Nek7 kinase is enriched at the centrosome, and is required for proper spindle assembly and mitotic progression

Abstract

Members of the NIMA-related kinases (NRK) family are recently emerging as central regulators of various aspects of the cell cycle. However, the cellular roles of the mammalian NRK, Nek7, remain obscure. We show here that the endogenous Nek7 protein is enriched at the centrosome in a microtubuleindependent manner. Overexpression of wt or kinase-defective Nek7 resulted in cells of rounder appearance, and higher proportions of multinuclear and apoptotic cells. Down-regulation of Nek7 using a small interfering RNA approach resulted in a significant increase in mitotic cells presenting multipolar spindle phenotype. These results suggest a role for Nek7 in regulating proper spindle assembly and mitotic progression.

Nek7 kinase targeting leads to early mortality, cytokinesis disturbance and polyploidy

“…The enrichment of Nek7 in the centrosome has been demonstrated (Yissachar et al, 2006;Kim et al, 2007), strengthening the idea that Nercc1 and Nek7 (and presumably also Nek6) are components of a mitotic spindle-signaling cascade. We have shown previously that knock down of Nek7 by small interfering RNA (siRNA) results in a range of mitotic defects, assigning Nek7 as a centrosomal protein involved in mitotic regulation (Yissachar et al, 2006). In line with these results, Nek7 involvement in g-tubulin recruitment to the centrosome, together with microtubule nucleation activity was recently reported (Kim et al, 2007).…”

“…We have previously reported that overexpression of a kinase-defective form of Nek7 or transfection of siRNA against Nek7 results in apoptosis, higher mitotic index and higher frequency of multinuclear cells (Yissachar et al, 2006). Similarly, it has been shown that siRNA against Nek7 leads to the suppression of spindle formation and an arrest at prometaphase or metaphase (Kim et al, 2007;O'Regan and Fry, 2009).…”

“…Nercc1 has been shown to function as a mitotic regulator required for accurate spindle assembly and cell cycle progression, and is recruited to the centrosome in its phosphorylated active form (Roig et al, 2005). The enrichment of Nek7 in the centrosome has been demonstrated (Yissachar et al, 2006;Kim et al, 2007), strengthening the idea that Nercc1 and Nek7 (and presumably also Nek6) are components of a mitotic spindle-signaling cascade. We have shown previously that knock down of Nek7 by small interfering RNA (siRNA) results in a range of mitotic defects, assigning Nek7 as a centrosomal protein involved in mitotic regulation (Yissachar et al, 2006).…”

“…Cells were classified by their morphology as: prophase, prometaphase, early, mid and late anaphase, and early and late telophase (Glotzer, 2009). Quite unexpectedly, and in contrast to the phenotypes observed after siRNA-mediated depletion of Nek6 and Nek7 (Yin et al, 2003;Yissachar et al, 2006;Kim et al, 2007;O'Regan and Fry, 2009), there was no evidence of the cells being arrested or delayed in any particular mitotic stages, and the incidence of cells in each of the mitotic stages was quite similar between WT and Nek7-mutant MEFs (Figure 5a). However, inspection of the mitotic mutant cells revealed a significantly higher percentage of cells exhibiting cytokinesis failures (15.8% compared with 7% of the mitotic cells; P-value ¼ 0.03 by two-tail Fisher exact test; Figure 5b).…”

“…We have previously demonstrated that Nek7 is localized to the centrosome, and that siRNA-mediated depletion of Nek7 result in multicentrosomal cells and spindle abnormalities (Yissachar et al, 2006). The reduction in the levels or activity of Nercc1, a kinase upstream of Nek6/7, inhibits spindle formation presumably by affecting g-tubulin recruitment and aster formation (Roig et al, 2002(Roig et al, , 2005.…”