Deficiency of Src family kinases Fgr and Hck results in activation of erythrocyte K/Cl cotransport

Abstract

Src-family kinases play a central role in regulation of hematopoietic cell functions. We found that mouse erythrocytes express the Src-family kinases Fgr and Hck, as well as Lyn. To directly test whether Fgr and Hck play any role in erythrocyte function, we analyzed red cells isolated from fgr(-/1), hck(-/1), and fgr(-/1) hck(-/1) knock-out mice. Mean corpuscular hemoglobin concentration and median density are increased, while K content is decreased, in fgr(-/1) hck(-/1) double-mutant erythrocytes compared with wild-type, fgr(-/1) or hck(-/1) erythrocytes. Na/K pump and Na/K/Cl cotransport were not altered, but K/Cl cotransport activity was significantly and substantially higher (approximately threefold) in fgr(- /1) hck(-/1) double-mutant erythrocytes. This enhanced K/Cl cotransport activity did not depend on cell age. In fact, in response to bleeding, K/Cl cotransport activity increased in parallel with reticulocytosis in wild-type erythrocytes, while abnormal K/Cl cotransport did not change as a consequence of reticulocytosis in fgr(-/1) hck(-/1) double-mutant erythrocytes. Okadaic acid, an inhibitor of a phosphatase that has been implicated in activation of the K/Cl cotransporter, inhibited K/Cl cotransport in wild- type and fgr(-/1) hck(-/1) double-mutant erythrocytes to a comparable extent. In contrast, staurosporine, an inhibitor of a kinase that has been suggested to negatively regulate this same phosphatase enhanced K/Cl cotransport in wild-type but not in fgr(-/1) hck(-/1) double-mutant erythrocytes. On the basis of these findings, we propose that Fgr and Hck are the kinases involved in the negative regulation of the K/Cl cotransporter- activating phosphatase. Abnormality of erythrocyte K/Cl cotransport in fgr(- /1) hck(-/1) double-mutant animals represents the first demonstration that Src-family kinases may be involved in regulation of membrane transport.