G-quadruplex-forming nucleic acids interact with splicing factor 3B subunit 2 and suppress innate immune gene...

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• G-quadruplex (G4) structures are non-canonical DNA/RNA motifs involved in gene regulation.
• Upregulation of innate immune/interferon-stimulated genes (ISGs) is linked to cancer progression.
• G4 structures can suppress ISG induction in cancer cells, but the mechanism is unclear.

Purpose of the Study:

• To elucidate the mechanism by which G4 structures suppress ISG expression in cancer cells.
• To identify proteins that interact with G4 structures and mediate their regulatory effects.
• To investigate the role of G4-SF3B2 interaction in regulating ISG expression and STAT1 phosphorylation.

Main Methods:

• Guanine-rich oligonucleotides and G4-stabilizing compounds were used to study G4 formation and function.
• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified G4-binding proteins.
• Western blotting assessed STAT1 phosphorylation and ISG expression levels.
• SF3B2 knockdown and splicing inhibition experiments were performed.

Main Results:

• SF3B2 was identified as a G4-binding protein in 3D-cultured cancer cells.
• G4 oligonucleotides and SF3B2 knockdown suppressed ISG induction.
• G4 binding to SF3B2 inhibited STAT1 phosphorylation and ISG expression.
• Phen-DC3, a G4 stabilizer, reversed G4-mediated ISG suppression and inhibited G4-SF3B2 binding.
• SF3B2's role in ISG induction was independent of RNA splicing.

Conclusions:

• G4 structures act as inhibitory trans-elements by binding to SF3B2.
• This G4-SF3B2 interaction disrupts STAT1 phosphorylation and down-regulates ISG expression in cancer cells.
• G4s represent a novel regulatory mechanism impacting innate immunity in cancer.