Downregulation of key B cell transcription factor Ets1 in response to antigen receptor signaling depends on IKK2 and unconventional downstream effectors.

Abstract The transcription factor (TF) Ets1 plays a critical role in maintaining B cell quiescence. High Ets1 levels in resting B cells prevent premature plasma cell differentiation and suppress autoimmune responses, but Ets1 must be downregulated to allow for proper B cell responses. Despite this vital role, it remains unknown how the Ets1 expression pattern is coordinated. Upon activation of antigen receptors (ARs), Ets1 is downregulated and quantification of newly transcribed pre-mRNA indicates that a decrease in Ets1 gene transcription is responsible. New protein synthesis is shown to be dispensable for this downregulation, suggesting that it does not rely on upregulation of a repressor but rather changes in abundance or activity of existing TFs. NFκB is activated in response to AR signaling and its binding motifs are found in putative regulatory elements identified near the Ets1 gene. Inhibition of NFκB-activating kinase IKK2 prevents the decrease in Ets1 transcription in response to AR stimulation. However, neither RelA nor cRel downstream of IKK2 are required for proper control of Ets1 expression. Next, we examined potential roles for Foxo3 and Rictor, unconventional downstream effectors of IKK2. Foxo3 has a similar expression pattern to Ets1 and is downregulated upon BCR stimulation, but B cells lacking Foxo3 regulate Ets1 expression in a manner similar to WT B cells. Rictor is a component of the mTORC2 complex, but inhibition of mTOR signaling does not impact Ets1 downregulation in response to BCR stimulation. Overall, these data suggest that Ets1 expression is coordinated by unconventional, but as of yet unidentified, downstream effectors of IKK2 in response to AR signaling. Funded by NIH R01 AI122720 and the Lupus Research Alliance.