Activation of Nuclear Factor of Activated T Cells-(NFAT) and Activating Protein 1 (AP-1) by Oncogenic 70Z Cbl Requires an Intact Phosphotyrosine Binding Domain but Not Crk(L) or p85 Phosphatidylinositol 3-Kinase Association*
- From the Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892
Abstract
The Cbl proto-oncogene product is a complex adapter protein that functions as a negative regulator of protein tyrosine kinases. It is rapidly tyrosine-phosphorylated and associates with Crk(L) and p85 phosphatidylinositol 3-kinase (PI3K) upon engagement of numerous receptors linked to tyrosine kinases. Elucidation of the mechanism(s) underlying Cbl deregulation is therefore of considerable interest. The 70Z Cbl oncoprotein shows increased baseline tyrosine phosphorylation in fibroblasts and enhances nuclear factor of activated T cells (NFAT) activity in Jurkat T cells. Its transforming ability has been proposed to relate to its increased phosphotyrosine content. We demonstrate that 70Z Cbl shows increased basal and activation-induced tyrosine phosphorylation and association with Crk(L) and p85 PI3K in Jurkat T cells. 70Z Cbl, however, retains the ability to enhance NFAT and activating protein 1 (AP1) activity in the absence of Crk(L)/p85 PI3K association. In contrast, the G306E mutation, which inactivates the phosphotyrosine binding domain of Cbl, blocks NFAT/AP1 activation by 70Z Cbl. We conclude that 70Z Cbl-induced NFAT/AP1 activation requires the phosphotyrosine binding domain but not Crk(L)/p85 PI3K association. We hypothesize that 70Z Cbl acts as a dominant negative by blocking the negative regulatory function of the Cbl phosphotyrosine binding domain on protein-tyrosine kinases.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Recipient of a postdoctoral fellowship award from the Cancer Research Institute. To whom correspondence should be addressed: Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892. Tel.: 301-496-4039; Fax: 301-402-0078; E-mail: vanleeuj{at}box-v.nih.gov.
- Abbreviations:
- PTB
-
phosphotyrosine binding
- PI3K
-
phosphatidylinositol 3-kinase
- SH3
-
Src homology 3
- FBS
-
fetal bovine serum
- Ab
-
antibody
- mAb
-
monoclonal antibody
- PAGE
-
polyacrylamide gel electrophoresis
- SEAP
-
secreted alkaline phosphatase
- PMA
-
phorbol 12-myristate 13-acetate
- HA
-
hemagglutinin
- wt
-
wild-type
- NFAT
-
nuclear factor of activated T cells
- AP1
-
activating protein 1
-
- Received September 2, 1998.
- Revision received November 25, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
