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Polo-like kinase 4 (Plk4), the major regulator of centriole biogenesis, has emerged as a putative therapeutic target in cancer due to its abnormal expression in human carcinomas, leading to centrosome number deregulation, mitotic defects and chromosomal instability. Moreover, Plk4 deregulation promotes tumor growth and metastasis in mouse models and is significantly associated with poor patient prognosis. Here, we further investigate the role of Plk4 in carcinogenesis and show that its overexpression significantly potentiates resistance to cell death by anoikis of nontumorigenic p53 knock-out (p53KO) mammary epithelial cells. Importantly, this effect is independent of Plk4’s role in centrosome biogenesis, suggesting that this kinase has additional cellular functions. Interestingly, the Plk4-induced anoikis resistance is associated with the induction of a stable hybrid epithelial-mesenchymal phenotype and is partially dependent on P-cadherin upregulation. Furthermore, we found that the conditioned media of Plk4-induced p53KO mammary epithelial cells also induces anoikis resistance of breast cancer cells in a paracrine way, being also partially dependent on soluble P-cadherin secretion. Our work shows, for the first time, that high expression levels of Plk4 induce anoikis resistance of both mammary epithelial cells with p53KO background, as well as of breast cancer cells exposed to their secretome, which is partially mediated through P-cadherin upregulation. These results reinforce the idea that Plk4, independently of its role in centrosome biogenesis, functions as an oncogene, by impacting the tumor microenvironment to promote malignancy.

Centrosome amplification (CA) is a common feature of human tumours and a promising target for cancer therapy. However, CA's pan-cancer prevalence, molecular role in tumourigenesis and therapeutic value in the clinical setting are still largely unexplored. Here, we used a transcriptomic signature (CA20) to characterise the landscape of CA-associated gene expression in 9,721 tumours from The Cancer Genome Atlas (TCGA). CA20 is upregulated in cancer and associated with distinct clinical and molecular features of breast cancer, consistently with our experimental CA quantification in patient samples. Moreover, we show that CA20 upregulation is positively associated with genomic instability, alteration of specific chromosomal arms and C>T mutations, and we propose novel molecular players associated with CA in cancer. Finally, high CA20 is associated with poor prognosis and, by integrating drug sensitivity with drug perturbation profiles in cell lines, we identify candidate compounds for selectively targeting cancer cells exhibiting transcriptomic evidence for CA.

How cells control the numbers of subcellular components is a fundamental question in biology. Given that biosynthetic processes are fundamentally stochastic it is utterly puzzling that some structures display no copy number variation within a cell population. Centriole biogenesis, with each centriole being duplicated once and only once per cell cycle, stands out due to its remarkable fidelity. This is a highly controlled process, which depends on low-abundance rate-limiting factors. How can exactly one centriole copy be produced given the variation in the concentration of these key factors? Hitherto, tentative explanations of this control evoked lateral inhibition- or phase separation-like mechanisms emerging from the dynamics of these rate-limiting factors but how strict centriole number is regulated remains unsolved. Here, a novel solution to centriole copy number control is proposed based on the assembly of a centriolar scaffold, the cartwheel. We assume that cartwheel building blocks accumulate around the mother centriole at supercritical concentrations, sufficient to assemble one or more cartwheels. Our key postulate is that once the first cartwheel is formed it continues to elongate by stacking the intermediate building blocks that would otherwise form supernumerary cartwheels. Using stochastic models and simulations, we show that this mechanism may ensure formation of one and only one cartwheel robustly over a wide range of parameter values. By comparison to alternative models, we conclude that the distinctive signatures of this novel mechanism are an increasing assembly time with cartwheel numbers and the translation of stochasticity in building block concentrations into variation in cartwheel numbers or length.

The centrosome is composed of two centrioles surrounded by a microtubule-nucleating pericentriolar material (PCM). Although centrioles are known to regulate PCM assembly, it is less known whether and how the PCM contributes to centriole assembly. Here we investigate the interaction between centriole components and the PCM by taking advantage of fission yeast, which has a centriole-free, PCM-containing centrosome, the SPB. Surprisingly, we observed that several ectopically-expressed animal centriole components such as SAS-6 are recruited to the SPB. We revealed that a conserved PCM component, Pcp1/pericentrin, interacts with and recruits SAS-6. This interaction is conserved and important for centriole assembly, particularly its elongation. We further explored how yeasts kept this interaction even after centriole loss and showed that the conserved calmodulin-binding region of Pcp1/pericentrin is critical for SAS-6 interaction. Our work suggests that the PCM not only recruits and concentrates microtubule-nucleators, but also the centriole assembly machinery, promoting biogenesis close by.

