Prohibitins and the cytoplasmic domain of CD86 cooperate to mediate CD86 signaling in B lymphocytes (42.5)

Abstract

Abstract CD86 engagement on a CD40L/IL-4-primed murine B cell activates signaling intermediates that increase Oct-2 and IgG1 mRNA and protein expression, independent of class switch recombination. One of the most proximal intermediates identified is PLCγ2. Since the cytoplasmic domain of CD86 lacks tyrosine residues reported to bind PLCγ2, we used a proteomics-based identification approach to show that the tyrosine-containing transmembrane adaptor proteins, prohibitin-1 (Phb1) and prohibitin-2 (Phb2), bind to CD86. Although basal expression of Phb1/2 and association with CD86 was low in resting B cells, expression and association increased after CD40 engagement. The CD86-induced increase in Oct-2 and IgG1 was less when either Phb1/2 expression was reduced by shRNA or the cytoplasmic domain of CD86 was truncated or mutated at serine/threonine PKC-phosphorylation sites, but did not affect Phb1/2 binding to CD86. Furthermore, Phb1/2 reduction and CD86 truncation revealed that the CD86-induced phosphorylation of PLCγ2 required Phb1/2 alone; whereas, IκBα and NF-κB (p65) phosphorylation required both Phb1/2 and the CD86 cytoplasmic domain. Together, these findings suggest that Phb1/2 and the CD86 cytoplasmic domain cooperate to mediate CD86 signaling in a B cell to regulate IgG1 production and is the first evidence to define the molecular basis of membrane-proximal CD86 signal transduction in B cells.