# Molecular Mechanisms of Complex Mixture Toxicity

> **NIH NIH R01** · UNIVERSITY OF CINCINNATI · 2021 · $448,297

## Abstract

PROJECT SUMMARY
 Environmental exposures to toxic compounds rarely result from the action of single toxicants. Often, the
toxic agent is a complex mixture of chemical entities in numbers ranging from a few, such as in occupational
exposures, to several thousand, as in cigarette smoke. The long-range goal of the research supported by this
grant is to develop an understanding of the mechanisms responsible for the adverse health effects of exposure
to mixtures of chromium (VI) and benzo[a]pyrene (BaP), focusing on the mechanisms causing gene expression
deregulation. We have shown that high-dose acute chromium treatment activates MAP kinases, interferes with
the assembly of transcriptional complexes, cross-links HDAC1∙DNMT1 complexes to promoter chromatin and
inhibits epigenetic phosphorylation, acetylation and methylation marks established by Cr/BaP-induced gene
transactivation in histones H3 and H4. These changes inhibit recruitment of RNA polymerase II to target
promoters, and block inducible gene expression, increasing genomic instability, DNA damage and apoptosis
while decreasing clonogenic ability. We used three different analytical approaches, namely FAIRE
(Formaldehyde-Assisted Isolation of Regulatory Elements), DANPOS (Dynamic Analysis of Nucleosome
Positioning and Occupancy by Sequencing), and ATAC (Assay for Transposase-Accessible Chromatin), to test
whether chromium could cause epigenetic changes in chromatin organization and architecture that could
explain this diversity of phenotypic effects. With high statistical significance, all three tests showed that
chromium causes chromatin domains surrounding the binding sites for CTCF (CCCTC binding factor) and its
analog, BORIS (Brother of the Regulator of Imprinted Sites) to switch from states of closed to open chromatin
or the reverse. CTCF/BORIS binding sites are the sole determinants of chromosome boundary-insulation in the
mammalian genome, playing a critical role in transcriptional regulation. In addition, CTCF is also uniquely
responsible for establishing chromatin topological domains and maintaining the 3-dimensional structure of the
genome. Our novel findings lead us to the hypothesis that Cr(VI) breaks the links created by CTCF connecting
genome architecture and function. Specifically, we propose that Cr(VI) disrupts 3-dimensional chromatin
organization and boundary formation between topologically associated domains in chromosomes, destroying
the interactions between transcription regulatory sequences. Based on these findings, we propose to test this
hypothesis by determining whether Cr(VI) treatment disrupts the long-range genome-wide intrachromosomal
and interchromosomal interactions established by CTCF and whether it interferes with the insulator function of
CTCF and disrupts transcriptional regulation in CTCF-bound domains. The knowledge derived from the
research proposed here will have a major impact on the biological and medical translation of epidemiological
findings of chromi...

## Key facts

- **NIH application ID:** 10172903
- **Project number:** 5R01ES010807-20
- **Recipient organization:** UNIVERSITY OF CINCINNATI
- **Principal Investigator:** Alvaro Puga
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $448,297
- **Award type:** 5
- **Project period:** 2001-01-16 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10172903

## Citation

> US National Institutes of Health, RePORTER application 10172903, Molecular Mechanisms of Complex Mixture Toxicity (5R01ES010807-20). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10172903. Licensed CC0.

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