Involvements of the ABC protein ABCF2 and α-actinin-4 in regulation of cell volume and anion channels in human epithelial cells

J Cell Physiol. 2012 Oct;227(10):3498-510. doi: 10.1002/jcp.24050.


After osmotic swelling, cell volume is regulated by a process called regulatory volume decrease (RVD). Although actin cytoskeletons are known to play a regulatory role in RVD, it is not clear how actin-binding proteins are involved in the RVD process. In the present study, an involvement of an actin-binding protein, α-actinin-4 (ACTN4), in RVD was examined in human epithelial HEK293T cells. Overexpression of ACTN4 significantly facilitated RVD, whereas siRNA-mediated downregulation of endogenous ACTN4 suppressed RVD. When the cells were subjected to hypotonic stress, the content of ACTN4 increased in a 100,000 × g pellet, which was sensitive to cytochalasin D pretreatment. Protein overlay assays revealed that ABCF2, a cytosolic member of the ABC transporter superfamily, is a binding partner of ACTN4. The ACTN4-ABCF2 interaction was markedly enhanced by hypotonic stimulation and required the NH(2) -terminal region of ABCF2. Overexpression of ABCF2 suppressed RVD, whereas downregulation of ABCF2 facilitated RVD. We then tested whether ABCF2 has a suppressive effect on the activity of volume-sensitive outwardly rectifying anion channel (VSOR), which is known to mediate Cl(-) efflux involved in RVD, because another ABC transporter member, CFTR, was shown to suppress VSOR activity. Whole-cell VSOR currents were largely reduced by overexpression of ABCF2 and markedly enhanced by siRNA-mediated depletion of ABCF2. Thus, the present study indicates that ACTN4 acts as an enhancer of RVD, whereas ABCF2 acts as a suppressor of VSOR and RVD, and suggests that a swelling-induced interaction between ACTN4 and ABCF2 prevents ABCF2 from suppressing VSOR activity in the human epithelial cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / metabolism*
  • Actinin / metabolism*
  • Anions / metabolism
  • Cell Line, Transformed
  • Cell Size
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism
  • Cytochalasin D / pharmacology
  • Down-Regulation / physiology
  • Epithelial Cells / cytology*
  • Epithelial Cells / metabolism
  • HEK293 Cells
  • Humans
  • Hypotonic Solutions / metabolism
  • Ion Channels / metabolism*
  • Microfilament Proteins / metabolism


  • ABCF2 protein, human
  • ACTN4 protein, human
  • ATP-Binding Cassette Transporters
  • Anions
  • Hypotonic Solutions
  • Ion Channels
  • Microfilament Proteins
  • Actinin
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Cytochalasin D