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A novel MDMX transcript expressed in a variety of transformed cell lines encodes a truncated protein with potent p53
R Rallapalli1, G Strachan, B Cho
1Department of Biochemistry and Molecular Pharmacology, Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Abstract:
The MDMX gene product is related to the MDM2 oncoprotein, both of which interact with the p53 tumor suppressor. We have identified a novel transcript of the MDMX gene that is expressed in a variety of cell lines, and in particular, in growing and transformed cells. This transcript is identical to the published sequence yet it has a short internal deletion of 68 base pairs. This deletion produces a shift in the reading frame after codon 114, resulting in the inclusion of a stop codon at amino acid residue 127 (full-length MDMX is 489 residues). This truncated MDMX protein is termed MDMX-S ("short form"), represents only the p53-binding domain, and appears to bind p53 better than full-length MDMX. The MDMX-S protein can be detected in cell extracts and when overexpressed is much more effective than MDMX at inhibiting p53-mediated transcriptional activation and induction of apoptosis. Since MDMX-S lacks the central and carboxyl-terminal regions contained within full-length MDMX, it is likely to play a key role in the regulation of cell proliferation and apoptosis in a way distinct from MDMX.
Insights
Researchers discovered a new short form of the MDMX protein (MDMX-S) that binds p53 better and inhibits tumor suppressor activity more effectively than the full-length version, impacting cell growth and apoptosis.
Area of Science:
- Molecular Biology
- Oncology
- Genetics
Background:
- The MDMX gene product is related to the MDM2 oncoprotein.
- Both MDMX and MDM2 interact with the p53 tumor suppressor protein.
- p53 is a critical tumor suppressor involved in cell cycle regulation and apoptosis.
Purpose of the Study:
- To identify and characterize novel transcripts of the MDMX gene.
- To investigate the functional properties of a newly identified truncated MDMX protein.
- To understand the distinct role of this truncated protein in regulating p53 activity.
Main Methods:
- Identification of a novel MDMX transcript using sequence analysis.
- Characterization of the protein product (MDMX-S) resulting from the transcript.
- Assays to evaluate p53 binding affinity and functional inhibition of p53-mediated transcription and apoptosis.
Main Results:
- A novel MDMX transcript with a 68-base pair internal deletion was identified.
- This deletion results in a truncated protein, MDMX-S, lacking central and carboxyl-terminal regions.
- MDMX-S exhibits enhanced binding to p53 and is more potent than full-length MDMX in inhibiting p53-mediated transcriptional activation and apoptosis induction.
Conclusions:
- MDMX-S represents a functionally distinct isoform of MDMX.
- This truncated protein plays a significant role in regulating cell proliferation and apoptosis.
- MDMX-S may represent a novel therapeutic target in cancer treatment.