Abstract
Our previous studies have shown that activation of a related adhesion focal tyrosine kinase (RAFTK) (also known as Pyk2) is required for dexamethasone (Dex)-induced apoptosis in multiple myeloma (MM) cells and that human interleukin-6 (IL-6), a known growth and survival factor for MM cells, blocks both RAFTK activation and apoptosis induced by Dex. However, the mechanism whereby IL-6 inhibits Dex-induced apoptosis is undefined. In this study, we demonstrate that protein-tyrosine phosphatase SHP2 mediates this protective effect. We show that IL-6 triggers selective activation of SHP2 and its association with RAFTK in Dex-treated MM cells. SHP2 interacts with RAFTK through a region other than its Src homology 2 domains. We demonstrate that RAFTK is a direct substrate of SHP2 both in vitro and in vivo, and that Tyr(906) in the C-terminal domain of RAFTK mediates its interaction with SHP2. Moreover, overexpression of dominant negative SHP2 blocked the protective effect of IL-6 against Dex-induced apoptosis. These findings demonstrate that SHP2 mediates the anti-apoptotic effect of IL-6 and suggest SHP2 as a novel therapeutic target in MM.
Highlights
Related Adhesion Focal Tyrosine Kinase (RAFTK), known as Proline-Rich Tyrosine Kinase 2 (Pyk2), calcium-dependent tyrosine kinase, and cellular adhesion kinase β, is a cytoplasmic tyrosine kinase and member of the Focal Adhesion Kinase (FAK) family [1,2,3]
We demonstrate that IL-6 activates SHP2 in MM cells, and that treatment of MM cells with IL-6 and Dex induces binding of SHP2 with related adhesion focal tyrosine kinase (RAFTK), resulting in dephosphorylation of RAFTK
Total cell lysates were subjected to immunoprecipitation with anti-RAFTK, and immunoprecipitates were incubated with purified SHP2 or phosphatase-dead SHP2
Summary
Related Adhesion Focal Tyrosine Kinase (RAFTK), known as Proline-Rich Tyrosine Kinase 2 (Pyk2), calcium-dependent tyrosine kinase, and cellular adhesion kinase β, is a cytoplasmic tyrosine kinase and member of the Focal Adhesion Kinase (FAK) family [1,2,3]. We demonstrate that IL-6 activates SHP2 in MM cells, and that treatment of MM cells with IL-6 and Dex induces binding of SHP2 with RAFTK, resulting in dephosphorylation of RAFTK. Total cell lysates were subjected to immunoprecipitation with anti-RAFTK and analyzed by immunoblotting with anti-P-Tyr. Dex induces tyrosine phosphorylation of RAFTK in MM.1S cells, which is inhibited by IL-6 (Fig 1A, upper panel).
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