Activation and Nuclear Translocation of Mitogen-activated Protein Kinases by Polyomavirus Middle-T or Serum Depend on Phosphatidylinositol 3-Kinase (*)
- Marc Urich(§),
- Mahmoud Y. M. El Shemerly,
- Daniel Besser(¶),
- Yoshikuni Nagamine and
- Kurt Ballmer-Hofer(**)
- **To whom correspondence should be addressed. Tel.: 61-697-6689; Fax: 61-697-3976.
Abstract
Several cellular signal transduction pathways activated by middle-T in polyomavirus-transformed cells are required for viral oncogenicity. Here we focus on the role of phosphatidylinositol 3-kinase (PI 3-kinase) and Ras and address the question how these signaling molecules cooperate during cell cycle activation. Ras activation is mediated through association with SHC• GRB2•SOS and leads to increased activity of several members of the mitogen-activated protein (MAP) kinase family, while activation of PI 3-kinase results in the generation of D3-phosphorylated phosphatidylinositides whose downstream targets remain elusive. PI 3-kinase activation might also ensue as a direct consequence of Ras activation. Oncogenicity of middle-T requires stimulation of both Ras- and PI 3-kinase-dependent pathways. Mutants of middle-T incapable to bind either SHC•GRB2•SOS or PI 3-kinase are not oncogenic. Sustained activation and nuclear localization of one of the MAP kinases, ERK1, was observed in wild type but not in mutant middle-T-expressing cells. Wortmannin, an inhibitor of PI 3-kinase, prevented MAP kinase activation and nuclear localization in middle-T-transformed cells. PI 3-kinase activity was also required for activation of the MAP kinase pathway in normal serum-stimulated cells, generalizing the concept that signaling through MAP kinases requires not only Ras- but also PI 3-kinase-mediated signals.
Footnotes
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↵§ Supported by the Emilia Guggenheim-Schnurr Stiftung.
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↵¶ Supported by the Daimler Benz Stiftung.
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↵(*) The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- PI 3-kinase
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phosphatidylinositol 3-kinase
- WT
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wild type
- MAP
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mitogen-activated protein
- DMEM
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Dulbecco's modified Eagle's medium
- uPA
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urokinase-type plasminogen activator.
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↵2E. Serfing, unpublished results.
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↵3S. Dilworth, unpublished data.
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- Received July 7, 1995.
- Revision received September 13, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
