Elevated p53 expression is associated with dysregulation of the ubiquitin-proteasome system in dilated cardiomyopathy.
OBJECTIVE
The molecular mechanisms that regulate cardiomyocyte apoptosis and their role in human heart failure (HF) are uncertain. Expression of the apoptosis regulator p53 is governed by minute double minute 2 (MDM2), an E3 enzyme that targets p53 for ubiquitination and proteasomal processing, and by the deubiquitinating enzyme, herpesvirus-associated ubiquitin-specific protease (HAUSP), which rescues p53 by removing ubiquitin chains from it. Here, we examined whether elevated expression of p53 was associated with dysregulation of ubiquitin-proteasome system (UPS) components and activation of downstream effectors of apoptosis in human dilated cardiomyopathy (DCM).


RESULTS
Left ventricular myocardial samples were obtained from patients with DCM (n = 12) or from non-failing (donor) hearts (n = 17). Western blotting and immunohistochemistry revealed that DCM tissues contained elevated levels of p53 and its regulators MDM2 and HAUSP (all P < 0.01) compared with non-failing hearts. DCM tissues also contained elevated levels of polyubiquitinated proteins and possessed enhanced 20S-proteasome chymotrypsin-like activities (P < 0.04) as measured in vitro using a fluorogenic substrate. DCM tissues contained activated caspases-9 and -3 (P < 0.001) and reduced expression of the caspase substrate PARP-1 (P < 0.05). Western blotting and immunohistochemistry revealed that DCM tissues contained elevated expression levels of caspase-3-activated DNAse (CAD; P < 0.001), which is a key effector of DNA fragmentation in apoptosis and also contained elevated expression of a potent inhibitor of CAD (ICAD-S; P < 0.01).


CONCLUSIONS
Expression of p53 in human DCM is associated with dysregulation of UPS components, which are known to regulate p53 stability. Elevated p53 expression and caspase activation in DCM was not associated with activation of both CAD and its inhibitor, ICAD-S. Our findings are consistent with the concept that apoptosis may be interrupted and therefore potentially reversible in human HF.
Birks
Emma J
EJ
Heart Science Centre, National Heart and Lung Institute, Imperial College London, Harefield Hospital, Harefield, UK.
Latif
Najma
N
Enesa
Karine
K
Folkvang
Tonje
T
Luong
Le Anh
le A
Sarathchandra
Padmini
P
Khan
Mak
M
Ovaa
Huib
H
Terracciano
Cesare M
CM
Barton
Paul J R
PJ
Yacoub
Magdi H
MH
Evans
Paul C
PC
D000328:Adult; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002311:Cardiomyopathy, Dilated / Q000201:enzymology* / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D053938:DNA Fragmentation; D003851:Deoxyribonucleases / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D043222:Ubiquitin Thiolesterase / Q000378:metabolism; D000076084:Ubiquitin-Specific Peptidase 7; D015854:Up-Regulation; D055815:Young Adult
D051017:Apoptosis Regulatory Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C109664:caspase-activated DNase inhibitor; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D003851:Deoxyribonucleases; C109663:caspase-activated deoxyribonuclease; C464569:USP7 protein, human; D043222:Ubiquitin Thiolesterase; D000076084:Ubiquitin-Specific Peptidase 7; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D046988:Proteasome Endopeptidase Complex