Overzealous MDM2-mediated ubiquitination of p53 characterizes and sustains over 50% of all human cancers. Successful targeted cancer therapy hinges on a thorough understanding of the ubiquitination process. Unfortunately, current steady-state enzyme kinetic models fail to accurately describe the ubiquitin-proteasome system, due to the assumption that the enzyme (E3 ligase) is expressed at infinitesimally smaller concentrations than the substrates (ubiquitin-conjugated E2 and target protein). This limitation of the quasi-steady state assumption prohibits the use of steady-state models when analyzing the cancerous consequences of extreme ubiquitin-ligase overexpression. This paper derives a novel non-steady-state mathematical model of reversible ordered ternary complex enzyme kinetics, which can be used to simulate the behavioral response of the ubiquitin-proteasome system to specific variations in the cellular concentrations of p53, MDM2, and ubiquitin-conjugated E2D3. Computer simulations of the model were used to study the effects of E2D3-Ub and MDM2 concentrations on the rates of p53 ubiquitination at different temperatures. In each process, it was observed that the ubiquitin-ligase MDM2 accelerates the carcinogenic ubiquitination process, while ubiquitin-conjugated E2 inhibits it. It was also discovered that E2D3-Ub is more effective inhibitor of overzealous p53 ubiquitination when present at higher concentrations. However, it was also observed that high concentrations of p53 hinder the ability of E2D3-Ub to decelerate the reaction. The mathematical model successfully reproduced the experimentally observed p53-MDM2 interaction. The derived model therefore suggests MDM2 as a prospective target for cancer therapy. In addition, the findings of this project propose recombinant E2D3-Ub as a new promising protein-based anticancer drug for targeting overzealous p53 ubiquitination. The derived model can suggest new therapeutic solutions for decreasing the harmful effects of many human cancers, bacterial infections, and inflammatory diseases (such as rheumatoid arthritis) characterized by an overzealous ubiquitin-proteasome system. Finally, computational simulation of this novel model provides a safe, fast, and cost-effective preliminary alternative to expensive in vitro experimentation.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C235.
Citation Format: Prem M. Talwai. An investigation of the p53 ubiquitin-proteasome system using a novel non-steady-state enzyme kinetic model. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C235.