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Decreased apoptosome activity with neuronal differentiation sets the threshold for strict IAP regulation of apoptosis.

Wright KM, Linhoff MW, Potts PR, Deshmukh M - J. Cell Biol. (2004)

Bottom Line: We report that the ability of endogenous IAPs to effectively regulate caspase activation depends on the differentiation state of the cell.Neuronal differentiation was also accompanied with a marked reduction in Apaf-1, resulting in a significant decrease in apoptosome activity.Importantly, this decrease in Apaf-1 protein was directly linked to the increased ability of IAPs to stringently regulate apoptosis in neuronally differentiated PC12 and primary cells.

View Article: PubMed Central - PubMed

Affiliation: Curriculum in Neurobiology, University of North Carolina, Chapel Hill, NC 27599, USA.

ABSTRACT
Despite the potential of the inhibitor of apoptosis proteins (IAPs) to block cytochrome c-dependent caspase activation, the critical function of IAPs in regulating mammalian apoptosis remains unclear. We report that the ability of endogenous IAPs to effectively regulate caspase activation depends on the differentiation state of the cell. Despite being expressed at equivalent levels, endogenous IAPs afforded no protection against cytochrome c-induced apoptosis in naive pheochromocytoma (PC12) cells, but were remarkably effective in doing so in neuronally differentiated cells. Neuronal differentiation was also accompanied with a marked reduction in Apaf-1, resulting in a significant decrease in apoptosome activity. Importantly, this decrease in Apaf-1 protein was directly linked to the increased ability of IAPs to stringently regulate apoptosis in neuronally differentiated PC12 and primary cells. These data illustrate specifically how the apoptotic pathway acquires increased regulation with cellular differentiation, and are the first to show that IAP function and apoptosome activity are coupled in cells.

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Naïve and neuronally differentiated cells express similar levels of IAPs. (A) Protein levels of XIAP, cIAP-1, cIAP-2, NAIP, and lactate dehydrogenase (LDH) were examined in naïve and neuronally differentiated PC12 cells (equal total protein loaded) by Western analysis. (B) Quantitation of protein levels from three independent experiments are shown as mean ± SEM. (C) Marked reduction in apoptosome activity with neuronal differentiation. Cytosolic lysates from naïve and neuronally differentiated cells were treated with either bovine cytochrome c alone (10 μM), yeast cytochrome c as a control (10 μM), or bovine cytochrome c with 1 μM of either wild-type AVPI-Smac or mutant MVPI-Smac. Cleavage of caspase-9 and caspase-3 in these treated extracts was examined by Western analysis.
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fig3: Naïve and neuronally differentiated cells express similar levels of IAPs. (A) Protein levels of XIAP, cIAP-1, cIAP-2, NAIP, and lactate dehydrogenase (LDH) were examined in naïve and neuronally differentiated PC12 cells (equal total protein loaded) by Western analysis. (B) Quantitation of protein levels from three independent experiments are shown as mean ± SEM. (C) Marked reduction in apoptosome activity with neuronal differentiation. Cytosolic lysates from naïve and neuronally differentiated cells were treated with either bovine cytochrome c alone (10 μM), yeast cytochrome c as a control (10 μM), or bovine cytochrome c with 1 μM of either wild-type AVPI-Smac or mutant MVPI-Smac. Cleavage of caspase-9 and caspase-3 in these treated extracts was examined by Western analysis.

Mentions: The selective ability of endogenous IAPs to block caspase activation in neuronally differentiated but not naïve cells was not due to elevated expression of IAPs in the neuronally differentiated cells. Naïve and neuronally differentiated PC12 cells expressed similar levels of multiple IAPs, including XIAP, cIAP-1, cIAP-2, and NAIP (Fig. 3, A and B).


Decreased apoptosome activity with neuronal differentiation sets the threshold for strict IAP regulation of apoptosis.

Wright KM, Linhoff MW, Potts PR, Deshmukh M - J. Cell Biol. (2004)

Naïve and neuronally differentiated cells express similar levels of IAPs. (A) Protein levels of XIAP, cIAP-1, cIAP-2, NAIP, and lactate dehydrogenase (LDH) were examined in naïve and neuronally differentiated PC12 cells (equal total protein loaded) by Western analysis. (B) Quantitation of protein levels from three independent experiments are shown as mean ± SEM. (C) Marked reduction in apoptosome activity with neuronal differentiation. Cytosolic lysates from naïve and neuronally differentiated cells were treated with either bovine cytochrome c alone (10 μM), yeast cytochrome c as a control (10 μM), or bovine cytochrome c with 1 μM of either wild-type AVPI-Smac or mutant MVPI-Smac. Cleavage of caspase-9 and caspase-3 in these treated extracts was examined by Western analysis.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172554&req=5

fig3: Naïve and neuronally differentiated cells express similar levels of IAPs. (A) Protein levels of XIAP, cIAP-1, cIAP-2, NAIP, and lactate dehydrogenase (LDH) were examined in naïve and neuronally differentiated PC12 cells (equal total protein loaded) by Western analysis. (B) Quantitation of protein levels from three independent experiments are shown as mean ± SEM. (C) Marked reduction in apoptosome activity with neuronal differentiation. Cytosolic lysates from naïve and neuronally differentiated cells were treated with either bovine cytochrome c alone (10 μM), yeast cytochrome c as a control (10 μM), or bovine cytochrome c with 1 μM of either wild-type AVPI-Smac or mutant MVPI-Smac. Cleavage of caspase-9 and caspase-3 in these treated extracts was examined by Western analysis.
Mentions: The selective ability of endogenous IAPs to block caspase activation in neuronally differentiated but not naïve cells was not due to elevated expression of IAPs in the neuronally differentiated cells. Naïve and neuronally differentiated PC12 cells expressed similar levels of multiple IAPs, including XIAP, cIAP-1, cIAP-2, and NAIP (Fig. 3, A and B).

Bottom Line: We report that the ability of endogenous IAPs to effectively regulate caspase activation depends on the differentiation state of the cell.Neuronal differentiation was also accompanied with a marked reduction in Apaf-1, resulting in a significant decrease in apoptosome activity.Importantly, this decrease in Apaf-1 protein was directly linked to the increased ability of IAPs to stringently regulate apoptosis in neuronally differentiated PC12 and primary cells.

View Article: PubMed Central - PubMed

Affiliation: Curriculum in Neurobiology, University of North Carolina, Chapel Hill, NC 27599, USA.

ABSTRACT
Despite the potential of the inhibitor of apoptosis proteins (IAPs) to block cytochrome c-dependent caspase activation, the critical function of IAPs in regulating mammalian apoptosis remains unclear. We report that the ability of endogenous IAPs to effectively regulate caspase activation depends on the differentiation state of the cell. Despite being expressed at equivalent levels, endogenous IAPs afforded no protection against cytochrome c-induced apoptosis in naive pheochromocytoma (PC12) cells, but were remarkably effective in doing so in neuronally differentiated cells. Neuronal differentiation was also accompanied with a marked reduction in Apaf-1, resulting in a significant decrease in apoptosome activity. Importantly, this decrease in Apaf-1 protein was directly linked to the increased ability of IAPs to stringently regulate apoptosis in neuronally differentiated PC12 and primary cells. These data illustrate specifically how the apoptotic pathway acquires increased regulation with cellular differentiation, and are the first to show that IAP function and apoptosome activity are coupled in cells.

Show MeSH
Related in: MedlinePlus