Loading...
7 results
Search Results
Now showing 1 - 7 of 7
- Dynein-dependent transport of spindle assembly checkpoint proteins off kinetochores toward spindle polesPublication . Silva, PMA; Patrícia M.A. Silva; Reis, Rita M.; Bolanos-Garcia, Victor M.; Florindo, Claudia; Tavares, Alvaro; Bousbaa, HassanA predominant mechanism of spindle assembly checkpoint (SAC) silencing is dynein-mediated transport of certain kinetochore proteins along microtubules. There are still conflicting data as to which SAC proteins are dynein cargoes. Using two ATP reduction assays, we found that the core SAC proteins Mad1, Mad2, Bub1, BubR1, and Bub3 redistributed from attached kinetochores to spindle poles, in a dynein-dependent manner. This redistribution still occurred in metaphase-arrested cells, at a time when the SAC should be satisfied and silenced. Unexpectedly, we found that a pool of Hec1 and Mis12 also relocalizes to spindle poles, suggesting KMN components as additional dynein cargoes. The potential significance of these results for SAC silencing is discussed. (C) 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
- Suppression of spindly delays mitotic exit and exacerbates cell death response of cancer cells treated with low doses of paclitaxelPublication . Silva, Patrícia M. A.; Ribeiro, Nilza; Lima, Raquel T.; Andrade, Claudia; Diogo, Vania; Teixeira, Joana; Florindo, C.; Tavares, Alvaro; Vasconcelos, M. Helena; Bousbaa, HassanMicrotubule-targeting agents (MTAs) are used extensively for the treatment of diverse types of cancer. They block cancer cells in mitosis through the activation of the spindle assembly checkpoint (SAC), the surveillance mechanism that ensures accurate chromosome segregation at the onset of anaphase. However, the cytotoxic activity of MTAs is limited by premature mitotic exit (mitotic slippage) due to SAC silencing. Here we have explored the dual role of the protein Spindly in chromosome attachments and SAC silencing to analyze the consequences of its depletion on the viability of tumor cells treated with clinically relevant doses of paclitaxel. As expected, siRNA-mediated Spindly suppression induced chromosome misalignment and accumulation of cells in mitosis. Remarkably, these cells were more sensitive to low-doses of paclitaxel. Sensitization was due to an increase in the length of mitotic arrest and high frequency of multinucleated cells, both correlated with an exacerbated post-mitotic cell death response as determined by cell fate profiling. Thus, by affecting both SAC silencing and chromosome attachment, Spindly targeting offers a double-edged sword that potentiates tumor cell killing by clinically relevant doses of paclitaxel, providing a rationale for combination chemotherapy against cancer. (C) 2017 Elsevier B.V. All rights reserved.
- Role of MOB4 in cell proliferation and neurogenesisPublication . Baião Santos, Inês; GARRIDO-MARAVER, JUAN; Gonçalves, Carolina; Oliveira, Bruna; Tavares, Alvaro A.Signaling pathways that integrate a large set of inputs (both extra- and intracellular) to control cell proliferation are essential during both development and adult stages to guarantee organism homeostasis. Mobs are small adaptor proteins that participate in several of these signaling pathways. Here, we review recent advances unravelling Mob4 cellular functions, a highly conserved non-catalytic protein, that plays a diversity of roles in cell proliferation, sperm cell differentiation and is simultaneously involved in synapse formation and neural development. In addition, the gene is often overexpressed in a large diversity of tumors and is linked to poor clinical outcomes. Nevertheless, Mob4 molecular functions remain poorly defined, although it integrates the core structure of STRIPAK, a kinase/phosphatase protein complex, that can act upstream of the Hippo pathway. In this review we focus on the recent findings of Mob4 functions, that have begun to clarify its critical role on cell proliferation and the development of tissues and individuals.
