Inhibition of centrosome protein assembly leads to p53-dependent exit from the cell cycle

Proximity Mapping of CCP6 Reveals Its Association with Centrosome Organization and Cilium Assembly

The cytosolic carboxypeptidase 6 (CCP6) catalyzes the deglutamylation of polyglutamate side chains, a post-translational modification that affects proteins such as tubulins or nucleosome assembly proteins. CCP6 is involved in several cell processes, such as spermatogenesis, antiviral activity, embryonic development, and pathologies like renal adenocarcinoma. In the present work, the cellular role of CCP6 has been assessed by BioID, a proximity labeling approach for mapping physiologically relevant protein-protein interactions (PPIs) and bait proximal proteins by mass spectrometry. We used HEK 293 cells stably expressing CCP6-BirA* to identify 37 putative interactors of this enzyme. This list of CCP6 proximal proteins displayed enrichment of proteins associated with the centrosome and centriolar satellites, indicating that CCP6 could be present in the pericentriolar material. In addition, we identified cilium assembly-related proteins as putative interactors of CCP6. In addition, the CCP6 proximal partner list included five proteins associated with the Joubert syndrome, a ciliopathy linked to defects in polyglutamylation. Using the proximity ligation assay (PLA), we show that PCM1, PIBF1, and NudC are true CCP6 physical interactors. Therefore, the BioID methodology confirms the location and possible functional role of CCP6 in centrosomes and centrioles, as well as in the formation and maintenance of primary cilia.

The role of UXT in tumors and prospects for its application in hepatocellular carcinoma

UXT is widely expressed in human and mouse tissues and aberrantly expressed in various tumor tissues. UXT may play a pro-cancer or tumor suppressor role in different tumor types and microenvironments with different mechanisms of action. Studies have shown that UXT can interact with related receptors to exert its functions and affect tumor proliferation and metastasis, leading to a poor prognosis when the biological functions of these tumors are changed. Interestingly, the signaling pathways and mechanism-related molecules that interact with UXT are closely related to the occurrence of hepatocellular carcinoma (HCC) during disease progression. This article reviews the research progress of UXT and prospects for its application in HCC, with the aim of providing possible scientific suggestions for the basic research, diagnosis and treatment of HCC.

Microtubule affinity regulating kinase 4: A promising target in the pathogenesis of atherosclerosis

Microtubule affinity regulating kinase 4 (MARK4), an important member of the serine/threonine kinase family, regulates the phosphorylation of microtubule-associated proteins and thus modulates microtubule dynamics. In human atherosclerotic lesions, the expression of MARK4 is significantly increased. Recently, accumulating evidence suggests that MARK4 exerts a proatherogenic effect via regulation of lipid metabolism (cholesterol, fatty acid, and triglyceride), inflammation, cell cycle progression and proliferation, insulin signaling, and glucose homeostasis, white adipocyte browning, and oxidative stress. In this review, we summarize the latest findings regarding the role of MARK4 in the pathogenesis of atherosclerosis to provide a rationale for future investigation and therapeutic intervention.

Triple deletion of TP53, PCNT, and CEP215 promotes centriole amplification in the M phase

Supernumerary centrioles are frequently observed in diverse types of cancer cells. In this study, we investigated the mechanism underlying the generation of supernumerary centrioles during the M phase. We generated the TP53;PCNT;CEP215 triple knockout (KO) cells and determined the configurations of the centriole during the cell cycle. The triple KO cells exhibited a precocious separation of centrioles and unscheduled centriole assembly in the M phase. Supernumerary centrioles in the triple KO cells were present throughout the cell cycle; however, among all the centrioles, only two maintained an intact composition, including CEP135, CEP192, CEP295 and CEP152. Intact centrioles were formed during the S phase and the rest of the centrioles may be generated during the M phase. M-phase-assembled centrioles lacked the ability to organize microtubules in the interphase; however, a fraction of them may acquire pericentriolar material to organize microtubules during the M phase. Taken together, our work reveals the heterogeneity of the supernumerary centrioles in the triple KO cells.  .

Unraveling the mysteries of centriolar satellites: time to rewrite the textbooks about the centrosome/cilium complex

Centriolar satellites are membraneless granules that localize and move around centrosomes and cilia. Once referred to as structures with no obvious function, research in the past decade has identified satellites as key regulators of a wide range of cellular and organismal processes. Importantly, these studies have revealed a substantial overlap between functions, proteomes, and disease links of satellites with centrosomes and cilia. Therefore, satellites are now accepted as the “third component” of the vertebrate centrosome/cilium complex, which profoundly changes the way we think about the assembly, maintenance, and remodeling of the complex at the cellular and organismal levels. In this perspective, we first provide an overview of the cellular and structural complexities of centriolar satellites. We then describe the progress in the identification of the satellite interactome, which have paved the way to a molecular understanding of their mechanism of action and assembly mechanisms. After exploring current insights into their functions as recently described by loss-of-function studies and comparative evolutionary approaches, we discuss major unanswered questions regarding their functional and compositional diversity and their functions outside centrosomes and cilia.

Centrosome Dynamics and Its Role in Inflammatory Response and Metastatic Process

Metastasis is a process by which cancer cells escape from the location of the primary tumor invading normal tissues at distant organs. Chromosomal instability (CIN) is a hallmark of human cancer, associated with metastasis and therapeutic resistance. The centrosome plays a major role in organizing the microtubule cytoskeleton in animal cells regulating cellular architecture and cell division. Loss of centrosome integrity activates the p38-p53-p21 pathway, which results in cell-cycle arrest or senescence and acts as a cell-cycle checkpoint pathway. Structural and numerical centrosome abnormalities can lead to aneuploidy and CIN. New findings derived from studies on cancer and rare genetic disorders suggest that centrosome dysfunction alters the cellular microenvironment through Rho GTPases, p38, and JNK (c-Jun N-terminal Kinase)-dependent signaling in a way that is favorable for pro-invasive secretory phenotypes and aneuploidy tolerance. We here review recent data on how centrosomes act as complex molecular platforms for Rho GTPases and p38 MAPK (Mitogen activated kinase) signaling at the crossroads of CIN, cytoskeleton remodeling, and immune evasion via both cell-autonomous and non-autonomous mechanisms.

Centrosome-phagy: implications for human diseases

Autophagy is a prominent mechanism to preserve homeostasis and the response to intracellular or extracellular stress. Autophagic degradation can be selectively targeted to dysfunctional subcellular compartments. Centrosome homeostasis is pivotal for healthy proliferating cells, but centrosome aberration is a hallmark of diverse human disorders. Recently, a process called centrosome-phagy has been identified. The process involves a panel of centrosomal proteins and centrosome-related pathways that mediate the specific degradation of centrosomal components via the autophagic machinery. Although autophagy normally mediates centrosome homeostasis, autophagy defects facilitate ageing and multiple human diseases, such as ciliopathies and cancer, which benefit from centrosome aberration. Here, we discuss the molecular systems that trigger centrosome-phagy and its role in human disorders.

