The role of the Crabtree effect and an endogenous fuel in the energy metabolism of resting and proliferating thymocytes

Abstract

Rat thymocytes have been used to characterize the changes in energy metabolism that occur as cells undergo a resting/proliferation transition. In the resting state, anaerobic ATP production accounts for only 4% of ATP turnover. The remainder is fueled by the oxidation of a mixture of an unidentified endogenous fuel (62%), glucose (18%) and glutamine (16%). 48 h after mitogen stimulation, the ATP turnover has increased twofold. In these proliferating cells, glucose inhibits oxygen consumption by 58%, indicating a profound Crabtree effect which is not present in resting cells. Consequently, proliferating cells, in the presence of glucose and glutamine, fuel the majority (61%) of ATP turnover anaerobically, producing lactate from glucose. The development of a Crabtree effect may be the result of the 8-10-fold increase in glycolytic enzyme activities which occurs with proliferation. Possible advantages of such a proliferative metabolism are a sparing of endogenous fuel, and a minimizing of oxidative metabolism, with its concurrent production of free radicals.The Crabtree effect (the inhibition of oxygen consumption by the addition of glucose) was first described in tumor tissue (Crabtree, 1929). A Crabtree effect must by necessity result in aerobic glycolysis (the production of lactate despite the presence of mitochondria and oxygen), a phenomenon that was documented by Warburg in 1929. The Crabtree effect and/or aerobic glycolysis has been demonstrated in a variety of cancer cells (Nelson et al., 1984;Racker, 1965;Sener et al., 1988;Burk et al., 1967;Brand et al., 1986), as well as non-cancer tissues such as pig platelets, coronary epithelium, guinea pig sperm, hamster embryos, thymocytes and smooth muscle (Nishimura and Minakami, 1975; No11 et al., 1990; Mujica et al., 1991 ;Seshagiri and Bavister, 1991 ;Brand, 1985;Barron et al., 1991).The more general occurrence, of at least aerobic glycolysis, led to the suggestion that these processes are a characteristic of proliferative metabolism rather than cancer metabolism per se (for a compilation of pertinant literature, see Wang et al., 1976). Proliferative metabolism is of course an integral part of cancer metabolism. Data on proliferative metabolism are rare, but two very recent studies do not support such a link. In Ehrlich ascites tumor cells, ATP turnover increases by 1.5-fold with proliferation, the increase is fueled oxidatively, and the rate of aerobic lactate production is constant and high, accounting for 35 -50% of ATP turnover (Schmidt et al., 1991). In this case, aerobic glycolysis is evident, but there is no evidence of glycolysis assuming a greater role in ATP production with proliferation, and a possible correlation between proliferation and a Crabtree effect was not investigated. Data on proliferating and differentiating mouse erythroid cells, although very limited, again suggest limited glucose oxidation, but no correlation between glycolytic ATP production and proliferatioddifferentiation (Kim et al., 1991).Rat thymocytes provide a model system for...

Metabolic reprogramming of the tumor

“…Nevertheless, Crabtree suggested already in 1929 that exacerbated glycolytic activity hampered respiration, not only in tumors but also in other mitotically active tissues. The inhibition of oxygen consumption by glucose in proliferating cells was then named the Crabtree effect (Guppy et al, 1993). Decades later, Weinhouse (1972) observed that tumor cells possess fetal isoforms of some glycolytic enzymes, suggesting this could be responsible for their increased glycolytic flux.…”

“…Glucose levels in blood are exquisitely maintained at approximately 5 mM under physiological conditions (Rodgers et al, 2005). Remarkably, this substrate represents the major energy (Guppy et al, 1993) and carbon source of proliferating cells; glucose deprivation can induce cellcycle arrest (Holley and Kiernan, 1974) and death (Ahmad et al, 2005). Thus, variations in glucose availability/utilization arising within specific cell niches generate clonal selection pressures.…”

“…On the other hand, glutamine is transported into the cell and then to the mitochondria, where glutaminase converts it to glutamate; the latter is then converted to a-ketoglutarate, a TCAC intermediate. The relative flux increases refer to cancer cells in general in comparison with normal cells (see also Cairns et al, 2011). into glycolysis, allowing greater ATP production rates (Guppy et al, 1993). Furthermore, part of glucose-6-phosphate is shunted to the pentose phosphate pathway, generating ribose and NADPH, which sustain increased nucleic acid and fatty acid biosynthetic demands (Ramos-Montoya et al, 2006).…”

Effect of Extracellular AMP on Cell Proliferation and Metabolism of Breast Cancer Cell Lines with High and Low Glycolytic Rates

“…1A). Cell proliferation is a process that consumes a great deal of energy with a 2-4-fold increase over nonproliferating cells (87)(88)(89). Therefore, the inhibition of cell proliferation under glucose starvation saves energy, and all of the ATP produced by glycolysis is used for the survival of the cells.…”

Fuel Choices by Human Platelets in Human Plasma

“…Oxygen consumption was not measured and would almost certainly demonstrate the oxidation of other fuels. Similarly it is now obvious that aerobic glycolysis contributes significantly (20 -50%) to ATP production under aerobic conditions in a variety of cell types (reviewed in Neermann and Wagner, 1996;Guppy et al, 1993) so lactate production must be measured if one is to get a meaningful measure of total ATP turnover.…”