# Impact of Arsenite on Transient and Persistent Histone H3 Modifications and Transcriptional Response

## TL;DR

This study shows that arsenite exposure alters histone modifications and DNA repair gene activity in lung cells, potentially contributing to cancer risk.

## Contribution

The study reveals that arsenite causes persistent epigenetic changes and transcriptional effects in both cancerous and noncancerous lung cells.

## Key findings

- Arsenite exposure leads to hypoacetylation of histone H3 at DNA repair gene promoters like MLH1 and XPA.
- H3K18ac is particularly sensitive to arsenite, with reduced acetylation observed in both cancerous and noncancerous lung cells.
- Arsenite's effects on histone acetylation involve delayed HAT activity and reduced HDAC activity, suggesting targeted enzyme interactions.

## Abstract

Arsenite-contaminated groundwater poses a major health
concern
affecting millions of people. Chronic exposure to elevated levels
of inorganic arsenic is implicated in carcinogenesis, with impaired
DNA repair and dysregulated DNA and histone modifications as key factors.
Using human A549 lung carcinoma cells, we investigated the persistence
of acute arsenite-induced cellular stress at the epigenetic and transcriptional
levels after 24 h of exposure to 1–25 μM NaAsO2, reflecting low to high acute exposure scenarios, followed by a
48 h arsenite-free postincubation period. The primary objective was
to analyze alterations in acetylation and methylation marks on both
bulk histone H3 and specific DNA repair gene loci. We conducted immunochemical
and proteomic analyses to assess alterations in histone modification
patterns. Transient effects were observed at both methylated and acetylated
residues, with hypoacetylation specifically detected at promoters
of certain DNA repair genes, including MLH1, MSH2, MPG, and XPA. Among
all modifications analyzed, H3K18ac exhibited the most pronounced
decline, suggesting its preferential sensitivity toward arsenite.
H3 hypoacetylation was further observed in noncancerous human BEAS-2B
lung cells, indicating that this effect is not cancer cell-specific.
Mechanistically, in A549 cells, increased total HDAC or decreased
HAT activity could be excluded. Instead, a persistent moderate decline
in HDAC activity and a delayed, pronounced induction of HAT activity
suggest targeted arsenite interactions with specific enzymes of the
histone acetylation regulatory network.