[show abstract][hide abstract] ABSTRACT: Most bona fide centrosome proteins including centrins, small calcium-binding proteins, participate in spindle function during mitosis and play a role in cilia assembly in non-cycling cells. Although the basic cellular functions of centrins have been studied in lower eukaryotes and vertebrate cells in culture, phenotypes associated with centrin depletion in vertebrates in vivo has not been directly addressed. To test this, we depleted centrin2 in zebrafish and found that it leads to ciliopathy phenotypes including enlarged pronephric tubules and pronephric cysts. Consistent with the ciliopathy phenotypes, cilia defects were observed in differentiated epithelial cells of ciliated organs such as the olfactory bulb and pronephric duct. The organ phenotypes were also accompanied by cell cycle deregulation namely mitotic delay resulting from mitotic defects. Overall, this work demonstrates that centrin2 depletion causes cilia-related disorders in zebrafish. Moreover, given the presence of both cilia and mitotic defects in the affected organs, it suggests that cilia disorders may arise from a combination of these defects.
[show abstract][hide abstract] ABSTRACT: Cilia dysfunction has long been associated with cyst formation and ciliopathies. More recently, misoriented cell division has been observed in cystic kidneys, but the molecular mechanism leading to this abnormality remains unclear. Proteins of the intraflagellar transport (IFT) machinery are linked to cystogenesis and are required for cilia formation in non-cycling cells. Several IFT proteins also localize to spindle poles in mitosis, indicating uncharacterized functions for these proteins in dividing cells. Here, we show that IFT88 depletion induces mitotic defects in human cultured cells, in kidney cells from the IFT88 mouse mutant Tg737(orpk) and in zebrafish embryos. In mitosis, IFT88 is part of a dynein1-driven complex that transports peripheral microtubule clusters containing microtubule-nucleating proteins to spindle poles to ensure proper formation of astral microtubule arrays and thus proper spindle orientation. This work identifies a mitotic mechanism for a cilia protein in the orientation of cell division and has important implications for the etiology of ciliopathies.
[show abstract][hide abstract] ABSTRACT: Pericentrin is an integral component of the centrosome that serves as a multifunctional scaffold for anchoring numerous proteins and protein complexes. Through these interactions, pericentrin contributes to a diversity of fundamental cellular processes. Recent studies link pericentrin to a growing list of human disorders. Studies on pericentrin at the cellular, molecular, and, more recently, organismal level, provide a platform for generating models to elucidate the etiology of these disorders. Although the complexity of phenotypes associated with pericentrin-mediated disorders is somewhat daunting, insights into the cellular basis of disease are beginning to come into focus. In this review, we focus on human conditions associated with loss or elevation of pericentrin and propose cellular and molecular models that might explain them.
The Journal of Cell Biology 12/2009; 188(2):181-90. · 10.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: The BRCA1-associated ring domain protein 1 (BARD1) interacts with BRCA1 via its RING finger domain. The BARD1-BRCA1 complex participates in DNA repair, cell cycle control, genomic stability, and mitotic spindle formation through its E3 ubiquitin ligase activity. Cancer cells express several BARD1 protein isoforms, including the RING finger-deficient variant BARD1beta. Here, we show that BARD1 has BRCA1-dependent and BRCA1-independent functions in mitosis. BARD1, but not BRCA1, localizes to the midbody at telophase and cytokinesis, where it colocalizes with Aurora B. The 97-kDa full-length (FL) BARD1 coimmunoprecipates with BRCA1, but the 82-kDa BARD1beta coimmunoprecipitates with Aurora B and BRCA2. We used selective small interfering RNAs to distinguish the functions of FL BARD1 and BARD1beta. Depletion of FL BARD1 had only minor effects on cell growth and did not abolish midbody localization of BARD1 staining, but resulted in massive up-regulation of Aurora B. In contrast, suppression of FL BARD1 and BARD1beta led to growth arrest and correlated with various mitotic defects and disappearance of midbody localization of BARD1 staining. Our data suggest a novel function of FL BARD1 in Aurora B ubiquitination and degradation, opposing a proproliferative function of BARD1beta in scaffolding Aurora B and BRCA2. Thus, loss of FL BARD1 and up-regulation of Aurora B, as observed in cancer cells, can be explained by an imbalance of FL BARD1 and BARD1beta.
