Protein 4.2 is a major component of the red blood cell (RBC) membrane skeleton. We used targeted mutagenesis in embryonic stem (ES) cells to elucidate protein 4.2 functions in vivo. Protein 4.2–null (4.2–/–) mice have mild hereditary spherocytosis (HS). Scanning electron microscopy and ektacytometry confirm loss of membrane surface in 4.2–/– RBCs. The membrane skeleton architecture is intact, and the spectrin and ankyrin content of 4.2–/– RBCs are normal. Band 3 and band 3–mediated anion transport are decreased. Protein 4.2–/– RBCs show altered cation content (increased K+/decreased Na+)resulting in dehydration. The passive Na+ permeability and the activities of the Na-K-2Cl and K-Cl cotransporters, the Na/H exchanger, and the Gardos channel in 4.2–/– RBCs are significantly increased. Protein 4.2–/– RBCs demonstrate an abnormal regulation of cation transport by cell volume. Cell shrinkage induces a greater activation of Na/H exchange and Na-K-2Cl cotransport in 4.2–/– RBCs compared with controls. The increased passive Na+ permeability of 4.2–/– RBCs is also dependent on cell shrinkage. We conclude that protein 4.2 is important in the maintenance of normal surface area in RBCs and for normal RBC cation transport.
Luanne L. Peters, Hitesh K. Jindel, Babette Gwynn, Cathy Korsgren, Kathryn M. John, Samuel E. Lux, Narla Mohandas, Carl M. Cohen, Michael R. Cho, David E. Golan, Carlo Brugnara