Targeted p21 activation by a new double stranded RNA suppresses human prostate cancer cells growth and metastasis

We have previously demonstrated that miR-1236-3p and its sequence homology dsRNA, dsRNA-245 (which is completely complementary to the p21 promoter) had potential ability to upregulate p21 expression by targeting specific promoter sequence and inhibited bladder cancer (BCa). However, we still know little about the effect of miR-1236-3p on prostate cancer and which dsRNA has an inhibitory effect on prostate cancer (PCa)? Here, we confirmed that miR-1236-3p was decreased in PCa cells and tissues. MiR-1236-3p inhibited PCa cells growth and metastasis by activating p21. Furthermore, we demonstrated that dsP21-245 could inhibit PCa cells growth and metastasis by activating p21 expression. Microarray experiments displayed that miR-1236-3p could affect AKT signaling pathway. We demonstrated that miR-1236-3p significantly suppressed the AKT pathway by inhibiting TLR2 expression while activating p21 expression in PCa cells; this influence was independent of p21 activation. In summary, our results provided evidence that both endogenous and exogenous small RNAs might function to induce p21 expression by interacting with the same promoter region, therefore impeding PCa development. Additionally, our results indicated that miRNA activation could activate the expression of some unknown genes as well as cell signaling pathways. This indicated the need for the further study of clinical applications of RNA activation.

Centrosome dysfunction: a link between senescence and tumor immunity

Centrosome aberrations are hallmarks of human cancers and contribute to the senescence process. Structural and numerical centrosome abnormalities trigger mitotic errors, cellular senescence, cell death, genomic instability and/or aneuploidy, resulting in human disorders such as aging and cancer and affecting immunity. Interestingly, centrosome dysfunction promotes the secretion of multiple inflammatory factors that act as pivotal drivers of senescence and tumor immune escape. In this review, we summarize the forms of centrosome dysfunction and further discuss recent advances indicating that centrosome defects contribute to acceleration of senescence progression and promotion of tumor cell immune evasion in different ways.

ANO9 Regulated Cell Cycle in Human Esophageal Squamous Cell Carcinoma

BACKGROUND

Few studies have reported the function and activation mechanism of ANO9 in esophageal squamous cell carcinoma (ESCC). The current study aimed to investigate the role of ANO9 in the regulation of tumor progression.

METHODS

Knockdown experiments with human ESCC cell lines were performed using ANO9 siRNA, and the effects on cell proliferation, the cell cycle, apoptosis, and cellular movement were analyzed. Immunohistochemistry (IHC) analysis was performed on 57 primary tumor samples obtained from ESCC patients.

RESULTS

In an in vitro study, depletion of ANO9 reduced cell proliferation, invasion, and migration in KYSE150 and KYSE 790 cells. In the cell cycle analysis, depletion of ANO9 increased the number of cells in G₀/G₁ arrest. In addition, the knockdown of ANO9 increased apoptosis. The results of the microarray analysis indicated that various centrosome-related genes such as CEP120, CNTRL, and SPAST were up- or downregulated in ANO9-depleted KYSE150 cells. The IHC results showed that high expression of ANO9 was associated with poor prognosis.

CONCLUSIONS

The results of the current study suggest that ANO9 regulates the cell cycle via centrosome-related genes in ESCC.

Silencing EPB41 Gene Expression Leads to Cell Cycle Arrest, Migration Inhibition, and Upregulation of Cell Surface Antigen in DC2.4 Cells

BACKGROUND Protein 4.1R (EPB41) is the main cytoskeleton component of the erythrocyte membrane and may be involved in cell migration and adhesion. Previous research discovered overexpression of 4.1R in the thymus of patients with myasthenia gravis (MG). The protein 4.1R on dendritic cells may play a pivotal role in MG pathogenesis. This research investigated the effects of small interfering RNA 4.1R-siRNA on cell migration, cell cycle, and surface antigen expression of DC2.4 mouse dendritic cells, thus providing a new direction for the study of MG pathogenesis. MATERIAL AND METHODS Three 4.1R-specific siRNAs were designed, and the expression of 4.1R was detected by real-time PCR at the mRNA level and Western blot analysis at the protein level to select out the most efficient siRNAs. Changes in cell morphology were observed and cell migration ability was analyzed by Transwell assay. Cell cycle and surface antigen were both analyzed by flow cytometry. RESULTS The cell bodies of DC2.4 diminished, the synapses were increased, and protuberance became more obvious after being transfected with 4.1R-siRNA. After knockdown of 4.1R, cell migration ability decreased and the proportion of cells in S phase significantly increased (both P<0.05). The expression levels of MHCII, CD80, and CD86 were all increased in DC2.4 cells (all <0.05). CONCLUSIONS Silencing the expression of 4.1R in dendritic cells resulted in inhibition of migration ability, cell cycle arrest, and increase in surface antigens, which suggest that 4.1R participates in MG autoimmunity.

p53 mitotic centrosome localization preserves centrosome integrity and works as sensor for the mitotic surveillance pathway

Centrosomal p53 has been described for three decades but its role is still unclear. We previously reported that, in proliferating human cells, p53 transiently moves to centrosomes at each mitosis. Such p53 mitotic centrosome localization (p53-MCL) occurs independently from DNA damage but requires ATM-mediated p53Ser15 phosphorylation (p53Ser15^P) on discrete cytoplasmic p53 foci that, through MT dynamics, move to centrosomes during the mitotic spindle formation. Here, we show that inhibition of p53-MCL, obtained by p53 depletion or selective impairment of p53 centrosomal localization, induces centrosome fragmentation in human nontransformed cells. In contrast, tumor cells or mouse cells tolerate p53 depletion, as expected, and p53-MCL inhibition. Such tumor- and species-specific behavior of centrosomal p53 resembles that of the recently identified sensor of centrosome-loss, whose activation triggers the mitotic surveillance pathway in human nontransformed cells but not in tumor cells or mouse cells. The mitotic surveillance pathway prevents the growth of human cells with increased chance of making mitotic errors and accumulating numeral chromosome defects. Thus, we evaluated whether p53-MCL could work as a centrosome-loss sensor and contribute to the activation of the mitotic surveillance pathway. We provide evidence that centrosome-loss triggered by PLK4 inhibition makes p53 orphan of its mitotic dock and promotes accumulation of discrete p53Ser15^P foci. These p53 foci are required for the recruitment of 53BP1, a key effector of the mitotic surveillance pathway. Consistently, cells from patients with constitutive impairment of p53-MCL, such as ATM- and PCNT-mutant carriers, accumulate numeral chromosome defects. These findings indicate that, in nontransformed human cells, centrosomal p53 contributes to safeguard genome integrity by working as sensor for the mitotic surveillance pathway.

Systematic characterization of germline variants from the DiscovEHR study endometrial carcinoma population

Background

Endometrial cancer (EMCA) is the fifth most common cancer among women in the world. Identification of potentially pathogenic germline variants from individuals with EMCA will help characterize genetic features that underlie the disease and potentially predispose individuals to its pathogenesis.

Methods

The Geisinger Health System’s (GHS) DiscovEHR cohort includes exome sequencing on over 50,000 consenting patients, 297 of whom have evidence of an EMCA diagnosis in their electronic health record. Here, rare variants were annotated as potentially pathogenic.

Results

Eight genes were identified as having increased burden in the EMCA cohort relative to the non-cancer control cohort. None of the eight genes had an increased burden in the other hormone related cancer cohort from GHS, suggesting they can help characterize the underlying genetic variation that gives rise to EMCA. Comparing GHS to the cancer genome atlas (TCGA) EMCA germline data illustrated 34 genes with potentially pathogenic variation and eight unique potentially pathogenic variants that were present in both studies. Thus, similar germline variation among genes can be observed in unique EMCA cohorts and could help prioritize genes to investigate for future work.

