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Published on: January 21, 2012
Regulation of the retinoblastoma-dependent Mdm2 and E2F-1 signaling pathways during neuronal apoptosis
E Trinh1, A L Boutillier, J P Loeffler
1UMR 7519 CNRS-21, rue René Descartes, Strasbourg Cedex, 67 084, France.
Abstract:
We have previously demonstrated that the apoptotic signaling pathway in K(+)-deprived cerebellar granule neurons involves a caspase-dependent cleavage of the retinoblastoma protein (Rb). Here, we have further investigated the functional consequences of this cleavage on two Rb-binding partners: the oncoprotein Mdm2 and the transcription factor E2F-1. A K(+) deprivation time course leads to a caspase inhibitor-sensitive degradation of Mdm2. Experimental blockade of Mdm2 expression with antisense oligodeoxynucleotides (ODN) results in neuronal death, suggesting an active role of Mdm2 in neuroprotection. By contrast, the E2F-1 protein accumulates in a caspase-independent manner following K(+) withdrawal, a consequence of increased gene transcription. This is likely to result from the rapid cyclin-dependent kinase 4 activation observed in LK, that correlates with a transient Rb phosphorylation. Counteracting E2F-1 upregulation with antisense ODNs prevents neuronal loss. Taken together, these data demonstrate that Rb is a central player in regulating both caspase-dependent and -independent events leading to apoptosis.
Insights
Retinoblastoma protein (Rb) cleavage in neurons triggers both caspase-dependent and -independent apoptosis. Mdm2 protects neurons, while E2F-1 promotes cell death, highlighting Rb
Area of Science:
- Neuroscience
- Molecular Biology
- Cellular Biology
Background:
- Previous studies established caspase-dependent cleavage of retinoblastoma protein (Rb) in potassium-deprived cerebellar granule neurons during apoptosis.
- The functional impact of Rb cleavage on its key binding partners, Mdm2 and E2F-1, remained to be fully elucidated.
Purpose of the Study:
- To investigate the functional consequences of Rb cleavage on Mdm2 and E2F-1.
- To determine the roles of Mdm2 and E2F-1 in neuronal apoptosis.
- To elucidate the regulatory mechanisms of apoptosis involving Rb.
Main Methods:
- Utilized potassium deprivation in cerebellar granule neurons.
- Employed caspase inhibitors to assess caspase dependency.
- Used antisense oligodeoxynucleotides (ODNs) to block Mdm2 and E2F-1 expression.
- Monitored protein degradation, accumulation, and neuronal survival.
Main Results:
- Potassium deprivation induced caspase inhibitor-sensitive degradation of Mdm2.
- Blocking Mdm2 expression with antisense ODNs led to neuronal death, indicating a neuroprotective role for Mdm2.
- E2F-1 protein accumulated in a caspase-independent manner due to increased gene transcription, linked to cyclin-dependent kinase 4 activation and Rb phosphorylation.
- Counteracting E2F-1 upregulation prevented neuronal loss.
Conclusions:
- Rb cleavage is central to regulating both caspase-dependent and -independent apoptotic pathways in neurons.
- Mdm2 plays a crucial neuroprotective role.
- E2F-1 accumulation contributes to neuronal apoptosis via a caspase-independent mechanism.
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