Identifying molecular mechanisms underlying the effects of ethanol on eukaryotic genome instability

Alcohol (ethanol) is toxic to all life forms and its consumption has been associated
with numerous diseases, including cancer. Epidemiological studies have identified
causal relationships between alcohol intake and the incidence of oral cavity, larynx,
pharynx, esophagus, liver, colorectum, and female breast cancer. Yet, the molecular
mechanisms underlying the carcinogenic effect of ethanol remain elusive. It is clear
that especially tissues that come into direct contact with ethanol are at risk for
ethanol-related cancers. For example, head and neck cancers, which originate in
the epithelial linings of the oral cavity, pharynx and larynx, show a strong ethanol
etiology. Surprisingly, there are very few reports on the effects of ethanol in tissues
of the upper digestive tract. Moreover, previous studies have focused on low levels
of ethanol that mimic typical blood alcohol concentrations. This prevents us from
drawing a detailed picture of the responses to ethanol in healthy epithelial cells.
Further understanding of ethanol-related cell damage can contribute to reducing or
treating alcohol-related cancers.
Here we aim to address the aforementioned research gaps by studying the
responses of an immortalized laryngeal cell line (HuLa-PC) to relatively high ethanol
concentrations. Bulk RNA sequencing showed that short- and long-term ethanol
exposure altered gene expression patterns in HuLa-PC cells. Several genes that
were differentially expressed show a link to alcohol-related diseases, which highlights
the validity of our model. Additionally, ethanol-stressed cells showed a significant
decrease in general metabolism which translated into a slower proliferation, a delayedG1 cell cycle phase progression, and replication fork stalling. We observed a similar
ethanol-induced decrease in the G1 cell cycle phase and replication fork progression
in four other cell lines of the upper digestive tract, suggesting a shared ethanol
stress response across different cell types. Most strikingly, acute ethanol exposure
directly affected replication fork progression which could affect genome stability in
cells. Finally, ethanol-exposed HuLa-PC cells strongly upregulated genes coding for
transmembrane ion transporters, which could be associated with membrane stress
in ethanol-containing growth medium.
Collectively, our data confirms and expands on the knowledge regarding the damaging
effects of ethanol. For instance, we noticed the upregulation of Wnt signaling ligands
and receptors in ethanol stress conditions. Aberrant activation of Wnt signaling is
known to promote tumor metastasis and therefore it will be intriguing to elucidate
its role in ethanol-related carcinogenesis in future studies. Together, these data
form a stepping stone toward new paradigms in ethanol-related carcinogenesis.