THE CAMP-RESPONSE ELEMENT MEDIATES INDUCTION OF SECRETOGRANIN-II BY CHX AND FSK IN GH(4)C(1) CELLS

The effect of cAMP on secretogranin II (SgII) gene transcription in GH (4)C(1) (GH) cells is not observed unless protein synthesis is inhibit ed. We have defined elements in the SgII promoter that mediate regulat ion by cycloheximide (CHX) and forskolin (FSK) and characterized the n uclear proteins that interact with them. GH cells were transfected wit h p2774Luc, p351Luc, p242Luc, and p223Luc containing 2,612, 189, 80, a nd 61 bp of the SgII promoter upstream of the luciferase gene, respect ively. Treatment with CHX and FSK increased promoter activity 8- to 12 -fold in cells transfected with p2774Luc, p351Luc, and p242Luc but had no effect in cells transfected with p223Luc. The same 19-bp element ( -80 to -62) mediates regulation by CHX alone, as CHX caused a 3.8-fold increase in activity in GH cells transfected with p242Luc but not p22 3Luc. Gel mobility shifts using sequences -84 to -53 resulted in three complexes, which contained cAMP response element-binding protein hete rodimerized with cAMP response element modulator or activating transcr iption factor-1. No differences were observed in complex formation whe n cells were treated with either CHX, FSK, or CHX and FSK. Thus CHX af fects the response to FSK in GH cells by inhibiting the synthesis of a protein, which does not itself interact with DNA or affect the bindin g of CRE-binding proteins with the SgII promoter, but likely interfere s with the interaction of CRE-binding proteins with the general transc riptional machinery.