Transcription factor Sp1 is necessary for basal calmodulin gene transcription and for its selective stimulation by insulin.
Insulin positively regulates transcription of rat calmodulin (CaM) I gene and activates the low Km cyclic AMP (cAMP) phosphodiesterase (PDE). To elucidate the mechanism of transcriptional regulation, rat hepatoma (H-411E) cells were transfected with DNA constructs containing the putative CaM promoters coupled to a luciferase reporter and challenged with insulin. Activation of the full length 1835 bp rat CaM I promoter containing all three Sp1 sites or truncated promoters with combinations of one to three of the Sp1 sites was studied in Sp1 deficient Drosophilia SL2 cells and in SL2 cells co-transfected with an Sp1 expression vector and re-challenged with insulin. Our results demonstrate that Sp1 is obligatory for basal activation of the CaM promoter. The maximal insulin stimulation of CaM promoter is elicited only if it contains at least two Sp1 sites.
Solomon
S S
SS
VAMC Research Service, Department of Medicine, University of Tennessee College of Medicine, Memphis, USA.
Palazzolo
M R
MR
Takahashi
T
T
Raghow
R
R
D000818:Animals; D002147:Calmodulin / Q000235:genetics*; D004330:Drosophila / Q000166:cytology; D007328:Insulin / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D051381:Rats; D016329:Sp1 Transcription Factor / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects* / Q000502:physiology*; D014407:Tumor Cells, Cultured
D002147:Calmodulin; D007328:Insulin; D016329:Sp1 Transcription Factor