Centrosome amplification in tumorigenesis

Mitotic kinases are emerging therapeutic targets against metastatic breast cancer

This review aims to outline mitotic kinase inhibitors' roles as potential therapeutic targets and assess their suitability as a stand-alone clinical therapy or in combination with standard treatments for advanced-stage solid tumors, including triple-negative breast cancer (TNBC). Breast cancer poses a significant global health risk, with TNBC standing out as the most aggressive subtype. Comprehending the role of mitosis is crucial for understanding how TNBC advances from a solid tumor to metastasis. Chemotherapy is the primary treatment used to treat TNBC. Some types of chemotherapeutic agents target cells in mitosis, thus highlighting the need to comprehend the molecular mechanisms governing mitosis in cancer. This understanding is essential for devising targeted therapies to disrupt these mitotic processes, prevent or treat metastasis, and improve patient outcomes. Mitotic kinases like Aurora kinase A, Aurora Kinase B, never in mitosis gene A-related kinase 2, Threonine-Tyrosine kinase, and Polo-kinase 1 significantly impact cell cycle progression by contributing to chromosome separation and centrosome homeostasis. When these kinases go awry, they can trigger chromosome instability, increase cell proliferation, and activate different molecular pathways that culminate in a transition from epithelial to mesenchymal cells. Ongoing clinical trials investigate various mitotic kinase inhibitors as potential biological treatments against advanced solid tumors. While clinical trials against mitotic kinases have shown some promise in the clinic, more investigation is necessary, since they induce severe adverse effects, particularly affecting the hematopoietic system.

Racgap1 knockdown results in cells with multiple cilia due to cytokinesis failure

Most mammalian cells have a single primary cilium that acts as a signalling hub in mediating cellular functions. However, little is known about the mechanisms that result in aberrant supernumerary primary cilia per cell. In this study, we re-analysed a previously published whole-genome siRNA-based reverse genetic screen for genes mediating ciliogenesis to identify knockdowns that permit multi-ciliation. We identified siRNA knockdowns that caused significant formation of supernumerary cilia, validated candidate hits in different cell-lines and confirmed that RACGAP1, a component of the centralspindlin complex, was the strongest candidate hit at the whole-genome level. Following loss of RACGAP1, mother centrioles were specified correctly prior to ciliogenesis and the cilia appeared normal. Live cell imaging revealed that increased cilia incidence was caused by cytokinesis failure which led to the formation of multinucleate cells with supernumerary cilia. This suggests that the signalling mechanisms for ciliogenesis are unable to identify supernumerary centrosomes and therefore allow ciliation of duplicated centrosomes as if they were in a new diploid daughter cell. These results, demonstrating that aberrant ciliogenesis is de-coupled from cell cycle regulation, have functional implications in diseases marked by centrosomal amplification.

Discovery of 2-(3-Benzamidopropanamido)thiazole-5-carboxylate Inhibitors of the Kinesin HSET (KIFC1) and the Development of Cellular Target Engagement Probes

The existence of multiple centrosomes in some cancer cells can lead to cell death through the formation of multipolar mitotic spindles and consequent aberrant cell division. Many cancer cells rely on HSET (KIFC1) to cluster the extra centrosomes into two groups to mimic the bipolar spindle formation of non-centrosome-amplified cells and ensure their survival. Here, we report the discovery of a novel 2-(3-benzamidopropanamido)thiazole-5-carboxylate with micromolar in vitro inhibition of HSET (KIFC1) through high-throughput screening and its progression to ATP-competitive compounds with nanomolar biochemical potency and high selectivity against the opposing mitotic kinesin Eg5. Induction of the multipolar phenotype was shown in centrosome-amplified human cancer cells treated with these inhibitors. In addition, a suitable linker position was identified to allow the synthesis of both fluorescent- and trans-cyclooctene (TCO)-tagged probes, which demonstrated direct compound binding to the HSET protein and confirmed target engagement in cells, through a click-chemistry approach.

Polo-like kinase 4 (Plk4) potentiates anoikis-resistance of p53KO mammary epithelial cells by inducing a hybrid EMT phenotype

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.

PLK4 Is a Potential Biomarker for Abnormal Tumor Proliferation, Immune Infiltration, and Prognosis in ccRCC

Background

PLK4 is highly expressed and associated with poor prognosis in various malignancies. However, the role of PLK4 in clear cell renal cell carcinoma (ccRCC) is still unclear. This study is aimed at analyzing the expression, the potential regulating mechanism, and the role of PLK4 in the ccRCC by bioinformatics.

Methods

PLK4 mRNA expression data and methylation levels in ccRCC were examined using TIMER, UALCAN, MethSurv, NCBI-GEO, and UCSC databases. Quantitative real-time PCR verifies the regulatory relationship between PLK4 and has-miR-214-3p. The GEPIA2 and STRING databases were used to find similar genes of PLK4 and then enriched with R language to analyze their similar genes. Correlations between PLK4 and tumor-infiltrating immune cells and cytokines exerting immunosuppression were analyzed using the TIMER database and the TISIDB databases.

Results

PLK4 mRNA expression levels were significantly higher in ccRCC tissues than in paracancerous tissues. ccRCC tissues had lower DNA methylation levels of PLK4 than normal tissues. Importantly, the high PLK4 expression was associated with poor prognosis in ccRCC patients. The has-miR-214-3p negatively regulates the expression of PLK4. GO and KEGG pathway analysis showed that PLK4 coexpressed genes were mainly associated with multiple immune-related pathways, including cytokinesis, sister chromatid adhesions, and mitotic nuclear division. Our data suggest that the PLK4 expression is closely related to the level of immune infiltration and the cytokines that exert immune suppression, and IPS was significantly higher in the PLK4 low expression group.

Conclusion

The PLK4 expression is associated with the prognosis of ccRCC patients and affects the immune microenvironment of ccRCC, and PLK4 is expected to be a new target for the diagnosis and treatment of ccRCC.

Effects of the PLK4 inhibitor Centrinone on the biological behaviors of acute myeloid leukemia cell lines

Polo-like kinase 4 (PLK4), a key regulator of centriole biogenesis, is frequently overexpressed in cancer cells. However, roles and the mechanism of PLK4 in the leukemiagenesis of acute myeloid leukemia (AML) remain unclear. In this study, the PLK4 inhibitor Centrinone and the shRNA knockdown were used to investigate roles and the mechanism of PLK4 in the leukemiagenesis of AML. Our results indicated that Centrinone inhibited the proliferation of AML cells in a dose- and time-dependent manner via reduced the expression of PLK4 both in the protein and mRNA levels. Moreover, colony formation assay revealed that Centrinone reduced the number and the size of the AML colonies. Centrinone induced AML cell apoptosis by increasing the activation of Caspase-3/poly ADP-ribose polymerase (PARP). Notably, Centrinone caused the G2/M phase cell cycle arrest by decreasing the expression of cell cycle-related proteins such as Cyclin A2, Cyclin B1, and Cyclin-dependent kinase 1 (CDK1). Consistent with above results, knockdown the expression of PLK4 also inhibited cell proliferation and colony formation, induced cell apoptosis, and caused G2/M phase cell cycle arrest without affecting cell differentiation. All in all, this study suggested that PLK4 inhibited the progression of AML in vitro, and these results herein may provide clues in roles of PLK4 in the leukemiagenesis of AML.

