PP4 deficiency leads to DNA replication stress that impairs immunoglobulin class switch efficiency

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• The serine/threonine phosphatase PP4 plays a role in DNA damage repair and cell cycle regulation.
• Previous studies indicated PP4's necessity for B cell development, germinal center formation, and immunoglobulin class switch recombination (CSR).

Purpose of the Study:

• To investigate the mechanisms by which PP4 influences B cell function, particularly during immunoglobulin class switch recombination.
• To elucidate PP4's role in preventing DNA replication stress that could impede CSR and antibody switching.

Main Methods:

• Analysis of PP4-deficient murine B lymphocytes.
• Assessment of DNA damage response pathways (ATM/p53, ATR), cell proliferation, and DNA repair complex retention (γH2AX-NBS1).
• Conditional deletion of PP4 and p53 using AID/cre system in B cells.

Main Results:

• PP4-deficient B cells exhibit proliferation defects and induced DNA damage response pathways (ATM/p53).
• These cells show inefficient ATR phosphorylation and reduced γH2AX-NBS1 complex retention, compromising IgG1 switching.
• Conditional deletion of PP4 restores IgG1 production, and co-deletion with p53 partially rescues IgG1 switching in vivo.

Conclusions:

• PP4 is essential for preventing DNA replication stress during the humoral immune response, thereby facilitating antibody switching.
• PP4's function is critical for maintaining genomic stability and efficient CSR in B cells.