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Updated: May 12, 2026
Inducible and Reversible Dominant-negative (DN) Protein Inhibition
Published on: January 7, 2019
The retinoblastoma protein induces apoptosis directly at the mitochondria
Keren I Hilgendorf1, Elizaveta S Leshchiner, Simona Nedelcu
1David H. Koch Institute for Integrative Cancer Research at MIT, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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.
Insights
The retinoblastoma protein (pRB) directly activates BAX, initiating mitochondrial apoptosis independently of its nuclear functions. This non-transcriptional role is crucial for suppressing tumor development.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- The retinoblastoma protein gene (RB-1) is frequently mutated in human cancers.
- pRB typically functions as a nuclear transcriptional coregulator in cell cycle control.
- A non-transcriptional role for pRB in apoptosis has not been previously established.
Purpose of the Study:
- To investigate a potential non-transcriptional role of pRB in apoptosis.
- To determine if pRB directly participates in mitochondrial apoptosis pathways.
- To explore the therapeutic potential of pRB's non-transcriptional apoptotic function in tumors.
Main Methods:
- Studied pRB's effect on TNFα-induced apoptosis with translation blocked.
- Assessed pRB's association with mitochondria and its interaction with BAX.
- Utilized recombinant pRB in vitro to test mitochondrial permeabilization.
- Generated and analyzed a mitochondrially-targeted pRB mutant (mito-tagged pRB).
- Expressed mito-tagged pRB in Rb(-/-);p53(-/-) tumor models.
Main Results:
- pRB potentiated TNFα-induced apoptosis independently of translation, indicating a non-transcriptional role.
- Endogenous pRB was found to associate with mitochondria and its proapoptotic function was BAX-dependent.
- Recombinant pRB directly induced BAX-dependent mitochondrial permeabilization in vitro.
- pRB directly bound and conformationally activated BAX.
- Mito-tagged pRB promoted apoptosis and suppressed tumor development in Rb(-/-);p53(-/-) mice.
Conclusions:
- pRB possesses a novel non-transcriptional function in directly activating BAX and inducing mitochondrial apoptosis.
- This direct apoptotic role of pRB is independent of its canonical nuclear functions.
- Targeting pRB to mitochondria demonstrates potent tumor-suppressive capabilities, highlighting a new therapeutic avenue.
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