Fraxetin down-regulates polo-like kinase 4 (PLK4) to inhibit proliferation, migration and invasion of prostate cancer cells through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway

Fraxetin, a natural product isolated from herb Cortex Fraxini, has been demonstrated to exhibit anti-cancer effects on various cancers. The aim of this work is to investigate the anti-tumor effect of Fraxetin in prostate cancer and the potential mechanisms. In this study, the prostatic epithelial cell RWPE-1 and prostate cancer cell DU145 were exposed to Fraxetin (10, 20, 40, and 80 μM) to detect the changes in cell viability using cell counting kit-8 (CCK-8) assay. Fraxetin (10, 20, and 40 μM) was utilized to treat DU145 cell, then the changes in cell proliferation, apoptosis, migration, and invasion were assessed. Western blot assay was employed to detect the expression of proteins that participate in the above cellular processes as well as Polo-like kinase 4 (PLK4), phosphatidylinositol 3-kinase (PI3K). In addition to 40 μM Fraxetin treatment, DU145 cells were overexpressed with PLK4, and then the above experiments were repeated. Results revealed that Fraxetin markedly decreased DU145 cell viability, but didn’t affect the cell viability of RWPE-1. Fraxetin suppressed cell proliferation, migration, invasion, and induced apoptosis of DU145 cells in a concentration-dependent manner. Furthermore, the expression of PLK4 and phosphorylated PI3K and protein kinase B (Akt) were reduced upon Fraxetin treatment. Finally, PLK4 overexpression significantly reversed all the effects of Fraxetin on DU145 cells. Collectively, Fraxetin acted as a cancer suppressor in prostate cancer through inhibiting PLK4 expression thereby inactivating PI3K/Akt signaling.

Daughter centrioles assemble preferentially towards the nuclear envelope in Drosophila syncytial embryos

Centrosomes are important organizers of microtubules within animal cells. They comprise a pair of centrioles surrounded by the pericentriolar material, which nucleates and organizes the microtubules. To maintain centrosome numbers, centrioles must duplicate once and only once per cell cycle. During S-phase, a single new ‘daughter’ centriole is built orthogonally on one side of each radially symmetric ‘mother’ centriole. Mis-regulation of duplication can result in the simultaneous formation of multiple daughter centrioles around a single mother centriole, leading to centrosome amplification, a hallmark of cancer. It remains unclear how a single duplication site is established. It also remains unknown whether this site is pre-defined or randomly positioned around the mother centriole. Here, we show that within Drosophila syncytial embryos daughter centrioles preferentially assemble on the side of the mother facing the nuclear envelope, to which the centrosomes are closely attached. This positional preference is established early during duplication and remains stable throughout daughter centriole assembly, but is lost in centrosomes forced to lose their connection to the nuclear envelope. This shows that non-centrosomal cues influence centriole duplication and raises the possibility that these external cues could help establish a single duplication site.

Polymorphism in miRNA target sites of CEP-63 and CEP-152 ring complex influences expression of CEP genes and favors tumorigenesis in glioma

Purpose: The present study was designed to screen the genetic polymorphisms and expression profiling of CEP-152 and CEP-63 genes in brain tumor patients. Methods: The amplification refractory mutation system PCR technique (ARMS-PCR) was used for mutation analysis using 300 blood samples of brain tumor patients and 300 overtly healthy controls. For expression analysis, 150 brain tumor tissue samples along with adjacent uninvolved/normal tissues (controls) were collected. Results: A significantly higher frequency of the mutant genotype of the CEP-152 single nucleotide polymorphism (rs2169757) and CEP-63 single nucleotide polymorphisms (rs9809619 and rs13060247) was observed in patients versus overtly healthy controls. The authors' results showed highly significant deregulation of CEP-152 (p < 0.0001) and CEP-63 (p < 0.0001) in glioma/meningioma tumor tissues versus adjacent normal tissue. Conclusion: The present study showed that variations in CEP-152 and CEP-63 genes were associated with an increased risk of brain tumor.

Centrosome amplification: a quantifiable cancer cell trait with prognostic value in solid malignancies

Numerical and/or structural centrosome amplification (CA) is a hallmark of cancers that is often associated with the aberrant tumor karyotypes and poor clinical outcomes. Mechanistically, CA compromises mitotic fidelity and leads to chromosome instability (CIN), which underlies tumor initiation and progression. Recent technological advances in microscopy and image analysis platforms have enabled better-than-ever detection and quantification of centrosomal aberrancies in cancer. Numerous studies have thenceforth correlated the presence and the degree of CA with indicators of poor prognosis such as higher tumor grade and ability to recur and metastasize. We have pioneered a novel semi-automated pipeline that integrates immunofluorescence confocal microscopy with digital image analysis to yield a quantitative centrosome amplification score (CAS), which is a summation of the severity and frequency of structural and numerical centrosome aberrations in tumor samples. Recent studies in breast cancer show that CA increases across the disease progression continuum, while normal breast tissue exhibited the lowest CA, followed by cancer-adjacent apparently normal, ductal carcinoma in situ and invasive tumors, which showed the highest CA. This finding strengthens the notion that CA could be evolutionarily favored and can promote tumor progression and metastasis. In this review, we discuss the prevalence, extent, and severity of CA in various solid cancer types, the utility of quantifying amplified centrosomes as an independent prognostic marker. We also highlight the clinical feasibility of a CA-based risk score for predicting recurrence, metastasis, and overall prognosis in patients with solid cancers.

Resveratrol attenuates diabetes-associated cell centrosome amplification via inhibiting the PKCα-p38 to c-myc/c-jun pathway

Type 2 diabetes increases the risk for cancer. Centrosome amplification can initiate tumorigenesis. We have described that type 2 diabetes increases the centrosome amplification of peripheral blood mononuclear cells, with high glucose, insulin, and palmitic acid as the triggers, which suggests that centrosome amplification is a candidate biological mechanism linking diabetes to cancer. In this study, we aimed to further investigate the signaling pathways of the diabetes-associated centrosome amplification and to examine whether and how resveratrol inhibits the centrosome amplification. The results showed that treatment with high glucose, insulin, and palmitic acid, alone or in combination, could increase the protein levels of phospho-protein kinase C alpha (p-PKCα), phospho-p38 mitogen-activated protein kinases (p-p38), c-myc, and c-jun, as well as the mRNA levels of c-myc and c-jun. PKCα inhibitor could inhibit the treatment-induced increase in the protein levels of p-p38, c-myc, and c-jun. Inhibitor or siRNA of p38 was also able to inhibit the treatment-induced increase in the levels of p-p38, c-myc, and c-jun. Meanwhile, knockdown of c-myc or c-jun did not alter the treatment-induced increase in the phosphorylation of PKCα or p38. Importantly, inhibition of the phosphorylation of PKCα or p38 and knockdown of c-myc or c-jun could attenuate the centrosome amplification. In diabetic mice, the levels of p-PKCα, p-p38, c-myc, and c-jun were all increased in the colon tissues. Interestingly, resveratrol, but not metformin, was able to attenuate the treatment-induced increase in the levels of p-PKCα, p-p38, c-myc, and c-jun, as well as the centrosome amplification. In conclusion, our results suggest that PKCα-p38 to c-myc/c-jun is the signaling pathway of the diabetes-associated centrosome amplification, and resveratrol attenuates the centrosome amplification by inhibiting this signaling pathway.

Kinesin Family Member C1 (KIFC1) Accelerates Proliferation and Invasion of Endometrial Cancer Cells Through Modulating the PI3K/AKT Signaling Pathway

Endometrial cancer (EC) is one of the most common cancers among women worldwide. Kinesin family member C1 (KIFC1) has been demonstrated to play crucial roles in various tumors. However, the function of KIFC1 in EC remains to be revealed. In this study, upregulation of KIFC1 expression in human EC tissues was found from analysis on data from The Cancer Genome Atlas (TCGA), and positively correlated with short survival outcome of EC patients. In addition, the mRNA and protein levels of KIFC1 were confirmed to be up-regulated in EC cells (Ishikawa, HEC-1B, HEC-1A and KLE) compared to human normal endometrial stromal cells (hESCs) by quantitative real time PCR and western blot. In vitro functional experiments showed that overexpression of KIFC1 promoted proliferation, migration and invasion of EC cells, while KIFC1 depletion showed the opposite results. Moreover, KIFC1 knockdown suppressed tumor growth in mice. Further mechanism analysis showed that KIFC1 participated in the regulation of EC progression through regulating the PI3K/AKT signaling pathway. Collectively, KIFC1 promoted proliferation and invasion through modulating PI3K/AKT signaling pathway in EC, implying that KIFC1 might provide a promising therapeutic target for the therapy of EC.

