Signal transduction during liver regeneration

Area of Science:

• Hepatology and Molecular Biology
• Cellular signaling pathways in liver regeneration

Background:

• Partial hepatectomy (PH) initiates a complex cascade of biochemical events preceding liver cell proliferation.
• Understanding the regulation of transcription factors like c-Jun and nuclear factor-kappa B (NFκB) is crucial for elucidating liver regeneration mechanisms.

Purpose of the Study:

• To investigate the role of c-Jun N-terminal kinase (JNK) and its upstream regulators in hepatic regeneration post-PH.
• To determine the physiological significance of nuclear factor-kappa B (NFκB) induction during liver regeneration.

Main Methods:

• Analysis of c-Jun mRNA levels, AP-1 binding activity, and JNK activity following varying degrees of PH in rats.
• In vitro studies using primary rat hepatocytes treated with growth factors.
• Inhibition of JNK activation using neutralizing antibodies to tumor necrosis factor-alpha (TNFα).
• Assessment of NFκB's role using adenoviral vectors expressing a super-repressor of NFκB activity (Ad5IκB) in vivo.

Main Results:

• PH significantly increased c-Jun mRNA, AP-1 binding activity, and JNK activity, with JNK activation dependent on TNFα.
• TNFα-mediated phosphorylation of c-Jun's activation domain enhanced AP-1-dependent gene transcription.
• Inhibition of NFκB activity led to increased apoptosis, cell cycle arrest, and liver failure following PH.

Conclusions:

• Hepatic regeneration involves TNFα-dependent JNK activation, leading to c-Jun phosphorylation and AP-1 transcriptional activation.
• NFκB plays a critical protective role during liver regeneration by preventing apoptosis and facilitating cell cycle progression.