Stimulation of Sky Receptor Tyrosine Kinase by the Product of Growth Arrest-specific Gene 6

Kazumasa Ohashi,Kyoko Nagata,Jiro Toshima,Toru Nakano,Hitoshi Arita,Hiroko Tsuda,Koji Suzuki,Kensaku Mizuno

doi:10.1074/jbc.270.39.22681

Abstract

Sky (also called Rse, Brt, and Tyro3) is a member of a subfamily of related receptor tyrosine kinases, including Axl/Ufo/Ark and c-Eyk/Mer. We obtained evidence that Gas6 (the product of growth arrest-specific gene 6) is a ligand of the Sky receptor tyrosine kinase. Gas6, but not protein S (an anticoagulant protein structurally similar to Gas6), specifically bound to the soluble form of Sky (Sky-Fc), composed of the extracellular domain of Sky fused to the Fc domain of human immunoglobulin G1. The native and recombinant Gas6, but not protein S, stimulated tyrosine phosphorylation of Sky ectopically expressed in Chinese hamster ovary cells. Stimulation of Sky in response to Gas6 was inhibited by Sky-Fc. The half-maximal concentration of Gas6 that stimulated Sky was about 1 nM. Thus, Gas6 as a ligand for Sky specifically binds to and stimulates Sky receptor tyrosine kinase.

Highlights

Receptor tyrosine kinases play a central role in transducing the external signals across cell membranes into intracellular signaling systems and these signals lead to cell proliferation, differentiation, and other responses [1]
1 The abbreviations used are: Gas6, the protein encoded by growth arrest-specific gene 6; APC, activated protein C; CHO, Chinese hamster ovary; EGF, epidermal growth factor; FGF, fibroblast growth factor; PAGE, polyacrylamide gel electrophoresis; PBS, phosphate-buffered saline, VSMC, vascular smooth muscle cells
Affinity adsorption and precipitation analysis using Fc fusion proteins in the presence of Protein A-Sepharose showed that Sky-Fc, but not Met-Fc, co-precipitated Gas6 protein (Fig. 1A)

Summary

Introduction

Receptor tyrosine kinases play a central role in transducing the external signals across cell membranes into intracellular signaling systems and these signals lead to cell proliferation, differentiation, and other responses [1]. Gas6, originally identified as a gene product expressed in response to growth arrest, has structural similarity to protein S with 42– 43% identity [16] and was seen to function as a potentiating factor for thrombin-induced proliferation of vascular smooth muscle cells (VSMC) [17].

Results

Conclusion