Secreted Wnt6 mediates diabetes-associated centrosome amplification via its receptor FZD4

We recently published that type 2 diabetes promotes cell centrosome amplification via upregulation of Rho-associated protein kinase 1 (ROCK1) and 14-3-3 protein-σ (14-3-3σ). This study further investigates the molecular mechanisms underlying diabetes-associated centrosome amplification. We found that treatment of cells with high glucose, insulin, and palmitic acid levels increased the intracellular and extracellular protein levels of Wingless-type MMTV integration site family member 6 (Wnt6) as well as the cellular level of β-catenin. The treatment also activated β-catenin and promoted its nuclear translocation. Treatment of cells with siRNA species for Wnt6, Frizzled-4 (FZD4), or β-catenin as well as introduction of antibodies against Wnt6 or FZD4 to the cell culture medium could all attenuate the treatment-triggered centrosome amplification. Moreover, we showed that secreted Wnt6-FZD4-β-catenin was the signaling pathway that was upstream of ROCK1 and 14-3-3σ. We found that advanced glycation end products (AGEs) were also able to increase the cellular and extracellular levels of Wnt6, the cellular protein level of β-catenin, and centrosome amplification. Treatment of the cells with siRNA species for Wnt6 or FZD4 as well as introduction of antibodies against Wnt6 or FZD4 to the cell culture could all inhibit the AGEs-elicited centrosome amplification. In colon tissues from a diabetic mouse model, the protein levels of Wnt6 and 14-3-3σ were increased. In conclusion, our results showed that the pathophysiological factors in type 2 diabetes, including AGEs, were able to induce centrosome amplification. It is suggested that secreted Wnt6 binds to FZD4 to activate the canonical Wnt6 signaling pathway, which is upstream of ROCK1 and 14-3-3σ, and that this is the cell signaling pathway underlying diabetes-associated centrosome amplification.

PLK4: a promising target for cancer therapy

PURPOSE

Polo-like kinase 4 (PLK4) is a serine/threonine protein kinase that regulates centriole duplication. PLK4 deregulation causes centrosome number abnormalities, mitotic defects, chromosomal instability and, consequently, tumorigenesis. Therefore, PLK4 has emerged as a therapeutic target for the treatment of multiple cancers. In this review, we summarize the critical role of centrosome amplification and PLK4 in cancer. We also highlight recent advances in the development of PLK4 inhibitors and discuss potential combination therapies for cancer.

METHODS

The relevant literature from PubMed is reviewed in this article. The ClinicalTrials.gov database was searched for clinical trials related to the specific topic.

RESULTS

PLK4 is aberrantly expressed in multiple cancers and has prognostic value. Targeting PLK4 with inhibitors suppresses tumor growth in vitro and in vivo.

CONCLUSIONS

PLK4 plays an important role in centrosome amplification and tumor progression. PLK4 inhibitors used alone or in combination with other drugs have shown significant anticancer efficacy, suggesting a potential therapeutic strategy for cancer. The results of relevant clinical trials await evaluation.

NudC-like protein 2 restrains centriole amplification by stabilizing HERC2

Centriole duplication is tightly controlled to occur once per cell cycle, and disruption of this synchrony causes centriole amplification, which is frequently observed in many cancers. Our previous work showed that nuclear distribution gene C (NudC)-like protein 2 (NudCL2) localizes to centrosomes; however, little is known about the role of NudCL2 in the regulation of centrosome function. Here, we find that NudCL2 is required for accurate centriole duplication by stabilizing the E3 ligase HECT domain and RCC1-like domain-containing protein 2 (HERC2). Knockout (KO) of NudCL2 using CRISPR/Cas9-based genome editing or depletion of NudCL2 using small interfering RNA causes significant centriole amplification. Overexpression of NudCL2 significantly suppresses hydroxyurea-induced centriole overduplication. Quantitative proteomic analysis reveals that HERC2 is downregulated in NudCL2 KO cells. NudCL2 is shown to interact with and stabilize HERC2. Depletion of HERC2 leads to the similar defects to that in NudCL2-downregulated cells, and ectopic expression of HERC2 effectively rescues the centriole amplification caused by the loss of NudCL2, whereas the defects induced by HERC2 depletion cannot be reversed by exogenous expression of NudCL2. Either loss of NudCL2 or depletion of HERC2 leads to the accumulation of ubiquitin-specific peptidase 33 (USP33), a centrosomal protein that positively regulates centriole duplication. Moreover, knockdown of USP33 reverses centriole amplification in both NudCL2 KO and HERC2-depleted cells. Taken together, our data suggest that NudCL2 plays an important role in maintaining the fidelity of centriole duplication by stabilizing HERC2 to control USP33 protein levels, providing a previously undescribed mechanism restraining centriole amplification.

Chromosomal Instability in Tumor Initiation and Development

Chromosomal instability (CIN) is one of the major forms of genomic instability in various human cancers and is recognized as a common hallmark of tumorigenesis and heterogeneity. However, some malignant tumors show a paucity of chromosomal alterations, suggesting that tumor progression and evolution can occur in the absence of CIN. It is unclear whether CIN is stable between precursor lesions, primary tumor, and metastases or if it evolves during these steps. In this review, we describe the influence of CIN on the various steps in tumor initiation and development. Given the recognized significant effects of CIN in cancer, CIN-targeted therapeutics could have a major impact on improving clinical outcomes.

Tumor‑suppressive microRNA‑223 targets WDR62 directly in bladder cancer

miRNA‑223 (miR‑223) has been reported to function not only as a tumor suppressor, but also as an oncogenic microRNA (miRNA or miR) in various cancer cells. Therefore, the functional role of miR‑223 has not been elucidated to date, at least to the best of our knowledge. We previously performed the deep sequencing analysis of clinical bladder cancer (BC) specimens. It was revealed that miR‑223 expression was significantly downregulated in BC, suggesting that miR‑223 functions as a tumor suppressor miRNA in BC. The aim of this study was to investigate the functional roles of miR‑223 and to identify its targets in BC. The expression levels of miR‑223 were significantly decreased in our clinical BC specimens. The Cancer Genome Atlas (TCGA) database indicated that miR‑223 expression was related to lymphovascular invasion and distant metastasis. The restoration of miR‑223 expression significantly inhibited tumor aggressiveness and induced apoptosis via caspase‑3/7 activation in BC cells. WD repeat domain 62 (WDR62), a candidate target of miR‑223 according to in silico analyses, has been previously proposed to play a role in neurodevelopment. Direct binding between WDR62 and miR‑223 was confirmed by luciferase assay. The TCGA database revealed positive associations between WDR62 mRNA expression and a higher tumor grade and stage in BC. The knockdown of WDR62 significantly inhibited tumor aggressiveness and induced the apoptosis of BC cells. On the whole, the findings of this study reveal a novel miR‑223 target, oncogenic WDR62, and provided insight into the oncogenesis of BC.

DGAT1 Inhibitor Suppresses Prostate Tumor Growth and Migration by Regulating Intracellular Lipids and Non-Centrosomal MTOC Protein GM130

Acyl-CoA:diacylglycerol acyltransferase I (DGAT1) is a key enzyme in lipogenesis which is increased in metabolically active cells to meet nutrient requirements. DGAT1 has been recognized as an anti-obesity target; however, its role in the tumor microenvironment remains unclear. We postulated that, in prostate cancer (PCa) cells, augmented lipogenesis and growth are due to increased DGAT1 expression leading to microtubule-organizing center (MTOC) amplification. Thus, therapeutic targeting of DGAT1 potentially has tumor suppressive activity. We tested whether blocking DGAT1 in PCa cells altered MTOC and lipid signaling. Western blot and immunofluorescence were performed for MTOC and triglyceride mediators. Treatment with a DGAT1 inhibitor was evaluated. We found a stepwise increase in DGAT1 protein levels when comparing normal prostate epithelial cells to PCa cells, LNCaP and PC-3. Lipid droplets, MTOCs, and microtubule-regulating proteins were reduced in tumor cells treated with a DGAT1 inhibitor. Depletion of the non-centrosomal MTOC protein GM130 reduced PCa cell proliferation and migration. Inhibition of DGAT1 reduced tumor growth both in vitro and in vivo, and a negative feedback loop was discovered between DGAT1, PEDF, and GM130. These data identify DGAT1 as a promising new target for suppressing PCa growth by regulating GM130, MTOC number and disrupting microtubule integrity.