Conclusion

In summary, this systematic characterization of potentially pathogenic germline variants describes the genetic underpinnings of EMCA through the use of data from a single hospital system.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0504-9) contains supplementary material, which is available to authorized users.

Centriolar satellites are required for efficient ciliogenesis and ciliary content regulation

Centriolar satellites are ubiquitous in vertebrate cells. They have recently emerged as key regulators of centrosome/cilium biogenesis, and their mutations are linked to ciliopathies. However, their precise functions and mechanisms of action remain poorly understood. Here, we generated a kidney epithelial cell line (IMCD3) lacking satellites by CRISPR/Cas9-mediated PCM1 deletion and investigated the cellular and molecular consequences of satellite loss. Cells lacking satellites still formed full-length cilia but at significantly lower numbers, with changes in the centrosomal and cellular levels of key ciliogenesis factors. Using these cells, we identified new ciliary functions of satellites such as regulation of ciliary content, Hedgehog signaling, and epithelial cell organization in three-dimensional cultures. However, other functions of satellites, namely proliferation, cell cycle progression, and centriole duplication, were unaffected in these cells. Quantitative transcriptomic and proteomic profiling revealed that loss of satellites affects transcription scarcely, but significantly alters the proteome. Importantly, the centrosome proteome mostly remains unaltered in the cells lacking satellites. Together, our findings identify centriolar satellites as regulators of efficient cilium assembly and function and provide insight into disease mechanisms of ciliopathies.

Up-regulation of E-cadherin by saRNA inhibits the migration and invasion of renal carcinoma cells

Previous studies have reported that double stranded RNAs (dsRNAs) have a potent ability to induce gene expression by targeting its promoter in cancer cells, which is called RNA activation (RNAa). In the present study, we have identified that a candidate dsRNA (dsEcad-215) could stimulate E-cadherin mRNA and protein expression via RNAa in renal cell carcinoma (RCC). Because the expression level of E-cadherin was down-regulated in RCC tissues compared to adjacent non-tumor tissues, dsEcad-215 was subsequently transfected into the RCC cell lines ACHN and 786-O. Expectedly, our results indicated that transfection of dsEcad-215 readily inhibited cell migration and invasion. In addition, several critical EMT-promoting genes (ZEB-1 and Vimentin) were down-regulated, while the anti-EMT gene β-catenin was up-regulated both at the mRNA and protein levels after dsEcad-215 transfection, suggesting that an enhanced E-cadherin level by dsEcad-215 suppressed EMT to inhibit cell motility. Collectively, our findings provide a potential effective therapeutic strategy for RCC, and dsEcad-215 might act as an alternative anti-cancer metastasis drug.

Albatross/FBF1 contributes to both centriole duplication and centrosome separation

The centrosome is a small but important organelle that participates in centriole duplication, spindle formation, and ciliogenesis. Each event is regulated by key enzymatic reactions, but how these processes are integrated remains unknown. Recent studies have reported that ciliogenesis is controlled by distal appendage proteins such as FBF1, also known as Albatross. However, the precise role of Albatross in the centrosome cycle, including centriole duplication and centrosome separation, remains to be determined. Here, we report a novel function for Albatross at the proximal ends of centrioles. Using Albatross monospecific antibodies, full-length constructs, and siRNAs for rescue experiments, we found that Albatross mediates centriole duplication by recruiting HsSAS-6, a cartwheel protein of centrioles. Moreover, Albatross participates in centrosome separation during mitosis by recruiting Plk1 to residue S348 of Albatross after its phosphorylation. Taken together, our results show that Albatross is a novel protein that spatiotemporally integrates different aspects of centrosome function, namely ciliogenesis, centriole duplication, and centrosome separation.

γ-Tubulin⁻γ-Tubulin Interactions as the Basis for the Formation of a Meshwork

In cytoplasm, protein γ-tubulin joins with various γ-tubulin complex proteins (GCPs) to form a heterotetramer γ-tubulin small complex (γ-TuSC) that can grow into a ring-shaped structure called the γ-tubulin ring complex (γ-TuRC). Both γ-TuSC and γ-TuRC are required for microtubule nucleation. Recent knowledge on γ-tubulin with regard to its cellular functions beyond participation in its creation of microtubules suggests that this protein forms a cellular meshwork. The present review summarizes the recognized functions of γ-tubulin and aims to unite the current views on this protein.

γ-tubulin as a signal-transducing molecule and meshwork with therapeutic potential

Knowledge of γ-tubulin is increasing with regard to the cellular functions of this protein beyond its participation in microtubule nucleation. γ-Tubulin expression is altered in various malignancies, and changes in the TUBG1 gene have been found in patients suffering from brain malformations. This review recapitulates the known functions of γ-tubulin in cellular homeostasis and discusses the possible influence of the protein on disease development and cancer.

Functional analyses of Pericentrin and Syne-2 interaction in ciliogenesis

Pericentrin (Pcnt) is a multifunctional scaffold protein and mutations in the human PCNT gene are associated with several diseases, including ciliopathies. Pcnt plays a crucial role in ciliary development in olfactory receptor neurons, but its function in the photoreceptor-connecting cilium is unknown. We downregulated Pcnt in the retina ex vivo and in vivo via a virus-based RNA interference approach to study Pcnt function in photoreceptors. ShRNA-mediated knockdown of Pcnt impaired the development of the connecting cilium and the outer segment of photoreceptors, and caused a nuclear migration defect. In protein interaction screens, we found that the outer nuclear membrane protein Syne-2 (also known as Nesprin-2) is an interaction partner of Pcnt in photoreceptors. Syne-2 is important for positioning murine photoreceptor cell nuclei and for centrosomal migration during early ciliogenesis. CRISPR/Cas9-mediated knockout of Syne-2 in cell culture led to an overexpression and mislocalization of Pcnt and to ciliogenesis defects. Our findings suggest that the Pcnt-Syne-2 complex is important for ciliogenesis and outer segment formation during retinal development and plays a role in nuclear migration.

S-phase kinase-associated protein 2 impairs the inhibitory effects of miR-1236-3p on bladder tumors

We have previously demonstrated that miR-1236-3p has the robust ability to up-regulate p21 expression by targeting the p21 promoter, thus inhibiting bladder cancer progression. Microarray experiments displayed that miR-1236-3p significantly increased the expression of the oncogenic F-box protein S-phase kinase-associate protein 2 (Skp2) while activating p21 expression in bladder cancer cells. Here, we confirmed that Skp2 was over-expressed following transfection with miR-1236-3p. Further, we demonstrated that miR-1236-3p and its sequence homology dsRNA, dsRNA-245 (which is completely complementary to the p21 promoter), both are able to potently induce p21 expression. We found that dsRNA-245 did not induce changes in Skp2 expression, while miR-1236-3p could increase Skp2 expression; this influence was independent of p21 activation. Moreover, transfection of miR-1236-3p or dsRNA-245 into bladder cancer cells significantly inhibited cell proliferation and clonegenesis and induced cell cycle arrest mainly by regulating p21 expression. However, the growth inhibition caused by dsRNA-245 was more effective than that caused by miR-1236-3p. This difference in effect size is mainly related to the miR-1236-3p-induced expression of Skp2. In summary, our results provided evidence that both endogenous and exogenous small RNAs might function to induce p21 expression by interacting with the same promoter region, therefore impeding bladder cancer cell growth. Additionally, our results indicated that microRNA activation can activate the expression of some tumor suppressor genes as well as some oncogenes. This indicated the need for the further study of clinical applications of RNA activation.

