Characterization of NIP2/centrobin, a novel substrate of Nek2, and its potential role in microtubule stabilization

Abstract

Nek2 is a mitotic kinase whose activity varies during the cell cycle. It is well known that Nek2 is involved in centrosome splitting, and a number of studies have indicated that Nek2 is crucial for maintaining the integrity of centrosomal structure and microtubule nucleation activity. In the present study, we report that NIP2, previously identified as centrobin, is a novel substrate of Nek2. NIP2 was daughter-centriole-specific, but was also found in association with a stable microtubule network of cytoplasm. Ectopic NIP2 formed aggregates but was dissolved by Nek2 into small pieces and eventually associated with microtubules. Knockdown of NIP2 showed significant reduction of microtubule organizing activity, cell shrinkage, defects in spindle assembly and abnormal nuclear morphology. Based on our results, we propose that NIP2 has a role in stabilizing the microtubule structure. Phosphorylation may be crucial for mobilization of the protein to a new microtubule and stabilizing it.

Centrobin regulates the assembly of functional mitotic spindles

“…Consistent with previous studies (Zou et al, 2005;Jeong et al, 2007), the C terminus was required for targeting Centrobin to the centrosome (Figure 1c). However, our study results show that the N terminus is required for Centrobin localization at the mitotic spindle.…”

“…Nek2A has recently been proposed as a kinase for Centrobin that might target it to the microtubules (Jeong et al, 2007). However, this phosphorylation event could have another role, such as priming Centrobin for phosphorylation by Plk1.…”

“…Mad2 siRNA duplexes (5 0 -AAGAGUCGGGACCACAGUUUA-3 0 ) are previously described elsewhere (Lampson and Kapoor, 2005) and were synthesized by Invitrogen (Carlsbad, CA, USA). Myc-Centrobin constructs were a gift from K Rhee and have been described previously (Jeong et al, 2007).…”

“…Centrobin was initially reported to be required for centriole duplication, with loss of Centrobin resulting in impaired cytokinesis (Zou et al, 2005). Recently, Centrobin was reported to have microtubule-bundling activity and was required for microtubule organization in interphase and spindle assembly in mitotic cells (Jeong et al, 2007). In addition, Centrobin was phosphorylated by Nek2a, which targets Centrobin to the microtubules.…”

Centrobin-mediated Regulation of the Centrosomal Protein 4.1-associated Protein (CPAP) Level Limits Centriole Length during Elongation Stage

“…Hence, it is believed that degradation of CPAP is a trigger to stop further elongation of the centrioles. Importantly, both centrobin and CPAP directly bind to tubulin and have microtubule-stabilizing property (49,52,63), suggesting that these proteins contribute to the actual polymerization of microtubules. Future studies will address how the tubulin binding property of centrobin and CPAP coordinates and contributes toward centriole assembly and regulation of centriole length during biogenesis.…”