Increased Genetic Instability and Accelerated Progression of Colitis-Associated Colorectal Cancer through Intestinal Epithelium-specific Deletion of Klf4

Krüppel-like factor 4 (KLF4), a zinc finger transcription factor, regulates homeostasis of the intestinal epithelium. Previously, it was reported that KLF4 functions as a tumor suppressor in colorectal cancer. Here, evidence demonstrates that KLF4 mitigates the development and progression of colitis-associated colorectal cancer (CAC) in a murine model. Mice with intestinal epithelium-specific deletion of Klf4 (Klf4^ΔIS ) and control mice (Klf4^fl/fl ) were used to explore the role of KLF4 in the development of azoxymethane (AOM) and dextran sodium sulfate (DSS)-induced CAC. Upon AOM and DSS treatment, KLF4 expression was progressively lost in colonic tissues of Klf4^fl/fl mice during tumor development. Klf4^ΔIS mice treated with AOM/DSS developed significantly more adenomatous polyps and carcinomas in situ in comparison with treated Klf4^fl/fl mice. Adenomatous polyps, but not normal-appearing mucosa, from colonic tissues of treated Klf4^ΔIS mice contained a significantly increased number of mitotic cells with more than 2 centrosomes relative to treated control mice. KLF4 and p53 colocalize to the centrosomes in mouse embryonic fibroblasts (MEF). Absence of KLF4 in Klf4^-/- MEFs inhibits and its overexpression restores p53 localization to the centrosomes in Klf4^-/- MEFs. IMPLICATIONS: Taken together, these results indicate that KLF4 plays a protective role against progression of CAC by guarding against genetic instability.

Chromosomal instability in first trimester miscarriage: a common cause of pregnancy loss?

BACKGROUND

First trimester miscarriage without underlying medical conditions is most commonly caused by chromosomal abnormalities reported to occur in 50% or more of cases. These chromosomal changes in early losses include both numerical abnormalities and structural alterations that result in gain and/or loss of genetic information. Structural alterations are much less common than numerical changes. Jumping translocations (JTs) are considered extremely rare with only four cases previously reported.

METHODS

We report 12 examples of chromosome instability seen in the fetal material of spontaneous first trimester miscarriages in a single study population.

RESULTS

In these examples, we observed different cell lines with related chromosomal alterations. Some may be considered to be JT, where a single donor site was observed with different recipients. Others involved more than one site on the "donor" chromosome. One reported miscarriage involved multiple aneuploidy. All alterations resulted in partial trisomies and monosomies which predisposed the pregnancy to chromosomal imbalance and subsequent demise. Patient demographic data did not indicate possible causes of the errors observed.

CONCLUSIONS

This is the first report of such a large cohort and is believed to be the result of increased knowledge and depth of analysis in this area, rather than a representation of confounding factors in this population. It is therefore proposed that identifying these chromosomal changes must be incorporated into the system of testing within the clinical environment. We must also recognize that some routine laboratory techniques will fail to detect such genetic changes.

KIFC1, a novel potential prognostic factor and therapeutic target in hepatocellular carcinoma

Kinesin family member C1 (KIFC1, also known as HSET) is a minus end-directed motor protein, which is critical in centrosome clustering. The present study investigated the expression of KIFC1 in paired hepatocellular carcinoma (HCC) tissues and adjacent non-cancerous tissues from 91 patients by immunohistochemical analysis; clinical data were concomitantly collected. KIFC1 was expressed at high levels in HCC tissues, compared with that in peritumoral tissues (54.9 vs. 14.3%; P<0.01), and its expression correlated with tumor emboli, metastasis, recurrence and time of recurrence. Kaplan-Meier analysis showed that the expression of KIFC1 was significantly associated with tumor-free survival rates. In addition, multivariate analyses revealed that the overexpression of KIFC1was an independent predictive marker in patients with HCC. Consistently, data derived from GEPIA was in agreement with the results. In vitro, KIFC1 knockdown effectively decreased HCC cell viability, and induced apoptosis and cell death. KIFC1 knockdown also significantly suppressed tumor cell migration and invasion in vitro. Mechanistically, the apoptosis-related protein, B-cell lymphoma-2 (Bcl-2), was downregulated in KIFC1 small interfering RNA-treated groups, whereas thee levels of Bcl-2-associated X protein and p53 were upregulated. In addition, the expression levels of phosphorylated phosphoinositide 3-kinase and phosphorylated AKT were decreased significantly when KIFC1 was silenced. The epithelial-mesenchymal transition-related proteins, N-cadherin, matrix metalloproteinase-2 (MMP-2), β-catenin, Slug, and Zinc finger E-box-binding homeobox 1, were downregulated, whereas the expression of E-cadherin was upregulated. The overexpression of KIFC1 was correlated closely with the progression of HCC and poor prognosis, and suggested that the expression levels of KIFC1 are a potential prognostic biomarker and therapeutic target in HCC.

Prevention effect of rare ginsenosides against stress-hormone induced MTOC amplification

Stress has been suggested as one of important cause of human cancer without molecular biological evidence. Thus, we test the effect of stress-related hormones on cell viability and mitotic fidelity. Similarly to estrogen, stress hormone cortisol and its relative cortisone increase microtubule organizing center (MTOC) number through elevated expression of γ-tubulin and provide the Taxol resistance to human cancer cell lines. However, these effects are achieved by glucocorticoid hormone receptor (GR) but not by estrogen receptor (ER). Since ginsenosides possess steroid-like structure, we hypothesized that it would block the stress or estrogen-induced MTOC amplification and Taxol resistance. Among tested chemicals, rare ginsenoside, CSH1 (Rg6) shows obvious effect on inhibition of MTOC amplification, γ-tubulin induction and Taxol resistance. Comparing to Fulvestant (FST), ER-α specific inhibitor, this chemical can block the cortisol/cortisone-induced MTOC deregulation as well as ER-α signaling. Our results suggest that stress hormone induced tumorigenesis would be achieved by MTOC amplification, and CSH1 would be useful for prevention of stress-hormone or steroid hormone-induced chromosomal instability.

The E2F activators control multiple mitotic regulators and maintain genomic integrity through Sgo1 and BubR1

The E2F1, E2F2, and E2F3a transcriptional activators control proliferation. However, how the E2F activators regulate mitosis to maintain genomic integrity is unclear. Centrosome amplification (CA) and unregulated spindle assembly checkpoint (SAC) are major generators of aneuploidy and chromosome instability (CIN) in cancer. Previously, we showed that overexpression of single E2F activators induced CA and CIN in mammary epithelial cells, and here we show that combined overexpression of E2F activators did not enhance CA. Instead, the E2F activators elevated expression of multiple mitotic regulators, including Sgo1, Nek2, Hec1, BubR1, and Mps1/TTK. cBioPortal analyses of the TCGA database showed that E2F overexpression in lobular invasive breast tumors correlates with overexpression of multiple regulators of chromosome segregation, centrosome homeostasis, and the SAC. Kaplan-Meier plots identified correlations between individual or combined overexpression of E2F1, E2F3a, Mps1/TTK, Nek2, BubR1, or Hec1 and poor overall and relapse-free survival of breast cancer patients. In MCF10A normal mammary epithelial cells co-overexpressing E2Fs, transient Sgo1 knockdown induced CA, high percentages of premature sister chromatid separation, chromosome losses, increased apoptosis, and decreased cell clonogenicity. BubR1 silencing resulted in chromosome losses without CA, demonstrating that Sgo1 and BubR1 maintain genomic integrity through two distinct mechanisms. Our results suggest that deregulated activation of the E2Fs in mammary epithelial cells is counteracted by activation of a Sgo1-dependent mitotic checkpoint.

