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The regulation of mitochondrial DNA copy number in glioblastoma cells.

Dickinson A, Yeung KY, Donoghue J, Baker MJ, Kelly RD, McKenzie M, Johns TG, St John JC - Cell Death Differ. (2013)

Bottom Line: As stem cells undergo differentiation, mitochondrial DNA (mtDNA) copy number is strictly regulated in order that specialized cells can generate appropriate levels of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) to undertake their specific functions.We show that human neural stem cells (hNSCs) increased their mtDNA content during differentiation in a process that was mediated by a synergistic relationship between the nuclear and mitochondrial genomes and results in increased respiratory capacity.However, prolonged depletion resulted in impaired mtDNA replication, reduced proliferation and induced the expression of early developmental and pro-survival markers including POU class 5 homeobox 1 (OCT4) and sonic hedgehog (SHH).

View Article: PubMed Central - PubMed

Affiliation: 1] The Mitochondrial Genetics Group, Centre for Genetic Diseases, Monash Institute of Medical Research, Monash University, 27-31 Wright Street, Clayton, Victoria 3168, Australia [2] Molecular Basis of Metabolic Disease, Division of Metabolic and Vascular Health, Warwick Medical School, The University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX, UK.

ABSTRACT
As stem cells undergo differentiation, mitochondrial DNA (mtDNA) copy number is strictly regulated in order that specialized cells can generate appropriate levels of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) to undertake their specific functions. It is not understood whether tumor-initiating cells regulate their mtDNA in a similar manner or whether mtDNA is essential for tumorigenesis. We show that human neural stem cells (hNSCs) increased their mtDNA content during differentiation in a process that was mediated by a synergistic relationship between the nuclear and mitochondrial genomes and results in increased respiratory capacity. Differentiating multipotent glioblastoma cells failed to match the expansion in mtDNA copy number, patterns of gene expression and increased respiratory capacity observed in hNSCs. Partial depletion of glioblastoma cell mtDNA rescued mtDNA replication events and enhanced cell differentiation. However, prolonged depletion resulted in impaired mtDNA replication, reduced proliferation and induced the expression of early developmental and pro-survival markers including POU class 5 homeobox 1 (OCT4) and sonic hedgehog (SHH). The transfer of glioblastoma cells depleted to varying degrees of their mtDNA content into immunocompromised mice resulted in tumors requiring significantly longer to form compared with non-depleted cells. The number of tumors formed and the time to tumor formation was relative to the degree of mtDNA depletion. The tumors derived from mtDNA depleted glioblastoma cells recovered their mtDNA copy number as part of the tumor formation process. These outcomes demonstrate the importance of mtDNA to the initiation and maintenance of tumorigenesis in glioblastoma multiforme.

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Related in: MedlinePlus

MtDNA copy number and gene expression in differentiating GBM cells and hNSCs. Mean mtDNA copy number in differentiating hNSCs, HSR-GBM1, GBM-L1 and GBM-L2 cells (a). Gene expression analysis of the nuclear-encoded mtDNA replication and transcription factors in differentiating HSR-GBM1 cells and hNSCs (b–f). Fold change in expression relative to undifferentiated cells, weighted to β-ACTIN, for TFAM (b), POLGA (c), POLGB (d), TWINKLE (e) and MTSSB (f). Bars represent mean values±S.E.M. *P<0.05, **P<0.01 and ***P<0.001
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fig1: MtDNA copy number and gene expression in differentiating GBM cells and hNSCs. Mean mtDNA copy number in differentiating hNSCs, HSR-GBM1, GBM-L1 and GBM-L2 cells (a). Gene expression analysis of the nuclear-encoded mtDNA replication and transcription factors in differentiating HSR-GBM1 cells and hNSCs (b–f). Fold change in expression relative to undifferentiated cells, weighted to β-ACTIN, for TFAM (b), POLGA (c), POLGB (d), TWINKLE (e) and MTSSB (f). Bars represent mean values±S.E.M. *P<0.05, **P<0.01 and ***P<0.001

Mentions: To determine whether GBM cells can modulate mtDNA copy number during differentiation, we induced three human GBM (HSR-GBM1, GBM-L1 and L2) and one human neural stem cell (hNSC) lines to undergo astrocyte differentiation (Figure 1a). hNSCs increased mtDNA copy number progressively resulting in a 3.23-fold increase by day 28 (P<0.001). Although HSR-GBM1 cells significantly increased (1.25-fold) mtDNA copy number on day 7 (P<0.001), this only increased to 1.37-fold by day 28 (P<0.001). A similar pattern was observed for GBM-L2 cells, except they had significantly more copies than HSR-GBM1 and GBM-L1 cells on day 28 (P<0.001). Although GBM-L1 cells displayed significant increases on days 7 and 14, levels were reduced by day 28. Nevertheless, cells from all three GBM lines had significantly fewer copies of mtDNA than the hNSCs by day 28 (P<0.001).


