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mTORC2 controls cancer cell survival by modulating gluconeogenesis

View Article: PubMed Central - PubMed

ABSTRACT

For rapid tumor growth, cancer cells often reprogram the cellular metabolic processes to obtain enhanced anabolic precursors and energy. The molecular changes of such metabolic rewiring are far from established. Here we explored the role of mTOR (mechanistic target of rapamycin), which serves as a key regulator of cell growth, proliferation and survival, in the metabolic reprograming of cancer cells. When we inhibited mTOR in human hepatocellular carcinoma (HCC) and renal cell carcinoma (RCC) cells, using pharmacologic inhibitors or by RNA interference, we noticed shuttle of the glycolytic flux to gluconeogenesis pathway along with reduction in cellular proliferation and survival. Augmentation of gluconeogenesis was mechanistically linked to upregulation of the key gluconeogenic enzymes PCK1 and G6PC expressions, enhanced lactate dehydrogenase activity and glucose-derived lipogenesis without causing any attenuation in mitochondrial function. Interestingly, concomitant knocking down of PCK1 and not G6PC along with mTOR pathway could overcome the inhibition of cancer cell proliferation and survival. These observations were validated by identifying distinctive diminution of PCK1 and G6PC expressions in human HCC and RCC transcriptome data. Significant correlation between mTOR-dependent upregulation of PCK1 and cell death in different cancer cell lines further emphasizes the physiological relevance of this pathway. We reveal for the first time that inhibition of mTORC2 and consequent redistribution of glycolytic flux can have a prosurvival role in HCC and RCC cancer cells only in the presence of downregulation of gluconeogenesis pathway genes, thus identifying novel pivots of cancer cell metabolic rewiring and targets for therapy.

No MeSH data available.


mTOR inhibition reduces metabolic flux to the mitochondria. (a–c) Cells were treated/transfected as described earlier and pyruvate, acetyl-coA and citrate levels were measured in triplicate samples in whole-cell lysates and normalized to the total cellular protein as described in Materials and Methods. All panels: n=4, *P<0.05, **P<0.01 compared with Con or sc cells.
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fig3: mTOR inhibition reduces metabolic flux to the mitochondria. (a–c) Cells were treated/transfected as described earlier and pyruvate, acetyl-coA and citrate levels were measured in triplicate samples in whole-cell lysates and normalized to the total cellular protein as described in Materials and Methods. All panels: n=4, *P<0.05, **P<0.01 compared with Con or sc cells.

Mentions: In the glycolytic pathway, glucose is metabolized to form acetyl-CoA, which condensed with oxaloacetate eventually generates citrate in the mitochondrial TCA cycle. The cytosolic pool of acetyl-CoA, the precursor of fatty acid synthesis, is predominantly contributed by the hydrolysis of mitochondria-derived citrate by the cytosolic ATP citrate lyase.37 Our results showing a decrease in the de novo lipogenesis as well as in the glucose-dependent lipogenesis could be attributed to the downregulation of SREBP-1c expression or because of a decrease in the available metabolic flux or both (Figures 1c–e). To examine whether mTOR modulates the metabolic flux in the glycolysis and TCA cycle, we measured concentrations of pyruvate, acetyl-CoA and citrate in mTOR-inhibited cells. Cellular pyruvate levels were found to be significantly enhanced (Figure 3a), whereas cellular acetyl-CoA and citrate levels were significantly reduced by torin1 treatment as well as by knockdown of raptor and rictor (Figures 3b and c).


mTORC2 controls cancer cell survival by modulating gluconeogenesis
mTOR inhibition reduces metabolic flux to the mitochondria. (a–c) Cells were treated/transfected as described earlier and pyruvate, acetyl-coA and citrate levels were measured in triplicate samples in whole-cell lysates and normalized to the total cellular protein as described in Materials and Methods. All panels: n=4, *P<0.05, **P<0.01 compared with Con or sc cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4979518&req=5

fig3: mTOR inhibition reduces metabolic flux to the mitochondria. (a–c) Cells were treated/transfected as described earlier and pyruvate, acetyl-coA and citrate levels were measured in triplicate samples in whole-cell lysates and normalized to the total cellular protein as described in Materials and Methods. All panels: n=4, *P<0.05, **P<0.01 compared with Con or sc cells.
Mentions: In the glycolytic pathway, glucose is metabolized to form acetyl-CoA, which condensed with oxaloacetate eventually generates citrate in the mitochondrial TCA cycle. The cytosolic pool of acetyl-CoA, the precursor of fatty acid synthesis, is predominantly contributed by the hydrolysis of mitochondria-derived citrate by the cytosolic ATP citrate lyase.37 Our results showing a decrease in the de novo lipogenesis as well as in the glucose-dependent lipogenesis could be attributed to the downregulation of SREBP-1c expression or because of a decrease in the available metabolic flux or both (Figures 1c–e). To examine whether mTOR modulates the metabolic flux in the glycolysis and TCA cycle, we measured concentrations of pyruvate, acetyl-CoA and citrate in mTOR-inhibited cells. Cellular pyruvate levels were found to be significantly enhanced (Figure 3a), whereas cellular acetyl-CoA and citrate levels were significantly reduced by torin1 treatment as well as by knockdown of raptor and rictor (Figures 3b and c).

View Article: PubMed Central - PubMed

ABSTRACT

For rapid tumor growth, cancer cells often reprogram the cellular metabolic processes to obtain enhanced anabolic precursors and energy. The molecular changes of such metabolic rewiring are far from established. Here we explored the role of mTOR (mechanistic target of rapamycin), which serves as a key regulator of cell growth, proliferation and survival, in the metabolic reprograming of cancer cells. When we inhibited mTOR in human hepatocellular carcinoma (HCC) and renal cell carcinoma (RCC) cells, using pharmacologic inhibitors or by RNA interference, we noticed shuttle of the glycolytic flux to gluconeogenesis pathway along with reduction in cellular proliferation and survival. Augmentation of gluconeogenesis was mechanistically linked to upregulation of the key gluconeogenic enzymes PCK1 and G6PC expressions, enhanced lactate dehydrogenase activity and glucose-derived lipogenesis without causing any attenuation in mitochondrial function. Interestingly, concomitant knocking down of PCK1 and not G6PC along with mTOR pathway could overcome the inhibition of cancer cell proliferation and survival. These observations were validated by identifying distinctive diminution of PCK1 and G6PC expressions in human HCC and RCC transcriptome data. Significant correlation between mTOR-dependent upregulation of PCK1 and cell death in different cancer cell lines further emphasizes the physiological relevance of this pathway. We reveal for the first time that inhibition of mTORC2 and consequent redistribution of glycolytic flux can have a prosurvival role in HCC and RCC cancer cells only in the presence of downregulation of gluconeogenesis pathway genes, thus identifying novel pivots of cancer cell metabolic rewiring and targets for therapy.

No MeSH data available.