Energy-sensitive regulation of Na⁺/K⁺-ATPase by Janus kinase 2

Abstract

Janus kinase 2 (JAK2) contributes to intracellular signaling of leptin and erythropoietin, hormones protecting cells during energy depletion. The present study explores whether JAK2 is activated by energy depletion and regulates Na+/K+-ATPase, the major energy-consuming pump. In Jurkat cells, JAK2 activity was determined by radioactive kinase assay, phosphorylated JAK2 detected by Western blotting, ATP levels measured by luciferase assay, as well as Na+/K+-ATPase α1-subunit transcript and protein abundance determined by real-time PCR and Western blotting, respectively. Ouabain-sensitive K+-induced currents (Ipump) were measured by whole cell patch clamp. Ipump was further determined by dual-electrode voltage clamp inXenopus oocytes injected with cRNA-encoding JAK2, active V617FJAK2, or inactive K882EJAK2. As a result, in Jurkat T cells, JAK2 activity significantly increased following energy depletion by sodium azide (NaN3) or 2,4- dinitro phenol (DNP). DNP- and NaN3-induced decrease of cellular ATP was significantly augmented by JAK2 inhibitor AG490 and blunted by Na+/K+-ATPase inhibitor ouabain. DNP decreased and AG490 enhanced Ipump as well as Na+/K+-ATPase α1-subunit transcript and protein abundance. The α1-subunit transcript levels were also enhanced by signal transducer and activator of transcription-5 inhibitor CAS 285986-31-4. In Xenopus oocytes,Ipump was significantly decreased by expression of JAK2 and V617FJAK2 but not of K882EJAK2, effects again reversed by AG490. In V617FJAK2-expressingXenopus oocytes, neither DNP nor NaN3 resulted in further decline of Ipump. In Xenopus oocytes, the effect of V617FJAK2 on Ipump was not prevented by inhibition of transcription with actinomycin. In conclusion, JAK2 is a novel energy-sensing kinase that curtails energy consumption by downregulating Na+/K+-ATPase expression and activity. © 2014 the American Physiological Society.