Sp1-like proteins function in the transcription of human ferredoxin genes

We characterized a regulatory element located in the -76 to -62 region of the human ferredoxin gene. This region bound to Sp1-like proteins with low affinity, as shown using electrophoretic mobility shift, competition, antibody binding, and Southwestern experiments. The similarity of the regulatory element to Sp1 extends beyond its DNA-binding domain, as cloned Sp1 functioned equally well when fused to a peptide that bound to an irrelevant site. The function of these Sp1-binding sites is mediated through the cAMP-dependent protein kinase (PKA) signaling pathway, because reporter genes downstream of the Sp1-binding sites were not activated in a PKA-deficient cell line. Transfection of the catalytic subunit of PKA restored activated transcription. Similar Sp1-binding sites identified in the CYP11A1 and CYP21 genes also controlled cAMP-dependent transcription of the reporter gene. Our finding of the function of Sp1-like proteins in steroidogenic gene transcription adds one more role Sp1 plays in controlling physiological events.