Acetylated sp3 is a transcriptional activator

Area of Science:

• Molecular Biology
• Gene Regulation
• Epigenetics

Background:

• The Sp3 transcription factor exhibits dual functionality, capable of both activating and repressing target gene expression.
• The precise molecular mechanisms governing Sp3's switch between activation and repression remain incompletely understood.
• Previous research indicated unmodified Sp3 functions as a repressor for transforming growth factor-beta receptors in specific breast cancer cells.

Purpose of the Study:

• To elucidate the molecular event controlling the dual function of the Sp3 transcription factor.
• To investigate the role of Sp3 acetylation in regulating transforming growth factor-beta receptor type II (RII) gene expression.
• To identify the specific signaling pathways and enzymes involved in Sp3-mediated gene regulation.

Main Methods:

• Utilized histone deacetylase inhibitor trichostatin A (TSA) to induce Sp3 acetylation in MCF-7L breast cancer cells.
• Performed mutation analysis on the RII promoter to identify Sp3/Sp1 binding sites critical for promoter activity.
• Employed ectopic Sp3 expression in Sp3-deficient MCF-7E cells to assess Sp3's function under varying conditions (TSA treatment).
• Investigated the interaction between Sp3 and histone acetyltransferase p300, including the role of p300's acetyltransferase domain.

Main Results:

• Trichostatin A (TSA) treatment induced Sp3 acetylation, converting its function from a repressor to an activator of the transforming growth factor-beta receptor type II (RII) gene.
• Mutation analysis confirmed that a GC box on the RII promoter, a known Sp1/Sp3 binding site, mediates the TSA-induced response.
• Ectopic Sp3 expression repressed RII promoter activity in Sp3-deficient cells without TSA, but activated it upon TSA treatment.
• Histone acetyltransferase p300 was identified as the enzyme responsible for acetylating Sp3, and its acetyltransferase activity was crucial for Sp3-mediated RII promoter activation.

Conclusions:

• Acetylation serves as a critical molecular switch, determining whether Sp3 acts as a transcriptional repressor or activator.
• The interplay between Sp3, histone acetyltransferase p300, and epigenetic modifications like acetylation governs the expression of key genes such as the transforming growth factor-beta receptor type II.
• These findings provide novel insights into the regulation of gene expression by Sp3 and have implications for understanding breast cancer biology.