Enhancing E-cadherin expression via promoter-targeted miR-373 suppresses bladder cancer cells growth and metastasis

Previous studies showed that miR-373 had the capacity to induce tumor suppressor gene E-cadherin expression in prostate cancer cells. However, whether miR-373 can activate the expression of E-cadherin in human bladder cancer (BCa) cells and inhibit cells remains to be elucidated. Here, we found that both miR-373 and E-cadherin were low expressed in BCa tissues and cell lines, and significantly correlated with tumor stage, grade, and lymph node metastasis. In addition, decreased E-cadherin expression or low expression of both miR-373 and E-cadherin is associated with poor overall survival in patients with BCa. Transfection of miR-373 into BCa cells readily activated E-cadherin expression by targeting promoter. Moreover, miR-373 exhibited robust capacity to inhibit cells proliferation, suppress migration and invasion by enhancing E-cadherin expression, and significantly suppress the growth of xenografts and metastasis in nude mice. Altogether, our findings indicate that miR-373 may as a tumor suppressor in BCa by activating E-cadherin expression.

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.

Chromosomal Instability as a Driver of Tumor Heterogeneity and Evolution

Large-scale, massively parallel sequencing of human cancer samples has revealed tremendous genetic heterogeneity within individual tumors. Indeed, tumors are composed of an admixture of diverse subpopulations-subclones-that vary in space and time. Here, we discuss a principal driver of clonal diversification in cancer known as chromosomal instability (CIN), which complements other modes of genetic diversification creating the multilayered genomic instability often seen in human cancer. Cancer cells have evolved to fine-tune chromosome missegregation rates to balance the acquisition of heterogeneity while preserving favorable genotypes, a dependence that can be exploited for a therapeutic benefit. We discuss how whole-genome doubling events accelerate clonal evolution in a subset of tumors by providing a viable path toward favorable near-triploid karyotypes and present evidence for CIN-induced clonal speciation that can overcome the dependence on truncal initiating events.

Centrosomes are multifunctional regulators of genome stability

The maintenance of genome stability is critical for proper cell function, and loss of this stability contributes to many human diseases and developmental disorders. Therefore, cells have evolved partially redundant mechanisms to monitor and protect the genome. One subcellular organelle implicated in the maintenance of genome stability is the centrosome, best known as the primary microtubule organizing center of most animal cells. Centrosomes serve many different roles throughout the cell cycle, and many of those roles, including mitotic spindle assembly, nucleation of the interphase microtubule array, DNA damage response, and efficient cell cycle progression, have been proposed to help maintain genome stability. As a result, the centrosome is itself a highly regulated entity. Here, we review evidence concerning the significance of the centrosome in promoting genome integrity. Recent advances permitting acute and persistent centrosome removal suggest we still have much to learn regarding the specific function and actual importance of centrosomes in different contexts, as well as how cells may compensate for centrosome dysfunction to maintain the integrity of the genome. Although many animal cells survive and proliferate in the absence of centrosomes, they do so aberrantly. Based on these and other studies, we conclude that centrosomes serve as critical, multifunctional organelles that promote genome stability.

PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma

Cellular senescence is a tumor suppressor mechanism where cells enter a permanent growth arrest following cellular stress. Oncogene-induced senescence (OIS) is induced in non-malignant cells following the expression of an oncogene or inactivation of a tumor suppressor. Previously, we have shown that protein kinase C iota (PKCι) depletion induces cellular senescence in glioblastoma cells in the absence of a detectable DNA damage response. Here we demonstrate that senescent glioblastoma cells exhibit an aberrant centrosome morphology. This was observed in basal levels of senescence, in p21-induced senescence, and in PKCι depletion-induced senescence. In addition, senescent glioblastoma cells are polyploid, Ki-67 negative and arrest at the G1/S checkpoint, as determined by expression of cell cycle regulatory proteins. These markers are all consistent with cells that have undergone mitotic slippage. Failure of the spindle assembly checkpoint to function properly can lead to mitotic slippage, resulting in the premature exit of mitotic cells into the G1 phase of the cell cycle. Although in G1, these cells have the replicated DNA and centrosomal phenotype of a cell that has entered mitosis and failed to divide. Overall, we demonstrate that PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma cells. To our knowledge, this is the first evidence of markers of mitotic slippage directly in senescent cells by co-staining for senescence-associated β-galactosidase and immunofluorescence markers in the same cell population. We suggest that markers of mitotic slippage be assessed in future studies of senescence to determine the extent of mitotic slippage in the induction of cellular senescence.

BRCA2 mediates centrosome cohesion via an interaction with cytoplasmic dynein

BRCA2 is responsible for familial breast and ovarian cancer and has been linked to DNA repair and centrosome duplication. Here we analyzed the mechanism by which the centrosomal localization signal (CLS) of BRCA2 interacts with cytoplasmic dynein 1 to localize BRCA2 to the centrosome. In vitro pull-down assays demonstrated that BRCA2 directly binds to the cytoplasmic dynein 1 light intermediate chain 2. A dominant-negative HA-CLS-DsRed fusion protein, the depletion of dynein by siRNA, and the inactivation of dynein by EHNA, inhibited the localization of BRCA2 at centrosomes and caused the separation of centrosome pairs during the S-phase. The double depletion of BRCA2 and C-Nap1 caused a larger dispersion of centrosome distances than the silencing of C-Nap1. These results suggest that cytoplasmic dynein 1 binds to BRCA2 through the latter's CLS and BRCA2 mediates the cohesion between centrosomes during the S phase, potentially serving as a cell-cycle checkpoint.

Targeted p53 activation by saRNA suppresses human bladder cancer cells growth and metastasis

BACKGROUND

Previous study showed that dsP53-285 has the capacity to induce tumor suppressor gene p53 expression by targeting promoter in non-human primates' cells. And it is well known that TP53 gene is frequently mutant or inactivated in human bladder cancer. Hereby, whether this small RNA can activate the expression of wild-type p53 and inhibit human bladder cancer cells remains to be elucidated.

METHODS

Oligonucleotide and lentivirus were used to overexpress dsP53-285 and dsControl. Real-time PCR and western blot were used to detect genes' mRNA and protein expression, respectively. Cell proliferation assay, colony formation, flow cytometry, transwell assay and wound healing assay were performed to determine the effects on bladder cancer cells proliferation and migration/invasion in vitro. Animal models were carried out to analyze the effects on cells growth and metastasis in vivo.

RESULTS

Transfection of dsP53-285 into human bladder cancer cell lines T24 and EJ readily activate wild-type p53 expression by targeting promoter. Moreover, dsP53-285 exhibited robust capacity to inhibit cells proliferation and colony formation, induce cells G0/G1 arrest, suppress migration and invasion. Besides, the Cyclin-CDK genes (Cyclin D1 and CDK4/6) were down-regulated and the EMT-associated genes (E-cadherin, β-catenin, ZEB1 and Vimentin) were also expressed inversely after dsP53-285 treatment. In addition, dsP53-285 could also significantly suppress the growth of bladder cancer xenografts and metastasis in nude mice. Most importantly, the anti-tumor effects mediated by dsP53-285 were mainly achieved by manipulating wild-type p53 expression.

