Abstract
Phosphatase of regenerating liver-3 (PTP4A3/PRL-3) is a dual-specificity phosphatase that is upregulated in various types of cancers and is related to poor prognosis and aggressive tumor behavior. The expression level of PRL-3 is elevated in response to several antiapoptotic cytokines, including IL6, in cancer cells from patients with multiple myeloma (MM) and can promote survival and migration. Here, it is demonstrated that PRL-3 activates Src kinase in the IL6-dependent MM cell line INA-6. Inhibition of PRL-3 by a small-molecule inhibitor of PRL-3 or by shRNA resulted in inactivation of Src. In addition to activation of Src, PRL-3 also activated the Src family kinase (SFK) members LYN and HCK in INA-6 cells. Forced expression of catalytically inactive mutant PRL-3 decreased the activation of these three SFK members while the total level of HCK and FYN remained elevated. Inhibitors of Src increased sensitivity of cells overexpressing PRL-3 to the PRL-3 inhibitor through joint downregulation of both PRL-3 and Mcl-1. In conclusion, PRL-3 protected MM cells against apoptosis by dysregulating both the total levels and the activation levels of specific SFK members that are important for IL6 signal transduction in MM cells. Eventually, this led to increased levels of Mcl-1. Implications: This study suggests PRL-3 and SFKs are key mediators of the IL6-driven signaling events and points to both PRL-3 and SFK members as potential targets for treatment of MM. Mol Cancer Res; 15(1); 69-77. ©2016 AACR.