Phosphothreonine Lyase Promotes p65 Degradation in a Mitogen-Activated Protein Kinase/Mitogen- and Stress-Activated...

Area of Science:

• Microbiology and Immunology
• Molecular Biology
• Cellular Signaling

Background:

• Bacterial phosphothreonine lyases are type III secretion system (T3SS) effectors targeting host mitogen-activated protein kinase (MAPK) signaling.
• The impact of these lyases on nuclear factor κB (NF-κB) signaling pathways remains poorly understood.
• Understanding these interactions is crucial for deciphering bacterial pathogenesis and host immune evasion strategies.

Purpose of the Study:

• To investigate the effect of bacterial phosphothreonine lyase on NF-κB signaling during *Edwardsiella piscicida* infection.
• To elucidate the molecular mechanisms by which phosphothreonine lyase influences p65, a key component of NF-κB.
• To explore the role of MAPK signaling in mediating the phosphothreonine lyase-induced regulation of p65.

Main Methods:

• Macrophage infection models with *Edwardsiella piscicida*.
• Detection of p65 protein degradation using protease inhibitors (MG132).
• Analysis of protein phosphorylation and ubiquitination status of signaling molecules (p65, MSK1, ERK1/2, p38α, JNK).

Main Results:

• Phosphothreonine lyase significantly induced p65 degradation in infected macrophages, an effect inhibited by MG132.
• The lyase inhibited phosphorylation of MSK1, ERK1/2, p38α, and JNK, leading to p65 dephosphorylation and ubiquitination.
• The catalytic active site of phosphothreonine lyase is essential for regulating the MAPK-MSK1-p65 signaling axis.

Conclusions:

• Bacterial phosphothreonine lyase actively degrades p65, a critical step in NF-κB pathway regulation during infection.
• This effector disrupts host innate immunity by targeting the MAPK-MSK1-p65 signaling cascade.
• The findings reveal a novel bacterial strategy for pathogenesis by manipulating host immune signaling pathways.