Functional cooperation between JunD and NF-kappaB in rat hepatocytes

Area of Science:

• Hepatology
• Molecular Biology
• Cellular Signaling

Background:

• Activating protein 1 (AP-1) and nuclear factor kappa B (NF-kappaB) are transcription factors rapidly activated during liver regeneration.
• The functional relationship between AP-1 and NF-kappaB during liver regeneration is not well understood.

Purpose of the Study:

• To investigate the functional implications of parallel AP-1 and NF-kappaB activation during liver regeneration.
• To determine if AP-1 influences NF-kappaB activity in hepatocytes.

Main Methods:

• Hepatocytes were stimulated with epidermal growth factor, hepatocyte growth factor, and tumor necrosis factor alpha.
• AP-1 and NF-kappaB binding activity was assessed using electrophoretic mobility shift assays.
• NF-kappaB-dependent transcription was measured using reporter assays.
• Dominant-negative AP-1 mutant (TAM67) and JunD overexpression were used to assess functional cooperation.
• NF-kappaB transactivation was compared in hepatocytes from JunD knockout and wild-type mice.

Main Results:

• Epidermal growth factor, hepatocyte growth factor, and tumor necrosis factor alpha increased AP-1 and NF-kappaB binding and activated NF-kappaB-dependent transcription.
• Inactivation of AP-1 by TAM67 significantly inhibited basal and cytokine-induced NF-kappaB transactivation.
• Overexpression of JunD, but not other Jun or Fos proteins, threefold increased NF-kappaB transactivation.
• Functional cooperation between JunD and p65 (a subunit of NF-kappaB) was demonstrated.
• NF-kappaB transactivation was reduced in hepatocytes from JunD knockout mice compared to wild-type mice.

Conclusions:

• AP-1 and NF-kappaB signaling pathways functionally cooperate during liver regeneration.
• JunD, a major component of AP-1, plays a crucial role in regulating NF-kappaB transactivation in hepatocytes.
• These findings elucidate a key molecular mechanism underlying liver regenerative processes.