Abstract 4388: beta-Carotene's oxidative breakdown inhibits p53 conformational folding and function

Abstract

Abstract Lipophilic electrophiles have been found to have the ability to inhibit wild-type p53 protein function through a thioredoxin-dependent inhibition of functional protein folding. One potential extension of this line of research may help to explain the curious findings of certain carotenoid-based chemopreventive clinical trials that found that beta-carotene may be a contributory causal risk of cancer development in patients who actively smoke. Chemical precepts dictate that wild-type p53 function may be inihibited through a similar mechanism by other other lipophilic compounds such as carotenoids within a high redox milieu of ongoing smoking. We ask the question whether the oxidative breakdown of beta-carotene could inhibit p53 function via a similar post-translational mechanism. Using resonance Raman spectroscopy, HPLC, spectrophotometry, and Western blot analysis, we exposed isolated cell-free and intracellular beta-carotene to various oxidant sources such as nitric oxide (NO·), superoxide (O·), and/or the combination of NO· and O· [i.e. SNAP (NO+ donor), Spermine-NONOate (NO. donor), and SIN-1 (NO·/O· donor), and Angeli's salt (an NO[[Unsupported Character - Codename ­]]- donor)] as a model of ongoing oxidative stress. Our results demonstrate that the oxidative breakdown of beta-carotene specifically by SIN-1 (the donor of NO·/O· causes stabilization of p53, attributable to the accumulation of both “functional” and “non-functional” conformational folding. Finally, we demonstrate that the oxidative breakdown products of beta-carotene can inhibit thioredoxin function, thus providing a biochemical mechanism for the inhibition of wild-type protein folding. Taken together, these data support the hypothesis that ongoing oxidation of beta-carotene can inhibit this key cancer-related molecular pathway, through the post-translational inhibition p53 folding and function. These data may provide one biochemical mechanism for the surprising results of initial carotenoid-based chemopreventive cancer trials. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4388.