title: Beta1PIX, the PAK-interacting exchange factor, requires localization via a coiled-coil region to promote microvillus-like structures and membrane ruffles.
abstract: PIX is a Rho-family guanine nucleotide exchange factor that binds PAK. We previously described two isoforms of PIX that differ in their N termini. Here, we report the identification of a new splice variant of betaPIX, designated beta2PIX, that is the dominant species in brain and that lacks the region of approximately 120 residues with predicted coiled-coil structure at the C terminus of beta1PIX. Instead, beta2PIX contains a serine-rich C terminus. To determine whether these splice variants differ in their cellular function, we studied the effect of expressing these proteins in HeLa cells. We found that the coiled-coil region plays a key role in the localization of beta1PIX to the cell periphery and is also responsible for PIX dimerization. Overexpression of beta1, but not beta2PIX, drives formation of membrane ruffles and microvillus-like structures (via activation of Rac1 and Cdc42, respectively), indicating that its function requires localized activation of these GTPases. Thus, beta1PIX, like other RhoGEFs, exerts specific morphological functions that are dependent on its intracellular location and are mediated by its C-terminal dimerization domain.
authors.affiliation: Glaxo-IMCB Group, Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609. mcbkohcg@imcb.nus.edu.sg
authors.forename: C G
authors.initials: CG
authors.lastname: Koh
authors.forename: E
authors.initials: E
authors.lastname: Manser
authors.forename: Z S
authors.initials: ZS
authors.lastname: Zhao
authors.forename: C P
authors.initials: CP
authors.lastname: Ng
authors.forename: L
authors.initials: L
authors.lastname: Lim
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002522:Chlorocebus aethiops; D019281:Dimerization; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008855:Microscopy, Electron, Scanning; D008871:Microvilli; D008969:Molecular Sequence Data; D010766:Phosphorylation; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D064067:Rho Guanine Nucleotide Exchange Factors; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D054462:p21-Activated Kinases
chemical_list: C576607:Arhgef7 protein, mouse; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases