F., Y. to prevent centrosome overduplication in S-phase-arrested cancer cells. Equal segregation of genetic material between daughter cells requires the mitotic spindle to be bipolar, with monopolar or multipolar spindles leading to abnormal segregation. Because spindle poles are organized by centrosomes, maintaining the right number of centrosomes is critical to the genetic integrity of dividing cells. Centrosomes normally duplicate once per cell cycle in a process that is tightly coordinated with the DNA replication cycle (9, 26, 42, 48, 62). However, the vast majority of human WEHI-539 hydrochloride cancer cells accumulate extra or supernumerary centrosomes and, likely as a consequence, exhibit aneuploidy and chromosome instability (12, 15, 54). Supernumerary centrosomes may arise through several different mechanisms. Prominent among these are (i) a failure of diploid cells to complete mitosis, leading to tetraploidization and doubling of the centrosome number; and (ii) a loss of coordination of the centrosome duplication and DNA replication cycles such that cells undergo multiple rounds of centrosome duplication within a single cell cycle. There is good evidence to suggest that both of these pathways contribute to supernumerary centrosomes in cancer cells (49). Centrosome duplication in dividing cells occurs in a semiconservative templated process. In G1 phase of the cell cycle, a centrosome consists of two centrioles surrounded by pericentriolar material (PCM). Centrioles are stable cylinders of 200 nm by 500 nm composed of nine triplets of posttranslationally modified microtubules (MTs) arranged in a pinwheel configuration (11, 40). After progression into S phase, two new procentrioles appear, elongating perpendicularly from the proximal ends of the older centrioles. In late G2, the two centrosomes, each now containing a pair of centrioles, separate to the two poles of the mitotic spindle. However, despite description of this process at the morphological level many years ago (34), the molecular events involved in biogenesis of new centrioles are only now beginning to be resolved (9, 16, 23, 38, 51). In addition to templated duplication, it has been demonstrated experimentally that centrioles can form using a de novo assembly pathway (30, 37, 41). Following laser ablation of centrioles, a focus of -tubulin appears in Chinese hamster ovary (CHO) cells, within which a random number of centrioles assemble (30), while in HeLa cells expressing a centrin1-green fluorescent protein (centrin1-GFP) construct, multiple small centrin-containing foci appear (37). These centrin-containing structures were termed precentrioles, and it has been suggested, although not shown, that these may also play a role during templated centrosome duplication. In the latter case, only those precentrioles that adhere to the docking site on the existing centrioles would subsequently elongate into DLL1 full centrioles, with the others eventually disappearing. Importantly for WEHI-539 hydrochloride genome integrity, de novo centriole formation is suppressed in the presence of preexisting centrioles (63); however, this control may be lost in cancer cells. Multiple centrioles also assemble in differentiating cells undergoing ciliogenesis (24). In this case, the multiple centrioles, referred to as basal bodies, subtend the MTs that form the ciliary axoneme. Basal systems assemble via both a centriolar pathway, where multiple basal systems assemble around specific centrioles, and an acentriolar pathway, where basal systems type around electron-dense buildings referred to as deuterosomes. Cells missing the tumor suppressor p53 overduplicate centrosomes if they are arrested in S stage with drugs such as for example hydroxyurea (HU) or aphidicolin (4, 60). It has scientific relevance, as much widely used anticancer realtors (e.g., 5-fluorouracil and arabinoside C) function WEHI-539 hydrochloride by interfering with DNA replication. Program of these medications could as a result WEHI-539 hydrochloride inadvertently speed up chromosome instability in those cells that survive the procedure due to marketing centrosome amplification (8). Furthermore, the E7 oncoprotein from high-risk individual papillomaviruses induces centrosome overduplication within an individual cell routine (19). Because of the prevalence of amplified centrosomes in cancers cells, we attempt to examine the molecular occasions necessary for centrosome overduplication during S-phase arrest. Treatment of cells with several inhibitors showed a requirement of MTs, dynein, Hsp90, WEHI-539 hydrochloride Cdk2, and nuclear export for useful centrosome overduplication. Unexpectedly, though, staining of the cells for centriole markers uncovered the current presence of intermediate buildings similar to those observed in the de novo duplication pathway as well as the centriolar and acentriolar pathways.

Related Posts