Centrosome amplification: a suspect in breast cancer and racial disparities

The multifaceted involvement of centrosome amplification (CA) in tumorigenesis is coming into focus following years of meticulous experimentation, which have elucidated the powerful abilities of CA to promote cellular invasion, disrupt stem cell division, drive chromosomal instability (CIN) and perturb tissue architecture, activities that can accelerate tumor progression. Integration of the extant in vitro, in vivo and clinical data suggests that in some tissues CA may be a tumor-initiating event, in others a consequential 'hit' in multistep tumorigenesis, and in some others, non-tumorigenic. However, in vivo data are limited and primarily focus on PLK4 (which has CA-independent mechanisms by which it promotes aggressive cellular phenotypes). In vitro breast cancer models suggest that CA can promote tumorigenesis in breast cancer cells in the setting of p53 loss or mutation, which can both trigger CA and promote cellular tolerance to its tendency to slow proliferation and induce aneuploidy. It is thus our perspective that CA is likely an early hit in multistep breast tumorigenesis that may sometimes be lost to preserve aggressive karyotypes acquired through centrosome clustering-mediated CIN, both numerical and structural. We also envision that the robust link between p53 and CA may underlie, to a considerable degree, racial health disparity in breast cancer outcomes. This question is clinically significant because, if it is true, then analysis of centrosomal profiles and administration of centrosome declustering drugs could prove highly efficacious in risk stratifying breast cancers and treating African American (AA) women with breast cancer.

Excess centrosomes induce p53-dependent senescence without DNA damage in endothelial cells

Tumor blood vessels support tumor growth and progression. Centrosomes are microtubule organization centers in cells, and often up to 30% of tumor endothelial cells (ECs) acquire excess (>2) centrosomes. Although excess centrosomes can lead to aneuploidy and chromosome instability in tumor cells, how untransformed ECs respond to excess centrosomes is poorly understood. We found that the frequency of primary human ECs with excess centrosomes was quickly reduced in a p53-dependent manner. Excess centrosomes in ECs were associated with p53 phosphorylation at Ser33, increased p21 levels, and decreased cell proliferation and expression of senescence markers, but independent of DNA damage and apoptosis. Aspects of the senescence-associated phenotype were also observed in mouse ECs that were isolated from tumors with excess centrosomes. Primary ECs with excess centrosomes in vascular sprouts also had elevated Ser33 p53 phosphorylation and expressed senescence markers. Our work demonstrates that nontransformed ECs respond differently to excess centrosomes than do most tumor cells-they undergo senescence in vascular sprouts and vessels, which suggests that pathologic outcomes of centrosome overduplication depend on the transformation status of cells.-Yu, Z., Ruter, D. L., Kushner, E. J., Bautch, V. L. Excess centrosomes induce p53-dependent senescence without DNA damage in endothelial cells.

Dysregulation of mitotic machinery genes precedes genome instability during spontaneous pre-malignant transformation of mouse ovarian surface epithelial cells

Background

Based in epidemiological evidence, repetitive ovulation has been proposed to play a role in the origin of ovarian cancer by inducing an aberrant wound rupture-repair process of the ovarian surface epithelium (OSE). Accordingly, long term cultures of isolated OSE cells undergo in vitro spontaneous transformation thus developing tumorigenic capacity upon extensive subcultivation. In this work, C57BL/6 mouse OSE (MOSE) cells were cultured up to passage 28 and their RNA and DNA copy number profiles obtained at passages 2, 5, 7, 10, 14, 18, 23, 25 and 28 by means of DNA microarrays. Gene ontology, pathway and network analyses were focused in passages earlier than 20, which is a hallmark of malignancy in this model.

Results

At passage 14, 101 genes were up-regulated in absence of significant DNA copy number changes. Among these, the top-3 enriched functions (>30 fold, adj p < 0.05) comprised 7 genes coding for centralspindlin, chromosome passenger and minichromosome maintenance protein complexes. The genes Ccnb1 (Cyclin B1), Birc5 (Survivin), Nusap1 and Kif23 were the most recurrent in over a dozen GO terms related to the mitotic process. On the other hand, Pten plus the large non-coding RNAs Malat1 and Neat1 were among the 80 down-regulated genes with mRNA processing, nuclear bodies, ER-stress response and tumor suppression as relevant terms. Interestingly, the earliest discrete segmental aneuploidies arose by passage 18 in chromosomes 7, 10, 11, 13, 15, 17 and 19. By passage 23, when MOSE cells express the malignant phenotype, the dysregulated gene expression repertoire expanded, DNA imbalances enlarged in size and covered additional loci.

Conclusion

Prior to early aneuploidies, overexpression of genes coding for the mitotic apparatus in passage-14 pre-malignant MOSE cells indicate an increased proliferation rate suggestive of replicative stress. Concomitant down-regulation of nuclear bodies and RNA processing related genes suggests altered control of nuclear RNA maturation, features recently linked to impaired DNA damage response leading to genome instability. These results, combined with cytogenetic analysis by other authors in this model, suggest that transcriptional profile at passage 14 might induce cytokinesis failure by which tetraploid cells approach a near-tetraploid stage containing primary chromosome aberrations that initiate the tumorigenic drive.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3068-5) contains supplementary material, which is available to authorized users.

Gamma-actin is involved in regulating centrosome function and mitotic progression in cancer cells

Reorganization of the actin cytoskeleton during mitosis is crucial for regulating cell division. A functional role for γ-actin in mitotic arrest induced by the microtubule-targeted agent, paclitaxel, has recently been demonstrated. We hypothesized that γ-actin plays a role in mitosis. Herein, we investigated the effect of γ-actin in mitosis and demonstrated that γ-actin is important in the distribution of β-actin and formation of actin-rich retraction fibers during mitosis. The reduced ability of paclitaxel to induce mitotic arrest as a result of γ-actin depletion was replicated with a range of mitotic inhibitors, suggesting that γ-actin loss reduces the ability of broad classes of anti-mitotic agents to induce mitotic arrest. In addition, partial depletion of γ-actin enhanced centrosome amplification in cancer cells and caused a significant delay in prometaphase/metaphase. This prolonged prometaphase/metaphase arrest was due to mitotic defects such as uncongressed and missegregated chromosomes, and correlated with an increased presence of mitotic spindle abnormalities in the γ-actin depleted cells. Collectively, these results demonstrate a previously unknown role for γ-actin in regulating centrosome function, chromosome alignment and maintenance of mitotic spindle integrity.

Polymorphisms of the centrosomal gene (FGFR1OP) and lung cancer risk: a meta-analysis of 14,463 cases and 44,188 controls

Centrosome abnormalities are often observed in premalignant lesions and in situ tumors and have been associated with aneuploidy and tumor development. We investigated the associations of 9354 single-nucleotide polymorphisms (SNPs) in 106 centrosomal genes with lung cancer risk by first using the summary data from six published genome-wide association studies (GWASs) of the Transdisciplinary Research in Cancer of the Lung (TRICL) (12,160 cases and 16 838 controls) and then conducted in silico replication in two additional independent lung cancer GWASs of Harvard University (984 cases and 970 controls) and deCODE (1319 cases and 26,380 controls). A total of 44 significant SNPs with false discovery rate (FDR) ≤ 0.05 were mapped to one novel gene FGFR1OP and two previously reported genes (TUBB and BRCA2). After combined the results from TRICL with those from Harvard and deCODE, the most significant association (P combined = 8.032 × 10(-6)) was with rs151606 within FGFR1OP. The rs151606 T>G was associated with an increased risk of lung cancer [odds ratio (OR) = 1.10, 95% confidence interval (95% CI) = 1.05-1.14]. Another significant tagSNP rs12212247 T>C (P combined = 9.589 × 10(-6)) was associated with a decreased risk of lung cancer (OR = 0.93, 95% CI = 0.90-0.96). Further in silico functional analyzes revealed that rs151606 might affect transcriptional regulation and result in decreased FGFR1OP expression (P trend = 0.022). The findings shed some new light on the role of centrosome abnormalities in the susceptibility to lung carcinogenesis.

