SPOP negatively regulates Toll-like receptor-induced inflammation by disrupting MyD88 self-association

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Toll-like receptor (TLR) signaling pathways are crucial for immune responses but require strict regulation to prevent host damage.
• Myeloid differentiation primary response gene 88 (MyD88) acts as a key adaptor protein in TLR signaling cascades.

Purpose of the Study:

• To identify novel regulators of MyD88 function.
• To elucidate the role of speckle-type POZ protein (SPOP) in TLR signaling pathways.

Main Methods:

• Co-immunoprecipitation to identify MyD88-associated proteins.
• Immunofluorescence microscopy to track SPOP localization.
• Western blotting and ELISA to assess NF-κB activation and cytokine production.
• RNA interference (RNAi) to deplete SPOP levels.

Main Results:

• Speckle-type POZ protein (SPOP) was identified as a Myeloid differentiation primary response gene 88 (MyD88)-associated protein.
• TLR4 activation induced SPOP recruitment to MyD88 and its translocation from the nucleus to the cytoplasm.
• SPOP depletion led to MyD88 aggregation and increased activation of downstream kinases (IRAK4, IRAK1, IRAK2).
• Overexpression of SPOP inhibited TLR4-mediated NF-κB activation and inflammatory cytokine production, while SPOP depletion enhanced these responses.
• Knockdown of SPOP also increased MyD88 aggregation and cytokine production upon activation of TLR2, TLR7, and TLR9.

Conclusions:

• Speckle-type POZ protein (SPOP) functions as a negative regulator of Myeloid differentiation primary response gene 88 (MyD88)-dependent Toll-like receptor signaling.
• SPOP plays a critical role in limiting inflammatory responses by preventing excessive MyD88 aggregation and downstream signaling.