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Transcriptional regulation of the human tumor suppressor p14(ARF) by E2F1, E2F2, E2F3, and Sp1-like factors
Tiziana Parisi1, Alessandra Pollice, Antonio Di Cristofano
1Department of Genetics, General and Molecular Biology, University of Naples Federico II, via Mezzocannone 8, 80134 Naples, Italy.
Abstract:
The human ARF/INK4a locus encodes two cell cycle inhibitors, p16(INK4a) and p14(ARF), by using separate promoters. A variety of mitogenic stimuli upregulate ARF but a direct modulation at the transcriptional level has been reported only for E2F-1. We show here that the ARF promoter is strongly responsive also to E2F2 and E2F3, thus providing a strong support to their suggested role in the induction of apoptosis. Through the usage of both deletion mutants and/or site-directed mutants, we surprisingly found that none of the four putative E2F consensus sites is strictly necessary for the upregulation of ARF expression, as a minimal deletion mutant, lacking all the putative E2F binding sites, is still transactivated by E2F. Moreover, our data suggest that the ARF promoter is regulated by E2F through both direct binding to the promoter sequences and indirectly, probably by being tethered to the ARF promoter by Sp1-like factors.
Insights
Researchers found that E2F2 and E2F3 activate the ARF promoter, crucial for cell cycle inhibition and apoptosis. Surprisingly, direct E2F binding sites are not essential for this ARF gene regulation.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The ARF/INK4a locus produces two cell cycle inhibitors, p16(INK4a) and p14(ARF), via distinct promoters.
- While mitogens upregulate ARF, only E2F-1 was previously known to directly modulate its transcription.
Purpose of the Study:
- To investigate the role of E2F family members (E2F2, E2F3) in regulating the ARF promoter.
- To elucidate the mechanism of E2F-mediated ARF transcriptional upregulation.
Main Methods:
- Utilized deletion mutants and site-directed mutagenesis of the ARF promoter.
- Assessed ARF promoter transactivation by E2F family members.
- Investigated potential direct and indirect E2F binding mechanisms.
Main Results:
- The ARF promoter is significantly activated by E2F2 and E2F3, supporting their role in apoptosis induction.
- Minimal ARF promoter mutants lacking all putative E2F binding sites remained responsive to E2F.
- Evidence suggests E2F regulates the ARF promoter both directly and indirectly via Sp1-like factors.
Conclusions:
- E2F2 and E2F3 are key transcriptional regulators of the ARF gene.
- ARF promoter regulation by E2F is complex, involving both direct and indirect mechanisms.
- These findings deepen the understanding of cell cycle control and apoptosis pathways.