title: Autonomous functions for the Sec14p/spectrin-repeat region of Kalirin.
abstract: Kalirin is a GDP/GTP exchange factor (GEF) for Rho proteins that modulates the actin cytoskeleton in neurons. Alternative splicing generates Delta-isoforms, which encode the RhoGEF domain, but lack the N-terminal Sec14p domain and first 4 spectrin-like repeats of the full-length isoforms. Splicing has functional consequences, with Kal7 but not DeltaKal7 causing formation of dendritic spines. Cells lacking endogenous Kalirin were used to explore differences between these splice variants. Expression of DeltaKal7 in this system induces extensive lamellipodial sheets, while expression of Kal7 induces formation of adherent compact, round cells with abundant cortical actin. Based on in vitro and cell-based assays, Kal7 and DeltaKal7 are equally active GEFs, suggesting that other domains are involved in controlling cell morphology. Catalytically inactive Kal7 and a Kalirin fragment which includes only Sec14p and spectrin-like domains retain the ability to produce compact, round cells and fractionate as high molecular weight complexes. Separating the Sec14p domain from the spectrin-like repeats eliminates the ability of Kal7 to cause this response. The isolated Sec14p domain binds PI(3,5)P2 and PI3P, but does not alter cell morphology. We conclude that the Sec14p and N-terminal spectrin-like domains of Kalirin play critical roles in distinguishing the actions of full-length and Delta-Kalirin proteins.
authors.affiliation: Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030, USA. schiller@nso.uchc.edu
authors.forename: Martin R
authors.initials: MR
authors.lastname: Schiller
authors.forename: Francesco
authors.initials: F
authors.lastname: Ferraro
authors.forename: Yanping
authors.initials: Y
authors.lastname: Wang
authors.forename: Xin-ming
authors.initials: XM
authors.lastname: Ma
authors.forename: Clifton E
authors.initials: CE
authors.lastname: McPherson
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Sobota
authors.forename: Noraisha I
authors.initials: NI
authors.lastname: Schiller
authors.forename: Richard E
authors.initials: RE
authors.lastname: Mains
authors.forename: Betty A
authors.initials: BA
authors.lastname: Eipper
mesh_terms: D000818:Animals; D048430:Cell Shape; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D004705:Endocytosis; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010641:Phenotype; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D051381:Rats; D020449:Repetitive Sequences, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C102365:Kalrn protein, rat; D050505:Mutant Proteins