CONCLUSION

Our findings indicate that the dsP53-285 can upregulate wild-type p53 expression in human bladder cancer cells through RNA activation, and suppresses cells proliferation and metastasis in vitro and in vivo.

Centriole continuity: out with the new, in with the old

Centrioles are essential microtubule-based organelles, typically present in pairs, which organize cilia and centrosomes. Their mode of biogenesis is unique for a subcellular organelle since, during cell division, each pre-existing centriole guides the formation of a new one, a process that is coordinated with DNA replication. After centriole duplication, the new centrosomes migrate in opposite direction and localize at each pole of the mitotic spindle. This singular dynamics led to think that centrioles were permanent self-replicating structures coordinating cytoplasm and nuclear division. This vision then fell gradually into disuse when centrioles were shown to be capable to form de novo, in the absence of a pre-existing structure, and to be actually dispensable for cell division. However, new data, which are reviewed here, have breathed new life into the old ideas.

Overexpression of p53 activated by small activating RNA suppresses the growth of human prostate cancer cells

Previous research has reported that a particular double-stranded RNA, named dsP53-285, has the capacity to induce expression of the tumor suppressor gene TP53 in chimpanzee cells by targeting its promoter. Usually, it is the wild-type p53 protein, rather than mutants, which exhibits potent cancer-inhibiting effects. In addition, nonhuman primates, such as chimpanzees, share almost identical genome sequences with humans. This prompted us to speculate whether dsP53-285 can trigger wild-type p53 protein expression in human prostate cancer (PCa) cells and consequently suppress cell growth. The human PCa cell lines LNCaP and DU145 were transfected with dsP53-285 for 72 hours. Compared with the dsControl and mock transfection groups, expression of both p53 messenger RNA and p53 protein was significantly enhanced after dsP53-285 transfection, and this enhancement was followed by upregulation of p21, which indirectly indicated that dsP53-285 induced wild-type p53 expression. Moreover, overexpression of wild-type p53 mediated by dsP53-285 downregulated the expression of Cyclin D1 and cyclin-dependent kinase 4/6, thereby inducing PCa cell cycle arrest in G0/G1 phase and then inhibiting cell proliferation and clonogenicity. More importantly, dsP53-285 suppressed PCa cells mainly by modulating wild-type p53 expression. In conclusion, our study provides evidence that dsP53-285 can significantly stimulate wild-type p53 expression in the human PCa cell lines LNCaP and DU145 and can exert potent antitumor effects.

Developmental alterations in centrosome integrity contribute to the post-mitotic state of mammalian cardiomyocytes

Mammalian cardiomyocytes become post-mitotic shortly after birth. Understanding how this occurs is highly relevant to cardiac regenerative therapy. Yet, how cardiomyocytes achieve and maintain a post-mitotic state is unknown. Here, we show that cardiomyocyte centrosome integrity is lost shortly after birth. This is coupled with relocalization of various centrosome proteins to the nuclear envelope. Consequently, postnatal cardiomyocytes are unable to undergo ciliogenesis and the nuclear envelope adopts the function as cellular microtubule organizing center. Loss of centrosome integrity is associated with, and can promote, cardiomyocyte G0/G1 cell cycle arrest suggesting that centrosome disassembly is developmentally utilized to achieve the post-mitotic state in mammalian cardiomyocytes. Adult cardiomyocytes of zebrafish and newt, which are able to proliferate, maintain centrosome integrity. Collectively, our data provide a novel mechanism underlying the post-mitotic state of mammalian cardiomyocytes as well as a potential explanation for why zebrafish and newts, but not mammals, can regenerate their heart.

DOI:http://dx.doi.org/10.7554/eLife.05563.001

Muscle cells in the heart contract in regular rhythms to pump blood around the body. In humans, rats and other mammals, the vast majority of heart muscle cells lose the ability to divide shortly after birth. Therefore, the heart is unable to replace cells that are lost over the life of the individual, for example, during a heart attack. If too many of these cells are lost, the heart will be unable to pump effectively, which can lead to heart failure. Currently, the only treatment option in humans with heart failure is to perform a heart transplant.

Some animals, such as newts and zebrafish, are able to replace lost heart muscle cells throughout their lifetimes. Thus, these species are able to fully regenerate their hearts even after 20% has been removed. This suggests that it might be possible to manipulate human heart muscle cells to make them divide and regenerate the heart. Recent research has suggested that structures called centrosomes, known to be required to separate copies of the DNA during cell division, are used as a hub to integrate the initial signals that determine whether a cell should divide or not.

Here, Zebrowski et al. studied the centrosomes of heart muscle cells in rats, newts and zebrafish. The experiments show that the centrosomes in rat heart muscle cells are dissembled shortly after birth. Centrosomes are made of several proteins and, in the rat cells, these proteins moved to the membrane that surrounded the nucleus. On the other hand, the centrosomes in the heart muscle cells of the adult newts and zebrafish remained intact.

Further experiments found that that breaking apart the centrosomes of heart muscle cells taken from newborn rats stops these cells from dividing. Zebrowski et al.'s findings suggest that the loss of centrosomes after birth is a possible reason why the hearts of adult humans and other mammals are unable to regenerate after injury. In the future, these findings may aid the development of methods to regenerate human heart muscle and new treatments that may limit division of cancer cells.

DOI:http://dx.doi.org/10.7554/eLife.05563.002

Urokinase-type plasminogen activator receptor regulates apoptotic sensitivity of colon cancer HCT116 cell line to TRAIL via JNK-p53 pathway

The urokinase-type plasminogen activator receptor (uPAR) serves not only as an anchor for urokinase-type plasminogen activator but also participates in intracellular signal transduction events. In this study, we investigated whether uPAR could modulate TRAIL-induced apoptosis in human colon cancer cells HCT116. Using an antisense strategy, we established a stable HCT116 cell line with down-regulated uPAR. The sensitivity to TRAIL-induced apoptosis was evaluated by FACS analysis. Our results show that the inhibition of uPAR could sensitize HCT116 to TRAIL-induced apoptosis. uPAR inhibition changed the expression of mitochondrial apoptotic pathway proteins, including Bcl-2, Bax, Bid and p53, in a pro-apoptotic manner. We also found that the inhibition of uPAR down-regulated the phosphorylation of FAK, ERK and JNK. The inhibition of p53 by RNA interference rescued cells from enhanced apoptosis, thus indicating that p53 is critical for enhancing TRAIL-induced apoptosis. Furthermore, JNK, but not ERK, inhibition involved in the up-regulation of p53. JNK negatively regulated p53 protein level. Overall, our results show that uPAR inhibition can sensitize colon cancer cells HCT116 to TRAIL-induced apoptosis via active p53 and mitochondrial apoptotic pathways that JNK inhibition is involved.

