Downregulation of ClC-2 by JAK2

Abstract

JAK2 (Janus kinase-2) is activated by cell shrinkage and may thus participate in cell volume regulation. Cell volume regulatory ion channels include the small conductance Cl^-channels ClC-2. The present study thus explored whether JAK2 influences ClC-2 activity. To this end, ClC-2 was expressed in Xenopus oocytes with or without wild type JAK2, active ^V617FJAK2 or inactive ^K882EJAK2 and the Cl channel activity determined by dual electrode voltage clamp. Expression of ClC-2 was followed by a marked increase of cell membrane conductance. The conductance was significantly decreased following coexpression of JAK2 or ^V617FJAK2, but not by coexpression of ^K882EJAK2. Exposure of the oocytes expressing ClC-2 together with ^V617FJAK2 to the JAK2 inhibitor AG490 (40 µM) resulted in a gradual increase of the conductance. According to chemiluminescence JAK2 decreased the channel protein abundance in the cell membrane. The decline of conductance in ClC-2 and ^V617FJAK2 coexpressing oocytes following inhibition of channel protein insertion by brefeldin A (5 µM) was similar in oocytes expressing ClC-2 with ^V617FJAK2 and oocytes expressing ClC-2 alone, indicating that ^V617FJAK2 might slow channel protein insertion into rather than accelerating channel protein retrieval from the cell membrane. In conclusion, JAK2 down-regulates ClC-2 activity and thus counteracts Cl^-exit, an effect which may impact on cell volume regulation.