Purified transcription factor AP-1 interacts with TPA-inducible enhancer elements

Area of Science:

• Molecular Biology
• Gene Regulation
• Transcription Factors

Background:

• Enhancer-binding protein AP-1 (activator protein 1) plays a role in gene regulation.
• The precise mechanism of AP-1's function in transcriptional activation and its response to cellular stimuli requires further elucidation.

Purpose of the Study:

• To purify and characterize the enhancer-binding protein AP-1.
• To investigate the role of AP-1 in the transcriptional activation of specific genes, including the human metallothionein IIA (hMT IIA) gene.
• To determine if AP-1 binding sites can function as inducible enhancers in response to cellular signaling.

Main Methods:

• Purification of AP-1 from HeLa cells using sequence-specific DNA affinity chromatography.
• In vitro transcription assays using wild-type and mutant hMT IIA promoters.
• DNAase I protection analysis to identify AP-1 binding sites in hMT IIA, SV40, and human collagenase genes.
• Transfection of HeLa cells with plasmid constructs containing synthetic AP-1 binding sites.

Main Results:

• AP-1 was purified to >95% homogeneity as a 47 kd polypeptide.
• Purified AP-1 activated transcription of the wild-type hMT IIA gene but not mutant promoters lacking AP-1 sites.
• A conserved TGACTCA motif was identified as the AP-1 binding site in hMT IIA, SV40, and human collagenase genes.
• Synthetic AP-1 binding sites acted as TPA-inducible enhancers in transfected HeLa cells.

Conclusions:

• AP-1 is a transcription factor that binds to specific enhancer elements.
• The activity of AP-1 may be modulated by TPA (12-O-tetradecanoylphorbol-13-acetate), a tumor promoter known to activate protein kinase C.
• AP-1 binding sites mediate TPA-inducible gene transcription, highlighting their role in cellular responses to external stimuli.