Inflammation-Driven Downregulation of CYP2E1 Is Associated with Attenuated Diethylnitrosamine (DEN)-Induced Hepatocarcinogenesis

TL;DR

Chronic liver inflammation reduces the risk of liver cancer by suppressing enzymes that activate carcinogens.

Contribution

A new 'metabolic gatekeeping' model is proposed where inflammation limits chemical-induced liver cancer via downregulation of xenobiotic metabolism.

Findings

Transgenic mice with chronic liver inflammation are resistant to DEN-induced hepatocarcinogenesis.

Inflammation suppresses CYP2E1 and other xenobiotic-metabolizing enzymes, reducing DNA damage and p53 activation.

Reduced HNF4α–PXR–CAR signaling and CYP2E1 activity blunt DEN bioactivation and tumor initiation.

Abstract

What are the main findings?
Transgenic (Tg)-IKKβΔhep mice develop spontaneous chronic hepatitis and fibrosis yet are resistant to DEN-induced hepatocarcinogenesis.Chronic inflammatory signaling suppresses pericentral CYP2E1 and broadly down-regulates hepatic xenobiotic-metabolism programs.

Transgenic (Tg)-IKKβΔhep mice develop spontaneous chronic hepatitis and fibrosis yet are resistant to DEN-induced hepatocarcinogenesis.

Chronic inflammatory signaling suppresses pericentral CYP2E1 and broadly down-regulates hepatic xenobiotic-metabolism programs.

What are the implications of the main findings?
Attenuated HNF4α–PXR–CAR transcriptional output is associated with reduced DEN-triggered DNA-damage responses and p53 activation.These data support an inflammation-driven “metabolic gatekeeping” model in which chronic liver injury can constrain chemical tumor initiation by suppressing procarcinogen-metabolizing capacity.

Attenuated HNF4α–PXR–CAR transcriptional output is associated with reduced DEN-triggered DNA-damage responses and p53 activation.

These data support an inflammation-driven “metabolic gatekeeping” model in which chronic liver injury can constrain chemical tumor initiation by suppressing procarcinogen-metabolizing capacity.

Inflammation is widely viewed as a driver of hepatocellular carcinoma (HCC), yet inflammatory signaling also reshapes hepatic xenobiotic metabolism. Here, we established transgenic (Tg) IKKβΔhep mice (Tg-IKKβΔhep), which combine hepatocyte-specific IKKβ deletion with liver expression of a nuclear, kinase-inactive IKKβ mutant (NLS-IKKβKN). Tg-IKKβΔhep mice developed spontaneous chronic hepatitis and progressive fibrosis but were strikingly resistant to diethylnitrosamine (DEN)-induced hepatocarcinogenesis, with markedly reduced tumor multiplicity and total tumor burden. Despite persistent inflammatory injury, DEN-triggered oxidative DNA damage and p53 activation were markedly attenuated, compatible with reduced tumor initiation. Transcriptomic and biochemical analyses revealed broad repression of xenobiotic-metabolizing cytochrome P450 genes, including the pericentral enzyme CYP2E1, accompanied by reduced CYP2E1 protein abundance. This was associated with impaired HNF4α–PXR–CAR transcriptional output and reduced HNF4α occupancy at target promoters. Acute TNFα or IL-1β exposure recapitulated this repression, in part through reduced PGC-1α expression and decreased RNA polymerase II recruitment to target promoters. In parallel, pericentral xenobiotic metabolism was blunted, a change that could plausibly diminish DEN bioactivation and genotoxic stress. Together, these findings support a “metabolic gatekeeping” model in which chronic inflammation can constrain chemical hepatocarcinogenesis by attenuating carcinogen-metabolizing capacity.

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