Phosphorylation of the menin tumor suppressor protein on serine 543 and serine 583

Area of Science:

• Molecular Biology
• Genetics
• Endocrinology

Background:

• Multiple endocrine neoplasia type 1 (MEN-1) is an inherited disorder characterized by tumors in endocrine glands.
• MEN-1 results from mutations in the MEN1 tumor-suppressor gene, which encodes the menin protein.
• Menin's role in transcriptional regulation and histone modification is known, but its own modifications are poorly understood.

Purpose of the Study:

• To investigate post-translational modifications of the menin protein.
• To determine the functional consequences of menin phosphorylation, specifically at Ser543 and Ser583.

Main Methods:

• Site-directed mutagenesis to create phosphorylation-defective menin mutants (Ser543 and Ser583).
• Assays to evaluate menin's histone methyltransferase activity.
• Co-immunoprecipitation to assess binding to Trithorax complex proteins and RNA polymerase II.
• Chromatin immunoprecipitation to analyze menin binding to the Hoxc8 locus.

Main Results:

• Menin protein undergoes phosphorylation on serine residues, including Ser543 and Ser583.
• Phosphorylation-defective mutants at Ser543 and/or Ser583 retained menin's histone methyltransferase activity.
• These mutants also maintained binding to Ash2L, Rbbp5, MLL2 (Trithorax complex members), and RNA polymerase II.
• Menin's association with the Hoxc8 locus was unaffected by phosphorylation at Ser543 or Ser583.

Conclusions:

• Phosphorylation of menin at Ser543 and Ser583 is not essential for its core functions in histone modification and protein complex formation.
• These specific phosphorylation sites do not appear to regulate menin's interaction with chromatin targets like the Hoxc8 locus.