Prostate apoptosis response 4 (Par-4) is a ubiquitously expressed proapoptotic tumor suppressor protein. Here, we show for the first time, that Par-4 is a novel substrate of caspase-3 during apoptosis.
We found that Par-4 is cleaved during cisplatin-induced apoptosis in human normal and cancer cell lines. Par-4 cleavage generates a C-terminal fragment of ~25 kDa, and the cleavage of Par-4 is completely inhibited by a caspase-3 inhibitor, suggesting that caspase-3 is directly involved in the cleavage of Par-4. Caspase-3-deficient MCF-7 cells do not show Par-4 cleavage in response to cisplatin treatment, and restoration of caspase-3 in MCF-7 cells produces a decrease in Par-4 levels, with the appearance of a cleaved fragment. Additionally, knockdown of Par-4 reduces caspase-3 activation and apoptosis induction. Site-directed mutagenesis reveals that Par-4 cleavage by caspase-3 occurs at an unconventional site, EEPD(131)↓G. Interestingly, overexpression of wild-type Par-4 but not the Par-4 D131A mutant sensitizes cells to cisplatin-induced apoptosis.
Upon caspase-3 cleavage, the cleaved fragment of Par-4 accumulates in the nucleus and displays increased apoptotic activity.
Overexpression of the cleaved fragment of Par-4 inhibits IκBα phosphorylation and blocks NF-κB nuclear translocation.
We have identified a novel specific caspase-3 cleavage site in Par-4, and the cleaved fragment of Par-4 retains proapoptotic activity.
2012-01-31
Eng.
Molecular and cellular biology
Research Group in Molecular Oncology and Endocrinology, Department of Chemistry-Biology, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada.
Mol Cell Biol. 2012 Feb;32(4):826-39
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