A feedback regulatory loop between methyltransferase PRMT1 and orphan receptor TR3.

Area of Science:

• Molecular Biology
• Cellular Signaling
• Epigenetics

Background:

• Protein arginine methyltransferase 1 (PRMT1) is crucial for cellular processes.
• Orphan receptors, like TR3, are key regulators of gene expression.
• Understanding protein-protein interactions and regulatory feedback loops is vital in cell biology.

Purpose of the Study:

• To elucidate the regulatory relationship between PRMT1 and the orphan receptor TR3.
• To investigate the role of PRMT1 in TR3 protein stability and activity.
• To characterize the impact of TR3 on PRMT1's methyltransferase function.

Main Methods:

• Co-immunoprecipitation to assess protein interactions.
• Western blotting to analyze protein levels and degradation.
• Reporter assays to measure transactivation activity.
• In vitro assays to determine methyltransferase activity.
• Gene knockdown and knockout models (TR3-knockdown cells, TR3-knockout mice).

Main Results:

• PRMT1 physically interacts with TR3 but does not methylate it.
• PRMT1 binding stabilizes TR3, increasing its cellular levels, DNA binding, and transactivation activity in a non-enzymatic manner.
• The coactivator SRC-2 enhances PRMT1's regulation of TR3.
• TR3 binds to PRMT1's catalytic domain, inhibiting its methyltransferase activity.
• This inhibition affects PRMT1 substrates like STAT3 and Sam68.
• TR3-mediated repression of PRMT1 was confirmed in knockdown/knockout models.

Conclusions:

• PRMT1 regulates TR3 activity and stability through a non-methyltransferase mechanism.
• TR3 acts as a negative regulator of PRMT1's methyltransferase activity, establishing a novel feedback loop.
• This study reveals a dual regulatory role for PRMT1 and a novel repressive function for TR3 in cellular signaling pathways.