Transforming Growth Factor β (TGF-β)-Smad Target Gene Protein Tyrosine Phosphatase Receptor Type Kappa Is Required for TGF-β Function

Abstract

Transforming growth factor β (TGF-β) inhibits proliferation and promotes cell migration. In TGF-β-treated MCF10A mammary epithelial cells overexpressing HER2 and by chromatin immunoprecipitation, we identified novel Smad targets including protein tyrosine phosphatase receptor type kappa (PTPRK). TGF-β up-regulated PTPRK mRNA and RPTPκ (receptor type protein tyrosine phosphatase kappa, the protein product encoded by the PTPRK gene) protein in tumor and nontumor mammary cells; HER2 overexpression down-regulated its expression. RNA interference (RNAi) of PTPRK accelerated cell cycle progression, enhanced response to epidermal growth factor (EGF), and abrogated TGF-β-mediated antimitogenesis. Endogenous RPTPκ associated with EGF receptor and HER2, resulting in suppression of basal and ErbB ligand-induced proliferation and receptor phosphorylation. In MCF10A/HER2 cells, TGF-β enhanced cell motility, FAK phosphorylation, F-actin assembly, and focal adhesion formation and inhibited RhoA activity. These responses were abolished when RPTPκ was eliminated by RNA interference (RNAi). In cells expressing RPTPκ RNAi, phosphorylation of Src at Tyr527 was increased and (activating) phosphorylation of Src at Tyr416 was reduced. These data suggest that (i) RPTPκ positively regulates Src; (ii) HER2 signaling and TGF-β-induced RPTPκ converge at Src, providing an adequate input for activation of FAK and increased cell motility and adhesion; and (iii) RPTPκ is required for both the antiproliferative and the promigratory effects of TGF-β.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

This work was supported in part by grant R01 CA62212 (to C.L.A.), Breast Cancer Specialized Program of Research Excellence (SPORE) grant P50 CA98131, and Vanderbilt-Ingram Comprehensive Cancer Center Support grant CA68485.

We thank Axel Ullrich for providing the RPTPκ antiserum; Joe Zhao, Jae Youn Yi, and Yasuhiro Koh for helpful comments; and Teresa Dugger for technical and administrative support.