Indirect activation of constitutive androstane receptor in three-dimensionally cultured HepG2 cells

Area of Science:

• Hepatology
• Molecular Biology
• Cell Biology

Background:

• Constitutive androstane receptor (CAR) is a nuclear receptor regulating gene transcription.
• CAR activation involves cytoplasmic retention in an inactive, phosphorylated state, followed by nuclear translocation.
• Traditional 2D cell cultures like HepG2 do not accurately reflect CAR's in vivo behavior, showing spontaneous nuclear accumulation.

Purpose of the Study:

• To investigate CAR activation and nuclear translocation in three-dimensionally (3D) cultured HepG2 cells.
• To determine if 3D-cultured HepG2 cells can mimic CAR regulation observed in primary hepatocytes.
• To identify factors influencing CAR nuclear translocation in a 3D cell culture model.

Main Methods:

• Utilized three-dimensionally (3D) cultured HepG2 cells.
• Treated cells with phenobarbital, an indirect CAR activator.
• Administered okadaic acid and epidermal growth factor to assess their effects on CAR translocation and gene activation.

Main Results:

• Phenobarbital treatment induced CYP3A4 gene transcription in 3D-cultured HepG2 cells.
• CAR translocated to the nucleus in its phosphorylated form in response to phenobarbital.
• Okadaic acid and epidermal growth factor inhibited phenobarbital-induced CAR nuclear translocation and CYP3A4 gene promoter activation.

Conclusions:

• 3D-cultured HepG2 cells provide a more accurate model for studying CAR activation compared to 2D cultures.
• This 3D model recapitulates the regulated CAR nuclear translocation and gene activation seen in hepatocytes.
• The findings highlight the importance of 3D culture systems for understanding nuclear receptor signaling pathways.