A NIMA-related Kinase, Fa2p, Localizes to a Novel Site in the Proximal Cilia ofChlamydomonasand Mouse Kidney Cells

Abstract

Polycystic kidney disease and related syndromes involve dysregulation of cell proliferation in conjunction with ciliary defects. The relationship between cilia and cell cycle is enigmatic, but it may involve regulation by the NIMA-family of kinases (Neks). We previously showed that the Nek Fa2p is important for ciliary function and cell cycle in Chlamydomonas. We now show that Fa2p localizes to an important regulatory site at the proximal end of cilia in both Chlamydomonas and a mouse kidney cell line. Fa2p also is associated with the proximal end of centrioles. Its localization is dynamic during the cell cycle, following a similar pattern in both cell types. The cell cycle function of Fa2p is kinase independent, whereas its ciliary function is kinase dependent. Mice with mutations in Nek1 or Nek8 have cystic kidneys; therefore, our discovery that a member of this phylogenetic group of Nek proteins is localized to the same sites in Chlamydomonas and kidney epithelial cells suggests that Neks play conserved roles in the coordination of cilia and cell cycle progression. INTRODUCTIONThe Nek family of kinases is defined by sequence similarity to NIMA, the Aspergillus kinase that is essential for entry into mitosis (reviewed by Morris and Enos, 1992;O'Connell et al., 2003). Fungi and higher plants encode only one or a few members of this family (Kambouris et al., 1993;Pu et al., 1995;Krien et al., 1998;Wang et al., 2003), but in organisms with centrioles and cilia, such as humans and Chlamydomonas, the family is expanded to 10 or more members (O'Connell et al., 2003;Bradley et al., 2004; Bradley and Quarmby, unpublished data), some of which affect ciliary length (Wloga, Rogowski, and Gaertig, ASCB meeting, 2003, Abstract 2439). We recently reported that the Chlamydomonas Nek Fa2p participates in ciliary function and cell cycle progression (Mahjoub et al., 2002).An emerging pattern suggests that a variety of human syndromes are related to defects in the assembly, maintenance, or function of cilia (Ong and Wheatley, 2003;Pazour and Witman, 2003;Li et al., 2004;Sun et al., 2004). Ciliopathies, including polycystic kidney disease, Bardet-Beidl syndrome, and nephronophthisis include kidney cyst formation as an important component of a pleiotropic syndrome (Mykytyn and Sheffield, 2004;Wilson, 2004). This important consequence of these diseases arises, in part, from dysregulation of cell proliferation in conjunction with ciliary dysfunction. Of particular relevance to the current study are reports that mutations in vertebrate Nek1 and Nek8 cause cystic kidneys in mice and zebrafish (Upadhya et al., 2000;Liu et al., 2002).The relationship between cilia and cell cycle progression is poorly understood. In many cells, entry into the cell cycle is preceded by ciliary disassembly, and exit from mitosis is accompanied by ciliary assembly, a relationship that may reflect the use of the basal bodies/centrioles as mitotic spindle poles (Tucker and Pardee, 1979;Ehler et al., 1995;Wheatley et al., 1996). Consistent with this idea, si...

Nek8 Regulates the Expression and Localization of Polycystin-1 and Polycystin-2

“…Fa2p, a NIMA-related kinase important for cilia disassembly, localized to proximal segment of the cilia in Chlamydomonas. 5 Our data showed that Nek 8 regulates cilium length and restricts polycystins entering cilia. Together with the specific localization of Nek8 to the proximal segment of primary cilia, it is tempting to hypothesize that the proximal segment may be an important site for gating the entry of proteins to the shaft of cilia.…”

“…4 Recently, Fa2p was found localized to the proximal end of cilia, in both Chlamydomonas and cultured kidney epithelial cells, and its kinase activity is required for deflagellation. 5 To date, 11 Nek family members have been cloned from mouse or human cells, of which Nek2 is considered to be the closest NIMA homolog and therefore has been the most intensively studied.…”

A NIMA-related kinase, Cnk2p, regulates both flagellar length and cell size inChlamydomonas

“…fa2 mutants are slow to transit the cell cycle owing to a G2-M delay and do not sever the nine outer doublet microtubules of the axoneme in response to deflagellation stimuli (Finst et al, 1998;Mahjoub et al, 2002). During interphase, Fa2p localizes to the proximal end of the flagella, whereas during mitosis it is associated with the polar region of the mitotic spindle (Mahjoub et al, 2004). This was the first report of a NIMA-related kinase with both cell cycle and ciliary functions; Cnk2p is the second.…”

Members of the NIMA-related Kinase Family Promote Disassembly of Cilia by Multiple Mechanisms

“…Fa2p is restricted to the transitional region between the BB and the axoneme (Mahjoub et al, 2004), and FA2 mutants are defective in flagellar autotomy, a process that is triggered by microtubule severing in the transitional region (Mahjoub et al, 2002). We show here that Nrk17p is mainly localized with the BBs and the most proximal part of the cilium.…”