DEPHOSPHORYLATION OF SP1 BY PROTEIN PHOSPHATASE-1 IS INVOLVED IN THE GLUCOSE-MEDIATED ACTIVATION OF THE ACETYL-COA CARBOXYLASE GENE

When mouse 30A5 preadipocytes are exposed to high glucose concentratio ns, acetyl-CoA carboxylase is induced through glucose activation of pr omoter II of the acetyl-CoA carboxylase gene. Glucose treatment of the cells increases Sp1 binding to two GC rich glucose response elements in promoter II. We have investigated the mechanism by which glucose in creases Sp1 binding and transactivation of promoter II in 30A5 cells. DNA mobility shift assays have shown that nuclear extracts from glucos e-treated cells exhibit increased Sp1 binding activity. This increase in the binding activity is not due to glucose-mediated changes in the amount of Sp1 in the nucleus but to an increase in the activity that m odifies Sp1 so that it binds more effectively to the promoter sequence , This Sp1 modifying activity is inhibited by okadaic acid and phospha tase inhibitor 2, and has a molecular mass of 38-42 kDa. The catalytic subunit of type 1 protein phosphatase, whose molecular mass is 38 kDa , also increased the ability of Sp1 to bind to prometer II. Treatment of nuclear extract with antibodies against the catalytic subunit parti ally suppressed the nuclear activity for Sp1 activation. From these re sults, we conclude that the Sp1 transcription factor exhibits enhanced binding to promoter II and transcriptional activation is the result o f glucose induced dephosphorylation by type 1 phosphatase.