PIP2 epigenetically represses rRNA genes transcription interacting with PHF8

Area of Science:

• Molecular Biology
• Epigenetics
• Cell Biology

Background:

• Phosphoinositides, including phosphatidylinositol-4,5-bisphosphate (PIP2), are crucial signaling molecules found in various cellular compartments.
• The role of nuclear phosphoinositides in regulating gene expression, particularly at the epigenetic level, remains incompletely understood.

Purpose of the Study:

• To investigate the function of nuclear phosphatidylinositol-4,5-bisphosphate (PIP2) in the regulation of ribosomal DNA (rDNA) transcription.
• To identify specific molecular interactions through which PIP2 exerts its regulatory effects on gene expression.

Main Methods:

• Biochemical assays to demonstrate direct interaction between PIP2 and the histone lysine demethylase PHF8 (PHD finger protein 8).
• Site-directed mutagenesis to identify the PIP2-binding domain within PHF8.
• Quantitative analysis of rDNA promoter activity and pre-rRNA gene expression using a PIP2-binding mutant of PHF8.
• Proteolytic digestion (trypsin) to assess conformational changes in PHF8 upon PIP2 binding.

Main Results:

• Phosphatidylinositol-4,5-bisphosphate (PIP2) directly binds to the histone lysine demethylase PHF8.
• PIP2 binding to PHF8 represses the demethylation of histone H3 lysine 9 dimethylation (H3K9me2).
• A PIP2-binding mutant of PHF8 exhibited significantly increased rDNA promoter activity (20%) and pre-rRNA gene expression (47S: 100%; 45S: 66%).
• PIP2 binding induces a conformational change in PHF8.

Conclusions:

• Nuclear PIP2 functions as an epigenetic regulator of rRNA gene transcription.
• The interaction between PIP2 and PHF8 is critical for controlling H3K9me2 demethylation and modulating rDNA transcription.
• PIP2 plays a role in the fine-tuning of ribosomal DNA transcription through its interaction with PHF8.