Spot 14 protein interacts and co-operates with chicken ovalbumin upstream promoter-transcription factor 1 in the transcription of the L-type pyruvatekinase gene through a specificity protein 1 (Sp1) binding site

In hepatocytes, the amount of the Spot 14 (S14) protein is closely related to the full expression of enzymes involved in the glycolytic and lipogenic pathways. In the present study we address the role played by this protein i n the control of transcription of the L-type pyruvate kinase (L-PK) gene in primary hepatocytes. We show that human S14, which by itself does not bind to the L-PK promoter, physically interacts with the human chicken ovalbumi n upstream promoter-transcription factor I (COUP-TF1) and induces the switc h of this factor from a repressor to an activator. However, the enhancing a ctivity of S14 and COUP-TF1 depends on the presence of a proximal GC-rich b ox (the LO element) that specifically binds nuclear proteins from the liver s of rats fed a glucose-rich diet. Moreover, the LO element, which strongly binds dephosphorylated specificity protein 1 (Spl), loses all affinity whe n this factor is phosphorylated by cAMP-dependent protein kinase. Mutations that affect binding of Sp1 and nuclear proteins to the LO box also decreas e basal transcription and impair glucose responsiveness of the promoter. Th ese results therefore shed light on the mechanism by which the S14 protein, whose concentration rapidly rises after glucose intake, contributes to the full activity of the L-PK promoter.