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Molecular and Cellular Biology, June 2000, p. 3817-3830, Vol. 20, No. 11
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Class II Phosphoinositide 3-Kinases Are Downstream Targets of Activated Polypeptide Growth Factor Receptors

Alexandre Arcaro,1,dagger Marketa J. Zvelebil,1 Christian Wallasch,2 Axel Ullrich,2 Michael D. Waterfield,1,3 and Jan Domin1,*

Ludwig Institute for Cancer Research, University College, London W1P 8BT,1 and Department of Biochemistry and Molecular Biology, University College, London WC1E 6BT,3 United Kingdom, and Max-Planck-Institut fur Biochemie, 82152 Martinsried, Federal Republic of Germany2

Received 7 September 1999/Returned for modification 19 October 1999/Accepted 15 February 2000

The class II phosphoinositide 3-kinases (PI3K) PI3K-C2alpha and PI3K-C2beta are two recently identified members of the large PI3K family. Both enzymes are characterized by the presence of a C2 domain at the carboxy terminus and, in vitro, preferentially utilize phosphatidylinositol and phosphatidylinositol 4-monophosphate as lipid substrates. Little is understood about how the catalytic activity of either enzyme is regulated in vivo. In this study, we demonstrate that PI3K-C2alpha and PI3K-C2beta represent two downstream targets of the activated epidermal growth factor (EGF) receptor in human carcinoma-derived A431 cells. Stimulation of quiescent cultures with EGF resulted in the rapid recruitment of both enzymes to a phosphotyrosine signaling complex that contained the EGF receptor and Erb-B2. Ligand addition also induced the appearance of a second, more slowly migrating band of PI3K-C2alpha and PI3K-C2beta immunoreactivity on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Since both PI3K enzymes can utilize Ca2+ as an essential divalent cation in lipid kinase assays and since the catalytic activity of PI3K-C2alpha is refractory to the inhibitor wortmannin, these properties were used to confirm the recruitment of each PI3K isozyme to the activated EGF receptor complex. To examine this interaction in greater detail, PI3K-C2beta was chosen for further investigation. EGF and platelet-derived growth factor also stimulated the association of PI3K-C2beta with their respective receptors in other cells, including epithelial cells and fibroblasts. The use of EGF receptor mutants and phosphopeptides derived from the EGF receptor and Erb-B2 demonstrated that the interaction with recombinant PI3K-C2beta occurs through E(p)YL/I phosphotyrosine motifs. The N-terminal region of PI3K-C2beta was found to selectively interact with the EGF receptor in vitro, suggesting that it mediates the association of this PI3K with the receptor. However, the mechanism of this interaction remains unclear. We conclude that class II PI3K enzymes may contribute to the generation of 3' phosphoinositides following the activation of polypeptide growth factor receptors in vivo and thus mediate certain aspects of their biological activity.

* Corresponding author. Present address: Renal Section, Division of Medicine, Imperial College School of Medicine, Du Cane Rd., London W12 ONN, United Kingdom. Phone: (0181) 383 2357. Fax: (0181) 383 2062. E-mail: jdomin{at}ic.ac.uk.

dagger Present address: Ludwig Institute for Cancer Research, Lausanne Branch, CH-1066 Epalinges, Switzerland.

Molecular and Cellular Biology, June 2000, p. 3817-3830, Vol. 20, No. 11
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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