Inhibition of DEPDC1A,a Bad Prognostic Marker in Multiple Myeloma,Delays Growth and Induces Mature Plasma Cell Markers in Malignant Plasma Cells

High throughput DNA microarray has made it possible to outline genes whose expression in malignant plasma cells is associated with short overall survival of patients with Multiple Myeloma (MM). A further step is to elucidate the mechanisms encoded by these genes yielding to drug resistance and/or patients’ short survival. We focus here on the biological role of the DEP (for Disheveled, EGL-10, Pleckstrin) domain contained protein 1A (DEPDC1A), a poorly known protein encoded by DEPDC1A gene, whose high expression in malignant plasma cells is associated with short survival of patients. Using conditional lentiviral vector delivery of DEPDC1A shRNA, we report that DEPDC1A knockdown delayed the growth of human myeloma cell lines (HMCLs), with a block in G2 phase of the cell cycle, p53 phosphorylation and stabilization, and p21^Cip1 accumulation. DEPDC1A knockdown also resulted in increased expression of mature plasma cell markers, including CXCR4, IL6-R and CD38. Thus DEPDC1A could contribute to the plasmablast features of MMCs found in some patients with adverse prognosis, blocking the differentiation of malignant plasma cells and promoting cell cycle.     

沉默DEPDC1基因表达对鼻咽癌细胞系HNE-1生长和细胞周期的影响

为探讨沉默DEPDC,基因表达对鼻咽癌细胞系HNE．1生长和细胞周期的影响,该实验设计合成靶向DEPDCl的小分子干扰RNA（smallinterferingRNA,siRNA）转染人鼻咽癌HNE-1细胞。转染后,采用荧光定量PCR、免疫印迹、MTT及流式细胞术方法检测细胞内DEPDCl的表达量以及细胞周期、生长增殖、凋亡的变化及其可能机制。结果显示,转染DEPDClsiRNA后,DEPDC1基因在mRNA及蛋白水平的表达量明显降低;大量细胞被阻滞于G2／M期,生长增殖减慢,凋亡增加。荧光定量PCR结果表明,抑制NF—KB激活的A20基因表达量明显上调,受NF-κB调控的肿瘤相关靶基因的表达量下降,包括C-MYC、MMP9、ICAM-1、BCL-2基因。由此说日月,沉默DEPDC1基因可以影响HNE-1细胞的周期,抑制其生长增殖,促进凋亡,其机制可能与抑制NF-κB通路有关。     

Mammalian neurogenesis requires Treacle-Plk1 for precise control of spindle orientation, mitotic progression, and maintenance of neural progenitor cells

The cerebral cortex is a specialized region of the brain that processes cognitive, motor, somatosensory, auditory, and visual functions. Its characteristic architecture and size is dependent upon the number of neurons generated during embryogenesis and has been postulated to be governed by symmetric versus asymmetric cell divisions, which mediate the balance between progenitor cell maintenance and neuron differentiation, respectively. The mechanistic importance of spindle orientation remains controversial, hence there is considerable interest in understanding how neural progenitor cell mitosis is controlled during neurogenesis. We discovered that Treacle, which is encoded by the Tcof1 gene, is a novel centrosome- and kinetochore-associated protein that is critical for spindle fidelity and mitotic progression. Tcof1/Treacle loss-of-function disrupts spindle orientation and cell cycle progression, which perturbs the maintenance, proliferation, and localization of neural progenitors during cortical neurogenesis. Consistent with this, Tcof1(+/-) mice exhibit reduced brain size as a consequence of defects in neural progenitor maintenance. We determined that Treacle elicits its effect via a direct interaction with Polo-like kinase1 (Plk1), and furthermore we discovered novel in vivo roles for Plk1 in governing mitotic progression and spindle orientation in the developing mammalian cortex. Increased asymmetric cell division, however, did not promote increased neuronal differentiation. Collectively our research has therefore identified Treacle and Plk1 as novel in vivo regulators of spindle fidelity, mitotic progression, and proliferation in the maintenance and localization of neural progenitor cells. Together, Treacle and Plk1 are critically required for proper cortical neurogenesis, which has important implications in the regulation of mammalian brain size and the pathogenesis of congenital neurodevelopmental disorders such as microcephaly.     

