title: Involvements of the ABC protein ABCF2 and α-actinin-4 in regulation of cell volume and anion channels in human epithelial cells.
abstract: 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.
authors.affiliation: Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan.
authors.forename: Yuhko
authors.initials: Y
authors.lastname: Ando-Akatsuka
authors.forename: Takahiro
authors.initials: T
authors.lastname: Shimizu
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Numata
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Okada
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000185:Actinin / Q000378:metabolism*; D000838:Anions / Q000378:metabolism; D002461:Cell Line, Transformed; D048429:Cell Size; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D015638:Cytochalasin D / Q000494:pharmacology; D015536:Down-Regulation / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007038:Hypotonic Solutions / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D008840:Microfilament Proteins / Q000378:metabolism
chemical_list: C507640:ABCF2 protein, human; C111453:ACTN4 protein, human; D018528:ATP-Binding Cassette Transporters; D000838:Anions; D007038:Hypotonic Solutions; D007473:Ion Channels; D008840:Microfilament Proteins; D000185:Actinin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D015638:Cytochalasin D