdown of G6PD did not alter AMPK activation despite decreased Ru-5-P and subsequent LKB1 activation, due to enhanced activity of PP2A, the upstream phosphatase of AMPK. In contrast, knockdown of 6PGD or PGLS reduced PP2A activity. Mechanistically, knockdown of G6PD or PGLS decreased or increased 6PGL level, respectively, which enhanced the inhibitory phosphorylation of PP2A by Src. There are two forms of 6PGL, ?-6-phosphogluconolactone (?-6PGL) is an oxiPPP byproduct with unknown function that is generated through intramolecular rearrangement of ?-6-phosphogluconolactone (?-6GL), while ?-6PGL is the only substrate of PGLS and can undergo quick spontaneous hydrolysis. Thus, ?-6PGL is relatively stable compared to ?-6GL but does not participate in oxiPPP. Further studies revealed that ?-6PGL, but not ?-6GL, promotes Src-PP2A association, probably by binding to Src but not PP2A and enhancing PP2A recruitment. Thus, we hypothesize that G6PD, PGLS and 6PGD play differential roles in regulation of AMPK homeostasis by balancing the opposing LKB1 and PP2A, through the oxiPPP intermediate Ru-5-P and an oxiPPP ?byproduct? ?-6PGL, respectively; and ?-6PGL, previously considered as a ?dead end? byproduct of the oxiPPP with unknown physiological function, functions as a signaling molecule that links the metabolic oxiPPP with the Src-PP2A-AMPK signaling pathway.
The specific aims are proposed: (1) To elucidate the molecular and signaling basis underlying ?-6PGL-dependent contribution to AMPK activation through inhibition of PP2A by Src; (2) To determine the differential effects of G6PD and PGLS on AMPK activation, redox homeostasis and tumor growth; and (3) To evaluate combined therapy with oxiPPP inhibitors and AMPK activator in the treatment of human leukemia and lung cancer cells in vitro and in vivo.
The oxidative pentose phosphate pathway (oxiPPP) regulates cell metabolism by producing metabolic intermediates and reductive NADPH, and inhibiting LKB1-AMPK signaling through ribulose-5-phosphate (Ru-5-P), the product of the third enzyme 6-phosphogluconate dehydrogenase (6PGD). We provide evidence supporting that ?-6-phosphogluconolactone (?-6PGL), a ?dead end? byproduct of the oxiPPP with unknown physiological function, serves as a signaling molecule that contributes to AMPK activation by enhancing inhibition of AMPK upstream phosphatase PP2A by Src. Thus, we hypothesize that oxiPPP regulates AMPK homeostasis by balancing the opposing LKB1 and PP2A.
|Lin, Ruiting; Xia, Siyuan; Shan, Changliang et al. (2018) The Dietary Supplement Chondroitin-4-Sulfate Exhibits Oncogene-Specific Pro-tumor Effects on BRAF V600E Melanoma Cells. Mol Cell 69:923-937.e8|
|Xia, Siyuan; Lin, Ruiting; Jin, Lingtao et al. (2017) Prevention of Dietary-Fat-Fueled Ketogenesis Attenuates BRAF V600E Tumor Growth. Cell Metab 25:358-373|
|Zhao, Liang; Fan, Jun; Xia, Siyuan et al. (2017) HMG-CoA synthase 1 is a synthetic lethal partner of BRAFV600E in human cancers. J Biol Chem 292:10142-10152|
|Elf, S; Lin, R; Xia, S et al. (2017) Targeting 6-phosphogluconate dehydrogenase in the oxidative PPP sensitizes leukemia cells to antimalarial agent dihydroartemisinin. Oncogene 36:254-262|
|Zhang, Ye; Xu, Ying-Ying; Yao, Chuan-Bo et al. (2017) Acetylation targets HSD17B4 for degradation via the CMA pathway in response to estrone. Autophagy 13:538-553|
|Fan, Jun; Lin, Ruiting; Xia, Siyuan et al. (2016) Tetrameric Acetyl-CoA Acetyltransferase 1 Is Important for Tumor Growth. Mol Cell 64:859-874|
|Gao, Xue; Lin, Shu-Hai; Ren, Feng et al. (2016) Acetate functions as an epigenetic metabolite to promote lipid synthesis under hypoxia. Nat Commun 7:11960|
|Lin, Ruiting; Elf, Shannon; Shan, Changliang et al. (2015) 6-Phosphogluconate dehydrogenase links oxidative PPP, lipogenesis and tumour growth by inhibiting LKB1-AMPK signalling. Nat Cell Biol 17:1484-96|
|Jin, Lingtao; Li, Dan; Alesi, Gina N et al. (2015) Glutamate dehydrogenase 1 signals through antioxidant glutathione peroxidase 1 to regulate redox homeostasis and tumor growth. Cancer Cell 27:257-70|
|Wang, Jing; Luo, Cheng; Shan, Changliang et al. (2015) Inhibition of human copper trafficking by a small molecule significantly attenuates cancer cell proliferation. Nat Chem 7:968-79|
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