The regulation of mitochondrial DNA copy number in glioblastoma cells.

Dickinson A, Yeung KY, Donoghue J, Baker MJ, Kelly RD, McKenzie M, Johns TG, St John JC - Cell Death Differ. (2013)

MtDNA copy number and gene expression in differentiating GBM cells and hNSCs. Mean mtDNA copy number in differentiating hNSCs, HSR-GBM1, GBM-L1 and GBM-L2 cells (a). Gene expression analysis of the nuclear-encoded mtDNA replication and transcription factors in differentiating HSR-GBM1 cells and hNSCs (b–f). Fold change in expression relative to undifferentiated cells, weighted to β-ACTIN, for TFAM (b), POLGA (c), POLGB (d), TWINKLE (e) and MTSSB (f). Bars represent mean values±S.E.M. *P<0.05, **P<0.01 and ***P<0.001
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3824586&req=5

fig1: MtDNA copy number and gene expression in differentiating GBM cells and hNSCs. Mean mtDNA copy number in differentiating hNSCs, HSR-GBM1, GBM-L1 and GBM-L2 cells (a). Gene expression analysis of the nuclear-encoded mtDNA replication and transcription factors in differentiating HSR-GBM1 cells and hNSCs (b–f). Fold change in expression relative to undifferentiated cells, weighted to β-ACTIN, for TFAM (b), POLGA (c), POLGB (d), TWINKLE (e) and MTSSB (f). Bars represent mean values±S.E.M. *P<0.05, **P<0.01 and ***P<0.001
Mentions: To determine whether GBM cells can modulate mtDNA copy number during differentiation, we induced three human GBM (HSR-GBM1, GBM-L1 and L2) and one human neural stem cell (hNSC) lines to undergo astrocyte differentiation (Figure 1a). hNSCs increased mtDNA copy number progressively resulting in a 3.23-fold increase by day 28 (P<0.001). Although HSR-GBM1 cells significantly increased (1.25-fold) mtDNA copy number on day 7 (P<0.001), this only increased to 1.37-fold by day 28 (P<0.001). A similar pattern was observed for GBM-L2 cells, except they had significantly more copies than HSR-GBM1 and GBM-L1 cells on day 28 (P<0.001). Although GBM-L1 cells displayed significant increases on days 7 and 14, levels were reduced by day 28. Nevertheless, cells from all three GBM lines had significantly fewer copies of mtDNA than the hNSCs by day 28 (P<0.001).

Bottom Line: As stem cells undergo differentiation, mitochondrial DNA (mtDNA) copy number is strictly regulated in order that specialized cells can generate appropriate levels of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) to undertake their specific functions.We show that human neural stem cells (hNSCs) increased their mtDNA content during differentiation in a process that was mediated by a synergistic relationship between the nuclear and mitochondrial genomes and results in increased respiratory capacity.However, prolonged depletion resulted in impaired mtDNA replication, reduced proliferation and induced the expression of early developmental and pro-survival markers including POU class 5 homeobox 1 (OCT4) and sonic hedgehog (SHH).

View Article: PubMed Central - PubMed

Affiliation: 1] The Mitochondrial Genetics Group, Centre for Genetic Diseases, Monash Institute of Medical Research, Monash University, 27-31 Wright Street, Clayton, Victoria 3168, Australia [2] Molecular Basis of Metabolic Disease, Division of Metabolic and Vascular Health, Warwick Medical School, The University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX, UK.

ABSTRACT
As stem cells undergo differentiation, mitochondrial DNA (mtDNA) copy number is strictly regulated in order that specialized cells can generate appropriate levels of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) to undertake their specific functions. It is not understood whether tumor-initiating cells regulate their mtDNA in a similar manner or whether mtDNA is essential for tumorigenesis. We show that human neural stem cells (hNSCs) increased their mtDNA content during differentiation in a process that was mediated by a synergistic relationship between the nuclear and mitochondrial genomes and results in increased respiratory capacity. Differentiating multipotent glioblastoma cells failed to match the expansion in mtDNA copy number, patterns of gene expression and increased respiratory capacity observed in hNSCs. Partial depletion of glioblastoma cell mtDNA rescued mtDNA replication events and enhanced cell differentiation. However, prolonged depletion resulted in impaired mtDNA replication, reduced proliferation and induced the expression of early developmental and pro-survival markers including POU class 5 homeobox 1 (OCT4) and sonic hedgehog (SHH). The transfer of glioblastoma cells depleted to varying degrees of their mtDNA content into immunocompromised mice resulted in tumors requiring significantly longer to form compared with non-depleted cells. The number of tumors formed and the time to tumor formation was relative to the degree of mtDNA depletion. The tumors derived from mtDNA depleted glioblastoma cells recovered their mtDNA copy number as part of the tumor formation process. These outcomes demonstrate the importance of mtDNA to the initiation and maintenance of tumorigenesis in glioblastoma multiforme.

Show MeSH
Related in: MedlinePlus