The Forkhead-associated Domain Protein Cep170 Interacts with Polo-like Kinase 1 and Serves as a Marker for Mature Centrioles

Abstract

We report the characterization of Cep170, a forkhead-associated (FHA) domain protein of previously unknown function. Cep170 was identified in a yeast two-hybrid screen for interactors of Polo-like kinase 1 (Plk1). In human cells, Cep170 is constantly expressed throughout the cell cycle but phosphorylated during mitosis. It interacts with Plk1 in vivo and can be phosphorylated by Plk1 in vitro, suggesting that it is a physiological substrate of this kinase. Both overexpression and small interfering RNA (siRNA)-mediated depletion studies suggest a role for Cep170 in microtuble organization and cell morphology. Cep170 associates with centrosomes during interphase and with spindle microtubules during mitosis. As shown by immunoelectron microscopy, Cep170 associates with subdistal appendages, typical of the mature mother centriole. Thus, anti-Cep170 antibodies stain only one centriole during G1, S, and early G2, but two centrioles during late G2 phase of the cell cycle. We show that Cep170 labeling can be used to discriminate bona fide centriole overduplication from centriole amplification that results from aborted cell division.

Antizyme, a mediator of ubiquitin-independent proteasomal degradation and its inhibitor localize to centrosomes and modulate centriole amplification

“…Moreover, overexpression of AZI increases cell proliferation and promotes cell transformation (Keren-Paz et al, 2006;Kim et al, 2006) and high levels of AZI have been observed in gastric tumors (Jung et al, 2000). Our results show that overexpression of AZI induces aberrant synthesis of daughter centrioles as reported previously for the papillomavirus-16 E7 oncoprotein (Guarguaglini et al, 2005). We have now identified AZI overexpression as an alternative cause for daughter centriole overamplification again suggesting that the antizyme 1/AZI system regulates centriole synthesis.…”

RNA polymerase II transcription is required for human papillomavirus type 16 E7- and hydroxyurea-induced centriole overduplication

“…These findings highlight that the HPV-16 E7-induced generation of immature daughter centrioles (Guarguaglini et al, 2005) is an active process with specific molecular requirements and not simply a consequence of cytokinesis defects, ploidy alterations or aberrant centriole splitting . It has been shown that other events leading to a deregulation of CDK2 activity such as loss of p16 INK4A can also stimulate abnormal centriole numbers following S phase arrest (McDermott et al, 2006).…”

“…Lastly, depletion of cyclin A2 has been suggested to cause changes in ploidy (Mihaylov et al, 2002). However, there is no indication so far that cells with altered ploidy cannot undergo additional rounds of centriole duplication (Mantel et al, 1999;Guarguaglini et al, 2005). We therefore interpret the abrogation of HU-induced centriole overduplication in cyclin A2 siRNA-transfected cells (Figure 4d) as a result of a depletion of a critical factor for centriole overduplication under conditions of a prolonged S phase.…”

“…It is conceivable that an accumulation of centrosomes due to impaired cytokinesis accounts for a large number of centrosome aberrations in malignant tumors (Bunz et al, 1998). However, it has recently been shown that a bona fide centriole overduplication can be induced in cells arrested in early S phase using the ribonucleotide reductase inhibitor hydroxyurea (HU) or following overexpression of the human papillomavirus type 16 (HPV-16) E7 oncoprotein (Duensing et al, 2000;Guarguaglini et al, 2005). HPV-16 E7 is a major transforming oncoprotein of high-risk HPVs and disrupts the G1/S cell cycle checkpoint on multiple levels including binding and degradation of the retinoblastoma tumor suppressor protein (pRB) and inactivation of the cyclin-dependentkinase (CDK) inhibitors p21 Cip1 and p27 Kip1 (Munger and Howley, 2002).…”

“…HPV-16 E7 is a major transforming oncoprotein of high-risk HPVs and disrupts the G1/S cell cycle checkpoint on multiple levels including binding and degradation of the retinoblastoma tumor suppressor protein (pRB) and inactivation of the cyclin-dependentkinase (CDK) inhibitors p21 Cip1 and p27 Kip1 (Munger and Howley, 2002). Cells treated with HU or overexpressing HPV-16 E7 show a phenotype in which multiple immature daughter centrioles are frequently found adjacent to a single mature centriole (Guarguaglini et al, 2005).…”