IGFBP-3 interacts with NONO and SFPQ in PARP-dependent DNA damage repair in triple-negative breast cancer

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Triple-negative breast cancer (TNBC) exhibits chemotherapy resistance, partly due to DNA double-strand break (DSB) repair mechanisms.
• Insulin-like growth factor-binding protein 3 (IGFBP-3) was previously shown to modulate DSB repair in TNBC cells by forming nuclear complexes with EGFR and DNA-PKcs.

Purpose of the Study:

• To identify novel IGFBP-3 binding partners involved in chemoresistance via enhanced DSB repair in TNBC.
• To elucidate the functional role of these interactions in DNA repair pathways and their modulation by therapeutic agents.

Main Methods:

• Proteomic analysis (LC-MS/MS) to identify IGFBP-3 interactome.
• Co-immunoprecipitation and proximity ligation assays to confirm protein interactions.
• In vitro DNA end-joining assays and γH2AX foci measurement to assess DSB repair.
• siRNA-mediated knockdown of LINP1 and pharmacological inhibition of EGFR, DNA-PKcs, and PARP.

Main Results:

• The DNA/RNA-binding proteins NONO and SFPQ were identified as novel IGFBP-3 binding partners in TNBC cells (HCC1806, MDA-MB-468).
• IGFBP-3/NONO/SFPQ complex formation was inhibited by gefitinib (EGFR inhibitor), NU7026 (DNA-PKcs inhibitor), and PARP inhibitors (veliparib, olaparib).
• Inhibition of these pathways reduced DNA end-joining activity and delayed γH2AX foci resolution, indicating impaired DSB repair.
• Downregulation of long noncoding RNA LINP1 disrupted IGFBP-3 interaction with NONO-SFPQ.

Conclusions:

• NONO and SFPQ play a PARP-dependent role in IGFBP-3-mediated DSB repair in TNBC.
• LINP1 is involved in the formation of the IGFBP-3/NONO-SFPQ complex.
• Targeting the DNA repair function of IGFBP-3, potentially through its interaction with NONO/SFPQ, may enhance chemosensitivity in basal-like TNBC.