Akt-mediated phosphorylation of Bmi1 modulates its oncogenic potential, E3 ligase activity, and DNA damage repair activity in mouse prostate cancer.
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ABSTRACT:
SUBMITTER: Nacerddine K
PROVIDER: S-EPMC3336972 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The Ubiquitin Proteasome System (UPS) has been shown to regulate neuronal development and synapse formation. Activity-dependent regulation of E3 ligase, a component of the UPS that targets specific proteins for proteasome-mediated degradation, is emerging as a pivotal player for the establishment of functional synapses. Here, we identified TRIM47 as a developmentally regulated E3 ligase that is expressed in rat hippocampus during the temporal window of synapse formation. We have demonstrated that the expression of TRIM47 is regulated by the glutamate-induced synaptic activity of hippocampal neurons in culture. In addition, the activity-dependent enhancement of TRIM47 expression is recapitulated following the object location test, a hippocampus-dependent spatial memory paradigm. We observed that this enhancement of TRIM47 expression requires NMDA receptor activation. The knockdown of TRIM47 leads to an enhancement of spine density without affecting dendritic complexity. Furthermore, we observed an increase in excitatory synapse development upon loss of TRIM47 function. Comprehensively, our study identified an activity-regulated E3 ligase that drives excitatory synapse formation in hippocampal neurons.
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Project description:The Hace1 E3 ligase is a tumor suppressor in stressed cells. Through unknown mechanisms, Hace1 indirectly targets the cyclin D1 proto-oncogene for proteasomal degradation during nutrient depletion. We now show that Hace1 targets HIF1alpha for VHL-dependent degradation during hypoxia. To better understand these diverse actions we performed mass spectrometry to identify Hace1-interacting proteins. We show that Hace1 interacts with cullin-associated NEDD8-dissociated protein 1 (CAND1) under nutrient depletion and hypoxia. CAND1 binds cullins and prevents their entry into cullin ring E3 ligase (CRL) complexes, thus blocking CRL activity. Hace1 binding releases CUL1/2 from CAND1, facilitating assembly of CRL complexes to degrade cyclin D1 and HIF1alpha, respectively. These findings suggest a broad role for Hace1 in regulating tumor suppressive CRL E3 ligases. In this study, we used gene expression profiling to characterize how Hace1 overexpression affect the transcriptional response to hypoxic stress Using Affymetrix exon-level microarrays, we compared the expression profile of HEK293 cells overexpressing either Hace1 or MSCV vector alone, under hypoxia or normoxia
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Project description:Polycomb group proteins Ring1b and Bmi1 (B-cell-specific Moloney murine leukaemia virus integration site 1) are critical components of the chromatin modulating PRC1 complex. Histone H2A ubiquitination by the PRC1 complex strongly depends on the Ring1b protein. Here we show that the E3-ligase activity of Ring1b on histone H2A is enhanced by Bmi1 in vitro. The N-terminal Ring-domains are sufficient for this activity and Ring1a can replace Ring1b. E2 enzymes UbcH5a, b, c or UbcH6 support this activity with varying processivity and selectivity. All four E2s promote autoubiquitination of Ring1b without affecting E3-ligase activity. We solved the crystal structure of the Ring-Ring heterodimeric complex of Ring1b and Bmi1. In the structure the arrangement of the Ring-domains is similar to another H2A E3 ligase, the BRCA1/BARD1 complex, but complex formation depends on an N-terminal arm of Ring1b that embraces the Bmi1 Ring-domain. Mutation of a critical residue in the E2/E3 interface shows that catalytic activity resides in Ring1b and not in Bmi1. These data provide a foundation for understanding the critical enzymatic activity at the core of the PRC1 polycomb complex, which is implicated in stem cell maintenance and cancer.
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