Centrosomes as signalling centres

Centrosomes-as well as the related spindle pole bodies (SPBs) of yeast-have been extensively studied from the perspective of their microtubule-organizing roles. Moreover, the biogenesis and duplication of these organelles have been the subject of much attention, and the importance of centrosomes and the centriole-ciliary apparatus for human disease is well recognized. Much less developed is our understanding of another facet of centrosomes and SPBs, namely their possible role as signalling centres. Yet, many signalling components, including kinases and phosphatases, have been associated with centrosomes and spindle poles, giving rise to the hypothesis that these organelles might serve as hubs for the integration and coordination of signalling pathways. In this review, we discuss a number of selected studies that bear on this notion. We cover different processes (cell cycle control, development, DNA damage response) and organisms (yeast, invertebrates and vertebrates), but have made no attempt to be comprehensive. This field is still young and although the concept of centrosomes and SPBs as signalling centres is attractive, it remains primarily a concept-in need of further scrutiny. We hope that this review will stimulate thought and experimentation.

Suppression of centrosome protein TACC3 induces G1 arrest and cell death through activation of p38-p53-p21 stress signaling pathway

The centrosome regulates diverse cellular processes, including cell proliferation and differentiation. TACC3, a member of the human transforming acidic coiled-coil protein family, is a key centrosomal protein that is up-regulated in many cancers. Previous studies have demonstrated that TACC3 is essential for the survival of vertebrates and is involved in cell cycle regulation in human cells. However, the details of the underlying mechanisms in its cell cycle regulatory activity remain poorly understood. In this study, we showed that suppression of TACC3 expression induced G1 cell cycle arrest and triggered cell death in human cells. TACC3 depletion-induced G1 arrest and cell death were significantly reduced in cells either lacking p53 or with pharmacologically-inhibited p38, indicating that G1 arrest and cell death induction both require p53 and p38. TACC3 depletion up-regulated the levels of p53 and p21 and induced the accumulation of p53 both in the nucleus and at the centrosome. Interestingly, TACC3 depletion led to the activation of p38 and stimulated the recruitment of activated p38 to the centrosome. Depletion of TACC3 up-regulated the phosphorylation of p53 at Serine 33, a site known to be phosphorylated by p38 under cellular stress and further induced the accumulation of phosphorylated p53 to the centrosome. Loss of TACC3 affected centrosome integrity by disrupting the localization of components of the γ-tubulin ring complex at the centrosome. The results demonstrate that TACC3 depletion induces G1 arrest and cell death by activating p38-p53-p21 signaling and triggering a centrosome-mediated cellular stress response.

Centriolar satellites: key mediators of centrosome functions

Centriolar satellites are small, microscopically visible granules that cluster around centrosomes. These structures, which contain numerous proteins directly involved in centrosome maintenance, ciliogenesis, and neurogenesis, have traditionally been viewed as vehicles for protein trafficking towards the centrosome. However, the recent identification of several new centriolar satellite components suggests that this model offers only an incomplete picture of their cellular functions. While the mechanisms controlling centriolar satellite status and function are not yet understood in detail, emerging evidence points to these structures as important hubs for dynamic, multi-faceted regulation in response to a variety of cues. In this review, we summarize the current knowledge of the roles of centriolar satellites in regulating centrosome functions, ciliogenesis, and neurogenesis. We also highlight newly discovered regulatory mechanisms targeting centriolar satellites and their functional status, and we discuss how defects in centriolar satellite components are intimately linked to a wide spectrum of human diseases.

Small organelle, big responsibility: the role of centrosomes in development and disease

The centrosome, a key microtubule organizing centre, is composed of centrioles, embedded in a protein-rich matrix. Centrosomes control the internal spatial organization of somatic cells, and as such contribute to cell division, cell polarity and migration. Upon exiting the cell cycle, most cell types in the human body convert their centrioles into basal bodies, which drive the assembly of primary cilia, involved in sensing and signal transduction at the cell surface. Centrosomal genes are targeted by mutations in numerous human developmental disorders, ranging from diseases exclusively affecting brain development, through global growth failure syndromes to diverse pathologies associated with ciliary malfunction. Despite our much-improved understanding of centrosome function in cellular processes, we know remarkably little of its role in the organismal context, especially in mammals. In this review, we examine how centrosome dysfunction impacts on complex physiological processes and speculate on the challenges we face when applying knowledge generated from in vitro and in vivo model systems to human development.

Importance of the CEP215-pericentrin interaction for centrosome maturation during mitosis

At the onset of mitosis, the centrosome undergoes maturation, which is characterized by a drastic expansion of the pericentriolar material (PCM) and a robust increase in microtubule-organizing activity. CEP215 is one of the major PCM components which accumulates at the centrosome during mitosis. The depletion phenotypes indicate that CEP215 is essential for centrosome maturation and bipolar spindle formation. Here, we performed a series of knockdown-rescue experiments to link the protein-protein interaction properties of CEP215 to its biological functions. The results showed that CEP215 and pericentrin, another major PCM component, is interdependent for their accumulation at the spindle poles during mitosis. As a result, The CEP215-pericentrin interaction is required for centrosome maturation and subsequent bipolar spindle formation during mitosis. On the other hand, CEP215 interaction with γ-tubulin is dispensable for centrosome maturation. Our results provide an insight how PCM components are assembled to form a spindle pole during mitosis.

LGALS3BP regulates centriole biogenesis and centrosome hypertrophy in cancer cells

Centrosome morphology and number are frequently deregulated in cancer cells. Here, to identify factors that are functionally relevant for centrosome abnormalities in cancer cells, we established a protein-interaction network around 23 centrosomal and cell-cycle regulatory proteins, selecting the interacting proteins that are deregulated in cancer for further studies. One of these components, LGALS3BP, is a centriole- and basal body-associated protein with a dual role, triggering centrosome hypertrophy when overexpressed and causing accumulation of centriolar substructures when downregulated. The cancer cell line SK-BR-3 that overexpresses LGALS3BP exhibits hypertrophic centrosomes, whereas in seminoma tissues with low expression of LGALS3BP, supernumerary centriole-like structures are present. Centrosome hypertrophy is reversed by depleting LGALS3BP in cells endogenously overexpressing this protein, supporting a direct role in centrosome aberration. We propose that LGALS3BP suppresses assembly of centriolar substructures, and when depleted, causes accumulation of centriolar complexes comprising CPAP, acetylated tubulin and centrin.

Primary ciliogenesis requires the distal appendage component Cep123

Primary cilium formation is initiated at the distal end of the mother centriole in a highly co-ordinated manner. This requires the capping of the distal end of the mother centriole with a ciliary vesicle and the anchoring of the basal body (mother centriole) to the cell cortex, both of which are mediated by the distal appendages. Here, we show that the distal appendage protein Cep123 (Cep89/CCDC123) is required for the assembly, but not the maintenance, of a primary cilium. In the absence of Cep123 ciliary vesicle formation fails, suggesting that it functions in the early stages of primary ciliogenesis. Consistent with such a role, Cep123 interacts with the centriolar satellite proteins PCM-1, Cep290 and OFD1, all of which play a role in primary ciliogenesis. These interactions are mediated by a domain in the C-terminus of Cep123 (400-783) that overlaps the distal appendage-targeting domain (500-600). Together, the data implicate Cep123 as a new player in the primary ciliogenesis pathway and expand upon the role of the distal appendages in this process.

