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Dormancy of cancer cells with suppression of AKT activity contributes to survival in chronic hypoxia.

Endo H, Okuyama H, Ohue M, Inoue M - PLoS ONE (2014)

Bottom Line: ATP turnover, an indicator of energy demand, was markedly decreased and accompanied by reduced AKT phosphorylation.Forced activation of AKT resulted in increased ATP turnover and massive cell death in vitro and a decreased number of dormant cells in vivo.Primary colorectal cancer cells in dormancy were resistant to chemotherapy.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.

ABSTRACT
A hypoxic microenvironment in tumors has been recognized as a cause of malignancy or resistance to various cancer therapies. In contrast to recent progress in understanding the acute response of cancer cells to hypoxia, the characteristics of tumor cells in chronic hypoxia remain elusive. We have identified a pancreatic cancer cell line, AsPC-1, that is exceptionally able to survive for weeks under 1% oxygen conditions while most tested cancer cell lines die after only some days under these conditions. In chronic hypoxia, AsPC-1 cells entered a state of dormancy characterized by no proliferation, no death, and metabolic suppression. They reversibly switched to active status after being placed again in optimal culture conditions. ATP turnover, an indicator of energy demand, was markedly decreased and accompanied by reduced AKT phosphorylation. Forced activation of AKT resulted in increased ATP turnover and massive cell death in vitro and a decreased number of dormant cells in vivo. In contrast to most cancer cell lines, primary-cultured colorectal cancer cells easily entered the dormant status with AKT suppression under hypoxia combined with growth factor-depleted conditions. Primary colorectal cancer cells in dormancy were resistant to chemotherapy. Thus, the ability to survive in a deteriorated microenvironment by entering into dormancy under chronic hypoxia might be a common property among cancer cells. Targeting the regulatory mechanism inducing this dormant status could provide a new strategy for treating cancer.

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Metabolic processes are suppressed under chronic hypoxia.A) Lactate production rate (left) was calculated from lactate concentration and integral cell number at indicated periods. O2 consumption rate (middle) was measured using a Clark type oxygen electrode. ATP turnover (right) was calculated from the lactate production rate and O2 consumption rate (dark gray: lactate; light gray: oxygen). N1, normoxia 1 day; H1, hypoxia 1 day; H7, hypoxia 7 days. ** p<0.01, ***p<0.001. B) Quantitative RT-PCR of a glucose transporter and glycolytic enzymes in AsPC-1 cells cultured in hypoxia for the indicated days.
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pone-0098858-g002: Metabolic processes are suppressed under chronic hypoxia.A) Lactate production rate (left) was calculated from lactate concentration and integral cell number at indicated periods. O2 consumption rate (middle) was measured using a Clark type oxygen electrode. ATP turnover (right) was calculated from the lactate production rate and O2 consumption rate (dark gray: lactate; light gray: oxygen). N1, normoxia 1 day; H1, hypoxia 1 day; H7, hypoxia 7 days. ** p<0.01, ***p<0.001. B) Quantitative RT-PCR of a glucose transporter and glycolytic enzymes in AsPC-1 cells cultured in hypoxia for the indicated days.

Mentions: We further assessed the status of energy metabolism of the cancer cells in the dormant state. As expected, AsPC-1 cells consumed more glucose and produced more lactate in the acute phase of hypoxia compared with normoxia. In contrast, after 7 days of hypoxia, glucose uptake and lactate production gradually attenuated (Figure 2A, S3A and S3B). The oxygen consumption rate was also decreased under chronic hypoxia (Figure 2A). We calculated the ATP turnover from lactate production rate and oxygen consumption rate (Figure 2A) and found that the ATP turnover decreased under chronic hypoxia. This finding was also supported by a slower decrease in cellular ATP levels after the addition of a cocktail of inhibitors of glycolysis and oxidative phosphorylation (Figure S3C and S3D) [21].