Loss of KLF14 triggers centrosome amplification and tumorigenesis

Centrosome amplification is frequent in cancer, but the underlying mechanisms remain unclear. Here we report that disruption of the Kruppel-like factor 14 (KLF14) gene in mice causes centrosome amplification, aneuploidy and spontaneous tumorigenesis. Molecularly, KLF14 functions as a transcriptional repressor of Plk4, a polo-like kinase whose overexpression induces centrosome overduplication. Transient knockdown of KLF14 is sufficient to induce Plk4-directed centrosome amplification. Clinically, KLF14 transcription is significantly downregulated, whereas Plk4 transcription is upregulated in multiple types of cancers, and there exists an inverse correlation between KLF14 and Plk4 protein expression in human breast and colon cancers. Moreover, KLF14 depletion promotes AOM/DSS-induced colon tumorigenesis. Our findings reveal that KLF14 reduction serves as a mechanism leading to centrosome amplification and tumorigenesis. On the other hand, forced expression of KLF14 leads to mitotic catastrophe. Collectively, our findings identify KLF14 as a tumour suppressor and highlight its potential as biomarker and therapeutic target for cancer.

Truncation of POC1A associated with short stature and extreme insulin resistance

We describe a female proband with primordial dwarfism, skeletal dysplasia, facial dysmorphism, extreme dyslipidaemic insulin resistance and fatty liver associated with a novel homozygous frameshift mutation in POC1A, predicted to affect two of the three protein products of the gene. POC1A encodes a protein associated with centrioles throughout the cell cycle and implicated in both mitotic spindle and primary ciliary function. Three homozygous mutations affecting all isoforms of POC1A have recently been implicated in a similar syndrome of primordial dwarfism, although no detailed metabolic phenotypes were described. Primary cells from the proband we describe exhibited increased centrosome amplification and multipolar spindle formation during mitosis, but showed normal DNA content, arguing against mitotic skipping, cleavage failure or cell fusion. Despite evidence of increased DNA damage in cells with supernumerary centrosomes, no aneuploidy was detected. Extensive centrosome clustering both at mitotic spindles and in primary cilia mitigated the consequences of centrosome amplification, and primary ciliary formation was normal. Although further metabolic studies of patients with POC1A mutations are warranted, we suggest that POC1A may be added to ALMS1 and PCNT as examples of centrosomal or pericentriolar proteins whose dysfunction leads to extreme dyslipidaemic insulin resistance. Further investigation of links between these molecular defects and adipose tissue dysfunction is likely to yield insights into mechanisms of adipose tissue maintenance and regeneration that are critical to metabolic health.

Building a ninefold symmetrical barrel: structural dissections of centriole assembly

Centrioles are short microtubule-based organelles with a conserved ninefold symmetry. They are essential for both centrosome formation and cilium biogenesis in most eukaryotes. A core set of five centriolar proteins has been identified and their sequential recruitment to procentrioles has been established. However, structures at atomic resolution for most of the centriolar components were scarce, and the underlying molecular mechanisms for centriole assembly had been a mystery--until recently. In this review, I briefly summarize recent advancements in high-resolution structural characterization of the core centriolar components and discuss perspectives in the field.

Regulation of the centrosome cycle

The centrosome, consisting of mother and daughter centrioles surrounded by the pericentriolar matrix (PCM), functions primarily as a microtubule organizing center (MTOC) in most animal cells. In dividing cells the centrosome duplicates once per cell cycle and its number and structure are highly regulated during each cell cycle to organize an effective bipolar spindle in the mitotic phase. Defects in the regulation of centrosome duplication lead to a variety of human diseases, including cancer, through abnormal cell division and inappropriate chromosome segregation. At the end of mitosis the daughter centriole disengages from the mother centriole. This centriole disengagement is an important licensing step for centrosome duplication. In S phase, one new daughter centriole forms perpendicular to each centriole. The centrosome recruits further PCM proteins in the late G2 phase and the two centrosomes separate at mitotic entry to form a bipolar spindle. Here, we summarize research findings in the field of centrosome biology, focusing on the mechanisms of regulation of the centrosome cycle in human cells.

KIFC1 is a novel potential therapeutic target for breast cancer

Kinesin-like protein KIFC1, a normally nonessential kinesin motor, plays a critical role in centrosome clustering in cancer cells and is essential for the survival of cancer cells. Herein, we reported that KIFC1 expression is up-regulated in breast cancer, particularly in estrogen receptor negative, progesterone receptor negative and triple negative breast cancer, and is not associated with epidermal growth factor receptor 2 status. In addition, KIFC1 is highly expressed in all 8 tested human breast cancer cell lines, but is absent in normal human mammary epithelial cells and weakly expressed in 2 human lung fibroblast lines. Moreover, KIFC1 silencing significantly reduced breast cancer cell viability. Finally, we found that PJ34, a potent small molecule inhibitor of poly(ADP-ribose) polymerase, suppressed KIFC1 expression and induced multipolar spindle formation in breast cancer cells, and inhibited cell viability and colony formation within the same concentration range, suggesting that KIFC1 suppression by PJ34 contributes to its anti-breast cancer activity. Together, these results suggest that KIFC1 is a novel promising therapeutic target for breast cancer.

Induction of centrosome amplification by formaldehyde, but not hydroquinone, in human lymphoblastoid TK6 cells

Benzene and formaldehyde (FA) are important industrial chemicals and environmental pollutants that cause leukemia by inducing DNA damage and chromosome aberrations in hematopoietic stem cells (HSC), the target cells for leukemia. Our previous studies showed that workers exposed to benzene and FA exhibit increased levels of aneuploidy in their blood cells. As centrosome amplification is a common phenomenon in human cancers, including leukemia, and is associated with aneuploidy in carcinogenesis, we hypothesized that benzene and FA would induce centrosome amplification in vitro. We treated human lymphoblastoid TK6 cells with a range of concentrations of hydroquinone (HQ, a benzene metabolite) or FA for 24 h, allowed the cells to recover in fresh medium for 24 h, and examined centrosome amplification; chromosomal gain, loss, and breakage; and cytotoxicity. We included melphalan and etoposide, chemotherapeutic drugs that cause therapy-related acute myeloid leukemia and that have been shown to induce centrosome amplification as well as chromosomal aneuploidy and breakage, as positive controls. Melphalan and etoposide induced centrosome amplification and chromosome gain and breakage in a dose-dependent manner, at cytotoxic concentrations. HQ, though cytotoxic, did not induce centrosome amplification or any chromosomal aberration. FA-induced centrosome amplification and cytotoxicity, but did not induce chromosomal aberrations. Our data suggest, for the first time, that centrosome amplification is a potential mechanism underlying FA-induced leukemogenesis, but not benzene-induced leukemogenesis, as mediated through HQ. Future studies are needed to delineate the mechanisms of centrosome amplification and its association with DNA damage, chromosomal aneuploidy and carcinogenesis, following exposure to FA.

Cep70 regulates microtubule stability by interacting with HDAC6

Microtubules, highly dynamic components of the cytoskeleton, are involved in mitosis, cell migration and intracellular trafficking. Our previous work has shown that the centrosomal protein Cep70 regulates microtubule organization and mitotic spindle orientation in mammalian cells. However, it remains elusive whether Cep70 is implicated in microtubule stability. Here we demonstrate that Cep70 enhances microtubule resistance to cold or nocodazole treatment. Our data further show that Cep70 promotes microtubule stability by regulating tubulin acetylation, and plays an important role in stabilizing microtubules. Mechanistic studies reveal that Cep70 interacts and colocalizes with histone deacetylase 6 (HDAC6) in the cytoplasm. These findings suggest that Cep70 promotes microtubule stability by interaction with HDAC6 and regulation of tubulin acetylation.

The molecular pathogenesis of colorectal cancer and its potential application to colorectal cancer screening

INTRODUCTION

Advances in our understanding of the molecular genetics and epigenetics of colorectal cancer have led to novel insights into the pathogenesis of this common cancer. These advances have revealed that there are molecular subtypes of colon polyps and colon cancer and that these molecular subclasses have unique and discrete clinical and pathological features. Although the molecular characterization of these subgroups of colorectal polyps and cancer is only partially understood at this time, it does appear likely that classifying colon polyps and cancers based on their genomic instability and/or epigenomic instability status will eventually be useful for informing approaches for the prevention and early detection of colon polyps and colorectal cancer.

CONCLUSIONS

In this review, we will discuss our current understanding of the molecular pathogenesis of the polyp to cancer sequence and the potential to use this information to direct screening and prevention programs.