A putative novel protein,DEPDC1B,is overexpressed in oral cancer patients,and enhanced anchorage-independent growth in oral cancer cells that is mediated by Rac1 and ERK

Background

The DEP domain is a globular domain containing approximately 90 amino acids, which was first discovered in 3 proteins: Drosophila disheveled, Caenorhabditis elegans EGL-10, and mammalian Pleckstrin; hence the term, DEP. DEPDC1B is categorized as a potential Rho GTPase-activating protein. The function of the DEP domain in signal transduction pathways is not fully understood. The DEPDC1B protein exhibits the characteristic features of a signaling protein, and contains 2 conserved domains (DEP and RhoGAP) that are involved in Rho GTPase signaling. Small GTPases, such as Rac, CDC42, and Rho, regulate a multitude of cell events, including cell motility, growth, differentiation, cytoskeletal reorganization and cell cycle progression.

Results

In this study, we found that it was a guanine nucleotide exchange factor and induced both cell migration in a cultured embryonic fibroblast cell line and cell invasion in cancer cell lines; moreover, it was observed to promote anchorage-independent growth in oral cancer cells. We also demonstrated that DEPDC1B plays a role in regulating Rac1 translocated onto cell membranes, suggesting that DEPDC1B exerts a biological function by regulating Rac1. We examined oral cancer tissue; 6 out of 7 oral cancer tissue test samples overexpressed DEPDC1B proteins, compared with normal adjacent tissue.

Conclusions

DEPDC1B was a guanine nucleotide exchange factor and induced both cell migration in a cultured embryonic fibroblast cell line and cell invasion in cancer cell lines; moreover, it was observed to promote anchorage-independent growth in oral cancer cells. We also demonstrated that DEPDC1B exerts a biological function by regulating Rac1. We found that oral cancer samples overexpressed DEPDC1B proteins, compared with normal adjacent tissue. Suggest that DEPDC1B plays a role in the development of oral cancer. We revealed that proliferation was linked to a novel DEPDC1B-Rac1-ERK1/2 signaling axis in oral cancer cell lines.     

Systematic epistatic mapping of cellular processes

Genetic screens have identified many novel components of various biological processes, such as components required for cell cycle and cell division. While forward genetic screens typically generate unstructured ‘hit’ lists, genetic interaction mapping approaches can identify functional relations in a systematic fashion. Here, we discuss a recent study by our group demonstrating a two-step approach to first screen for regulators of the mitotic cell cycle, and subsequently guide hypothesis generation by using genetic interaction analysis. The screen used a high-content microscopy assay and automated image analysis to capture defects during mitotic progression and cytokinesis. Genetic interaction networks derived from process-specific features generate a snapshot of functional gene relations in those processes, which follow a temporal order during the cell cycle. This complements a recently published approach, which inferred directional genetic interactions reconstructing hierarchical relationships between genes across different phases during mitotic progression. In conclusion, this strategy leverages unbiased, genome-wide, yet highly sensitive and process-focused functional screening in cells.     

Inhibitors of phosphatidylinositol 3'-kinases promote mitotic cell death in HeLa cells

The phosphatidylinositol 3-kinase (PI3K) pathway plays an important role in many biological processes, including cell cycle progression, cell growth, survival, actin rearrangement and migration, and intracellular vesicular transport. However, the involvement of the PI3K pathway in the regulation of mitotic cell death remains unclear. In this study, we treated HeLa cells with the PI3K inhibitors, 3-methyladenine (3-MA, as well as a widely used autophagy inhibitor) and wortmannin to examine their effects on cell fates using live cell imaging. Treatment with 3-MA decreased cell viability in a time- and dose-dependent manner and was associated with caspase-3 activation. Interestingly, 3-MA-induced cell death was not affected by RNA interference-mediated knockdown (KD) of beclin1 (an essential protein for autophagy) in HeLa cells, or by deletion of atg5 (an essential autophagy gene) in mouse embryonic fibroblasts (MEFs). These data indicate that cell death induced by 3-MA occurs independently of its ability to inhibit autophagy. The results from live cell imaging studies showed that the inhibition of PI3Ks increased the occurrence of lagging chromosomes and cell cycle arrest and cell death in prometaphase. Furthermore, PI3K inhibitors promoted nocodazole-induced mitotic cell death and reduced mitotic slippage. Overexpression of Akt (the downstream target of PI3K) antagonized PI3K inhibitor-induced mitotic cell death and promoted nocodazole-induced mitotic slippage. These results suggest a novel role for the PI3K pathway in regulating mitotic progression and preventing mitotic cell death and provide justification for the use of PI3K inhibitors in combination with anti-mitotic drugs to combat cancer.     

