B-cell receptor activation induces BIC/miR-155 expression through a conserved AP-1 element

Area of Science:

• Immunology
• Molecular Biology
• Oncology

Background:

• MicroRNA-155 (miR-155) is an oncogenic microRNA essential for B-cell maturation and immunoglobulin production.
• B-cell receptor (BCR) cross-linking induces miR-155 and its primary transcript, B-cell integration cluster (BIC).

Purpose of the Study:

• To elucidate the signaling pathways and transcription factors involved in BCR-mediated induction of BIC/miR-155.
• To identify key regulatory elements in the miR-155 promoter responsive to BCR signaling.

Main Methods:

• Pharmacological inhibition of signaling pathways (ERK, JNK, p38) in Ramos human B-cell line.
• Analysis of transcription factor induction (c-Fos, FosB, JunB) and reporter assays.
• Chromatin immunoprecipitation (ChIP) to assess transcription factor binding to the miR-155 promoter.

Main Results:

• BCR signaling activates BIC and miR-155 expression via ERK and JNK pathways, but not p38.
• BCR activation induces c-Fos, FosB, and JunB, which are suppressed by ERK/JNK inhibitors.
• A conserved AP-1 site in the miR-155 promoter is critical for induction; NF-kappaB and c-Ets sites are not.
• FosB and JunB are recruited to the miR-155 promoter upon BCR activation.

Conclusions:

• The study identifies ERK and JNK as key mediators of BCR-induced miR-155 expression.
• FosB and JunB binding to the AP-1 site on the miR-155 promoter is essential for its induction.
• These findings clarify the molecular mechanisms regulating miR-155 in B-cell activation and oncogenesis.