Role of early B-cell factor 1 (EBF1) in Hodgkin lymphoma.

A hallmark of classical Hodgkin lymphoma (cHL) is that the B-cell-derived Hodgkin and Reed-Sternberg (HRS) tumor cells have largely lost the B-cell-typical gene expression program. The factors causing this 'reprogramming' of HRS cells are only partly understood. As early B-cell factor 1 (EBF1), a major B-cell transcription factor, is downregulated in HRS cells, we analyzed whether this downregulation contributes to the lost B-cell phenotype and tested the consequences of EBF1 re-expression in cHL cell lines. EBF1 re-expression caused an upregulation of B-cell genes, such as CD19, CD79A and CD79B, although the B-cell genes FOXO1 and PAX5 remained lowly expressed. The re-expression of CD19, CD79A and CD79B occurred largely without demethylation of promoter CpG motifs of these genes. In the cHL cell line L-1236 fitness decreased after EBF1 re-expression. These data show that EBF1 has the ability to reintroduce part of the B-cell signature in cHL cell lines. Loss of EBF1 expression in HRS cells therefore contributes to their lost B-cell phenotype. Notably, in the cHL cell line KM-H2 destructive mutations were found in one allele of EBF1, indicating that genetic lesions may sometimes have a role in impairing EBF1 expression.