title: Filopodia are induced by aquaporin-9 expression.
abstract: Understanding filopodial formation in motile cells is a pertinent task in cell biology. In the present study we show that expression of the human water channel aquaporin-9 (AQP9) in different cell lines induces the formation of numerous filopodial extensions. Several lines of evidence support the role of aquaporins functioning both as a water channel and signaling participant. The number of filopodia is decreased by site-directed serine substitutions in putative PKC-binding or -phosphorylation sites at amino acid position 11 and 222 in AQP9. The filopodial phenotype obtained with wild-type AQP9 is associated with elevated levels of active Cdc42, while serine-deleted mutants have reduced levels of GTP-Cdc42. Co-transfection with inhibitory N-WASP CRIB completely abolishes wild-type AQP9-induced filopodia formation. Active PKC(zeta) phosphorylates wild-type AQP9 and myristoylated PKC(zeta) pseudosubstrate inhibits the formation of filopodia in AQP9-expressing cells. Expression of wild-type AQP9, but not mock or serine substituted mutants, increases sensitivity to hypo-osmolaric conditions, yielding a rapid morphological rounding of cells and cell death starting as early as 24 h post-transfection. We propose that increased water influx through AQP9 is critically involved in the formation of membrane protrusions, and that AQP9-induced actin polymerization is augmented by activation of Cdc42 and PKC(zeta).
authors.affiliation: Department of Cell and Developmental Biology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA. veslo@imk.liu.se
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Loitto
authors.forename: Cai
authors.initials: C
authors.lastname: Huang
authors.forename: Yury J
authors.initials: YJ
authors.lastname: Sigal
authors.forename: Ken
authors.initials: K
authors.lastname: Jacobson
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D016466:CHO Cells; D019556:COS Cells; D002460:Cell Line; D002465:Cell Movement; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D009994:Osmolar Concentration; D010750:Phosphoproteins / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D012694:Serine / Q000235:genetics; D014162:Transfection; D000099221:Protein Kinase C zeta
chemical_list: D020346:Aquaporins; D020690:GTPase-Activating Proteins; D049452:Green Fluorescent Proteins; D010750:Phosphoproteins; D011493:Protein Kinase C; D012694:Serine; D000099221:Protein Kinase C zeta; C109669:AQP9 protein, human; C514543:ARHGAP31 protein, human