Chicken ovalbumin upstream promoter-transcription factor II, a new partnerof the glucose response element of the L-type pyruvate kinase gene, acts as an inhibitor of the glucose response

Transcription of the L-type pyruvate kinase (L-PK) gene is induced by gluco se in the presence of insulin and repressed by glucagon via cyclic AMP, The DNA regulatory sequence responsible for mediating glucose and cyclic AMP r esponses, called glucose response element (GlRE), consists of two degenerat ed E boxes spaced by 5 base pairs and is able to bind basic helix-loop-heli x/leucine zipper proteins, in particular the upstream stimulatory factors ( USFs), From ex vivo and in vivo experiments, it appears that USFs are requi red for correct response of the L-PK gene to glucose, but their expression and binding activity are not known to be regulated by glucose. A genetic sc reen in yeast has allowed us to identify a novel transcriptional factor bin ding to the GlRE, i.e. the chicken ovalbumin upstream promoter-transcriptio n factor II (COUP-TFII), Binding of COUP-TFII to the GlRE was confirmed by electrophoretic mobility shift assays, and COUP-TFII-containing complexes w ere detectable in liver nuclear extracts. Neither abundance nor binding act ivity of COUP-TFII appeared to be significantly regulated by diets. In foot printing experiments, two COUP-TFII-binding sites overlapping the E boxes w ere detected. Overexpression of COUP-TFII abrogated the USF-dependent trans activation of an artificial GlRE-dependent promoter in COS cells and the gl ucose responsiveness of the L-PK promoter in hepatocytes in primary culture . In addition, a mutated GlRE with increased affinity for USF and very low affinity for COUP-TFII conferred a dramatically decreased glucose responsiv eness on the L-PK promoter in hepatocytes in primary culture by increasing activity of the reporter gene in low glucose condition. We propose that COU P-TFII could be a negative regulatory component of the glucose sensor compl ex assembled on the GlRE of the L-PK gene and most likely of other glucose- responsive genes as well.