Midbody localization of vinexin recruits rhotekin to facilitate cytokinetic abscission

Vinexin is a SH3 domain-containing adaptor protein that has diverse roles in cell adhesion, signal transduction, gene regulation and stress granule assembly. In this study, we found that vinexin localizes at the midbody during cell division and facilitates cytokinesis. Knockdown of vinexin in HeLa cells delayed the mitotic cell cycle progression and increased the time of cell abscission and the failure to resolve the cytoplasmic bridge. Midbody-localized vinexin is essential for recruiting rhotekin to this structure for cytokinesis because overexpression of a vinexin mutant without a rhotekin-binding motif or knockdown of rhotekin also impaired cytokinetic abscission and increased the number of cells arrested at the midbody stage. Aberrant expression of vinexin and rhotekin in various cancers has been implicated to promote metastasis because of their functions in cell adhesion and signaling. Our findings reveal a novel role of vinexin and rhotekin in cytokinetic abscission and provide another perspective of how both molecules may affect oncogenic transformation via this fundamental cell cycle process.     

Centriolin,a centriole-appendage protein,regulates peripheral spindle migration and asymmetric division in mouse meiotic oocytes

Unlike somatic cells mitosis, germ cell meiosis consists of 2 consecutive rounds of division that segregate homologous chromosomes and sister chromatids, respectively. The meiotic oocyte is characterized by an absence of centrioles and asymmetric division. Centriolin is a relatively novel centriolar protein that functions in mitotic cell cycle progression and cytokinesis. Here, we explored the function of centriolin in meiosis and showed that it is localized to meiotic spindles and concentrated at the spindle poles and midbody during oocyte meiotic maturation. Unexpectedly, knockdown of centriolin in oocytes with either siRNA or Morpholino micro-injection, did not affect meiotic spindle organization, cell cycle progression, or cytokinesis (as indicated by polar body emission), but led to a failure of peripheral meiotic spindle migration, large polar body emission, and 2-cell like oocytes. These data suggest that, unlike in mitotic cells, the centriolar protein centriolin does not regulate cytokinesis, but plays an important role in regulating asymmetric division of meiotic oocytes.     

DEPDC1B regulates the progression of human chordoma through UBE2T-mediated ubiquitination of BIRC5

Chordoma is a rare bone malignancy with a high rate of local recurrence and distant metastasis. Although DEP domain-containing protein 1B (DEPDC1B) is implicated in a variety of malignancies, its relationship with chordoma is unclear. In this study, the biological role and molecular mechanism of DEPDC1B in chordoma were explored. The function of DEPDC1B in chordoma cells was clarified through loss-of-function assays in vitro and in vivo. Furthermore, molecular mechanism of DEPDC1B in chordoma cells was recognized by RNA sequencing and Co-Immunoprecipitation (Co-IP) assay. The malignant behaviors of DEPDC1B knockdown chordoma cells was significantly inhibited, which was characterized by reduced proliferation, enhanced apoptosis, and hindered migration. Consistently, decreased expression of DEPDC1B suppressed tumor growth in xenograft mice. Mechanically, DEPDC1B affected the ubiquitination of baculoviral inhibitor of apoptosis repeat-containing 5 (BIRC5) through ubiquitin-conjugating enzyme E2T (UBE2T). Simultaneous downregulation of BIRC5 and DEPDC1B may exacerbate the inhibitory effects of chordoma. Moreover, BIRC5 overexpression reduced the inhibitory effects of DEPDC1B knockdown in chordoma cells. In conclusion, DEPDC1B regulates the progression of human chordoma through UBE2T-mediated ubiquitination of BIRC5, suggesting that it may be a promising candidate target with potential therapeutic value.Subject terms: CNS cancer, Oncogenes     

The transforming acidic coiled coil 3 protein is essential for spindle-dependent chromosome alignment and mitotic survival

