Cellular Stress Response Pathway System as a Sentinel Ensemble in Toxicological Screening

Abstract

High costs, long test times, and societal concerns related to animal use have required the development of in vitro assays for the rapid and cost-effective toxicological evaluation and characterization of compounds in both the pharmaceutical and environmental arenas. Although the pharmaceutical industry has developed very effective, high-throughput in vitro assays for determining the therapeutic potential of compounds, the application of this approach to toxicological screening has been limited. A primary reason for this is that while drug candidate screens are directed to a specific target/mechanism, xenobiotics can cause toxicity through any of a myriad of undefined interactions with cellular components and processes. Given that it is not practical to design assays that can interrogate each potential toxicological target, an integrative approach is required if there is to be a rapid and low-cost toxicological evaluation of chemicals. Cellular stress response pathways offer a viable solution to the creation of a set of integrative assays as there is a limited and hence manageable set (a small ensemble of 10 or less) of major cellular stress response pathways through which cells mount a homoeostatic response to toxicants and which also participate in cell fate/death decisions. Further, over the past decades, these pathways have been well characterized at a molecular level thereby enabling the development of high-throughput cell-based assays using the components of the pathways. Utilization of the set of cellular stress response pathway-based assays as indicators of toxic interactions of chemicals with basic cellular machinery will potentially permit the clustering of chemicals based on biological response profiles of common mode of action (MOA) and also the inference of the specific MOA of a toxicant. This article reviews the biochemical characteristics of the stress response pathways, their common architecture that enables rapid activation during stress, their participation in cell fate decisions, the essential nature of these pathways to the organism, and the biochemical basis of their cross-talk that permits an assay ensemble screening approach. Subsequent sections describe how the stress pathway ensemble assay approach could be applied to screening potentially toxic compounds and discuss how this approach may be used to derive toxicant MOA from the biological activity profiles that the ensemble strategy provides. The article concludes with a review of the application of the stress assay concept to noninvasive in vivo assessments of chemical toxicants.

NADPH Oxidase-Mediated Redox Signaling: Roles in Cellular Stress Response, Stress Tolerance, and Tissue Repair

“…Cells react to various stresses primarily through a number of specific and well conserved adaptive intracellular signaling pathways that attempt to alleviate damage and maintain or re-establish homeostasis, known as cellular stress response, which is present in all cell types of metazoans (Simmons et al, 2009). At the cellular level, the stress response can be initiated by external environmental factors that cause damage to biological macromolecules including lipids, proteins, and nucleic acids (Kü ltz, 2005).…”

“…The cellular stress response entails a series of coordinated transcription and translational events leading to the accumulation of protective proteins that may counteract the stress-induced damage, and temporarily increase cellular tolerance to such damage; otherwise, cellular stress response may trigger programmed cell death (apoptosis) to remove terminally damaged cells (Welch, 1987;Kü ltz, 2005). On the other hand, cellular stress response can also be set off by internal deleterious changes, in forms of genomic stress and endoplasmic reticulum (ER 1 ) stress for example (Simmons et al, 2009). Genomic stress response is induced by DNA damage caused by endogenous and exogenous reasons such as genotoxic chemicals, ionizing radiation, hypoxia, mitotic spindle damage, or ribonucleotide depletion, in which the transcription factor p53 plays a central role in orchestrating the signaling events.…”

“…ER stress, also known as unfolded protein response, is caused by conditions under which the ER function is disrupted. ER is the organelle responsible for protein biosynthesis as well as protein folding and maturation for membrane incorporation and secretion (Simmons et al, 2009). The chaperone protein BiP/GRP78 mediates ER stress response, which is the sensor for accumulation of misfolded proteins in the ER.…”

Toxicogenomics for transcription factor-governed molecular pathways: moving on to roles beyond classification and prediction

“…Transducers relay information from primary transcription factor activation through a broader suite of cooperating TFs. Seven of eight canonical stress pathways (oxidative stress, heat shock response, DNA damage, hypoxia, ER stress, metal stress, and inflammation) have a common structure including sensor, transcription factor, and transducers (Simmons et al 2009). In these pathways, transduction of information generally occurs through various protein kinases that phosphorylate transcription factors.…”

Development of stable HSPA1A promoter-driven luciferase reporter HepG2 cells for assessing the toxicity of organic pollutants present in air

“…Hence, a rapid and cost-effective toxicity assessment bioassay is needed to determine the toxic potential of complex chemical mixtures. Bioassays using reporter vectors regulated by cellular stress-responsive gene promoters have been suggested as promising tools for toxicity assessment (Simmons et al 2009). …”