Development of a curated Hershberger database.

A systematic literature review was conducted to identify Hershberger bioassays for ∼3200 chemicals including those used to validate the OECD/US EPA guideline assay, US EPA's chemicals screened for endocrine activity, and the library of chemicals run in US EPA 's ToxCast in vitro assays. For 134 chemicals that met pre-defined criteria, experimental results were extracted into a database used to characterize uncertainty in results and evaluate the concordance of the Hershberger assay with other in vivo rodent studies that measure androgen-responsive endpoints. Of 25 chemicals tested in >1 Hershberger study, 28% had disagreements between studies (i.e. ≥1 positive and ≥1 negative study), and of the 65 chemicals tested in Hershberger studies and other in vivo studies with androgen-responsive endpoints, 43% indicated disagreements, though in some cases these may be explained by differences in study designs or physiology of the animal model. Ultimately, 49 chemicals were identified with reproducible androgen pathway responses confirmed in ≥2 in vivo rodent studies that could be considered reference chemicals useful for validating alternative methods.

Evaluation of androgen assay results using a curated Hershberger database.

A set of 39 reference chemicals with reproducible androgen pathway effects in vivo, identified in the companion manuscript [1], were used to interrogate the performance of the ToxCast/Tox 21 androgen receptor (AR) model based on 11 high throughput assays. Cytotoxicity data and specificity confirmation assays were used to distinguish assay loss-of-function from true antagonistic signaling suppression. Overall agreement was 66% (19/29), with ten additional inconclusive chemicals. Most discrepancies were explained using in vitro to in vivo extrapolation to estimate equivalent administered doses. The AR model had 100% positive predictive value for the in vivo response, i.e. there were no false positives, and chemicals with conclusive AR model results (agonist or antagonist) were consistently positive in vivo. Considering the lack of reproducibility of the in vivo Hershberger assay, the in vitro AR model may better predict specific AR interaction and can rapidly and cost-effectively screen thousands of chemicals without using animals.

Ribosome biogenesis surveillance: probing the ribosomal protein-Mdm2-p53 pathway.

The dynamic processes of cell growth and cell division remain under constant surveillance. As one of the primary 'gatekeepers' of the cell, p53 has a major role in sensing a variety of stressors to maintain cellular homeostasis. Growth is driven by new protein synthesis, a process that requires robust manufacture of ribosomes in the nucleolus. Ribosome biogenesis is a complex process comprising transcription, modification, and processing of ribosomal RNA, production of ribosomal proteins (RPs) and auxiliary factors, and coordinated assembly of ribonucleoprotein particles to produce mature ribosomes. As the major function of the nucleolus, ribosome biogenesis demands a considerable amount of resources and must be maintained in a coordinated manner to ensure fidelity of the process. Perturbations to many aspects of ribosome biogenesis are thought to contribute to 'nucleolar stress' and trigger a RP-Mdm2-p53 stress response pathway. In this review, we will clarify how disruption to three major components of ribosome biogenesis can trigger nucleolar stress and activate p53, thereby lending support to a RP-Mdm2-p53 ribosome biogenesis surveillance pathway.