Critical role of WNK1 in MYC-dependent early mouse thymocyte development.

Robert Köchl,Harald Hartweger,Probir Chakravarty,Jennifer Cowan,Miriam Llorian Sopena,Kathryn Fountain,Graham Anderson,Victor Lj Tybulewicz,Lesley Vanes,Andrea White

doi:10.7554/elife.56934

Abstract

WNK1, a kinase that controls kidney salt homeostasis, also regulates adhesion and migration in CD4+ T cells. Wnk1 is highly expressed in thymocytes, and since migration is important for thymocyte maturation, we investigated a role for WNK1 in mouse thymocyte development. We find that WNK1 is required for the transition of double negative (DN) thymocytes through the β-selection checkpoint and subsequent proliferation and differentiation into double positive (DP) thymocytes. Furthermore, we show that WNK1 negatively regulates LFA1-mediated adhesion and positively regulates CXCL12-induced migration in DN thymocytes. Despite this, migration defects of WNK1-deficient thymocytes do not account for the developmental arrest. Instead, we show that in DN thymocytes WNK1 transduces pre-TCR signals via OXSR1 and STK39 kinases, and the SLC12A2 ion co-transporter that are required for post-transcriptional upregulation of MYC and subsequent proliferation and differentiation into DP thymocytes. Thus, a pathway regulating ion homeostasis is a critical regulator of thymocyte development.

Highlights

With No Lysine kinase 1 (WNK1) is a member of a family of four mammalian serine/threonine-specific protein kinases that are broadly conserved across evolution and are found in all multicellular organisms (Verıssimo and Jordan, 2001)
We show here that WNK1 and its kinase activity are absolutely required for the transition of double negative (DN) to double positive (DP) thymocytes at the b-selection checkpoint
In the absence of WNK1 there is a failure of the proliferative expansion of TCRb+ DN4 cells and subsequent differentiation into DP cells, hallmarks of b-selection

Summary

Introduction

With No Lysine kinase 1 (WNK1) is a member of a family of four mammalian serine/threonine-specific protein kinases that are broadly conserved across evolution and are found in all multicellular organisms (Verıssimo and Jordan, 2001). WNK kinases phosphorylate and activate the related OXSR1 and STK39 kinases, which in turn phosphorylate and activate the Na+K+Cl- co-transporters SLC12A1 and SLC12A2 and the Na+Cl- co-transporter SLC12A3 (Rafiqi et al, 2010; Thastrup et al, 2012), allowing Na+, K+, and Cl- ions to enter the cell. They phosphorylate and inhibit the K+Cl- cotransporters SLC12A4, SLC12A5, SLC12A6, SLC12A7 (Mercado et al, 2016), blocking K+ and Clfrom leaving the cell. Beyond its role in ion homeostasis, WNK1 has been proposed to regulate vesicular trafficking, proliferation and cell volume (de Los Heros et al, 2018; McCormick and Ellison, 2011)

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Conclusion