Key Points Polo-like kinases (PLKs) are a family of Ser/Thr kinases that have a pivotal role in cell cycle progression, the centrosome cycle, mitosis and cellular responses to DNA damage, which makes them attractive targets for treatments against several diseases. PLK1 is the most ancestral and best-conserved member of the family; it is found in most eukaryotic organisms, except for higher land plants. PLK4 is the most divergent member of the family. PLK2, PLK3 and PLK5 have evolved very recently, probably from a PLK1 gene duplication in vertebrates. PLK1 and PLK4 have distinct structural organizations and are phosphorylated at different residues, which correlate with different mode of actions. The amino-terminal kinase domain and carboxy-terminal polo box domains that characterize PLKs are crucial for regulation of their kinase catalytic activity in time and space, and for controlling subcellular PLK localization. Recent studies show non-canonical functions for PLKs in asymmetric cell division and cilia disassembly. PLKs function in centriole and centrosome biogenesis; PLK1 integrates various external stimuli with cell cycle inputs to coordinate mitotic progression and the centrosome cycle, whereas PLK4 drives centriole assembly. PLK2 and PLK3 have roles in DNA replication and in the DNA damage response and are also expressed in non-proliferative tissues, in which they have a role in cell differentiation and homeostasis (for example, PLK2 and PLK5 regulate neuronal activity). Members of the polo-like kinase (PLK) family are crucial regulators of cell cycle progression, centriole duplication, mitosis, cytokinesis and the DNA damage response. Recent structural and molecular studies have revealed how such processes depend on the tight regulation of PLK abundance, activity, localization and interactions with other proteins, and how dysregulation may be associated with disease. Members of the polo-like kinase (PLK) family are crucial regulators of cell cycle progression, centriole duplication, mitosis, cytokinesis and the DNA damage response. PLKs undergo major changes in abundance, activity, localization and structure at different stages of the cell cycle. They interact with other proteins in a tightly controlled spatiotemporal manner as part of a network that coordinates key cell cycle events. Their essential roles are highlighted by the fact that alterations in PLK function are associated with cancers and other diseases. Recent knowledge gained from PLK crystal structures, evolution and interacting molecules offers important insights into the mechanisms that underlie their regulation and activity, and suggests novel functions unrelated to cell cycle control for this family of kinases.

Key Points The centrosome is the major microtubule-organizing centre (MTOC) in eukaryotic cells, being comprised of two centrioles surrounded by an electron-dense matrix, the pericentriolar material (PCM). The capacity of the centrosome to organize microtubule (MT) arrays, such as the mitotic spindle, depends on its ability to nucleate, anchor and release MTs. In many species, spindles can form without centrosomes owing to chromosome-mediated MT-nucleation pathways. However, in the absence of centrosomes, the fidelity of cell division is decreased and problems are observed in the context of specialized cell divisions, such as male meiosis and asymmetrical cell divisions. Centrosomes might also be important to regulate the G1–S transition. In ciliated or flagellated cells, centrioles also function as basal bodies, structures anchored below the plasma membrane to seed axonemes, the MT-based structure of cilia and flagella. In recent years, evidence has accumulated for an indispensable role for cilia and flagella in various cellular and developmental processes, motility, propagation of morphogenetic signals in embryogenesis and sensory perception. Centriole duplication ensures that each daughter cell inherits two centrioles. It proceeds in four consecutive steps: disengagement of the centrioles at the end of mitosis, nucleation of the daughter centrioles (also known as procentrioles before they acquire full centriolar length) in G1–S, elongation of the daughter centrioles (S and G2) and separation of the centrosomes (G2–M). The recent availability of several complete genome sequences, together with advances in proteomics and functional genomics, has enabled the identification of both centriole components and putative regulatory molecules for the duplication cycle. This has revealed a strong evolutionary conservation of the molecules involved in centriole biogenesis. SAK/PLK4 (or ZYG-1 in Caenorhabditis elegans ), SAS4, SAS6, centrin and γ-tubulin are conserved molecules that regulate centriole duplication. Overexpression of SAK/PLK4 and SAS6 leads to the amplification of MTOCs. Recent studies have drawn attention to a group of molecules that inhibit the re-replication of DNA and might also be involved in inhibiting centriole reduplication. These results suggest a licensing mechanism for the regulation of centriole duplication: the cycle is divided into two stages, one during which duplication can start (licensing zone) and the other during which duplication only proceeds. This ensures that duplication occurs at the right time only. Separase, SAK/PLK4 and SAS6 have all been suggested as potential players. Centrioles can also form de novo in the absence of a template. A view has emerged that there could be a universal mechanism for canonical, de novo and ciliogenic centriole formation. In all of these, procentrioles might be formed in the cytoplasm and be stabilized or catalysed by a mother centriole, or they might take longer to form if no centriole is present. It is clear that the assembly of centrioles de novo is inhibited by the presence of a single centriole. Recent large-scale functional genomics and proteomics analyses have revealed novel molecules that are involved in regulating centrosome function and biogenesis. Other studies indicate that certain molecules that inhibit the re-replication of DNA might also inhibit centriole reduplication, thereby linking chromosome and centrosome cycles. Centrosomes, which were first described in the late 19th century, are found in most animal cells and undergo duplication once every cell cycle so that their number remains stable, like the genetic material of a cell. However, their function and regulation have remained elusive and controversial. Only recently has some understanding of these fundamental aspects of centrosome function and biogenesis been gained through the concerted application of genomics and proteomics, which we term 'centrosomics'. The identification of new molecules has highlighted the evolutionary conservation of centrosome function and provided a conceptual framework for understanding centrosome behaviour and how it can go awry in human disease.

