NF-E2p18/mafK is required in DMSO-induced differentiation of Friend erythroleukemia cells by enhancing NF-E2 activity

When Friend murine erythroleukemia (F-MEL) cells are induced to differentiate by dimethylsulfoxide (DMSO), erythroid-specific genes are transcriptionally activated. The erythroid transcription factor NF-E2 is essential for enhancer activity of the globin locus control regions. NF-E2 functions as a heterocomplex consisting of a 45-kDa subunit (NF-E2p45) and a 18-kDa subunit (NF-E2p18). The larger subunit NF-E2p45 is tissue-restricted and is believed to play a role in globin gene expression in F-MEL cells. The expression of the smaller subunit NF-E2p18, which is a Maf family member (MafK), is cell type- and developmental stage-specific. We have investigated the possible role of NF-E2p18 in Friend erythroid differentiation by stably transfecting either sense and antisense p18 constructs into differentiation-sensitive 745A and partially defective-differentiation TFP10 cell lines. Overexpression of NF-E2p18 induced expression of globin transcripts in both cell lines and increased their sensitivity to erythroid differentiation when exposed to DMSO. Conversely, inhibition of p18 expression by antisense transcripts resulted in the inhibition of DMSO-induced differentiation in both cell lines. These results indicate that NF-EPp18 is necessary for globin expression in F-MEL cells and that it is the predominant gene of the Maf family involved in DMSO-induced erythroid differentiation. Moreover F-MEL clones overexpressing NF-E2p18 showed an increase in specific NF-ES DNA-binding activity whereas this activity was decreased in clones expressing antisense p18. Finally, studies using transient transfection assays showed that p18 activated NF-E2 site-dependent transcription in F-MEL cells. These data suggest that NF-E2p18 can participate in DMSO-induced erythroid differentiation of F-MEL cells by enhancing NF-E2 activity.