EBF1 and PAX5 control pro-B cell expansion via inverse regulation of the c-Myc gene.

EBF1 and PAX5 are two transcription factors targeted in human B-ALL. Their importance for normal B-cell differentiation has led to the suggestion that impaired function of these proteins contributes to the developmental block observed in B-lineage leukemia. However, increased understanding of the function of these proteins has suggested more complex roles in malignant transformation. We here report that the loss of EBF1 function in B-cell progenitors results in reduced expression of c-MYC. Ectopic expression of c-MYC rescues B-cell expansion in the absence of EBF1 both in vivo and in vitro and ChIP-seq analysis identifies multiple binding sites for EBF1 in putative regulatory elements of the mouse c-Myc gene. On the contrary, expression of PAX5 in EBF1 deficient cells resulted in down regulation of c-Myc and inhibition of cell expansion. Since both EBF1 and PAX5 bind multiple regulatory elements in the c-Myc gene, these data suggest that EBF1 and PAX5 have opposing functions with regard to regulation of c-Myc expression. This suggests the existence of a lineage restricted regulatory loop controlling the expansion of B-lineage progenitors. The binding of EBF1 and PAX5 to multiple regulatory elements in the human c-MYC gene indicate that this regulatory loop may be of relevance for our understanding of leukemia formation. Overall design: Ebf1-/- B-cell progenitor cells extracted from murine bone marrow were transduced with constructs encoding either Ebf1 or Ebf1-ER. Transduced cells were maintained in the precense of 4-OHT (Tamoxifen) and RNA-seq was perfomed after depletion of 4-OHT from cultures.