title: Negative regulation of ERK and Elk by protein kinase B modulates c-Fos transcription.
abstract: In this study, we have identified novel regulatory steps involved in the cross-talk between protein kinase B (PKB) and MAPK signaling pathways. We found that PKB down-regulates the Ras-Raf-MEK-ERK pathway by reducing the activity of ERK, which leads to inactivation of the transcription factor Elk1. In addition, PKB is able to reduce protein levels of Elk1. Both events lead to suppression of serum response element (SRE)-dependent transcription and a consequent decrease in the transcription of SRE-containing genes, such as c-fos. Because activation of the Ras/MAPK cascade is reported to increase c-fos transcription before apoptosis, our results are consistent with a specific role for PKB in promoting cell survival. Decrease in c-Fos protein levels in glioblastoma cells with constitutively active PKB provides further support for our observations. Therefore, our findings delineate a novel mechanism regulating immediate-early transcription, which may be involved in the initial steps in PKB-induced oncogenic transformation.
authors.affiliation: Friedrich Miescher Institute, P. O. Box 2543, CH-4002 Basel, Switzerland.
authors.forename: Ivana
authors.initials: I
authors.lastname: Galetic
authors.forename: Sauveur-Michel
authors.initials: SM
authors.lastname: Maira
authors.forename: Mirjana
authors.initials: M
authors.lastname: Andjelkovic
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hemmings
mesh_terms: D017209:Apoptosis / Q000235:genetics; D004268:DNA-Binding Proteins; D016762:Genes, fos; D006801:Humans; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D050807:ets-Domain Protein Elk-1
chemical_list: D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases