c-Jun represses the human insulin promoter activity that depends on multiple cAMP response elements

Area of Science:

• Molecular Biology
• Endocrinology
• Genetics

Background:

• Glucose stimulates cAMP production in pancreatic beta cells, which influences insulin gene expression.
• Understanding the precise mechanisms of cAMP-mediated insulin gene regulation is crucial for metabolic research.

Purpose of the Study:

• To identify and characterize cAMP response elements (CREs) in the human insulin gene.
• To investigate the role of identified CREs and the c-Jun protein in regulating insulin gene expression in response to glucose.

Main Methods:

• DNase I footprinting to identify CREs bound by CRE-BP1.
• Reporter gene assays using chloramphenicol acetyl-transferase (CAT) linked to insulin promoter constructs in HIT cells.
• Co-transfection assays with c-Jun expression plasmids.
• Northern blot analysis to assess c-jun mRNA levels.

Main Results:

• Four CREs were identified in the human insulin gene (two upstream, one in exon 1, one in intron 1).
• These four CREs additively contribute to cAMP-induced insulin promoter activity.
• c-Jun repressed cAMP-induced insulin promoter activity.
• Glucose deprivation significantly increased c-jun mRNA levels in HIT cells.

Conclusions:

• The human insulin gene is regulated by glucose through multiple CREs.
• c-Jun acts as a repressor of cAMP-induced insulin gene expression.
• Glucose may regulate human insulin gene expression via CREs and c-Jun, suggesting a complex regulatory network.