Upregulation of the large conductance voltage- and Ca2+-activated K+ channels by Janus kinase 2

Abstract

The iberiotoxin-sensitive large conductance voltage- and Ca2+-activated potassium (BK) channels (maxi-K+-channels) hyperpolarize the cell membrane thus supporting Ca2+ entry through Ca2+-release activated Ca2+ channels. Janus kinase-2 (JAK2) has been identified as novel regulator of ion transport. To explore whether JAK2 participates in the regulation of BK channels, cRNA encoding Ca2+-insensitive BK channels (BKM513I+Δ899–903) was injected into Xenopus oocytes with or without cRNA encoding wild-type JAK2, gain-of-function V617FJAK2, or inactive K882EJAK2. K+ conductance was determined by dual electrode voltage clamp and BK-channel protein abundance by confocal microscopy. In A204 alveolar rhabdomyosarcoma cells, iberiotoxin-sensitive K+ current was determined utilizing whole cell patch clamp. A204 cells were further transfected with JAK2 and BK-channel transcript, and protein abundance was quantified by RT-PCR and Western blotting, respectively. As a result, the K+ current in BKM513I+Δ899–903-expressing oocytes was significantly increased following coexpression of JAK2 or V617FJAK2 but not K882EJAK2. Coexpression of the BK channel with V617FJAK2 but not K882EJAK2 enhanced BK-channel protein abundance in the oocyte cell membrane. Exposure of BK-channel and V617FJAK2-expressing oocytes to the JAK2 inhibitor AG490 (40 μM) significantly decreased K+ current. Inhibition of channel insertion by brefeldin A (5 μM) decreased the K+ current to a similar extent in oocytes expressing the BK channel alone and in oocytes expressing the BK channel and V617FJAK2. The iberiotoxin (50 nM)-sensitive K+ current in rhabdomyosarcoma cells was significantly decreased by AG490 pretreatment (40 μM, 12 h). Moreover, overexpression of JAK2 in A204 cells significantly enhanced BK channel mRNA and protein abundance. In conclusion, JAK2 upregulates BK channels by increasing channel protein abundance in the cell membrane.