EGF stimulates gastrin promoter through activation of Sp1 kinase activity.
Epidermal growth factor (EGF) receptor activation stimulates gastrin gene expression through a GC-rich element called gastrin EGF response element (gERE). This element is bound by Sp1 family members and is a target of the ras-extracellular signal-regulated kinase (Erk) signal transduction cascade. This raised the possibility that Sp1 may be phosphorylated by kinases of this signaling pathway. Erk is capable of phosphorylating other mitogen-inducible transcription factors, e.g., Elk and Sap, suggesting that Erk may also mediate EGF-dependent phosphorylation of Sp1. This possibility was tested by studying Sp1-dependent kinase activity in extracts prepared from EGF-activated AGS cells by use of solid-phase kinase assays and immunoprecipitation of metabolically labeled Sp1. The results revealed that Sp1 kinase activity (like gastrin promoter activation) is inhibited by PD-98059 and, therefore, is dependent on mitogen-activated protein kinase kinase 1 (Mek 1). However, EGF-dependent activation of endogenous Erk did not account for most of the Sp1 kinase activity, since Erk and additional Sp1 kinase activity analyzed in a solid-phase kinase assay eluted from an ion-exchange column in different fractions. Phosphoamino acid analysis of in vivo radiolabeled Sp1 demonstrated that the kinase phosphorylates Sp1 on Ser and Thr in response to EGF. Therefore, most EGF-stimulated Sp1 kinase activity is Mek 1 dependent and distinct from Erk.
Chupreta
S
S
Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109, USA.
Du
M
M
Todisco
A
A
Merchant
J L
JL
D001665:Binding Sites / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005755:Gastrins / Q000235:genetics*; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014407:Tumor Cells, Cultured
D005755:Gastrins; D004815:Epidermal Growth Factor; D011494:Protein Kinases; C065999:Sp1 kinase; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human