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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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AsPC-1 cells can be in a dormant status in chronic hypoxia.Viable cell number (A) and percent cell death (B) of AsPC-1 cells cultured in normoxia (20% O2) or hypoxia (1% O2). C) Phase-contrast and PI-stained images of AsPC-1 cells cultured under the indicated conditions. Scale bar  = 50 µm. D) Cell cycle analysis of AsPC-1 cells at day 1 in normoxia or day 1 and day 7 in hypoxia. Cells were pulsed with BrdU for 2 h and analyzed by flow cytometry after staining with anti-BrdU antibody and PI. Percentages of the cells in S phase are indicated. E) Re-growth of AsPC-1 cells in a dormant status. AsPC-1 cells were cultured in hypoxia for 14 days, and the cell counts were monitored after re-seeding in normoxic conditions.
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pone-0098858-g001: AsPC-1 cells can be in a dormant status in chronic hypoxia.Viable cell number (A) and percent cell death (B) of AsPC-1 cells cultured in normoxia (20% O2) or hypoxia (1% O2). C) Phase-contrast and PI-stained images of AsPC-1 cells cultured under the indicated conditions. Scale bar  = 50 µm. D) Cell cycle analysis of AsPC-1 cells at day 1 in normoxia or day 1 and day 7 in hypoxia. Cells were pulsed with BrdU for 2 h and analyzed by flow cytometry after staining with anti-BrdU antibody and PI. Percentages of the cells in S phase are indicated. E) Re-growth of AsPC-1 cells in a dormant status. AsPC-1 cells were cultured in hypoxia for 14 days, and the cell counts were monitored after re-seeding in normoxic conditions.

Mentions: In contrast, AsPC-1, a pancreatic cancer cell line, was exceptionally able to survive under prolonged hypoxic conditions (Figure 1A and C). In the acute phase, AsPC-1 cells in hypoxia grew as well as in normoxic conditions, but the proliferation rate gradually decreased until day 7, and the cell number plateaued around day 10 at less than 80% confluence in the experimental conditions. The cells in normoxia showed massive cell death after 14 days, probably because of the depletion of growth factors or nutrients (Figure 1B and C). In contrast, the cells in hypoxia were viable for more than three weeks without any sign of cell death while the medium was not changed at all. Cell cycle analysis revealed that S-phase cells drastically decreased at day 7 in hypoxia compared with at day 1 in normoxia or hypoxia (Figure 1D). The cells were accumulated in either G0/1 or G2/M phase. This decreased proliferation was reversible; once re-oxygenized and re-plated into the fresh medium, the AsPC-1 cells showed a recovery of the proliferation rate to control levels with a little delay, even after having been cultured for 14 days in hypoxia (Figure 1E). These results indicated that AsPC-1 cells could reversibly enter an inactive status, dormancy, under prolonged hypoxic conditions.


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)

AsPC-1 cells can be in a dormant status in chronic hypoxia.Viable cell number (A) and percent cell death (B) of AsPC-1 cells cultured in normoxia (20% O2) or hypoxia (1% O2). C) Phase-contrast and PI-stained images of AsPC-1 cells cultured under the indicated conditions. Scale bar  = 50 µm. D) Cell cycle analysis of AsPC-1 cells at day 1 in normoxia or day 1 and day 7 in hypoxia. Cells were pulsed with BrdU for 2 h and analyzed by flow cytometry after staining with anti-BrdU antibody and PI. Percentages of the cells in S phase are indicated. E) Re-growth of AsPC-1 cells in a dormant status. AsPC-1 cells were cultured in hypoxia for 14 days, and the cell counts were monitored after re-seeding in normoxic conditions.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0098858-g001: AsPC-1 cells can be in a dormant status in chronic hypoxia.Viable cell number (A) and percent cell death (B) of AsPC-1 cells cultured in normoxia (20% O2) or hypoxia (1% O2). C) Phase-contrast and PI-stained images of AsPC-1 cells cultured under the indicated conditions. Scale bar  = 50 µm. D) Cell cycle analysis of AsPC-1 cells at day 1 in normoxia or day 1 and day 7 in hypoxia. Cells were pulsed with BrdU for 2 h and analyzed by flow cytometry after staining with anti-BrdU antibody and PI. Percentages of the cells in S phase are indicated. E) Re-growth of AsPC-1 cells in a dormant status. AsPC-1 cells were cultured in hypoxia for 14 days, and the cell counts were monitored after re-seeding in normoxic conditions.
Mentions: In contrast, AsPC-1, a pancreatic cancer cell line, was exceptionally able to survive under prolonged hypoxic conditions (Figure 1A and C). In the acute phase, AsPC-1 cells in hypoxia grew as well as in normoxic conditions, but the proliferation rate gradually decreased until day 7, and the cell number plateaued around day 10 at less than 80% confluence in the experimental conditions. The cells in normoxia showed massive cell death after 14 days, probably because of the depletion of growth factors or nutrients (Figure 1B and C). In contrast, the cells in hypoxia were viable for more than three weeks without any sign of cell death while the medium was not changed at all. Cell cycle analysis revealed that S-phase cells drastically decreased at day 7 in hypoxia compared with at day 1 in normoxia or hypoxia (Figure 1D). The cells were accumulated in either G0/1 or G2/M phase. This decreased proliferation was reversible; once re-oxygenized and re-plated into the fresh medium, the AsPC-1 cells showed a recovery of the proliferation rate to control levels with a little delay, even after having been cultured for 14 days in hypoxia (Figure 1E). These results indicated that AsPC-1 cells could reversibly enter an inactive status, dormancy, under prolonged hypoxic conditions.

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