c-Src Promotes Tumorigenesis and Tumor Progression by Activating PFKFB3.

Reprogramming of glucose metabolism is a key event in tumorigenesis and progression. Here, we show that active c-Src stimulates glycolysis by phosphorylating (Tyr194) and activating PFKFB3, a key enzyme that boosts glycolysis by producing fructose-2,6-bisphosphate and activating PFK1. Increased glycolysis intermediates replenish non-oxidative pentose phosphate pathway (PPP) and serine pathway for biosynthesis of cancer cells. PFKFB3 knockout (KO) cells and their counterpart reconstituted with PFKFB3-Y194F show comparably impaired abilities for proliferation, migration, and xenograft formation. Furthermore, PFKFB3-Y194F knockin mice show impaired glycolysis and, mating of these mice with APCmin/+ mice attenuates spontaneous colon cancer formation in APCmin/+ mice. In summary, we identify a specific mechanism by which c-Src mediates glucose metabolism to meet cancer cells' requirements for maximal biosynthesis and proliferation. The PFKFB3-Tyr194 phosphorylation level highly correlates with c-Src activity in clinical tumor samples, indicating its potential as an evaluation for tumor prognosis.

Sedoheptulose-1,7-bisphospate Accumulation and Metabolic Anomalies in Hepatoma Cells Exposed to Oxidative Stress.

We have previously shown that GSH depletion alters global metabolism of cells. In the present study, we applied a metabolomic approach for studying the early changes in metabolism in hydrogen peroxide- (H2O2-) treated hepatoma cells which were destined to die. Levels of fructose 1,6-bisphosphate and an unusual metabolite, sedoheptulose 1,7-bisphosphate (S-1,7-BP), were elevated in hepatoma Hep G2 cells. Deficiency in G6PD activity significantly reduced S-1,7-BP formation, suggesting that S-1,7-BP is formed in the pentose phosphate pathway as a response to oxidative stress. Additionally, H2O2 treatment significantly increased the level of nicotinamide adenine dinucleotide phosphate (NADP+) and reduced the levels of ATP and NAD+. Severe depletion of ATP and NAD+ in H2O2-treated Hep G2 cells was associated with cell death. Inhibition of PARP-mediated NAD+ depletion partially protected cells from death. Comparison of metabolite profiles of G6PD-deficient cells and their normal counterparts revealed that changes in GSH and GSSG per se do not cause cell death. These findings suggest that the failure of hepatoma cells to maintain energy metabolism in the midst of oxidative stress may cause cell death.

Stable Isotope-Labeled Lipidomics to Unravel the Heterogeneous Development Lipotoxicity.

Non-alcoholic fatty liver disease (NAFLD) as a global health problem has clinical manifestations ranging from simple non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH), cirrhosis, and cancer. The role of different types of fatty acids in driving the early progression of NAFL to NASH is not understood. Lipid overload causing lipotoxicity and inflammation has been considered as an essential pathogenic factor. To correlate the lipid profiles with cellular lipotoxicity, we utilized palmitic acid (C16:0)- and especially unprecedented palmitoleic acid (C16:1)-induced lipid overload HepG2 cell models coupled with lipidomic technology involving labeling with stable isotopes. C16:0 induced inflammation and cell death, whereas C16:1 induced significant lipid droplet accumulation. Moreover, inhibition of de novo sphingolipid synthesis by myriocin (Myr) aggravated C16:0 induced lipoapoptosis. Lipid profiles are different in C16:0 and C16:1-treated cells. Stable isotope-labeled lipidomics elucidates the roles of specific fatty acids that affect lipid metabolism and cause lipotoxicity or lipid droplet formation. It indicates that not only saturation or monounsaturation of fatty acids plays a role in hepatic lipotoxicity but also Myr inhibition exasperates lipoapoptosis through ceramide in-direct pathway. Using the techniques presented in this study, we can potentially investigate the mechanism of lipid metabolism and the heterogeneous development of NAFLD.