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Characterization of p73 functional domains necessary for transactivation and growth suppression
Susan Nozell1, Yijun Wu, Kelly McNaughton
1Department of Cell Biology, The University of Alabama at Birmingham, Birmingham, AL 35294-0005, USA.
Abstract:
p73, a p53 family member, is highly similar to p53 in both structure and function. Like p53, the p73 protein contains an N-terminal activation domain, a DNA-binding domain, a tetramerization domain, and several PXXP motifs. Previously, we and others have shown that some functional domains in p53, such as the DNA-binding and tetramerization domains, are required for inducing both cell cycle arrest and apoptosis whereas others, such as the second activation domain, the proline-rich domain, and the C-terminal basic domain, are only required for inducing apoptosis. To determine the activity of p73 functional domains, we have generated stable inducible cell lines that express p73beta and various mutants deficient in one or more functional domains. We found that in addition to the DNA-binding domain, p73-mediated growth suppression requires the N-terminal activation domain and the tetramerization domain. However, unlike p53, p73-mediated apoptosis does not require the region adjacent to the activation domain or the entire C-terminal region. Interestingly, while the N- or the C-terminal PXXP motifs are dispensable for p73 function, deletion of both the N- and the C-terminal PXXP motifs renders p73 inactive in transactivation. In addition, we found that substitution of two conserved tandem hydrophobic residues with two hydrophilic ones, which can abrogate the activity of the first activation domain in p53, has no effect on p73 transcriptional activity. Together, we showed that the p73 protein has its own unique determinants for transactivation and growth suppression.
Insights
The p73 protein, a p53 family member, has unique functional domains for transactivation and growth suppression. Its DNA-binding, N-terminal activation, and tetramerization domains are crucial for growth suppression, with distinct requirements for apoptosis compared to p53.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- The p73 protein is a structural and functional homolog of the tumor suppressor p53.
- p53's functional domains are critical for its roles in cell cycle arrest and apoptosis.
- Understanding p73's domain functions is essential for elucidating its role in cellular processes.
Purpose of the Study:
- To delineate the specific functional domains of the p73 protein.
- To compare the domain requirements for p73-mediated growth suppression and apoptosis with those of p53.
- To investigate the role of PXXP motifs and activation domains in p73 transactivation and function.
Main Methods:
- Generation of stable inducible cell lines expressing p73beta and various functional domain mutants.
- Assessing p73-mediated growth suppression and apoptosis induction.
- Evaluating p73 transactivation activity through domain deletions and substitutions.
Main Results:
- p73-mediated growth suppression requires the DNA-binding, N-terminal activation, and tetramerization domains.
- p73-mediated apoptosis has different domain requirements than p53, notably not needing the C-terminal region.
- Deletion of both N- and C-terminal PXXP motifs inactivates p73 transactivation, while specific activation domain substitutions have no effect.
Conclusions:
- The p73 protein possesses unique determinants for transactivation and growth suppression.
- p73's functional domain requirements differ from p53, highlighting distinct roles within the p53 family.
- These findings contribute to a deeper understanding of p73's molecular mechanisms in cellular regulation.