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Molecular and Cellular Biology, November 2001, p. 7429-7441, Vol. 21, No. 21
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.21.7429-7441.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Downregulation of the Ras-Mitogen-Activated Protein Kinase Pathway by the EphB2 Receptor Tyrosine Kinase Is Required for Ephrin-Induced Neurite Retraction

Sabine Elowe,1,2 Sacha J. Holland,1,dagger Sarang Kulkarni,1 and Tony Pawson1,2,*

Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5,1 and Department of Molecular and Medical Genetics, University of Toronto, Toronto, Ontario M5G 1A8,2 Canada

Received 2 May 2001/Returned for modification 24 May 2001/Accepted 24 July 2001

Activation of the EphB2 receptor tyrosine kinase by clustered ephrin-B1 induces growth cone collapse and neurite retraction in differentiated NG108 neuronal cells. We have investigated the cytoplasmic signaling events associated with EphB2-induced cytoskeletal reorganization in these neuronal cells. We find that unlike other receptor tyrosine kinases, EphB2 induces a pronounced downregulation of GTP-bound Ras and consequently of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway. A similar inhibition of the Ras-MAPK pathway was observed on stimulation of endogenous EphB2 in COS-1 cells. Inactivation of Ras, induced by ephrin B1 stimulation of NG108 neuronal cells, requires EphB2 tyrosine kinase activity and is blocked by a truncated form of p120-Ras GTPase-activating protein (p120-RasGAP), suggesting that EphB2 signals through the SH2 domain protein p120-RasGAP to inhibit the Ras-MAPK pathway. Suppression of Ras activity appears functionally important, since expression of a constitutively active variant of Ras impaired the ability of EphB2 to induce neurite retraction. In addition, EphB2 attenuated the elevation in ERK activation induced by attachment of NG108 cells to fibronectin, indicating that the EphB2 receptor can modulate integrin signaling to the Ras GTPase. These results suggest that a primary function of EphB2, a member of the most populous family of receptor tyrosine kinases, is to inactivate the Ras-MAPK pathway in a fashion that contributes to cytoskeletal reorganization and adhesion responses in neuronal growth cones.

* Corresponding author. Mailing address: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Ave., Toronto, Ontario, Canada M5G 1X5. Phone: (416) 586-8262. Fax: (416) 586-8869. E-mail: pawson{at}mshri.on.ca.

dagger Present address: Rigel Inc., South San Francisco, CA 94080.

Molecular and Cellular Biology, November 2001, p. 7429-7441, Vol. 21, No. 21
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.21.7429-7441.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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