Promoter hijack reveals pericentrin functions in mitosis and the DNA damage response

Centrosomes, the principal microtubule-organizing centers of animal somatic cells, consist of two centrioles embedded in the pericentriolar material (PCM). Pericentrin is a large PCM protein that is required for normal PCM assembly. Mutations in PCNT cause primordial dwarfism. Pericentrin has also been implicated in the control of DNA damage responses. To test how pericentrin is involved in cell cycle control after genotoxic stress, we disrupted the Pcnt locus in chicken DT40 cells. Pericentrin-deficient cells proceeded through mitosis more slowly, with a high level of monopolar spindles, and were more sensitive to spindle poisons than controls. Centriole structures appeared normal by light and electron microscopy, but the PCM did not recruit γ-tubulin efficiently. Cell cycle delays after ionizing radiation (IR) treatment were normal in pericentrin-deficient cells. However, pericentrin disruption in Mcph1-/- cells abrogated centrosome hyperamplification after IR. We conclude that pericentrin controls genomic stability by both ensuring appropriate mitotic spindle activity and centrosome regulation.

The centrosomal protein Tax1 binding protein 2 is a novel tumor suppressor in hepatocellular carcinoma regulated by cyclin-dependent kinase 2

Deregulation of cellular-signaling pathways by the inactivation of tumor-suppressor genes is one of the major causes of hepatocellular carcinoma (HCC). In this study, we identified Tax1 binding protein 2 (TAX1BP2) as a novel tumor-suppressor gene in HCC. TAX1BP2 transcript was frequently underexpressed (42.2% with T/NT <0.5; P < 0.03) in HCCs, and underexpression of TAX1BP2 was associated with poorer overall survival rates in patients after surgical resection. An effector domain (ED) for TAX1BP2 tumor-suppressor activity was mapped to the amino-acid residues 267-756. Transient or stable expression of either full-length or ED of TAX1BP2 significantly suppressed HCC cell tumorigenicity through the activation of the p38/p53/p21 pathway. In contrast, silencing of TAX1BP2 by short interfering RNA remarkably suppressed the activation of the p38/p53/p21 pathway. Finally, phosphorylation of TAX1BP2 at serine-763 by cyclin-dependent kinase (CDK)2 abolished the TAX1BP2-mediated p38 activation and tumor-suppressive activity, indicating that TAX1BP2 can adapt CDK2 signaling to the p38/p53/p21 pathway.

CONCLUSION

Taken together, our data provide the first evidence that TAX1BP2 is a CDK2-regulated tumor-suppressor gene in HCC and is a novel activator of the p38/p53/p21 pathway.

γ-Tubulin plays a key role in inactivating APC/C(Cdh1) at the G(1)-S boundary

Failure to inactivate APC/C^CdhA at the G₁–S boundary of the cell cycle as a result of a γ-tubulin mutation that disrupts the APC/C^CdhA localization prevents cell cycle progression.

A γ-tubulin mutation in Aspergillus nidulans, mipA-D159, causes failure of inactivation of the anaphase-promoting complex/cyclosome (APC/C) in interphase, resulting in failure of cyclin B (CB) accumulation and removal of nuclei from the cell cycle. We have investigated the role of CdhA, the A. nidulans homologue of the APC/C activator protein Cdh1, in γ-tubulin–dependent inactivation of the APC/C. CdhA was not essential, but it targeted CB for destruction in G₁, and APC/C^CdhA had to be inactivated for the G₁–S transition. mipA-D159 altered the localization pattern of CdhA, and deletion of the gene encoding CdhA allowed CB to accumulate in all nuclei in strains carrying mipA-D159. These data indicate that mipA-D159 causes a failure of inactivation of APC/C^CdhA at G₁–S, perhaps by altering its localization to the spindle pole body, and, thus, that γ-tubulin plays an important role in inactivating APC/C^CdhA at this point in the cell cycle.

Centrosome loss or amplification does not dramatically perturb global gene expression in Drosophila

Centrosome defects are a common feature of many cancers, and they can predispose fly brain cells to form tumours. In flies, centrosome defects perturb the asymmetric division of the neural stem cells, but it is unclear how this might lead to malignant transformation. One possibility is that centrosome defects might also perturb cellular homeostasis: for example, stress pathways are often activated in response to centrosome defects in cultured cells, and stress contributes to tumourigenesis in some fly models. Here we attempt to assess whether centrosome loss or centrosome amplification perturbs cell physiology in vivo by profiling the global transcriptome of Drosophila larval brains and imaginal discs that either lack centrosomes or have too many centrosomes. Surprisingly, we find that centrosome loss or amplification leads to few changes in the transcriptional profile of these cells, indicating that centrosome defects are surprisingly well tolerated by these cells. These observations indicate that centrosome defects can predispose fly brain cells to form tumours without, at least initially, dramatically altering their physiology.

PLK1 phosphorylation of pericentrin initiates centrosome maturation at the onset of mitosis

The microtubule-organizing activity of the centrosome oscillates during the cell cycle, reaching its highest level at mitosis. At the onset of mitosis, the centrosome undergoes maturation, which is characterized by a drastic expansion of the pericentriolar matrix (PCM) and a robust increase in microtubule-organizing activity. It is known that PLK1 is critical for the initiation of centrosome maturation. In this paper, we report that pericentrin (PCNT), a PCM protein, was specifically phosphorylated by PLK1 during mitosis. Phosphoresistant point mutants of PCNT did not recruit centrosomal proteins, such as CEP192, GCP-WD (γ-complex protein with WD repeats), γ-tubulin, Aurora A, and PLK1, into the centrosome during mitosis. However, centrosomal recruitment of CEP215 depended on PCNT irrespective of its phosphorylation status. Furthermore, ectopic expression of PLK1-PCNT fusion proteins induced the centrosomal accumulation of CEP192, GCP-WD, and γ-tubulin even in interphase cells, mimicking centrosome maturation. Based on these results, we propose that PLK1-mediated phosphorylation of PCNT initiates centrosome maturation by organizing the spindle pole-specific PCM lattice.

A flow cytometry-based screen of nuclear envelope transmembrane proteins identifies NET4/Tmem53 as involved in stress-dependent cell cycle withdrawal

Disruption of cell cycle regulation is one mechanism proposed for how nuclear envelope protein mutation can cause disease. Thus far only a few nuclear envelope proteins have been tested/found to affect cell cycle progression: to identify others, 39 novel nuclear envelope transmembrane proteins were screened for their ability to alter flow cytometry cell cycle/DNA content profiles when exogenously expressed. Eight had notable effects with seven increasing and one decreasing the 4N∶2N ratio. We subsequently focused on NET4/Tmem53 that lost its effects in p53^−/− cells and retinoblastoma protein-deficient cells. NET4/TMEM53 knockdown by siRNA altered flow cytometry cell cycle/DNA content profiles in a similar way as overexpression. NET4/TMEM53 knockdown did not affect total retinoblastoma protein levels, unlike nuclear envelope-associated proteins Lamin A and LAP2α. However, a decrease in phosphorylated retinoblastoma protein was observed along with a doubling of p53 levels and a 7-fold increase in p21. Consequently cells withdrew from the cell cycle, which was confirmed in MRC5 cells by a drop in the percentage of cells expressing Ki-67 antigen and an increase in the number of cells stained for ß-galactosidase. The ß-galactosidase upregulation suggests that cells become prematurely senescent. Finally, the changes in retinoblastoma protein, p53, and p21 resulting from loss of NET4/Tmem53 were dependent upon active p38 MAP kinase. The finding that roughly a fifth of nuclear envelope transmembrane proteins screened yielded alterations in flow cytometry cell cycle/DNA content profiles suggests a much greater influence of the nuclear envelope on the cell cycle than is widely held.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Human NDR kinases control G(1)/S cell cycle transition by directly regulating p21 stability

