title: Nak1 interacts with Hob1 and Wsp1 to regulate cell growth and polarity in Schizosaccharomyces pombe.
abstract: We have previously reported that Nak1, a group-II germinal center (GC) kinase, is essential for polarized growth in Schizosaccharomyces pombe. Here, we provide evidence that Nak1 regulates cell growth and polarity, in part, through its interactions with Hob1 (an Rvs167/amphiphysin homolog) and Wsp1 (Wiskott-Aldrich-syndrome-protein homolog). We found that Nak1, Hob1 and Wsp1 interact physically, and that both Hob1/green-fluorescent-protein (Hob1-GFP) and Wsp1-GFP fusion proteins localized to F-actin patches at growing cell ends and medial division sites. Hob1-GFP was dissociated from patches in cells lacking Wsp1. Also, Hob1 overexpression dissociated Wsp1-GFP from foci, inhibited Wsp1-directed F-actin formation in vitro and partially restored polarity defects associated with Wsp1 overexpression or nak1 repression. Furthermore, loss of both Wsp1 and Hob1 resulted in rounded cells, slow growth and multiple septae. Together, these observations suggest that Hob1 and Wsp1 cooperate to mediate cell polarity, growth and division. Repression of nak1 resulted in a random redistribution of Hob1-GFP and Wsp1-GFP foci, and inhibition of Wsp1-directed F-actin formation in vitro. Furthermore, hob1delta and wsp1delta mutants exhibited synthetic growth defects in combination with nak1 repression, suggesting that Nak1 has redundant functions with Hob1 and Wsp1. Collectively, our results suggest that Nak1 both regulates and cooperates with Hob1 and Wsp1 to promote F-actin formation and polarized cell growth.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB T2N 4N1, Canada.
authors.forename: Timothy Y
authors.initials: TY
authors.lastname: Huang
authors.forename: Margaret
authors.initials: M
authors.lastname: Renaud-Young
authors.forename: Dallan
authors.initials: D
authors.lastname: Young
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D016764:Cell Polarity / Q000235:genetics*; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D009154:Mutation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012568:Schizosaccharomyces / Q000254:growth & development*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; D011993:Recombinant Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; C417034:Wsp1 protein, S pombe; C491080:hob1 protein, S pombe; D049452:Green Fluorescent Proteins; C500976:Nak1 protein, S pombe; D017346:Protein Serine-Threonine Kinases