Accelerated plasma-cell differentiation in Bach2-deficient mouse B cells is caused by altered IRF4 functions

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Antibody class-switch recombination (CSR) and plasma cell (PC) differentiation are critical B lymphocyte functions.
• Transcription factors BACH2 and IRF4 play opposing roles in these processes.

Purpose of the Study:

• To elucidate the interaction between BACH2 and IRF4 during CSR and PC differentiation.
• To understand the molecular mechanisms governing their opposing functions.

Main Methods:

• Analysis of gene expression and chromatin organization in mouse splenic B cells.
• Investigation of protein-protein interactions and signaling pathways (AKT-mTOR).
• Utilized B cells deficient in Bach2 to study IRF4 regulation.

Main Results:

• BACH2 induces heterochromatin formation at target gene loci, including those regulated by IRF4 (Aicda, Prdm1).
• B-cell receptor stimulation releases these loci from heterochromatin, linked to AKT-mTOR pathway activation.
• In Bach2-deficient cells, PC gene activation relies on IRF4 protein accumulation, not increased Irf4 mRNA.
• A PU.1-IRF4 heterodimer promotes BACH2 function, while elevated AKT activity in Bach2-deficient cells enhances IRF4 protein levels.

Conclusions:

• BACH2 and IRF4 mutually regulate each other's activity.
• BACH2 inhibits PC differentiation by repressing PC genes and restricting IRF4 protein accumulation.
• This interplay is crucial for balancing CSR and PC differentiation in B lymphocytes.