Barrett's esophagus is the major risk factor for esophageal adenocarcinoma. It has a low but non-neglectable risk, high surveillance costs and no reliable risk stratification markers. We sought to identify early biomarkers, predictive of Barrett's malignant progression, using a meta-analysis approach on gene expression data. This in silico strategy was followed by experimental validation in a cohort of patients with extended follow up from the Instituto Português de Oncologia de Lisboa de Francisco Gentil EPE (Portugal). Bioinformatics and systems biology approaches singled out two candidate predictive markers for Barrett's progression, CYR61 and TAZ. Although previously implicated in other malignancies and in epithelial-to-mesenchymal transition phenotypes, our experimental validation shows for the first time that CYR61 and TAZ have the potential to be predictive biomarkers for cancer progression. Experimental validation by reverse transcriptase quantitative PCR and immunohistochemistry confirmed the up-regulation of both genes in Barrett's samples associated with high-grade dysplasia/adenocarcinoma. In our cohort CYR61 and TAZ up-regulation ranged from one to ten years prior to progression to adenocarcinoma in Barrett's esophagus index samples. Finally, we found that CYR61 and TAZ over-expression is correlated with early focal signs of epithelial to mesenchymal transition. Our results highlight both CYR61 and TAZ genes as potential predictive biomarkers for stratification of the risk for development of adenocarcinoma and suggest a potential mechanistic route for Barrett's esophagus neoplastic progression.

Cilia are evolutionarily conserved structures with many sensory and motility-related functions. The ciliary base, composed of the basal body and the transition zone, is critical for cilia assembly and function, but its contribution to cilia diversity remains unknown. Hence, we generated a high-resolution structural and biochemical atlas of the ciliary base of four functionally distinct neuronal and sperm cilia types within an organism, Drosophila melanogaster . We uncovered a common scaffold and diverse structures associated with different localization of 15 evolutionarily conserved components. Furthermore, CEP290 (also known as NPHP6) is involved in the formation of highly diverse transition zone links. In addition, the cartwheel components SAS6 and ANA2 (also known as STIL) have an underappreciated role in basal body elongation, which depends on BLD10 (also known as CEP135). The differential expression of these cartwheel components contributes to diversity in basal body length. Our results offer a plausible explanation to how mutations in conserved ciliary base components lead to tissue-specific diseases. Using electron and three-dimensional structured illumination microscopy methods, Jana et al. characterize the ciliary base in four different cilia types in Drosophila , discovering structural and protein component differences that may be linked to the diversified functions of cilia.

Centrosomes are the major microtubule organising centres of animal cells. Deregulation in their number occurs in cancer and was shown to trigger tumorigenesis in mice. However, the incidence, consequence and origins of this abnormality are poorly understood. Here, we screened the NCI-60 panel of human cancer cell lines to systematically analyse centriole number and structure. Our screen shows that centriole amplification is widespread in cancer cell lines and highly prevalent in aggressive breast carcinomas. Moreover, we identify another recurrent feature of cancer cells: centriole size deregulation. Further experiments demonstrate that severe centriole over-elongation can promote amplification through both centriole fragmentation and ectopic procentriole formation. Furthermore, we show that overly long centrioles form over-active centrosomes that nucleate more microtubules, a known cause of invasiveness, and perturb chromosome segregation. Our screen establishes centriole amplification and size deregulation as recurrent features of cancer cells and identifies novel causes and consequences of those abnormalities. Cancer cells are characterised by abnormalities in the number of centrosomes and this phenotype is linked with tumorigenesis. Here the authors report centriole length deregulation in a subset of cancer cell lines and suggest a link with subsequent alterations in centriole numbers and chromosomal instability.

The Basal Body is the template for the axoneme, the internal scaffolding of cilia andflagella. Bettencourt‐Dias and colleagues comment on an article by DavidAgard's group, in which they characterize the structure of the basal body byelectron cryo‐tomography and reveal new clues into its biogenesis and function.