Gα_i Signaling Promotes Marginal Zone B Cell Development by Enabling Transitional B Cell ADAM10 Expression

The follicular (FO) versus marginal zone (MZ) B cell fate decision in the spleen depends upon BCR, BAFF, and Notch2 signaling. Whether or how G_i signaling affects this fate decision is unknown. Here, we show that direct contact with Notch ligand expressing stromal cells (OP9-Delta-like 1) cannot promote normal MZ B cell development when progenitor B cells lack Gα_i proteins, or if Gi signaling is disabled. Consistent with faulty ADAM10-dependent Notch2 processing, Gα_i-deficient transitional B cells had low ADAM10 membrane expression levels and reduced Notch2 target gene expression. Immunoblotting Gα_i-deficient B cell lysates revealed a reduction in mature, processed ADAM10. Suggesting that Gα_i signaling promotes ADAM10 membrane expression, stimulating normal transitional B cells with CXCL12 raised it, while inhibiting Gα_i nucleotide exchange blocked its upregulation. Surprisingly, inhibiting Gα_i nucleotide exchange in transitional B cells also impaired the upregulation of ADAM10 that occurs following antigen receptor crosslinking. These results indicate that Gα_i signaling supports ADAM10 maturation and activity in transitional B cells, and ultimately Notch2 signaling to promote MZ B cell development.