Dok-3, a Novel Adapter Molecule Involved in the Negative Regulation of Immunoreceptor Signaling

Abstract

Adapters are typically viewed as molecules coordinating the recruitment of positive effectors of cell signaling. Herein, we report the identification of Dok-3, a novel adapter molecule belonging to the Dok family. Our studies show that Dok-3 is highly expressed in several hemopoietic cell types, including B cells and macrophages. It undergoes rapid tyrosine phosphorylation in response to immunoreceptor-mediated cellular activation, seemingly as a result of the action of Src family kinases. This phosphorylation induces the binding of Dok-3 to at least two inhibitory molecules, the 5′ inositol phosphatase SHIP and the protein tyrosine kinase Csk. We also demonstrate that augmented expression of wild-type Dok-3 in a B-cell line results in an inhibition of immunoreceptor-mediated nuclear factor of activated T-cells (NFAT) activation and cytokine release, while introduction of a Dok-3 mutant with impaired ability to associate with SHIP and Csk enhances B-cell responsiveness. Taken together, these results indicate that Dok-3 is an adapter involved in the recruitment of inhibitory molecules and that it may play a significant role in the negative regulation of immunoreceptor signaling in hemopoietic cells such as B cells and macrophages.

ACKNOWLEDGMENTS

We thank Gerry Krystal, Yuji Yamanashi, David Baltimore, Pierre Laneuville, Gerry Crabtree, and Lou Matis for their gifts of reagents. We also acknowledge A. Chan for advice regarding the transient transfection assays.

This work was funded by grants from the Medical Research Council of Canada and the National Cancer Institute of Canada to A.V. S. Lemay was supported by a Fellowship from the Kidney Foundation of Canada and by a Joseph Kaufmann Fellowship from the Faculty of Medicine, McGill University, while S. Latour was awarded a Fellowship from the Medical Research Council of Canada. A.V. is a Senior Scientist of the Medical Research Council of Canada.

S. Lemay and D. Davidson contributed equally to this work.