Abstract
The volume-sensitive outwardly rectifying Cl− channel (VSOR) is known to be involved in cell volume regulation after osmotic swelling called regulatory volume decrease (RVD), cell proliferation, cell cycle, and cell death. However, neither its molecular identity nor its activation mechanism is unknown. Since both VSOR and RVD have been reported to be dependent on cytoskeletons, here, we searched cytoskeleton-related proteins involved in regulation of VSOR and RVD in human epithelial cells. Detergent solubility assays of the microsomal fraction suggested that α-actinin 4 (ACTN4) becomes associated with cytoskeletons when Intestine 407 and HEK293T cells were exposed to hypotonic solution. Cell volume measurements demonstrated that RVD was facilitated by ACTN4 overexpression whereas RVD was suppressed by siRNA-mediated ACTN4 downregulation. Protein overlay assays revealed that ABCF2, a member of ABC transporter superfamily, is a binding partner of ACTN4. Their interaction requires the NH2-terminal regions of both ACTN4 and ABCF2 and is enhanced by hypotonic stimulation. ABCF2 overexpression inhibited RVD, whereas its downregulation facilitated RVD after osmotic swelling. Moreover, the whole-cell VSOR current was suppressed by overexpression with ABCF2 in HEK293T cells. Thus, it is concluded that ABCF2 is an ACTN4-binding protein which is involved in regulation of VSOR and RVD. [J Physiol Sci. 2007;57 Suppl:S124]
