The E26 Transformation-Specific-family transcription factor Spi-C is dynamically regulated by external signals in B cells

Abstract

Spi-C is an E26 transformation-specific transcription factor closely related to PU.1 and Spi-B. Spi-C has lineage-instructive functions important in antibody-generating responses, B cell development, and red pulp macrophage generation. Spi-C is inducible by heme- and NF-{kappa}B-dependent pathways in macrophages. The present research aimed to examine the regulation of Spi-C expression in B cells. RT-qPCR analysis revealed that Spic expression was reduced in B cells following addition of lipopolysaccharide, anti-IgM antibodies, CD40L, or cytokines BAFF + IL-4 + IL-5. Cytochalasin treatment partially prevented downregulation of Spic. Unstimulated B cells upregulated Spic over time in culture. To determine the mechanism of Spic regulation, we examined the Spic promoter and upstream regulatory elements. The Spic promoter had unidirectional activity, which was reduced by mutation of an NF-{kappa}B binding site. Spic was repressed by an upstream regulatory region interacting with the heme-binding regulator Bach2. Taken together, these data indicate that Spi-C is dynamically regulated by external signals in B cells and provide insight into the mechanism of regulation.