Anatomy of a pressure sensing protein kinase

Cells respond to hydrostatic pressure to maintain cellular, organ and organism level functions, to set and respond to blood pressure, tissue perfusion, filtration rates and other processes. Pressure sensing is thought to occur at membranes where proteins can respond to mechanical cues. Thus, proteins implicated as direct pressure sensors have been mainly ion channels, and more recently G-protein coupled receptors. Here we show, contrary to expectations, that hydrostatic pressure directly induces autophosphorylation and activation of an intracellular protein kinase, With No Lysine kinase-3 (WNK3), and to a lesser extent, WNK1. The pressure sensitivity is a property of the kinase domains alone of WNK1 and WNK3. The crystal structure of the unphosphorylated inactive WNK1 kinase domain (iWNK1) suggests that a dimer to monomer equilibrium and changes in hydration are central to pressure sensing. Aspects of this mechanism are supported by mutagenic analysis. We further show that hydrostatic pressure activates full-length WNK3 in Drosophila tubules.