Mechanisms of FOXC2- and FOXD1-mediated regulation of the RIα subunit of cAMP-dependent protein kinase include release of transcriptional repression and activation by protein kinase Bα and cAMP

We have reported recently that mice overexpressing the forkhead/winged helix transcription factor FOXC2 are lean and show increased responsiveness to insulin due to sensitization of the beta-adrenergic cAMP-PKA(+) pathway and increased levels of the RIalpha subunit of cAMP-dependent protein kinase (PKA) (Cederberg, A., Gronning, L.M., Ahren, B., Tasken, K., Carlsson, P., and Enerback, S. (2001) Cell 106, 563-573). In this present study, we reveal that FOXC2 and a related factor, FOXD1, specifically activate the 1b promoter of the RIa gene in adipocytes and testicular Sertoli cells, respectively. By deletional mapping, we discovered two different mechanisms by which the Fox proteins activated expression from the RIalpha1b promoter. In 3T3-L1 adipocytes, an upstream region represses promoter activity under basal conditions. Bandshift experiments indicate that overexpression of FOXC2 promotes the release of a potential repressor from this region. In Sertoli cells, sequences downstream of the transcription start sites mediate the activating effect of FOXD1, and protein kinase Balpha/Akt1 strongly induces this effect. Furthermore, we show that an inactive FOXD1 mutant lowers the cAMP-mediated induction of the RIalpha1b reporter construct. In summary, winged helix transcription factors of the FOXC/FOXD families function as regulators of the RIalpha subunit of PKA and may integrate hormonal signals acting through protein kinase B and cAMP in a cell-specific manner.