The Human Polo-like Kinase 4 is a Regulator of Centrosome Duplication

Polo-like kinase 4 (Plk4), also known as Snk/Fnk-akin kinase (Sak), is the most structurally divergent member of the Polo-like kinase family (Fode et al., 1994; Leung et al., 2002) and has been associated with cell proliferation (Fode et al., 1994). Most importantly, Plk4-/- mice were found to be embryonically lethal whereas heterozygous Plk+/- mice exhibited an increased incidence of tumorigenesis (Hudson et al., 2001; Ko et al., 2005). However, very little data has been reported on the function of human Plk4. Here, we embarked on a functional characterisation of human Plk4 in cultured cells. This kinase localised to the centrosome throughout the cell cycle, and overexpression studies revealed that an excess of wild type Plk4 induced the overduplication of centrioles in cells. This process was dependent on the cyclin-dependent kinase (Cdk) 2 in addition to CP110 and human Sas-6, two proteins shown to be involved in centriole duplication (Chen et al., 2002b; Leidel et al., 2005). Conversely, depletion of endogenous Plk4 resulted in an inhibition of centriole duplication leading to a loss of centrioles from dividing cells. These data from gain-of-function and loss-of-function experiments demonstrated that Plk4 is an essential regulator of centriole duplication. Further microscopic studies revealed that excess Plk4 activity resulted in the formation of rosette-like structures around centrioles. These structures recruited CPAP which is the human homologue of Sas-4, a protein required for centriole duplication in the nematode worm (Caenorhabditis elegans). We propose that these structures represent centriole precursors. The study presented here is a starting point for further work. The identification of Plk4 as a central regulator of centriole duplication will allow the characterisation of upstream and downstream regulatory pathways, whereas a continued search for interaction partners should resolve the function of this kinase. In particular, the analysis of rosette-like centriole precursors is a promising avenue to provide insights into the mechanism of centriole duplication

Cep152 and Plk4 form a double act

Two centrosomal proteins work together to duplicate centrioles

Polo-like kinase 4 kinase activity limits centrosome overduplication by autoregulating its own stability

Plk4 phosphorylates itself in trans to prevent accumulation and self-limit kinase activity, which may be important for regulating centriole duplication

Ana3 is a conserved protein required for the structural integrity of centrioles and basal bodies

Centriolar protein Ana3 is essential for basal body formation, not centriole duplication, as previously thought

Cep152 interacts with Plk4 and is required for centriole duplication

Cep152, the orthologue of Drosophila Asterless, is a Plk4 target that functions with Plk4 in centriole assembly

Functional central spindle assembly requires de novo microtubule generation in the interchromosomal region during anaphase

The augmin protein complex nucleates noncentrosomal microtubules during anaphase to promote completion of cell division

Aberrant methylation of Polo-like kinase CpG islands in Plk4 heterozygous mice

<p>Abstract</p> <p>Background</p> <p>Hepatocellular carcinoma (HCC), one of the most common cancers world-wide occurs twice as often in men compared to women. Predisposing conditions such as alcoholism, chronic viral hepatitis, aflatoxin B1 ingestion, and cirrhosis all contribute to the development of HCC.</p> <p>Methods</p> <p>We used a combination of methylation specific PCR and bisulfite sequencing, qReal-Time PCR (qPCR), and Western blot analysis to examine epigenetic changes for the <it>Polo-like kinases </it>(<it>Plks</it>) during the development of hepatocellular carcinoma (HCC) in <it>Plk4 </it>heterozygous mice and murine embryonic fibroblasts (MEFs).</p> <p>Results</p> <p>Here we report that the promoter methylation of <it>Plk4 </it>CpG islands increases with age, was more prevalent in males and that <it>Plk4 </it>epigenetic modification and subsequent downregulation of expression was associated with the development of HCC in <it>Plk4 </it>mutant mice. Interestingly, the opposite occurs with another Plk family member, <it>Plk1 </it>which was typically hypermethylated in normal liver tissue but became hypomethylated and upregulated in liver tumours. Furthermore, upon alcohol exposure murine embryonic fibroblasts exhibited increased <it>Plk4 </it>hypermethylation and downregulation along with increased centrosome numbers and multinucleation.</p> <p>Conclusions</p> <p>These results suggest that aberrant <it>Plk </it>methylation is correlated with the development of HCC in mice.</p

Cep120 is asymmetrically localized to the daughter centriole and is essential for centriole assembly

Cep120, a protein involved in maintenance of neural progenitor cells, is required for centriole duplication in cycling cells and for centriole amplification in tracheal epithelial cells

Drosophila Ana2 is a conserved centriole duplication factor

Drosophila protein Ana2 supports de novo formation of centrioles and may be a functional homologue of the C. elegans centriole duplication protein SAS-5