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The E2F-1 transcription factor is negatively regulated by its interaction with the MDMX protein
Gordon D Strachan1, Kelly L Jordan-Sciutto, Ravikumar Rallapalli
1Department of Pathology, University of Pennsylvania School of Dental Medicine, 4010 Locust St, Rm 312 Levy Research, Philadelphia 19104-6002, USA.
Abstract:
Several proteins with important roles in oncogenesis have been shown to regulate the function of the E2F-1 transcription factor, which is known to activate the expression of genes required for proliferation and apoptosis. Here we identify the MDMX oncoprotein as an E2F-1-binding factor, from a yeast-two hybrid screen using a portion of the E2F-1 protein as "bait." We demonstrate that the region within MDMX needed for the E2F-1:MDMX interaction is located in the central part of the protein, C-terminal of the p53-binding domain. The region within E2F-1 needed for this association is adjacent to the DNA binding domain. Further, when expressed in vivo or in vitro the MDMX protein migrates as two isoforms on SDS-PAGE, the faster migrating isoform having the stronger affinity for the E2F-1 proteins. It appears that this interaction reduces the ability of E2F-1 to bind DNA. Expression of MDMX along with E2F-1 and Dp-1 in Saos2 cells reduces the ability of E2F-1 to bind to its consensus DNA sequence, without altering E2F-1 protein levels. These data indicate that the MDMX protein is capable of associating with E2F-1 and negatively regulating its DNA binding ability.
Insights
Researchers identified the MDMX oncoprotein as a binding partner for the E2F-1 transcription factor. This interaction negatively regulates E2F-1
Area of Science:
- Molecular Biology
- Oncogenesis
- Gene Regulation
Background:
- E2F-1 transcription factor regulates genes crucial for cell proliferation and apoptosis.
- Oncogenic proteins often modulate E2F-1 activity.
- Understanding E2F-1 regulation is key to cancer research.
Purpose of the Study:
- To identify novel E2F-1 binding partners.
- To investigate the functional consequence of MDMX-E2F-1 interaction on E2F-1 activity.
Main Methods:
- Yeast-two hybrid screening to identify protein interactions.
- In vitro and in vivo expression studies.
- SDS-PAGE to analyze protein isoforms.
- DNA binding assays in Saos2 cells.
Main Results:
- MDMX oncoprotein identified as an E2F-1 binding factor.
- Specific interaction domains within MDMX and E2F-1 were mapped.
- MDMX expression, particularly a faster migrating isoform, reduces E2F-1's DNA binding ability.
- MDMX binding to E2F-1 does not alter E2F-1 protein levels.
Conclusions:
- MDMX associates with E2F-1.
- MDMX negatively regulates E2F-1 DNA binding activity.
- This interaction represents a novel mechanism of E2F-1 regulation in oncogenesis.