Activation of the TASK-2 channel after cell swelling is dependent on tyrosine phosphorylation

Kirkegaard SS, Lambert IH, Gammeltoft S, Hoffmann EK. Activation of the TASK-2 channel after cell swelling is dependent on tyrosine phosphorylation. Am J Physiol Cell Physiol 299: C844-C853, 2010. First published July 14, 2010; doi:10.1152/ajpcell.00024.2010.-The swelling-activated K+ currents (I-K,I-vol) in Ehrlich ascites tumor cells (EATC) has been reported to be through the two-pore domain (K-2p), TWIK-related acid-sensitive K+ channel 2 (TASK-2). The regulatory volume decrease (RVD), following hypotonic exposure in EATC, is rate limited by IK, vol indicating that inhibition of RVD reflects inhibition of TASK-2. We find that in EATC the tyrosine kinase inhibitor genistein inhibits RVD by 90%, and that the tyrosine phosphatase inhibitor monoperoxo(picolinato)-oxo-vanadate(V) [mpV(pic)] shifted the volume set point for inactivation of the channel to a lower cell volume. Swelling-activated K+ efflux was impaired by genistein and the Src kinase family inhibitor 4-amino-5-(4-chloro-phenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine (PP2) and enhanced by the tyrosine phosphatase inhibitor mpV(pic). With the use of the TASK-2 inhibitor clofilium, it is demonstrated that mpV(pic) increased the volume-sensitive part of the K+ efflux 1.3 times. To exclude K+ efflux via a KCl cotransporter, cellular Cl- was substituted with NO3-. Also under these conditions K+ efflux was completely blocked by genistein. Thus tyrosine kinases seem to be involved in the activation of the volume-sensitive K+ channel, whereas tyrosine phosphatases appears to be involved in inactivation of the channel. Overexpressing TASK-2 in human embryonic kidney (HEK)-293 cells increased the RVD rate and reduced the volume set point. TASK-2 has tyrosine sites, and precipitation of TASK-2 together with Western blotting and antibodies against phosphotyrosines revealed a cell swelling-induced, time-dependent tyrosine phosphorylation of the channel. Even though we found an inhibiting effect of PP2 on RVD, neither Src nor the focal adhesion kinase (FAK) seem to be involved. Inhibitors of the epidermal growth factor receptor tyrosine kinases had no effect on RVD, whereas the Janus kinase (JAK) inhibitor cucurbitacin inhibited the RVD by 40%. It is suggested that the cytokine receptor-coupled JAK/STAT pathway is upstream of the swelling-induced phosphorylation and activation of TASK-2 in EATC.