Organization of the alpha-globin promoter and possible role of nuclear factor I in an alpha-globin-inducible and a noninducible cell line.

Nuclear factor I (NFI) was suggested to be involved in the expression of the human alpha-globin gene. Two established cell lines, which express alpha-globin differentially, were therefore compared for differences in binding of NFI at the alpha-globin promoter in vivo. HeLa cells, in which alpha-globin is repressed, show a high density promoter occupation with several proteins associated with structurally distorted DNA. Cell line K562, which is inducible for alpha-globin, surprisingly was found to be heterogeneous consisting mainly of cells (approximately 95%) unable to express alpha-globin. However, the promoter of the nonexpressing K562 cells was clearly different from that of HeLa cells, being occupied only at basal transcriptional elements. Therefore, the alpha-globin gene in these K562 cells may not be truly repressed, but in an intermediate state between repression and active transcription. The NFI site of the alpha-globin promoter appeared occupied in HeLa but free of proteins in K562 cells. All cells of both cell lines produce NFI, but the composition and DNA binding affinity of NFI species differ significantly between the two cell lines. Therefore, distinct forms of NFI may repress alpha-globin transcription in HeLa cells. However, NFI is apparently not involved in establishing the latent transcriptional state of the majority of K562 cells.