Limits...
Reduced Apaf-1 levels in cardiomyocytes engage strict regulation of apoptosis by endogenous XIAP.

Potts MB, Vaughn AE, McDonough H, Patterson C, Deshmukh M - J. Cell Biol. (2005)

Bottom Line: The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone.Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP.These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center, Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
Overexpression studies have identified X-linked inhibitor of apoptosis protein (XIAP) as a potent inhibitor of caspases. However, the exact function of endogenous XIAP in regulating mammalian apoptosis is less clear. Endogenous XIAP strictly regulates cytochrome c-dependent caspase activation in sympathetic neurons but not in many mitotic cells. We report that postmitotic cardiomyocytes, unlike fibroblasts, are remarkably resistant to cytosolic microinjection of cytochrome c. The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone. Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP. These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

Show MeSH

Related in: MedlinePlus

Apaf-1 but not caspase-9 levels are markedly reduced in cardiomyocytes in comparison to fibroblasts. (A) Western blots showing levels of Apaf-1 and caspase-9 proteins (and LDH and Troponin I as controls) in cultures of rat dermal fibroblasts and cardiomyocytes. (B) Quantitation of the data in which Apaf-1 and caspase-9 protein levels detected in cardiomyocyte cultures are expressed as a percentage of the levels (normalized to LDH) seen in fibroblast cultures. Data shown are the mean ± SEM of three independent experiments.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2171313&req=5

fig4: Apaf-1 but not caspase-9 levels are markedly reduced in cardiomyocytes in comparison to fibroblasts. (A) Western blots showing levels of Apaf-1 and caspase-9 proteins (and LDH and Troponin I as controls) in cultures of rat dermal fibroblasts and cardiomyocytes. (B) Quantitation of the data in which Apaf-1 and caspase-9 protein levels detected in cardiomyocyte cultures are expressed as a percentage of the levels (normalized to LDH) seen in fibroblast cultures. Data shown are the mean ± SEM of three independent experiments.

Mentions: We recently reported that the effectiveness of endogenous XIAP to regulate apoptosis is inversely coupled to the Apaf-1–dependent apoptosome activity in cells (Wright et al., 2004). To determine whether the strict control of cytochrome c–mediated death by XIAP in cardiomyocytes is regulated by a similar mechanism, we examined the levels of Apaf-1. As a comparison, we also examined Apaf-1 levels in dermal fibroblasts. Unlike cardiomyocytes, fibroblasts show no strict regulation by endogenous XIAP and die with injection of cytochrome c alone (Fig. 1). We found that the level of Apaf-1 protein in cardiomyocytes was strikingly reduced to <25% of the Apaf-1 levels found in fibroblasts (Fig. 4). This decrease in Apaf-1 was not an artifact of maintaining cardiomyocytes in culture for 6–8 d, as similar low levels of Apaf-1 were seen in cardiomyocytes immediately after their isolation (Fig. S1 A, available at http://www.jcb.org/cgi/content/full/jcb.200504082/DC1).


Reduced Apaf-1 levels in cardiomyocytes engage strict regulation of apoptosis by endogenous XIAP.

Potts MB, Vaughn AE, McDonough H, Patterson C, Deshmukh M - J. Cell Biol. (2005)

Apaf-1 but not caspase-9 levels are markedly reduced in cardiomyocytes in comparison to fibroblasts. (A) Western blots showing levels of Apaf-1 and caspase-9 proteins (and LDH and Troponin I as controls) in cultures of rat dermal fibroblasts and cardiomyocytes. (B) Quantitation of the data in which Apaf-1 and caspase-9 protein levels detected in cardiomyocyte cultures are expressed as a percentage of the levels (normalized to LDH) seen in fibroblast cultures. Data shown are the mean ± SEM of three independent experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171313&req=5

fig4: Apaf-1 but not caspase-9 levels are markedly reduced in cardiomyocytes in comparison to fibroblasts. (A) Western blots showing levels of Apaf-1 and caspase-9 proteins (and LDH and Troponin I as controls) in cultures of rat dermal fibroblasts and cardiomyocytes. (B) Quantitation of the data in which Apaf-1 and caspase-9 protein levels detected in cardiomyocyte cultures are expressed as a percentage of the levels (normalized to LDH) seen in fibroblast cultures. Data shown are the mean ± SEM of three independent experiments.
Mentions: We recently reported that the effectiveness of endogenous XIAP to regulate apoptosis is inversely coupled to the Apaf-1–dependent apoptosome activity in cells (Wright et al., 2004). To determine whether the strict control of cytochrome c–mediated death by XIAP in cardiomyocytes is regulated by a similar mechanism, we examined the levels of Apaf-1. As a comparison, we also examined Apaf-1 levels in dermal fibroblasts. Unlike cardiomyocytes, fibroblasts show no strict regulation by endogenous XIAP and die with injection of cytochrome c alone (Fig. 1). We found that the level of Apaf-1 protein in cardiomyocytes was strikingly reduced to <25% of the Apaf-1 levels found in fibroblasts (Fig. 4). This decrease in Apaf-1 was not an artifact of maintaining cardiomyocytes in culture for 6–8 d, as similar low levels of Apaf-1 were seen in cardiomyocytes immediately after their isolation (Fig. S1 A, available at http://www.jcb.org/cgi/content/full/jcb.200504082/DC1).

Bottom Line: The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone.Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP.These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center, Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
Overexpression studies have identified X-linked inhibitor of apoptosis protein (XIAP) as a potent inhibitor of caspases. However, the exact function of endogenous XIAP in regulating mammalian apoptosis is less clear. Endogenous XIAP strictly regulates cytochrome c-dependent caspase activation in sympathetic neurons but not in many mitotic cells. We report that postmitotic cardiomyocytes, unlike fibroblasts, are remarkably resistant to cytosolic microinjection of cytochrome c. The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone. Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP. These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

Show MeSH
Related in: MedlinePlus