The G(1) phase of the cell cycle is an important integrator of internal and external cues, allowing a cell to decide whether to proliferate, differentiate, or die. Multiple protein kinases, among them the cyclin-dependent kinases (Cdks), control G(1)-phase progression and S-phase entry. With the regulation of apoptosis, centrosome duplication, and mitotic chromosome alignment downstream of the HIPPO pathway components MST1 and MST2, mammalian NDR kinases have been implicated to function in cell cycle-dependent processes. Although they are well characterized in terms of biochemical regulation and upstream signaling pathways, signaling mechanisms downstream of mammalian NDR kinases remain largely unknown. We identify here a role for human NDR in regulating the G(1)/S transition. In G(1) phase, NDR kinases are activated by a third MST kinase (MST3). Significantly, interfering with NDR and MST3 kinase expression results in G(1) arrest and subsequent proliferation defects. Furthermore, we describe the first downstream signaling mechanisms by which NDR kinases regulate cell cycle progression. Our findings suggest that NDR kinases control protein stability of the cyclin-Cdk inhibitor protein p21 by direct phosphorylation. These findings establish a novel MST3-NDR-p21 axis as an important regulator of G(1)/S progression of mammalian cells.

SOCS1, a novel interaction partner of p53 controlling oncogene-induced senescence

Members of the signal transducers and activators of transcription (STATs) family of proteins, which connect cytokine signaling to activation of transcription, are frequently activated in human cancers. Suppressors of cytokine signaling (SOCS) are transcriptional targets of activated STAT proteins that negatively control STAT signaling. SOCS1 expression is silenced in multiple human cancers suggesting a tumor suppressor role for this protein. However, SOCS1 not only regulates STAT signaling but can also localize to the nucleus and directly interact with the p53 tumor suppressor through its central SH2 domain. Furthermore, SOCS1 contributes to p53 activation and phosphorylation on serine 15 by forming a ternary complex with ATM or ATR. Through this mechanism SOCS1 regulates the process of oncogene-induced senescence, which is a very important tumor suppressor response. A mutant SOCS1 lacking the SOCS box cannot interact with ATM/ATR, stimulate p53 or induce the senescence phenotype, suggesting that the SOCS box recruits DNA damage activated kinases to its interaction partners bound to its SH2 domain. Proteomic analysis of SOCS1 interaction partners revealed other potential targets of SOCS1 in the DNA damage response. These newly discovered functions of SOCS1 help to explain the increased susceptibility of Socs1 null mice to develop cancer as well as their propensity to develop autoimmune diseases. Consistently, we found that mice lacking SOCS1 displayed defects in the regulation of p53 target genes including Mdm2, Pmp22, PUMA and Gadd45a. The involvement of SOCS1 in p53 activation and the DNA damage response defines a novel tumor suppressor pathway and intervention point for future cancer therapeutics.

The centrosomal protein TACC3 controls paclitaxel sensitivity by modulating a premature senescence program

Microtubule-interfering cancer drugs such as paclitaxel (PTX) often cause chemoresistance and severe side effects, including neurotoxicity. To explore potentially novel antineoplastic molecular targets, we investigated the cellular response of breast carcinoma cells to short hairpin(sh)RNA-mediated depletion of the centrosomal protein transforming acidic coiled coil (TACC) 3, an Aurora A kinase target expressed during mitosis. Unlike PTX, knockdown of TACC3 did not trigger a cell death response, but instead resulted in a progressive loss of the pro-apoptotic Bcl-2 protein Bim that links microtubule integrity to spindle poison-induced cell death. Interestingly, TACC3-depleted cells arrested in G₁ through a cellular senescence program characterized by the upregulation of nuclear p21(WAF), downregulation of the retinoblastoma protein and extracellular signal-regulated kinase 1/2, formation of HP1γ (phospho-Ser83)-positive senescence-associated heterochromatic foci and increased senescence-associated β-galactosidase activity. Remarkably, the onset of senescence following TACC3 knockdown was strongly accelerated in the presence of non-toxic PTX concentrations. Thus, we conclude that mitotic spindle stress is a major trigger of premature senescence and propose that the combined targeting of the centrosomal Aurora A-TACC3 axis together with drugs interfering with microtubule dynamics may efficiently improve the chemosensitivity of cancer cells.

Control of ciliogenesis by FOR20, a novel centrosome and pericentriolar satellite protein

Cilia and flagella are evolutionary conserved organelles that generate fluid movement and locomotion, and play roles in chemosensation, mechanosensation and intracellular signalling. In complex organisms, cilia are highly diversified, which allows them to perform various functions; however, they retain a 9+0 or 9+2 microtubules structure connected to a basal body. Here, we describe FOR20 (FOP-related protein of 20 kDa), a previously uncharacterized and highly conserved protein that is required for normal formation of a primary cilium. FOR20 is found in PCM1-enriched pericentriolar satellites and centrosomes. FOR20 contains a Lis1-homology domain that promotes self-interaction and is required for its satellite localization. Inhibition of FOR20 expression in RPE1 cells decreases the percentage of ciliated cells and the length of the cilium on ciliated cells. It also modifies satellite distribution, as judged by PCM1 staining, and displaces PCM1 from a detergent-insoluble to a detergent-soluble fraction. The subcellular distribution of satellites is dependent on both microtubule integrity and molecular motor activities. Our results suggest that FOR20 could be involved in regulating the interaction of PCM1 satellites with microtubules and motors. The role of FOR20 in primary cilium formation could therefore be linked to its function in regulating pericentriolar satellites. A role for FOR20 at the basal body itself is also discussed.

CSPP is a ciliary protein interacting with Nephrocystin 8 and required for cilia formation

We described previously the cell cycle- and microtubule-related functions of two splice isoforms of the centrosome spindle pole-associated protein (CSPP and CSPP-L). Here, we show that endogenous CSPP isoforms not only localize to centrosomes and the midbody in cycling cells but also extend to the cilia axoneme in postmitotic resting cells. They are required for ciliogenesis in hTERT-RPE1 cells in vitro and are expressed in ciliated renal, retinal, and respiratory cells in vivo. We report that CSPP isoforms require their common C-terminal domain to interact with Nephrocystin 8 (NPHP8/RPGRIP1L) and to form a ternary complex with NPHP8 and NPHP4. We find CSPP-L to be required for the efficient localization of NPHP8 but not NPHP4 to the basal body. The ciliogenesis defect in hTERT-RPE1 cells is, however, not mediated through loss of NPHP8. Similar to the effects of ectopical expression of CSPP-L, cilia length increased in NPHP8-depleted cells. Our results thus suggest that CSPP proteins may be involved in further cytoskeletal organization of the basal body and its primary cilium. To conclude, we have identified a novel, nonmitotic function of CSPP proteins placing them into a ciliary protein network crucial for normal renal and retinal tissue architecture and physiology.