CACCC and GATA-1 sequences make the constitutively expressed α-globin gene erythroid-responsive in mouse erythroleukemia cells

Although the human α-globin and β-globin genes are co-regulated in adult life, they achieve the same end by very different mechanisms. For example, a transfected β-globin gene is expressed in an inducible manner in mouse erythroleukemia (MEL) cells while a transfected α-globin gene is constitutively expressed at a high level in induced and uninduced MEL cells. Interestingly, when the α-globin gene is transferred into MEL cells as part of human chromosome 16, it is appropriately expressed in an inducible manner. We explored the basis for the lack of erythroid-responsiveness of the proximal regulatory elements of the human α-globin gene. Since the α-globin gene is the only functional human globin gene that lacks CACCC and GATA-1 motifs, we asked whether their addition to the α-globin promoter would make the gene erythroid-responsive in MEL cells. The addition of each of these binding sites to the α-globin promoter separately did not result in inducibility in MEL cells. However, when both sites were added together, the α-globin gene became inducible in MEL cells. This suggests that erythroid non-responsiveness of the α-globin gene results from the lack of erythroid binding sites and is not necessarily a function of the constitutively active, GC rich promoter.