Downstream effectors of BCR signaling control transcription of autoimmunity-associated transcription factor Ets1

Abstract

The transcription factor (TF) Ets1 is a critical regulator of B cell quiescence. Its expression must be maintained at a high level in resting B cells to prevent inappropriate differentiation and autoimmune responses, and its downregulation in response to antigen receptor stimulation is vital for proper B cell responses. How Ets1 expression is controlled remains unstudied. Quantification of newly-transcribed Ets1 pre-mRNA shows that Ets1 gene transcription is reduced upon BCR stimulation. Inhibition of new protein synthesis did not prevent repression of Ets1 transcription in response to stimulation, suggesting that the phenomenon depends on modulation of existing TF binding to Ets1 regulatory elements (REs) rather than de novo synthesis of a repressor protein. Epigenetic analyses identified numerous putative REs in the mouse Ets1 locus. A 217 kb BAC transgenic construct containing potential RE sequences drives eGFP reporter expression in a manner that recapitulates that of endogenous Ets1. To identify REs that may be important for regulating Ets1 expression and stimulation-induced repression, we performed ATAC-seq in untreated and BCR-stimulated B cells, and observed potentially meaningful changes to chromatin accessibility. Motifs for highly relevant TFs are enriched in accessible regions in the Ets1 locus, including members of the Smad, ETS, AP-1, and NFκB families. Following up on NFκB as a potential regulator of Ets1 expression, downregulation of Ets1 transcription was found to be dependent upon IKK2 activity but did not require RelA. These analyses suggest a potentially complex regulatory network behind the expression of Ets1 as it safeguards the resting B cell state. Funded by NIH R01 AI122720 and Lupus Research Alliance.