BRK phosphorylates PSF promoting its cytoplasmic localization and cell cycle arrest

Area of Science:

• Molecular Biology
• Cancer Research
• Signal Transduction

Background:

• Protein kinase 6 (BRK), a non-receptor tyrosine kinase, is overexpressed in breast carcinoma and serves as a prognostic marker.
• BRK functions downstream of epidermal growth factor (EGF) signaling, influencing cell proliferation and migration.

Purpose of the Study:

• To identify substrates and interacting proteins of BRK using a proteomic approach.
• To elucidate the functional relationship between BRK and its identified interacting partners in the context of EGF signaling.

Main Methods:

• Proteomic analysis using mass spectrometry to identify proteins interacting with BRK.
• Co-immunoprecipitation assays to confirm BRK-PSF interaction in BT-20 breast cancer cells.
• Analysis of PSF phosphorylation sites and functional consequences of phosphorylation.

Main Results:

• Polypyrimidine tract-binding protein-associated splicing factor (PSF) was identified as a BRK-interacting protein and substrate.
• BRK and PSF form a complex regulated by EGF stimulation, with interaction mediated by SH3 domain-polyproline binding.
• BRK phosphorylates PSF at its C-terminal tyrosines, leading to cytoplasmic relocalization, impaired RNA binding, and cell cycle arrest.

Conclusions:

• BRK directly targets the RNA-binding protein PSF in response to EGF stimulation.
• The phosphorylation of PSF by BRK plays a critical role in regulating PSF's cellular localization, RNA binding, and cell cycle progression.
• These findings reveal a novel mechanism by which BRK contributes to breast cancer progression downstream of EGF signaling.