The retinoblastoma protein induces apoptosis directly at the mitochondria
- Keren I. Hilgendorf1,2,
- Elizaveta S. Leshchiner3,4,5,6,7,
- Simona Nedelcu1,2,
- Mindy A. Maynard1,
- Eliezer Calo1,2,9,
- Alessandra Ianari1,8,
- Loren D. Walensky4,5,6,7 and
- Jacqueline A. Lees1,2,10
- 1David H. Koch Institute for Integrative Cancer Research at MIT, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
- 2Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
- 3Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA;
- 4Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA;
- 5Program in Cancer Chemical Biology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA;
- 6Division of Hematology and Oncology, Children's Hospital Boston, Boston, Massachusetts 02115, USA;
- 7Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115, USA;
- 8Department of Molecular Medicine, Sapienza University, Rome 00161, Italy
Abstract
The retinoblastoma protein gene RB-1 is mutated in one-third of human tumors. Its protein product, pRB (retinoblastoma protein), functions as a transcriptional coregulator in many fundamental cellular processes. Here, we report a nonnuclear role for pRB in apoptosis induction via pRB's direct participation in mitochondrial apoptosis. We uncovered this activity by finding that pRB potentiated TNFα-induced apoptosis even when translation was blocked. This proapoptotic function was highly BAX-dependent, suggesting a role in mitochondrial apoptosis, and accordingly, a fraction of endogenous pRB constitutively associated with mitochondria. Remarkably, we found that recombinant pRB was sufficient to trigger the BAX-dependent permeabilization of mitochondria or liposomes in vitro. Moreover, pRB interacted with BAX in vivo and could directly bind and conformationally activate BAX in vitro. Finally, by targeting pRB specifically to mitochondria, we generated a mutant that lacked pRB's classic nuclear roles. This mito-tagged pRB retained the ability to promote apoptosis in response to TNFα and also additional apoptotic stimuli. Most importantly, induced expression of mito-tagged pRB in Rb−/−;p53−/− tumors was sufficient to block further tumor development. Together, these data establish a nontranscriptional role for pRB in direct activation of BAX and mitochondrial apoptosis in response to diverse stimuli, which is profoundly tumor-suppressive.
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↵10 Corresponding author
E-mail jalees{at}mit.edu
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Supplemental material is available for this article.
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Article published online ahead of print. Article and publication date are online at http://www.genesdev.org/cgi/doi/10.1101/gad.211326.112.
- Received November 30, 2012.
- Accepted March 29, 2013.
- Copyright © 2013 by Cold Spring Harbor Laboratory Press