Role of chromosomal aberrations in clonal diversity and progression of acute myeloid leukemia

Genetic abnormalities are a hallmark of cancer. Hereby, cytogenetic aberrations and small-scale abnormalities, such as single-nucleotide variations and insertion/deletion mutations, have emerged as two alternative modes of genetic diversification. Both mechanisms are at work in acute myeloid leukemia (AML), in which conventional karyotyping and molecular studies demonstrate that gene mutations occur predominantly in cytogenetically normal AML, whereas chromosomal changes are a driving force of development and progression of disease in aberrant karyotype AML. All steps of disease evolution in AML, ranging from the transformation of preleukemic clones into overt leukemia to the expansion and recurrence of malignant clones, are paralleled by clonal evolution at either the gene mutation or chromosome aberration level. Preleukemic conditions, such as Fanconi anemia and Bloom syndrome, demonstrate that the acquisition of chromosomal aberrations can contribute to leukemic transformation. Similar to what has been shown at the mutational level, expansion and recurrence of AML clones goes along with increasing genetic diversification. Hereby, cytogenetically more evolved subclones are at a proliferative advantage and outgrow ancestor clones or have evolved toward a more aggressive behavior with additional newly acquired aberrations as compared with the initial leukemic clone, respectively.

Causes of Chromosomal Instability

The majority of human cancer cells are highly aneuploid harboring chromosome numbers deviating from the modal number of 46. In cancer, aneuploidy is a consequence of an increased rate of whole chromosome missegregation during mitosis, a process known as chromosomal instability (CIN). In fact, CIN is a hallmark of human cancer and is thought to contribute to tumorigenesis, tumor progression, and the development of therapy resistance by providing a high genetic variability that might foster rapid adaptation processes. However, the molecular mechanisms that cause chromosome missegregation in cancer cells are still poorly understood. So far, several mechanisms underlying CIN have been proposed and some of them are indeed detectable in human cancer cells exhibiting CIN. Examples include, for instance, weakened spindle checkpoint signaling, supernumerary centrosomes, defects in chromatid cohesion, abnormal kinetochore-microtubule attachments and increased spindle microtubule dynamics. Here, the mechanisms leading to CIN in human cancer cells are summarized.

Structure of the C. elegans ZYG-1 cryptic polo box suggests a conserved mechanism for centriolar docking of Plk4 kinases

Plk4 family kinases control centriole assembly. Plk4s target mother centrioles through an interaction between their cryptic polo box (CPB) and acidic regions in the centriolar receptors SPD-2/Cep192 and/or Asterless/Cep152. Here, we report a crystal structure for the CPB of C. elegans ZYG-1, which forms a Z-shaped dimer containing an intermolecular β sheet with an extended basic surface patch. Biochemical and in vivo analysis revealed that electrostatic interactions dock the ZYG-1 CPB basic patch onto the SPD-2-derived acidic region to promote ZYG-1 targeting and new centriole assembly. Analysis of a different crystal form of the Drosophila Plk4 (DmPlk4) CPB suggests that it also forms a Z-shaped dimer. Comparison of the ZYG-1 and DmPlk4 CPBs revealed structural changes in the ZYG-1 CPB that confer selectivity for binding SPD-2 over Asterless-derived acidic regions. Overall, our findings suggest a conserved mechanism for centriolar docking of Plk4 homologs that initiate daughter centriole assembly.

Mitochondrial genome regulates mitotic fidelity by maintaining centrosomal homeostasis

Centrosomes direct spindle morphogenesis to assemble a bipolar mitotic apparatus to enable error-free chromosome segregation and preclude chromosomal instability (CIN). Amplified centrosomes, a hallmark of cancer cells, set the stage for CIN, which underlies malignant transformation and evolution of aggressive phenotypes. Several studies report CIN and a tumorigenic and/or aggressive transformation in mitochondrial DNA (mtDNA)-depleted cells. Although several nuclear-encoded proteins are implicated in centrosome duplication and spindle organization, the involvement of mtDNA encoded proteins in centrosome amplification (CA) remains elusive. Here we show that disruption of mitochondrial function by depletion of mtDNA induces robust CA and mitotic aberrations in osteosarcoma cells. We found that overexpression of Aurora A, Polo-like kinase 4 (PLK4), and Cyclin E was associated with emergence of amplified centrosomes. Supernumerary centrosomes in rho0 (mtDNA-depleted) cells resulted in multipolar mitoses bearing "real" centrosomes with paired centrioles at the multiple poles. This abnormal phenotype was recapitulated by inhibition of respiratory complex I in parental cells, suggesting a role for electron transport chain (ETC) in maintaining numeral centrosomal homeostasis. Furthermore, rho0 cells displayed a decreased proliferative capacity owing to a G 2/M arrest. Downregulation of nuclear-encoded p53 in rho0 cells underscores the importance of mitochondrial and nuclear genome crosstalk and may perhaps underlie the observed mitotic aberrations. By contrast, repletion of wild-type mtDNA in rho0 cells (cybrid) demonstrated a much lesser extent of CA and spindle multipolarity, suggesting partial restoration of centrosomal homeostasis. Our study provides compelling evidence to implicate the role of mitochondria in regulation of centrosome duplication, spindle architecture, and spindle pole integrity.

STK31 is a cell-cycle regulated protein that contributes to the tumorigenicity of epithelial cancer cells

Serine/threonine kinase 31 (STK31) is one of the novel cancer/testis antigens for which its biological functions remain largely unclear. Here, we demonstrate that STK31 is overexpressed in many human colorectal cancer cell lines and tissues. STK31 co-localizes with pericentrin in the centrosomal region throughout all phases of the cell cycle. Interestingly, when cells undergo mitosis, STK31 also localizes to the centromeres, central spindle, and midbody. This localization behavior is similar to that of chromosomal passenger proteins, which are known to be the important players of the spindle assembly checkpoint. The expression of STK31 is cell cycle-dependent through the regulation of a putative D-box near its C-terminal region. Ectopically-expressed STK31-GFP increases cell migration and invasive ability without altering the proliferation rate of cancer cells, whereas the knockdown expression of endogenous STK31 by lentivirus-derived shRNA results in microtubule assembly defects that prolong the duration of mitosis and lead to apoptosis. Taken together, our results suggest that the aberrant expression of STK31 contributes to tumorigenicity in somatic cancer cells. STK31 might therefore act as a potential therapeutic target in human somatic cancers.

RRM1 maintains centrosomal integrity via CHK1 and CDK1 signaling during replication stress

DNA lesion-induced centrosomal abnormalities during the replication phase are relatively unknown. Here, we report that RNAi-mediated depletion of RRM1 induces cell-cycle arrest at the replication phase, along with severe DNA damage and centrosomal amplification. Interestingly, CHK1 depletion synergistically increased RRM1-depletion-induced centrosomal amplification. In response to hydroxyurea, CHK1 was delocalized from the centrosome by RRM1 depletion. Moreover, CDK1, which functions in centrosome separation and is inhibited by CHK1, was found to be essential for RRMI1-depletion-induced centrosomal amplification. Thus, we herein demonstrate that RRM1 preserves chromosomal stability via the CHK1- and CDK1-dependent stabilization of the centrosomal integrity at the replication stage.

