Related Experiment Videos
Differential modulation of cellular and viral promoters by p73 and p53
1Department of Biochemistry and Molecular Biophysics and the Massey Cancer Center, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA.
Abstract:
p73 has been shown to transcriptionally activate genes positively responsive to wild-type p53. In order to undertake a comparative study of functions of p53 and p73 we have cloned the cDNA of p73 from MCF-7 cells. Adenovirus onco-protein E1A inhibits the transactivation by p73; a deletion mutant of E1A incapable of interacting with p300 and CREB-binding protein (CBP) fails to disrupt the transactivation. Furthermore, CBP increases the transactivation mediated by p73 suggesting that CBP may function as a co-activator and E1A inhibits p73-mediated transactivation by sequestering p300 or CBP. We show that p73 can transcriptionally inhibit a number of cellular and viral promoters. However, wild-type p53, p73 alpha and p73 beta differ in their ability to inhibit transcriptional activity of different promoters. While wild-type p53 inhibits the promoters of the human cytomegalovirus (CMV) immediate-early gene, the long terminal repeat of human immunodeficiency virus type 1 (HIV LTR), human cyclin A (cyc A) gene, and insulin-like growth factor receptor I (IGF-I-R), p73 alpha only inhibits the HIV LTR and cyc A promoters significantly; and p73 beta inhibits the CMV, HIV LTR and cyc A promoters. A mutant of p73 alpha having amino acid substitutions at positions 268 and 300 on the presumptive DNA-binding domain fails to transactivate the p21 promoter but represses the CMV and the HIV LTR promoter quite efficiently showing that the mechanisms of transactivation and repression by p73 are different. Interestingly, p73 alpha transactivates the IGF-I-R promoter, which is inhibited by wild-type p53; p73 beta has no significant effect on this promoter. This is a unique situation where p73 alpha differs from p73 beta as well as p53.
Insights
The p73 protein, similar to p53, regulates gene transcription. Researchers found p73
Area of Science:
- Molecular Biology
- Cancer Research
- Gene Regulation
Background:
- The p53 tumor suppressor protein plays a critical role in cellular responses to stress.
- The p73 protein shares structural and functional similarities with p53, suggesting overlapping roles in gene regulation.
- Understanding the distinct functions of p53 and p73 is crucial for cancer research.
Purpose of the Study:
- To compare the transcriptional functions of p53 and p73.
- To investigate the role of adenovirus oncoprotein E1A and its interaction with co-activators p300 and CBP in p73-mediated transactivation.
- To elucidate the differential inhibitory effects of p53, p73 alpha, and p73 beta on various cellular and viral promoters.
Main Methods:
- Cloning of p73 cDNA from MCF-7 cells.
- Assessing the impact of wild-type and mutant adenovirus E1A oncoprotein on p73 transactivation.
- Evaluating the co-activation role of CBP in p73-mediated transactivation.
- Comparing the transcriptional inhibition of human cytomegalovirus (CMV) immediate-early gene, HIV LTR, human cyclin A (cyc A), and insulin-like growth factor receptor I (IGF-I-R) promoters by p53, p73 alpha, and p73 beta.
- Analyzing the transactivation and repression activities of a p73 alpha mutant defective in DNA binding.
Main Results:
- Adenovirus E1A inhibits p73 transactivation, an effect dependent on its interaction with p300 and CBP. CBP enhances p73 transactivation, suggesting it acts as a co-activator.
- p73 exhibits both transactivation and transcriptional inhibition capabilities.
- p53, p73 alpha, and p73 beta display distinct patterns of promoter inhibition. p73 alpha and p73 beta show differential inhibition of CMV, HIV LTR, and cyc A promoters.
- A p73 alpha mutant with impaired DNA binding retains repression activity but loses transactivation ability, indicating distinct mechanisms for these functions.
- p73 alpha uniquely transactivates the IGF-I-R promoter, which is repressed by p53, highlighting a functional divergence between p73 alpha, p73 beta, and p53.
Conclusions:
- CBP acts as a co-activator for p73, and E1A inhibits p73 activity by sequestering p300 or CBP.
- p73 isoforms (p73 alpha and p73 beta) exhibit distinct transcriptional regulatory roles compared to wild-type p53.
- The differential regulation of promoters like IGF-I-R by p73 alpha underscores its unique biological functions and potential as a therapeutic target.