Abstract
Cancer cells may survive under oxygen and nutrient deprivation by metabolic reprogramming for high levels of anaerobic glycolysis, which contributes to tumor growth and drug resistance. Abnormally expressed glucose transporters (GLUTs) are colocalized with hypoxia (Hx) inducible factor (HIF)1α in peri-necrotic regions in human colorectal carcinoma. However, the underlying mechanisms of anti-necrotic resistance conferred by glucose metabolism in hypoxic cancer cells remain poorly understood. Our aim was to investigate signaling pathways of Hx-induced necroptosis and explore the role of glucose pyruvate metabolite in mechanisms of death resistance. Human colorectal carcinoma cells were Hx exposed with or without glucose, and cell necroptosis was examined by receptor-interacting protein (RIP)1/3 kinase immunoprecipitation and 32P kinase assays. Our results showed increased RIP1/3 complex formation and phosphorylation in hypoxic, but not normoxic cells in glucose-free media. Blocking RIP1 signaling, by necrostatin-1 or gene silencing, decreased lactodehydrogenase (LDH) leakage and plasma membrane disintegration. Generation of mitochondrial superoxide was noted after hypoxic challenge; its reduction by antioxidants inhibited RIP signaling and cell necrosis. Supplementation of glucose diminished the RIP-dependent LDH leakage and morphological damage in hypoxic cells, whereas non-metabolizable sugar analogs did not. Hypoxic cells given glucose showed nuclear translocation of HIF1α associated with upregulation of GLUT-1 and GLUT-4 expression, as well as increase of intracellular ATP, pyruvate and lactate levels. The glucose-mediated death resistance was ablated by iodoacetate (an inhibitor to glyceraldehyde-3-phosphate dehydrogenase), but not by UK5099 (an inhibitor to mitochondrial pyruvate carrier), suggesting that glycolytic pathway was involved in anti-necrotic mechanism. Lastly, replacing glucose with cell-permeable pyruvate derivative also led to decrease of Hx-induced necroptosis by suppression of mitochondrial superoxide in an energy-independent manner. In conclusion, glycolytic metabolism confers resistance to RIP-dependent necroptosis in hypoxic cancer cells partly through pyruvate scavenging of mitochondrial free radicals.
Highlights
HIF1a.6–12 To date, glucose-mediated mechanisms involved in promoting tumor survival against hypoxic stress remain incompletely understood
Necrosis has been traditionally regarded as an uncontrolled form of cell death, recent data indicated that programmed necrosis or necroptosis is regulated by receptor-interacting protein (RIP)
Human colorectal carcinoma Caco-2 cells were exposed to normoxia (Nx) or Hx in glucose-free media (F) for various time points, and a time-dependent increase of lactodehydrogenase (LDH) leakage was observed in Hx þ F but not Nx þ F cells (Figure 1a)
Summary
HIF1a.6–12 To date, glucose-mediated mechanisms involved in promoting tumor survival against hypoxic stress remain incompletely understood. Recent reports documented that HIF1a and GLUT-1 colocalize at peri-necrotic regions in human colorectal tumors,[13,22] suggesting that glucose metabolism may confer anti-necrotic resistance to hypoxic stress. Glucose is catalyzed to ATP and pyruvate by a cascade of glycolytic enzymes, such as glucokinase and glyceraldehyde-3-phosphate dehydrogenase (GPD).[23] The final glycolytic product pyruvate is the starting substrate for tricarboxylic acid cycle after being transported across inner mitochondrial membrane by mitochondrial pyruvate carrier (MPC).[24,25] Aside from its critical role as the link between glycolysis and mitochondrial respiration, pyruvate scavenges ROS through a non-enzymatic reaction.[26] Numerous studies have suggested that chemoresistance may be due in part to glycolytic ATP as a preferential energy source for promoting cancer cell survival.[27,28] whether glycolytic pyruvate metabolite has a role in circumventing Hx-induced necrotic death has yet to be explored
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
