Surface Ig receptor-induced nuclear AP-1-dependent gene expression in B lymphocytes

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• The molecular mechanisms linking B lymphocyte antigen receptor (sIgR) signaling to gene expression changes remain unclear.
• Activator protein 1 (AP-1) transcription factors are crucial in cellular responses, but their role in B cell sIgR signaling is not well-defined.

Purpose of the Study:

• To investigate the expression and function of AP-1 proteins in response to sIgR cross-linking in a murine B lymphoma cell line (BAL-17).
• To elucidate how sIgR-mediated signaling influences AP-1 activity and subsequent gene expression.

Main Methods:

• Utilized electrophoretic mobility shift assays (EMSA) to detect AP-1 DNA-binding activity.
• Employed immunoprecipitation with specific antisera to identify AP-1 protein components (Jun and Fos family members).
• Performed transient transfection assays with reporter gene constructs to assess AP-1 trans-activation potential.

Main Results:

• sIgR cross-linking significantly induced nuclear AP-1 binding activity in BAL-17 B cells.
• The induced AP-1 complex comprised Jun and Fos proteins, with de novo synthesis of Jun-B, c-Jun, and c-Fos observed.
• sIgR-induced AP-1 differentially regulated gene expression, activating a TRE-containing HSV-tk promoter but not a collagenase promoter dependent on c-Jun.

Conclusions:

• This study provides the first evidence for a functional role of sIgR-mediated AP-1 in B lymphoid cells.
• AP-1, particularly Jun-B containing complexes, acts as a key mediator coupling sIgR signaling to alterations in nuclear gene expression.