Downregulation of chloride channel ClC-2 by Janus kinase 3

摘要

Janus kinase-3 (JAK3) fosters proliferation and counteracts apoptosis of lymphocytes and tumor cells. The gain of function mutation A572VJAK3 has been discovered in acute megakaryoplastic leukemia. JAK3 is inactivated by replacement of lysine by alanine in the catalytic subunit (K855AJAK3) . Regulation of cell proliferation and apoptosis involves altered activity of Cl- channels. The present study, thus, explored whether JAK3 modifies the function of the small conductance Cl- channel ClC-2. To this end, ClC-2 was expressed in Xenopus oocytes with or without wild-type JAK3, A568VJAK3 or K851AJAK3, and the Cl- channel activity determined by dual-electrode voltage clamp. Channel protein abundance in the cell membrane was determined utilizing chemiluminescence. As a result, expression of ClC-2 was followed by a marked increase of cell membrane conductance. The conductance was significantly decreased following coexpression of JAK3 or A568VJAK3, but not by coexpression of K851AJAK3. Exposure of the oocytes expressing ClC-2 together with A568VJAK3 to the JAK3 inhibitor WHI-P154 (4-[(3'-bromo-4'- hydroxyphenyl)amino]-6,7-dimethoxyquinazoline, 22 μM) increased the conductance. Coexpression of A568VJAK3 decreased the ClC-2 protein abundance in the cell membrane of ClC-2 expressing oocytes. The decline of conductance in ClC-2 and A568VJAK3 coexpressing oocytes following inhibition of channel protein insertion by brefeldin A (5 μM) was similar in oocytes expressing ClC-2 with A568VJAK3 and oocytes expressing ClC-2 alone, indicating that A568VJAK3 might slow channel protein insertion into rather than accelerating channel protein retrieval from the cell membrane. In conclusion, JAK3 downregulates ClC-2 activity and thus counteracts Cl - exit - an effect possibly influencing cell proliferation and apoptosis.