Cancer Research 02/2009; 69(3):1125-34. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Pericentrin is an integral centrosomal component that anchors regulatory and structural molecules to centrosomes. In a yeast two-hybrid screen with pericentrin we identified chromodomain helicase DNA-binding protein 4 (CHD4/Mi2beta). CHD4 is part of the multiprotein nucleosome remodeling deacetylase (NuRD) complex. We show that many NuRD components interacted with pericentrin by coimmunoprecipitation and that they localized to centrosomes and midbodies. Overexpression of the pericentrin-binding domain of CHD4 or another family member (CHD3) dissociated pericentrin from centrosomes. Depletion of CHD3, but not CHD4, by RNA interference dissociated pericentrin and gamma-tubulin from centrosomes. Microtubule nucleation/organization, cell morphology, and nuclear centration were disrupted in CHD3-depleted cells. Spindles were disorganized, the majority showing a prometaphase-like configuration. Time-lapse imaging revealed mitotic failure before chromosome segregation and cytokinesis failure. We conclude that pericentrin forms complexes with CHD3 and CHD4, but a distinct CHD3-pericentrin complex is required for centrosomal anchoring of pericentrin/gamma-tubulin and for centrosome integrity.
Molecular Biology of the Cell 10/2007; 18(9):3667-80. · 4.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: The development of cancer is a multistep process. To understand oncogenesis and adapt appropriate treatments it is important to have a better definition of a number of factors, including the number and order of oncogenic steps, the identity of the targeted cells and deregulated cellular components, and the genes and pathways altered at each step. We propose here a hypothesis of oncogenesis based on the targeting of the cell cycle in two major steps. Oncogenic hits may occur in two sequences: in one scenario a first oncogenic hit alters the regulation of the G1 phase of the cell cycle leading to a proliferative, premalignant syndrome; oncogenesis is completed when a second oncogenic hit relieves the checkpoints of the late phases of the cell cycle. Alternatively, a genetic alteration may hit the late phases first; this leads to a premalignant disease with signs of senescence. In this scenario, the second hit targets the G1 phase. In the two sequences, oncogenesis is based on the cooperation of two hits targeting different phases of the cell cycle and relieving major checkpoints. Stem cells and progenitor cells of various tissues may be variably sensitive to these hits.
International Journal of Oncology 05/2007; 30(5):1051-8. · 2.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Centrosomes organize the microtubule cytoskeleton for both interphase and mitotic functions. They are implicated in cell-cycle progression but the mechanism is unknown. Here, we show that depletion of 14 out of 15 centrosome proteins arrests human diploid cells in G1 with reduced Cdk2-cyclin A activity and that expression of a centrosome-disrupting dominant-negative construct gives similar results. Cell-cycle arrest is always accompanied by defects in centrosome structure and function (for example, duplication and primary cilia assembly). The arrest occurs from within G1, excluding contributions from mitosis and cytokinesis. The arrest requires p38, p53 and p21, and is preceded by p38-dependent activation and centrosomal recruitment of p53. p53-deficient cells fail to arrest, leading to centrosome and spindle dysfunction and aneuploidy. We propose that loss of centrosome integrity activates a checkpoint that inhibits G1-S progression. This model satisfies the definition of a checkpoint in having three elements: a perturbation that is sensed, a transducer (p53) and a receiver (p21).