Dormancy of cancer cells with suppression of AKT activity contributes to survival in chronic hypoxia.

Endo H, Okuyama H, Ohue M, Inoue M - PLoS ONE (2014)

Metabolic processes are suppressed under chronic hypoxia.A) Lactate production rate (left) was calculated from lactate concentration and integral cell number at indicated periods. O2 consumption rate (middle) was measured using a Clark type oxygen electrode. ATP turnover (right) was calculated from the lactate production rate and O2 consumption rate (dark gray: lactate; light gray: oxygen). N1, normoxia 1 day; H1, hypoxia 1 day; H7, hypoxia 7 days. ** p<0.01, ***p<0.001. B) Quantitative RT-PCR of a glucose transporter and glycolytic enzymes in AsPC-1 cells cultured in hypoxia for the indicated days.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4048292&req=5

pone-0098858-g002: Metabolic processes are suppressed under chronic hypoxia.A) Lactate production rate (left) was calculated from lactate concentration and integral cell number at indicated periods. O2 consumption rate (middle) was measured using a Clark type oxygen electrode. ATP turnover (right) was calculated from the lactate production rate and O2 consumption rate (dark gray: lactate; light gray: oxygen). N1, normoxia 1 day; H1, hypoxia 1 day; H7, hypoxia 7 days. ** p<0.01, ***p<0.001. B) Quantitative RT-PCR of a glucose transporter and glycolytic enzymes in AsPC-1 cells cultured in hypoxia for the indicated days.
Mentions: We further assessed the status of energy metabolism of the cancer cells in the dormant state. As expected, AsPC-1 cells consumed more glucose and produced more lactate in the acute phase of hypoxia compared with normoxia. In contrast, after 7 days of hypoxia, glucose uptake and lactate production gradually attenuated (Figure 2A, S3A and S3B). The oxygen consumption rate was also decreased under chronic hypoxia (Figure 2A). We calculated the ATP turnover from lactate production rate and oxygen consumption rate (Figure 2A) and found that the ATP turnover decreased under chronic hypoxia. This finding was also supported by a slower decrease in cellular ATP levels after the addition of a cocktail of inhibitors of glycolysis and oxidative phosphorylation (Figure S3C and S3D) [21].

Bottom Line: ATP turnover, an indicator of energy demand, was markedly decreased and accompanied by reduced AKT phosphorylation.Forced activation of AKT resulted in increased ATP turnover and massive cell death in vitro and a decreased number of dormant cells in vivo.Primary colorectal cancer cells in dormancy were resistant to chemotherapy.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.

ABSTRACT
A hypoxic microenvironment in tumors has been recognized as a cause of malignancy or resistance to various cancer therapies. In contrast to recent progress in understanding the acute response of cancer cells to hypoxia, the characteristics of tumor cells in chronic hypoxia remain elusive. We have identified a pancreatic cancer cell line, AsPC-1, that is exceptionally able to survive for weeks under 1% oxygen conditions while most tested cancer cell lines die after only some days under these conditions. In chronic hypoxia, AsPC-1 cells entered a state of dormancy characterized by no proliferation, no death, and metabolic suppression. They reversibly switched to active status after being placed again in optimal culture conditions. ATP turnover, an indicator of energy demand, was markedly decreased and accompanied by reduced AKT phosphorylation. Forced activation of AKT resulted in increased ATP turnover and massive cell death in vitro and a decreased number of dormant cells in vivo. In contrast to most cancer cell lines, primary-cultured colorectal cancer cells easily entered the dormant status with AKT suppression under hypoxia combined with growth factor-depleted conditions. Primary colorectal cancer cells in dormancy were resistant to chemotherapy. Thus, the ability to survive in a deteriorated microenvironment by entering into dormancy under chronic hypoxia might be a common property among cancer cells. Targeting the regulatory mechanism inducing this dormant status could provide a new strategy for treating cancer.

Show MeSH
Related in: MedlinePlus