Increased OXPHOS activity precedes rise in glycolytic rate in H-RasV12/E1A transformed fibroblasts that develop a Warburg phenotype.
BACKGROUND
The Warburg phenotype in cancer cells has been long recognized, but there is still limited insight in the consecutive metabolic alterations that characterize its establishment. We obtained better understanding of the coupling between metabolism and malignant transformation by studying mouse embryonic fibroblast-derived cells with loss-of-senescence or H-RasV12/E1A-transformed phenotypes at different stages of oncogenic progression.


RESULTS
Spontaneous immortalization or induction of senescence-bypass had only marginal effects on metabolic profiles and viability. In contrast, H-RasV12/E1A transformation initially caused a steep increase in oxygen consumption and superoxide production, accompanied by massive cell death. During prolonged culture in vitro, cell growth rate increased gradually, along with tumor forming potential in in vitro anchorage-independent growth assays and in vivo tumor formation assays in immuno-deficient mice. Notably, glucose-to-lactic acid flux increased with passage number, while cellular oxygen consumption decreased. This conversion in metabolic properties was associated with a change in mitochondrial NAD+/NADH redox, indicative of decreased mitochondrial tricarboxic acid cycle and OXPHOS activity.


CONCLUSIONS
The high rate of oxidative metabolism in newly transformed cells is in marked contrast with the high glycolytic rate in cells in the later tumor stage. In our experimental system, with cells growing under ambient oxygen conditions in nutrient-rich media, the shift towards this Warburg phenotype occurred as a step-wise adaptation process associated with augmented tumorigenic capacity and improved survival characteristics of the transformed cells. We hypothesize that early-transformed cells, which potentially serve as founders for new tumor masses may escape therapies aimed at metabolic inhibition of tumors with a fully developed Warburg phenotype.
de Groof
Ad J C
AJ
Department of Cell Biology, Nijmegen Centre for Molecular Life Sciences, Radboud University Medical Centre, Nijmegen, The Netherlands. a.degroof@ncmls.ru.nl
te Lindert
Mariska M
MM
van Dommelen
Michiel M T
MM
Wu
Min
M
Willemse
Marieke
M
Smift
Amy L
AL
Winer
Mike
M
Oerlemans
Frank
F
Pluk
Helma
H
Fransen
Jack A M
JA
Wieringa
Bé
B
D017500:Adenovirus E1A Proteins / Q000235:genetics / Q000502:physiology; D000818:Animals; D002461:Cell Line, Transformed; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D006019:Glycolysis; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D055442:Metabolome; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008855:Microscopy, Electron, Scanning; D008928:Mitochondria / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption; D012190:Retroviridae / Q000235:genetics; D013481:Superoxides / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000502:physiology
D017500:Adenovirus E1A Proteins; D009243:NAD; D013481:Superoxides; D019344:Lactic Acid; D018631:ras Proteins