FGFR4 phosphorylates MST1 to confer breast cancer cells resistance to MST1/2-dependent apoptosis

S Pauliina Turunen,Pernilla Von Nandelstadh,Brinton Seashore-Ludlow,Tiina Öhman,Beatriz Martins,Markku Varjosalo,Päivi Östling,Katrin Höpfner,Ville Rantanen,Erika Gucciardo,Huini Li,Kaisa Lehti

doi:10.1038/s41418-019-0321-x

Abstract

Cancer cells balance with the equilibrium of cell death and growth to expand and metastasize. The activity of mammalian sterile20-like kinases (MST1/2) has been linked to apoptosis and tumor suppression via YAP/Hippo pathway-independent and -dependent mechanisms. Using a kinase substrate screen, we identified here MST1 and MST2 among the top substrates for fibroblast growth factor receptor 4 (FGFR4). In COS-1 cells, MST1 was phosphorylated at Y433 residue in an FGFR4 kinase activity-dependent manner, as assessed by mass spectrometry. Blockade of this phosphorylation by Y433F mutation induced MST1 activation, as indicated by increased threonine phosphorylation of MST1/2, and the downstream substrate MOB1, in FGFR4-overexpressing T47D and MDA-MB-231 breast cancer cells. Importantly, the specific knockdown or short-term inhibition of FGFR4 in endogenous models of human HER2+ breast cancer cells likewise led to increased MST1/2 activation, in conjunction with enhanced MST1 nuclear localization and generation of N-terminal cleaved and autophosphorylated MST1. Unexpectedly, MST2 was also essential for this MST1/N activation and coincident apoptosis induction, although these two kinases, as well as YAP, were differentially regulated in the breast cancer models analyzed. Moreover, pharmacological FGFR4 inhibition specifically sensitized the HER2+ MDA-MB-453 breast cancer cells, not only to HER2/EGFR and AKT/mTOR inhibitors, but also to clinically relevant apoptosis modulators. In TCGA cohort, FGFR4 overexpression correlated with abysmal HER2+ breast carcinoma patient outcome. Therefore, our results uncover a clinically relevant, targetable mechanism of FGFR4 oncogenic activity via suppression of the stress-associated MST1/2-induced apoptosis machinery in tumor cells with prominent HER/ERBB and FGFR4 signaling-driven proliferation.

Highlights

Cancer cells rely on oncogenic signaling by receptor tyrosine kinases (RTKs) to drive tumor initiation and progression [1]
The top five substrates included four Hippo tumor suppressor pathway proteins; MST2 (STK3), protein kinase C iota (PRKCI), casein kinase I delta (CSNK1D) [45], and MST1 (STK4) (Fig. 1b; STK3 and PRKCI identified as two splice variants), suggesting that fibroblast growth factor receptor 4 (FGFR4) can directly phosphorylate the Hippo serine/threonine kinase pathway proteins (Fig. 1b)
To identify the FGFR4 phosphorylated tyrosine residue (s), immunoprecipitated MST1 was subjected to mass spectrometry (Fig. S1A)

Summary

Introduction

Cancer cells rely on oncogenic signaling by receptor tyrosine kinases (RTKs) to drive tumor initiation and progression [1]. Among RTKs, fibroblast growth factor receptors (FGFRs) trigger intracellular signaling cascades that control key cellular processes including survival, proliferation, differentiation, and migration/invasion, as well as angiogenesis—each dysregulated in cancer [2]. FGFR4 is dispensable for mouse development [3]. This coupled with specific FGFR4 induction in certain cancers, along with structural differences and drug selectivity relative to other FGFRs, supports the efficacy of FGFR4 as a therapeutic intervention [4,5,6,7,8,9]

Methods

Results

Conclusion