[show abstract][hide abstract] ABSTRACT: Centrosomes organize the microtubule cytoskeleton for both interphase and mitotic functions. They are implicated in cell-cycle progression but the mechanism is unknown. Here, we show that depletion of 14 out of 15 centrosome proteins arrests human diploid cells in G1 with reduced Cdk2–cyclin A activity and that expression of a centrosome-disrupting dominant-negative construct gives similar results. Cell-cycle arrest is always accompanied by defects in centrosome structure and function (for example, duplication and primary cilia assembly). The arrest occurs from within G1, excluding contributions from mitosis and cytokinesis. The arrest requires p38, p53 and p21, and is preceded by p38-dependent activation and centrosomal recruitment of p53. p53-deficient cells fail to arrest, leading to centrosome and spindle dysfunction and aneuploidy. We propose that loss of centrosome integrity activates a checkpoint that inhibits G1–S progression. This model satisfies the definition of a checkpoint in having three elements: a perturbation that is sensed, a transducer (p53) and a receiver (p21).
[show abstract][hide abstract] ABSTRACT: Some myeloproliferative disorders (MPD) result from a reciprocal translocation that involves the FGFR1 gene and a partner gene. The event creates a chimeric gene that encodes a fusion protein with constitutive FGFR1 tyrosine kinase activity. FGFR1-MPD is a rare disease, but its study may provide interesting clues on different processes such as cell signalling, oncogenesis and stem cell renewal. Some partners of FGFR1 are centrosomal proteins. The corresponding oncogenic fusion kinases are targeted to the centrosome. Constitutive phosphorylation at this site may perturbate centrosome function and the cell cycle. Direct attack at this small organelle may be an efficient way for oncogenes to alter regulation of signalling for proliferation and survival and get rid of checkpoints in cell cycle progression. The same effect might be triggered by other fusion kinases in other MPD and non-MPD malignancies.
[show abstract][hide abstract] ABSTRACT: Myeloproliferative disorders (MPD) are malignant diseases of hematopoietic progenitor cells. Many MPDs result from a chromosomal translocation that creates a fusion gene encoding a chimeric kinase. The fibroblast growth factor receptor 1 (FGFR1)-MPD is characterized by the fusion of the FGFR1 kinase with various partners, including FOP. We show here that both normal FOP and FOP-FGFR1 fusion kinase localize to the centrosome. The fusion kinase encounters substrates at the centrosome where it induces strong phosphorylation on tyrosine residues. Treatment with FGFR1 kinase inhibitor SU5402 abolishes FOP-FGFR1-induced centrosomal phosphorylation and suppresses the proliferative and survival potentials of FOP-FGFR1 Ba/F3 cells. We further show that FOP-FGFR1 allows cells to overcome G1 arrest. Therefore, the FOP-FGFR1 fusion kinase targets the centrosome, activates signaling pathways at this organelle, and sustains continuous entry in the cell cycle. This could represent a potential new mechanism of oncogenic transformation occurring specifically at the centrosome.
Cancer Research 09/2005; 65(16):7231-40. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The case of a patient presenting with a myeloproliferative disorder (MPD) characterized by a t(8;22) (p12;q11) translocation was investigated. The rearrangement resulted in the production of BCR-FGFR1 and FGFR1-BCR chimeric transcripts after in-frame fusions of BCR exon 4 with FGFR1 exon 9 and FGFR1 exon 8 with BCR exon 5, respectively. The four previously reported patients with such translocation presented with an atypical chronic myeloid leukemia (CML) without Philadelphia chromosome. In addition to a myeloproliferation, the patient had a B cell proliferation. The phenotypic characterization of the lymphoid cells in the bone marrow showed a continuum of maturation from blast B cells to polyclonal lymphocytes. In the blood, B cells showed a complete polyclonal maturation. The BCR-FGFR1 gene fusion was detected by dual-color fluorescence in situ hybridization in both CD19- and CD19+ populations. In contrast to the other FGFR1-MPDs that show myeloid and T cell proliferation, we propose that this t(8;22) MPD is a myeloid and B cell disease, and potentially a novel type of hematological disease. Although the FGFR1-MPD is rare, its study provides interesting clues to the understanding of hematopoietic stem cell biology and oncogene activation.
