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DeltaNp73beta is active in transactivation and growth suppression
Gang Liu1, Susan Nozell, Hui Xiao
1Department of Cell Biology, The University of Alabama at Birmingham, 1530 3rd Avenue, Birmingham, AL 35294-0005, USA.
Molecular and Cellular Biology
|January 1, 2004
Summary
The p73 protein family includes isoforms like DeltaNp73beta that can actively suppress cell growth and induce apoptosis, contrary to prior assumptions. Specific N-terminal residues are crucial for this newly identified tumor suppressor function.
Area of Science:
- Molecular Biology
- Cancer Biology
- Cellular Signaling
Background:
- p73, a p53 family protein, shares similarities with p53 but has multiple isoforms.
- DeltaNp73 variants, lacking the N-terminal activation domain, were presumed transcriptionally inactive and dominant-negative.
- The p73 gene generates DeltaNp73 isoforms via a cryptic promoter in intron 3.
Purpose of the Study:
- To systematically analyze the biological activity of DeltaNp73 variants, particularly DeltaNp73beta.
- To investigate the role of the N-terminal region in DeltaNp73 function.
- To determine if DeltaNp73beta possesses tumor suppressor activities.
Main Methods:
- Generation of stable cell lines with inducible expression of DeltaNp73 isoforms and mutants using a tetracycline-inducible system.
- Analysis of cell cycle arrest, apoptosis, and cell growth suppression.
- Site-directed mutagenesis to identify critical residues within the DeltaNp73beta N-terminus.
Main Results:
- DeltaNp73beta was found to be active in inducing cell cycle arrest and apoptosis.
- Physiologically relevant levels of DeltaNp73beta suppressed cell growth in a cell-type-independent manner.
- A novel activation domain comprising 13 unique N-terminal residues and PXXP motifs was identified, with residues 6-10 being critical for function.
- DeltaNp73beta induced some p53 target genes, and DeltaNp73gamma also showed transactivation activity, while DeltaNp73alpha did not suppress cell growth.
Conclusions:
- DeltaNp73beta exhibits distinct biological activities, including cell growth suppression and apoptosis induction, challenging previous assumptions.
- The N-terminal region of DeltaNp73beta contains a novel activation domain essential for its tumor suppressor functions.
- DeltaNp73beta may play unique roles in cellular regulation under specific conditions, suggesting a complex functional repertoire within the p73 family.