The calcium/calmodulin-dependent protein phosphatase calcineurin is the major Elk-1 phosphatase.
The transcription factor Elk-1 is a component of ternary complex factor and regulates gene expression in response to a wide variety of extracellular stimuli. Phosphorylation of the C-terminal domain of Elk-1, especially at serine 383, is important for its transactivation activity. Recently mitogen-activated protein kinases, such as extracellular signal-regulated kinase, stress-activated protein kinase, and p38 mitogen-activated protein kinase have been demonstrated to be Elk-1 kinases. However, negative regulators of Elk-1, such as protein phosphatases, still remain to be identified. Here we report that COS cell lysates were able to dephosphorylate an extracellular signal-regulated kinase-phosphorylated glutathione S-transferase-Elkc fusion protein, including serine 383. The phosphatase activity was inhibited by cyclosporin A (a calcineurin inhibitor) but not by okadaic acid (a PP1 and PP2A inhibitor). Purified calcineurin also could efficiently dephosphorylate glutathione S-transferase-Elkc in vitro. Pretreatment of COS cells with cyclosporin A significantly enhanced epidermal growth factor-induced serine 383 Elk-1 phosphorylation whereas ionomycin inhibited the Elk-1 phosphorylation. These data provide both in vitro and in vivo evidence that calcineurin is the major Elk-1 phosphatase and plays a critical role in Elk-1 regulation. The identification of calcineurin as the major Elk-1 phosphatase may provide a mechanism for Elk-1 regulation by Ca2+ signals as well as a possible biochemical basis for the neurotoxicity and nephrotoxicity of the immunosuppressant drug cyclosporin A.
Sugimoto
T
T
Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Stewart
S
S
Guan
K L
KL
D000818:Animals; D019556:COS Cells; D019703:Calcineurin / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D016572:Cyclosporine / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D050807:ets-Domain Protein Elk-1
D065095:Calcineurin Inhibitors; D004268:DNA-Binding Proteins; C494113:Elk1 protein, mouse; D004791:Enzyme Inhibitors; D007476:Ionophores; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D019319:Okadaic Acid; D015759:Ionomycin; D004815:Epidermal Growth Factor; D016572:Cyclosporine; D020794:Receptor Protein-Tyrosine Kinases; D019703:Calcineurin