The Toxicologist - Society of Toxicology

38 ROLE OF RIBOTOXIC STRESS AND INNATE IMMUNE
ACTIVATION IN TRICHOTHECENE-INDUCED IGA
NEPHROPATHY.
J. J. Pestka. Microbiology and Molecular Genetics, Michigan State University, East
Lansing, MI.
Prolonged dietary exposure to the 8-ketotrichothecene mycotoxins deoxynivalenol
(DON) and nivalenol (NIV) in the mouse induces aberrant polyclonal IgA upregulation
and subsequent kidney IgA deposition in a manner that mimics the early
stages of human IgA nephropathy (IgAN). A critical underlying mechanism for
DON-induced IgA hyperproduction is systemic upregulation of IL-6 via transcriptional
and post-transcriptional mechanisms. Induction of IL-6 and other proinflammatory
genes is mediated by activation of mitogen-activated protein kinases in
macrophages and monocytes - effects that can be recapitulated in intact animals.
One initiating mechanism for the DON-induced ribotoxic stress response involves
the activation of constitutive ribosome-associated protein kinases (1)doublestranded
RNA (dsRNA)-activated protein kinase (PKR) and (2)hematopoetic cell
kinase (Hck), a non-receptor associated Src oncogene family kinase. A second
mechanism involves autophagy of the chaperone GRP78 with consequent activation
of the ER stress response. A coherent model will be presented for the sequence
of molecular events at the ribosome level that modulate intracellular signaling,
drive IL-6 induction and ultimately induce aberrant IgA upregulation.
39 RICIN AND SHIGA TOXINS INTERACT DIFFERENTLY
WITH THE RIBOSOMAL STALK.
N. Tumer 1 , J. Chiou 1 , X. Li 1 , M. Remacha 2 and J. P. Ballesta 2 . 1 Rutgers
University, New Brunswick, NJ and 2 Universidad Autonoma de Madrid, Madrid,
Spain. Sponsor: J. Pestka.
The A subunits of Shiga-like toxins (Stx1 and Stx2) and ricin (RTA) are N-glycosidases
that specifically remove an adenine from the α–sarcin/ricin loop (SRL) of the
large rRNA, resulting in inhibition of protein synthesis. In our previous work, we
showed that P proteins of the ribosomal stalk are critical for RTA to depurinate the
SRL in yeast. The interaction between RTA and ribosomes did not follow a simple
1:1 interaction model and was characterized by a two-step binding model. Using
purified, in vivo assembled, ribosomal stalk complexes from yeast, we showed a direct
interaction between RTA and the isolated stalk complex that fit a simple 1:1
interaction model. Therefore, the interaction between the isolated stalk and RTA
represented one of the two binding steps of the two-step binding model. We
showed that P proteins of the ribosomal stalk are also critical for Stx1 and Stx2 to
depurinate the SRL in yeast. Stx1 depurinated ribosomes less efficiently than RTA
or Stx2 in a yeast strain with a modified stalk (ΔAB), in which P protein binding
sites are deleted, suggesting that cytosolic P1/P2 proteins stimulate the depurination
activity of Stx1 when they are able to bind to the stalk. The addition of purified
P1α/P2β heterodimer stimulated in vitro depurination of ribosomes from the
ΔP1 strain, which contains the binding sites for P1/P2 heterodimers, but not ribosomes
from the ΔAB strain. The stimulation was greater for Stx1 than for RTA or
Stx2, indicating that cytosolic P1/P2 proteins are more critical for Stx1 to access the
ribosomal stalk. Addition of the P1α/P2β heterodimer did not stimulate depurination
of ribosomes from the ΔAB strain, indicating that the free P1/P2 proteins do
not directly stimulate the enzymatic activity of the toxins. Instead, they appear to
bind to the toxins in the cytosol and recruit them to the ribosomal stalk. These results
provide the first evidence that differences in the interaction of RTA, Stx1 and
Stx2 with the ribosomal stalk contribute to their relative depurination activity and
cytotoxicity.
40 DISEASE PREVENTION: THE NEXT 50 YEARS.
H. Zarbl. Environmental and Occupational Health Sciences Institiute, Robert Wood
Johnson Medical School, Piscataway, NJ.
The science of toxicology has had a tremendous impact on preventing adverse effects
of environmental toxicants, consumer products, and drugs on human health.
The Society of Toxicology played a pivotal role in developing the practice of toxicology
as a profession and a research discipline. As the Society embarks on its next
fifty years, new opportunities and challenges will no doubt change the role of toxicology
in the improving human health. High- throughput genomic technologies
are increasingly providing mechanistic insights into how exposure to toxicants interacts
with other exposures, genetic background, diet, lifestyle, co-morbid disease
and numerous other factors to modulate the disease risk. The Society thus has an
opportunity to once again play a leading role in improving public health by not
only preventing toxicity, but by developing approaches to predicting and preventing
disease in those already exposed and, by identifying individuals or populations
8 SOT 2011 ANNUAL MEETING
at increased risk from exposures. Therefore, the future of toxicology should include
an increasing presence in disease prevention through biomarker based exposure and
risk assessment, and individualized intervention, chemoprevention, and predictive
toxicology. These emerging approaches will be reviewed to provide a roadmap for
increasing the role of mechanistically based, predictive toxicology and ‘omics technologies
in disease prevention.
41 ASSESSING THE IMPACT OF INTER-INDIVIDUAL
GENETIC VARIABILITY ON TOXICITY THROUGH
TOXICOGENOMIC DATA.
I. Rusyn. Environmental Science and Engineering, University of North Carolina,
Chapel Hill, NC.
In the field of toxicogenomics, little attention is paid to the fact that transcript expression
is a heritable trait and that genetic control of mRNA levels may present a
challenge for using genomics in population studies. Gene expression Quantitative
Trait Locus (eQTL) mapping is one of the new tools to evaluate the association between
transcript expression and genotype in order to find genomic locations that
are likely to regulate transcript expression. The availability of both gene expression
and high density genotype data has enabled eQTL mapping in animal and human
populations. These analyses have contributed significantly to our understanding of
the impact that SNPs have on the physiological processes in multiple tissues, in
both animals and humans. Furthermore, these studies show that genetic regulation
of gene expression is a key contributor to population diversity through previously
unknown mechanisms. eQTL mapping is a key new approach in toxicogenomic
analyses for the evaluation of the potential role of genetic polymorphisms in the role
that environmental exposures may play in the pathogenesis of common diseases.
42 COMBINING THE GENOME WITH ITS EXPOSOME
FOR MECHANISTICALLY-BASED DISEASE
PREVENTION.
C. P. Wild. International Agency for Cancer Research, Lyon, France. Sponsor: H. Zarbl.
It has long been appreciated that both genes and environment play a critical role in
the etiopathogenesis of disease. While genetic background can now be accurately
and rapidly determined using high-throughput technologies, exposure assessment
still faces the limitations inherent in questionnaire data or extrapolation from ambient
toxicant levels, for example. However the availability of –omics technologies
and other advances in laboratory sciences coupled with new insights into underlying
disease mechanisms (e.g. epigenetics) present exciting opportunities to refine
environmental exposure assessment. On this basis the concept of the exposome was
proposed, representing the sum of all exposures from conception onward, to complement
the genome as a critical quantitative measure on which to investigate disease
risk and prevention. The presentation will introduce the concept of the exposome,
evaluate its potential applications, limitations and outline the roles of
epidemiologists and laboratory scientists in elucidating the components of the
human exposome.
43 TOP-DOWN EXPOSOMIC STRATEGIES TO
CHARACTERIZE THE HUMAN EXPOSOME.
M. Smyth. University of California, Berkeley, CA.
Researchers interested in the causes of disease rely upon increasingly sophisticated
gene-wide association studies (GWAS) to evaluate genetic differences across populations,
while using questionnaires to characterize environmental exposures.
Because inaccurate and imprecise estimation of ‘environmental’ exposures (including
stress, diet, and both exogenous and endogenous chemical exposures) can severely
bias inferences regarding environmental causes of diseases and gene-environment
(G x E) interactions, this imbalance in data quality between genetic and
environmental factors is problematic. What we need are environmental analogs of
GWAS to characterize the “exposome” and open the door to discovery of the environmental
causes of disease. Currently researchers use bottom-up exposomics
where they assume a priori that they know what to look for and try to measure it.
In top-down exposomics you take an agnostic discovery-based view and look for
patterns, then attempt to find out what those patterns reflect in terms of exposure.
Using a combination of omic high-throughput technologies, it should be possible
to characterize the “human exposome”, in which exposures from all environmental
sources (diet, stress, chemicals etc) are assessed. This top-down discovery-based approach
should work because the technologies are available now but currently require
too much material and are too expensive (similar to DNA sequencing 20