Insulin regulates the activity of the AP-1 (activator protein-1) transcriptional complex in several cell types. One component of the AP-1 complex is the transcription factor Fra-1 (fos-related antigen-1), and we have demonstrated previously that insulin stimulates the expression of Fra-1 mRNA in CHO.T cells [Griffiths, Black, Culbert, Dickens, Shaw, Gillespie and Tavaré (1998) Biochem. J. 335, 19—26]. Here we demonstrate that insulin stimulates the activity of a fra-1 promoter linked to a luciferase reporter gene, indicating that the ability of insulin to induce expression of Fra-1 mRNA is due, at least in part, to an increase in gene transcription. Furthermore, we found that insulin induces the serine phosphorylation of Fra-1 and reduces its mobility during SDS/PAGE as a result of phosphorylation. The ability of insulin to induce the accumulation of Fra-1 mRNA, stimulate the fra-1 promoter and stimulate phosphorylation of Fra-1 all require the mitogen-activated protein (MAP) kinase cascade, which leads to the activation of extracellular-signal-regulated kinase (Erk) 1/2. Consequently, our results demonstrate that the Erk cascade plays a dual role in the co-ordinated regulation of the transcription and the phosphorylation of Fra-1 by insulin.
- AP-1 (activator protein-1) complex
- mitogen-activated protein kinase (MAP kinase)
↵1 These authors contributed equally to this work.
↵2 Present address: GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, U.K.
Abbreviations used: AP-1, activator protein-1; AdtTA, recombinant adenovirus expressing tTA; CMV, cytomegalovirus; Erk, extracellular-signal-regulated kinase; Fra-1, fos-related antigen-1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HA, haemagglutinin; MAP kinase, mitogen-activated protein kinase; MEK, MAP kinase/Erk kinase; MEK-A, dominant-negative MEK; MEK-E, constitutively active MEK; MOI, multiplicity of infection; p.f.u., plaque-forming units; RT-PCR, reverse transcription—PCR; TRE, tetracycline response element; tTA, Tet-Off tetracycline transactivator.
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