BRCA1 and FancJ cooperatively promote interstrand crosslinker induced centrosome amplification through the activation of polo-like kinase 1

DNA damage response (DDR) and the centrosome cycle are 2 of the most critical cellular processes affecting the genome stability in animal cells. Yet the cross-talks between DDR and the centrosome are poorly understood. Here we showed that deficiency of the breast cancer 1, early onset gene (BRCA1) induces centrosome amplification in non-stressed cells as previously reported while attenuating DNA damage-induced centrosome amplification (DDICA) in cells experiencing prolonged genotoxic stress. Mechanistically, the function of BRCA1 in promoting DDICA is through binding and recruiting polo-like kinase 1 (PLK1) to the centrosome. In a recent study, we showed that FancJ also suppresses centrosome amplification in non-stressed cells while promoting DDICA in both hydroxyurea and mitomycin C treated cells. FancJ is a key component of the BRCA1 B-complex. Here, we further demonstrated that, in coordination with BRCA1, FancJ promotes DDICA by recruiting both BRCA1 and PLK1 to the centrosome in the DNA damaged cells. Thus, we have uncovered a novel role of BRCA1 and FancJ in the regulation of DDICA. Dysregulation of DDR or centrosome cycle leads to aneuploidy, which is frequently seen in both solid and hematological cancers. BRCA1 and FancJ are known tumor suppressors and have well-recognized functions in DNA damage checkpoint and DNA repair. Together with our recent findings, we demonstrated here that BRCA1 and FancJ also play an important role in centrosome cycle especially in DDICA. DDICA is thought to be an alternative fail-safe mechanism to prevent cells experiencing severe DNA damage from becoming carcinogenic. Therefore, BRCA1 and FancJ are potential liaisons linking early DDR with the DDICA. We propose that together with their functions in DDR, the role of BRCA1 and FancJ in the activation of DDICA is also crucial for their tumor suppression functions in vivo.

The centrosomal adaptor TACC3 and the microtubule polymerase chTOG interact via defined C-terminal subdomains in an Aurora-A kinase-independent manner

The cancer-associated, centrosomal adaptor protein TACC3 (transforming acidic coiled-coil 3) and its direct effector, the microtubule polymerase chTOG (colonic and hepatic tumor overexpressed gene), play a crucial function in centrosome-driven mitotic spindle assembly. It is unclear how TACC3 interacts with chTOG. Here, we show that the C-terminal TACC domain of TACC3 and a C-terminal fragment adjacent to the TOG domains of chTOG mediate the interaction between these two proteins. Interestingly, the TACC domain consists of two functionally distinct subdomains, CC1 (amino acids (aa) 414-530) and CC2 (aa 530-630). Whereas CC1 is responsible for the interaction with chTOG, CC2 performs an intradomain interaction with the central repeat region of TACC3, thereby masking the TACC domain before effector binding. Contrary to previous findings, our data clearly demonstrate that Aurora-A kinase does not regulate TACC3-chTOG complex formation, indicating that Aurora-A solely functions as a recruitment factor for the TACC3-chTOG complex to centrosomes and proximal mitotic spindles. We identified with CC1 and CC2, two functionally diverse modules within the TACC domain of TACC3 that modulate and mediate, respectively, TACC3 interaction with chTOG required for spindle assembly and microtubule dynamics during mitotic cell division.

Discovery and mechanistic study of a small molecule inhibitor for motor protein KIFC1

Centrosome amplification is observed in many human cancers and has been proposed to be a driver of both genetic instability and tumorigenesis. Cancer cells have evolved mechanisms to bundle multiple centrosomes into two spindle poles to avoid multipolar mitosis that can lead to chromosomal segregation defects and eventually cell death. KIFC1, a kinesin-14 family protein, plays an essential role in centrosomal bundling in cancer cells, but its function is not required for normal diploid cell division, suggesting that KIFC1 is an attractive therapeutic target for human cancers. To this end, we have identified the first reported small molecule inhibitor AZ82 for KIFC1. AZ82 bound specifically to the KIFC1/microtubule (MT) binary complex and inhibited the MT-stimulated KIFC1 enzymatic activity in an ATP-competitive and MT-noncompetitive manner with a Ki of 0.043 μM. AZ82 effectively engaged with the minus end-directed KIFC1 motor inside cells to reverse the monopolar spindle phenotype induced by the inhibition of the plus end-directed kinesin Eg5. Treatment with AZ82 caused centrosome declustering in BT-549 breast cancer cells with amplified centrosomes. Consistent with genetic studies, our data confirmed that KIFC1 inhibition by a small molecule holds promise for targeting cancer cells with amplified centrosomes and provided evidence that functional suppression of KIFC1 by inhibiting its enzymatic activity could be an effective means for developing cancer therapeutics.

Antagonistic functional duality of cancer genes

Cancer evolution is a stochastic process both at the genome and gene levels. Most of tumors contain multiple genetic subclones, evolving in either succession or in parallel, either in a linear or branching manner, with heterogeneous genome and gene alterations, extensively rewired signaling networks, and addicted to multiple oncogenes easily switching with each other during cancer progression and medical intervention. Hundreds of discovered cancer genes are classified according to whether they function in a dominant (oncogenes) or recessive (tumor suppressor genes) manner in a cancer cell. However, there are many cancer "gene-chameleons", which behave distinctly in opposite way in the different experimental settings showing antagonistic duality. In contrast to the widely accepted view that mutant NADP(+)-dependent isocitrate dehydrogenases 1/2 (IDH1/2) and associated metabolite 2-hydroxyglutarate (R)-enantiomer are intrinsically "the drivers" of tumourigenesis, mutant IDH1/2 inhibited, promoted or had no effect on cell proliferation, growth and tumorigenicity in diverse experiments. Similar behavior was evidenced for dozens of cancer genes. Gene function is dependent on genetic network, which is defined by the genome context. The overall changes in karyotype can result in alterations of the role and function of the same genes and pathways. The diverse cell lines and tumor samples have been used in experiments for proving gene tumor promoting/suppressive activity. They all display heterogeneous individual karyotypes and disturbed signaling networks. Consequently, the effect and function of gene under investigation can be opposite and versatile in cells with different genomes that may explain antagonistic duality of cancer genes and the cell type- or the cellular genetic/context-dependent response to the same protein. Antagonistic duality of cancer genes might contribute to failure of chemotherapy. Instructive examples of unexpected activity of cancer genes and "paradoxical" effects of different anticancer drugs depending on the cellular genetic context/signaling network are discussed.

A double-edged sword: how oncogenes and tumor suppressor genes can contribute to chromosomal instability

Most solid tumors are characterized by abnormal chromosome numbers (aneuploidy) and karyotypic profiling has shown that the majority of these tumors are heterogeneous and chromosomally unstable. Chromosomal instability (CIN) is defined as persistent mis-segregation of whole chromosomes and is caused by defects during mitosis. Large-scale genome sequencing has failed to reveal frequent mutations of genes encoding proteins involved in mitosis. On the contrary, sequencing has revealed that most mutated genes in cancer fall into a limited number of core oncogenic signaling pathways that regulate the cell cycle, cell growth, and apoptosis. This led to the notion that the induction of oncogenic signaling is a separate event from the loss of mitotic fidelity, but a growing body of evidence suggests that oncogenic signaling can deregulate cell cycle progression, growth, and differentiation as well as cause CIN. These new results indicate that the induction of CIN can no longer be considered separately from the cancer-associated driver mutations. Here we review the primary causes of CIN in mitosis and discuss how the oncogenic activation of key signal transduction pathways contributes to the induction of CIN.

Cdk4 and nek2 signal binucleation and centrosome amplification in a her2+ breast cancer model

Centrosome amplification (CA) is a contributor to carcinogenesis, generating aneuploidy, and chromosome instability. Previous work shows that breast adenocarcinomas have a higher frequency of centrosome defects compared to normal breast tissues. Abnormal centrosome phenotypes are found in pre-malignant lesions, suggesting an early role in breast carcinogenesis. However, the role of CA in breast cancers remains elusive. Identification of pathways and regulatory molecules involved in the generation of CA is essential to understanding its role in breast tumorigenesis. We established a breast cancer model of CA using Her2-positive cells. Our goal was to identify centrosome cycle molecules that are deregulated by aberrant Her2 signaling and the mechanisms driving CA. Our results show some Her2+ breast cancer cell lines harbor both CA and binucleation. Abolishing the expression of Cdk4 abrogated both CA and binucleation in these cells. We also found the source of binucleation in these cells to be defective cytokinesis that is normalized by downregulation of Cdk4. Protein levels of Nek2 diminish upon Cdk4 knockdown and vice versa, suggesting a molecular connection between Cdk4 and Nek2. Knockdown of Nek2 reduces CA and binucleation in this model while its overexpression further enhances centrosome amplification. We conclude that CA is modulated through Cdk4 and Nek2 signaling and that binucleation is a likely source of CA in Her2+ breast cancer cells.