- Co-silencing of human Bub3 and dynein highlights an antagonistic relationship in regulating kinetochore-microtubule attachmentsPublication . Silva, Patricia M. A.; Tavares, Alvaro A.; Bousbaa, HassanWe previously reported that the spindle assembly checkpoint protein Bub3 is involved in regulating kinetochore-microtubule (KT-MT) attachments. Also, Bub3 was reported to interact with the microtubule motor protein dynein. Here we examined how this interaction contributes to KT-MT attachments. Depletion of Bub3 or dynein induced misaligned chromosomes, consistent with their role in KT-MT attachments. Unexpectedly, co-silencing of both proteins partially suppressed the misalignment phenotype and restored chromosome congression. Consistent with these observations, KT-MT attachments in co-depleted cells were stable, able to drive chromosome congression, and produce inter-and intra-kinetochore stretch, indicating they are functional. We suggest that a mutual antagonism exists between Bub3 and dynein to ensure optimal KT-MT attachments. (C) 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
- Spindly and Bub3 expression in oral cancer: Prognostic and therapeutic implicationsPublication . Silva, Patricia M. A.; Delgado, Maria Leonor; Ribeiro, Nilza; Florindo, Claudia; Tavares, Alvaro A.; Ribeiro, Diana; Lopes, Carlos; do Amaral, Barbas; Bousbaa, Hassan; Monteiro, Luis SilvaObjectives Bub3 and Spindly are essential proteins required for the activation and inactivation of the spindle assembly checkpoint, respectively. Here, we explored the clinicopathological significance and the therapeutic potential of the opposing roles of the two proteins in oral squamous cell carcinoma (OSCC). Materials and Methods Bub3 and Spindly expression was evaluated by immunohistochemistry in 62 tissue microarrays from OSCC and by real-time PCR in OSCC cell lines and in normal human oral keratinocytes. The results were analyzed as to their clinicopathological significance. RNA interference-mediated Spindly or Bub3 inhibition was combined with cisplatin treatment, and the effect on the viability of OSCC cells was assessed. Results Overexpression of Bub3 and Spindly was detected in OSCC patients. High expression of Spindly, Bub3, or both was an independent prognostic indicator for cancer-specific survival and was associated with increased cellular proliferation. Accordingly, Bub3 and Spindly were upregulated in OSCC cells comparatively to their normal counterpart. Inhibition of Bub3 or Spindly was cytotoxic to OSCC cells and enhanced their chemosensitivity to cisplatin. Conclusions The data point out Bub3 and Spindly as potential markers of proliferation and prognosis, and highlight the potential therapeutic benefit of combining their inhibition with cisplatin.
- Mob1: defining cell polarity for proper cell divisionPublication . Tavares, Alexandra; Gonçalves, João; Florindo, Claudia; Tavares, Alvaro A.; Soares, HelenaMob1 is a component of both the mitotic exit network and Hippo pathway, being required for cytokinesis, control of cell proliferation and apoptosis. Cell division accuracy is crucial in maintaining cell ploidy and genomic stability and relies on the correct establishment of the cell division axis, which is under the control of the cell's environment and its intrinsic polarity. The ciliate Tetrahymena thermophila possesses a permanent anterior posterior axis, left right asymmetry and divides symmetrically. These unique features of Tetrahymena prompted us to investigate the role of Tetrahymena Mob1. Unexpectedly, we found that Mob1 accumulated in basal bodies at the posterior pole of the cell, and is the first molecular polarity marker so far described in Tetrahymena. In addition, Mob1 depletion caused the abnormal establishment of the cell division plane, providing clear evidence that Mob1 is important for its definition. Furthermore, cytokinesis was arrested and ciliogenesis delayed in Tetrahymena cells depleted of Mob1. This is the first evidence for an involvement of Mob1 in cilia biology. In conclusion, we show that Mob1 is an important cell polarity marker that is crucial for correct division plane placement, for cytokinesis completion and for normal cilia growth rates.
- Human Mob1 proteins are required for cytokinesis by controlling microtubule stabilityPublication . Florindo, Claudia; Perdigao, Joana; Fesquet, Didier; Schiebel, Elmar; Pines, Jonathon; Tavares, Alvaro A.The completion of cytokinesis requires abscission of the midbody, a microtubule-rich cytoplasmic bridge that connects the daughter cells before their final separation. Although it has been established that both the midbody structure and membrane fusion are essential for abscission, the biochemical machinery and the cellular processes of abscission remain ill-defined. Here we report that human Mob1A and Mob1B proteins are involved in the regulation of abscission of the intercellular bridge. The Mob family is a group of highly conserved proteins in eukaryotes, described as binding partners as well as co-activators of protein kinases of the Ndr family, and as members of the Hippo pathway. We show that depletion of Mob1A and Mob1B by RNAi causes abscission failure as a consequence of hyper-stabilization of microtubules in the midbody region. Interestingly, depleting Mob1 also increases cell motility after cytokinesis, and induces prolonged centriole separation in G1 phase. In contrast, centrosomes fail to split when either Mob1A or Mob1B is overexpressed. Our findings indicate that human Mob1 proteins are involved in the regulation of microtubule stability at the midbody. We conclude that Mob1A and Mob1B are needed for cell abscission and centriole re-joining after telophase and cytokinesis.