Cancer-associated centrosomal transforming acidic coiled coil (TACC) proteins are involved in mitotic spindle function. By employing gene targeting, we have recently described a nonredundant and essential role of TACC3 in regulating cell proliferation. In this study, we used an inducible RNA interference approach to characterize the molecular function of TACC3 and its role in mitotic progression and cell survival. Our data demonstrate that a TACC3 knockdown arrests G(1) checkpoint-compromised HeLa cells prior to anaphase with aberrant spindle morphology and severely misaligned chromosomes. Interestingly, TACC3-depleted cells fail to accumulate the mitotic kinase Aurora B and the checkpoint protein BubR1 to normal levels at kinetochores. Moreover, localization of the structural protein Ndc80 at outer kinetochores is reduced, indicating a defective kinetochore-microtubule attachment in TACC3-deficient cells. As a consequence of prolonged TACC3 depletion, cells undergo caspase-dependent cell death that relies on a spindle checkpoint-dependent mitotic arrest. TACC3 knockdown cells that escape from this arrest by mitotic slippage become highly polyploid and accumulate supernumerary centrosomes. Similarly, deficiency of the post-mitotic cell cycle inhibitor p21(WAF) exacerbates the effects of TACC3 depletion. Our findings therefore point to an essential role of TACC3 in spindle assembly and cellular survival and identify TACC3 as a potential therapeutic target in cancer cells.     

中心体蛋白Centlein的敲除促进细胞周期进程

中心体是大部分动物细胞的微管组织中心,它确保了有序的细胞周期进程以及染色体的精确分离,我们之前报道了中心体蛋白Centlein作为一个分子连接,与C-Nap1和Cep68一起形成复合物维持中心体的连接. 然而,关于Centlein的其他功能我们还知之甚少. 在本研究中,建立了Centlein的敲除细胞系,并且运用RNA-seq技术分析了敲除细胞系和正常野生型细胞系之间转录水平的差异. 发现Centlein敲除细胞系中细胞周期相关基因PLK1、CCNB1、CCNA2和CDC20的表达量上调,流式结果又表明Centlein的敲除促进了细胞周期进程. 同时发现Centlein与PLK1之间存在细胞内相互作用,于是我们提出了Centlein通过与PLK1的作用参与细胞周期进程.     

The essential role of LIS1, NDEL1 and Aurora-A in polarity formation and microtubule organization during neurogensis

Lissencephaly is a devastating neurological disorder due to defective neuronal migration. LIS1 (or PAFAH1B1), the gene mutated in lissencephaly patients and its binding protein NDEL1 were found to regulate cytoplasmic dynein function and localization. LIS1 and NDEL1 also play a pivotal role on a microtubule regulation and determination of cell polarity. For example, LIS1 is required for the precise control of mitotic spindle orientation in both neuroepithelial stem cells and radial glial progenitor cells. On the other hand, NDEL1 is essential for mitotic entry as an effector molecule of Aurora-A kinase. In addition, an atypical protein kinase C (aPKC)-Aurora-A-NDEL1 pathway is critical for the regulation of microtubule organization during neurite extension. These findings suggest that physiological functions of LIS1 and NDEL1 in neurons have been ascribed for proteins fundamentally required for cell cycle progression and control. In turn, cell cycle regulators may exert other functions during neurogenesis in a direct or an indirect fashion. Thus far, only a handful of cell cycle regulators have been shown to play physiological cell-cycle-independent roles in neurons. Further identification of such proteins and elucidation of their underlying mechanisms of action will likely reveal novel concepts and/or patterns that provide a clear link between their seemingly distinct cell cycle and neuronal functions.     

Novel response to microtubule perturbation in meiosis

During the mitotic cell cycle, microtubule depolymerization leads to a cell cycle arrest in metaphase, due to activation of the spindle checkpoint. Here, we show that under microtubule-destabilizing conditions, such as low temperature or the presence of the spindle-depolymerizing drug benomyl, meiotic budding yeast cells arrest in G(1) or G(2), instead of metaphase. Cells arrest in G(1) if microtubule perturbation occurs as they enter the meiotic cell cycle and in G(2) if cells are already undergoing premeiotic S phase. Concomitantly, cells down-regulate genes required for cell cycle progression, meiotic differentiation, and spore formation in a highly coordinated manner. Decreased expression of these genes is likely to be responsible for halting both cell cycle progression and meiotic development. Our results point towards the existence of a novel surveillance mechanism of microtubule integrity that may be particularly important during specialized cell cycles when coordination of cell cycle progression with a developmental program is necessary.