International Journal of Oncology 07/2005; 26(6):1485-92. · 2.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Taxins are a family of centrosomal proteins important for the regulation of mitosis and microtubule dynamics. Cytokinesis, the last step of M phase, is essential for chromosomal integrity and cell division. It is highly regulated and involves a reorganization of microtubules and actin filaments. We show here that TACC1 localizes diffusely to the midzone spindle in anaphase and strongly to the midbody during cytokinesis, indicating a possible involvement of this protein in the exit of M phase. TACC1 also relocalizes to the nucleolus in interphase. We demonstrate that TACC1 and the mitotic kinase Aurora B belong to the same complex during cytokinesis. We further show that Aurora B knocked down by RNA-mediated interference prevents the formation of the midbody - and consequently affects TACC1 localization at this site - and leads to abnormal cell division and multinucleated cells.
[show abstract][hide abstract] ABSTRACT: Constitutive activation of aberrant fibroblast growth factor receptor 1 (FGFR1) kinase as a consequence of gene fusion such as FOP-FGFR1 associated with t(6; 8)(q27;p11-12) translocation, is the hallmark of an atypical aggressive stem cell myeloproliferative disorder (MPD) in humans. In this study, we show that expression of FOP-FGFR1 in primary bone marrow cells induced by retroviral transduction generates a MPD in mice. Constitutive FOP-FGFR1 kinase activity was both essential and sufficient to cause a chronic myeloproliferative syndrome in the murine bone marrow transplantation model. In contrast to the human disorder, lymphoproliferation and progression to acute phase were not observed. Lymphoid symptoms, however, appeared when onset of the disease was delayed as the result of mutation of FOP-FGFR1 at tyrosine 511, the phospholipase C gamma (PLCgamma) binding site.
[show abstract][hide abstract] ABSTRACT: The three human TACC (transforming acidic coiled-coil) genes encode a family of proteins with poorly defined functions that are suspected to play a role in oncogenesis. A Xenopus TACC homolog called Maskin is involved in translational control, while Drosophila D-TACC interacts with the microtubule-associated protein MSPS (Mini SPindleS) to ensure proper dynamics of spindle pole microtubules during cell division. We have delineated here the interactions of TACC1 with four proteins, namely the microtubule-associated chTOG (colonic and hepatic tumor-overexpressed gene) protein (ortholog of Drosophila MSPS), the adaptor protein TRAP (tudor repeat associator with PCTAIRE2), the mitotic serine/threonine kinase Aurora A and the mRNA regulator LSM7 (Like-Sm protein 7). To measure the relevance of the TACC1-associated complex in human cancer we have examined the expression of the three TACC, chTOG and Aurora A in breast cancer using immunohistochemistry on tissue microarrays. We show that expressions of TACC1, TACC2, TACC3 and Aurora A are significantly correlated and downregulated in a subset of breast tumors. Using siRNAs, we further show that depletion of chTOG and, to a lesser extent of TACC1, perturbates cell division. We propose that TACC proteins, which we also named 'Taxins', control mRNA translation and cell division in conjunction with microtubule organization and in association with chTOG and Aurora A, and that these complexes and cell processes may be affected during mammary gland oncogenesis.
[show abstract][hide abstract] ABSTRACT: The three human TACC genes encode a family of proteins that are suspected to play a role in carcinogenesis. Their function is not precisely known; a Xenopus TACC protein called Maskin is involved in translational control, while the Drosophila D-TACC associates with microtubules and centrosomes. We have characterized the human TACC1 gene and its products. The TACC1 gene is located in region p12 of chromosome 8; its mRNA is ubiquitously expressed and encodes a protein with an apparent molecular mass of 125 kDa, which is cytoplasmic and mainly perinuclear. We show that TACC1 mRNA gene expression is down-regulated in various types of tumors. Using immunohistochemistry of tumor tissue-microarrays and sections, we confirm that the level of TACC1 protein is down-regulated in breast cancer. Finally, using the two-hybrid screen in yeast, GST pull-downs and co-immunoprecipitations, we identified two potential binding partners for TACC1, LSM7 and SmG. They constitute a conserved subfamily of Sm-like small proteins that associate with U6 snRNPs and play a role in several aspects of mRNA processing. We speculate that down-regulation of TACC1 may alter the control of mRNA homeostasis in polarized cells and participates in the oncogenic processes.