Transforming growth factor β-induced epithelial to mesenchymal transition requires the Ste20-like kinase SLK independently of its catalytic activity

// Jillian Conway 1, 2 , Khalid N. Al-Zahrani 1, 2 , Benjamin R. Pryce 1, 2 , John Abou-Hamad 1,2 and Luc A. Sabourin 1, 2 1 University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, K1H8M5, Canada 2 Ottawa Hospital Research Institute, Cancer Therapeutics, Ottawa, Ontario, K1H8L6, Canada Correspondence to: Luc A. Sabourin, email: lsabourin@ohri.ca Keywords: SLK; Stk2; EMT; TGFβ; invasion Received: June 06, 2017     Accepted: August 26, 2017     Published: October 19, 2017 ABSTRACT Invasion can be stimulated in vitro using the soluble ligand transforming growth factor-β (TGFβ) to induce a process called epithelial-to-mesenchymal transition (EMT) characterized by cell-cell junction breakdown and an invasive phenotype. We have previously demonstrated a role for Ste20-like kinase SLK cell migration and invasion. Here we show that SLK depletion in NMuMG mammary epithelial cells significantly impairs their TGFβ-induced migration and invasion. Immunofluorescence studies show that a fraction of SLK localizes to E-cadherin-positive adherens junction and that SLK impairs the breakdown of cell-cell contacts. We find that SLK-depleted cultures express significantly lower levels of vimentin protein as well as Snai1 and E-cadherin mRNA levels following TGF-β treatment. Surprisingly, our data show that SLK depletion does not affect the activation and nuclear translocation of Smad3. Furthermore, we show that expression of a dominant negative kinase does not impair tight junction breakdown and rescues Snai1 mRNA expression levels. Together these data suggest that SLK plays a novel role in TGFβ-induced EMT, independent of Smads, in a kinase activity-independent manner.