MEI-1/MEI-2 katanin-like microtubule severing activity is required for Caenorhabditis elegans meiosis

The Caenorhabditis elegans meiotic spindle is morphologically distinct from the first mitotic spindle, yet both structures form in the same cytoplasm approximately 20 minutes apart. The mei-1 and mei-2 genes of C. elegans are required for the establishment of the oocyte meiotic spindle but are not required for mitotic spindle function. mei-1 encodes an AAA ATPase family member with similarity to the p60 catalytic subunit of the heterodimeric sea urchin microtubule-severing protein, katanin. We report that mei-2 encodes a 280-amino acid protein containing a region similar to the p80-targeting subunit of katanin. MEI-1 and MEI-2 antibodies decorate the polar ends of meiotic spindle microtubules and meiotic chromatin. We find that the subcellular location of MEI-2 depends on wild-type mei-1 activity and vice versa. These experiments, combined with MEI-1 and MEI-2's similarity to p60 and p80 katanin, suggest that the C. elegans proteins function as a complex. In support of this idea, MEI-1 and MEI-2 physically associate in HeLa cells. Furthermore, co-expression of MEI-1 and MEI-2 in HeLa cells results in the disassembly of microtubules. These data lead us to conclude that MEI-1/MEI-2 microtubule-severing activity is required for meiotic spindle organization in C. elegans.     

ADPEAF mutations reduce levels of secreted LGI1, a putative tumor suppressor protein linked to epilepsy

Mutations in LGI1 have been linked to autosomal dominant partial epilepsy with auditory features (ADPEAF), an unusual inherited human partial epilepsy phenotype. In addition, decreases in LGI1 expression are observed in glioblastoma patient samples and glioblastoma cell lines. LGI1, one member of the LGI gene family, encodes a approximately 63 kDa protein, with strong regional expression in neurons within the temporal lobe. Although the function of LGI proteins remains unknown, structural analyses suggest that LGI1 could be either localized to the membrane or secreted. Here, we show that LGI1-4 exhibit overlapping patterns of diffuse mRNA expression in the adult mouse brain, with some areas of specific localization characteristic of each family member. We find robust secretion of mouse LGI1 protein following transfection into 293T cells. LGI family members, LGI3, LGI4 and a newly identified splice form of LGI2, LGI2B, are also secreted in culture, indicating that secretion is a conserved feature of this protein family. Introduction of mutations in LGI1, including those identified in ADPEAF pedigrees, reveals that the mutant proteins either are not secreted or are unstable. These results demonstrate loss-of-function as a pathogenic basis for LGI1-mediated ADPEAF.     

Regulation of mTOR function in response to hypoxia by REDD1 and the TSC1/TSC2 tumor suppressor complex

Mammalian target of rapamycin (mTOR) is a central regulator of protein synthesis whose activity is modulated by a variety of signals. Energy depletion and hypoxia result in mTOR inhibition. While energy depletion inhibits mTOR through a process involving the activation of AMP-activated protein kinase (AMPK) by LKB1 and subsequent phosphorylation of TSC2, the mechanism of mTOR inhibition by hypoxia is not known. Here we show that mTOR inhibition by hypoxia requires the TSC1/TSC2 tumor suppressor complex and the hypoxia-inducible gene REDD1/RTP801. Disruption of the TSC1/TSC2 complex through loss of TSC1 or TSC2 blocks the effects of hypoxia on mTOR, as measured by changes in the mTOR targets S6K and 4E-BP1, and results in abnormal accumulation of Hypoxia-inducible factor (HIF). In contrast to energy depletion, mTOR inhibition by hypoxia does not require AMPK or LKB1. Down-regulation of mTOR activity by hypoxia requires de novo mRNA synthesis and correlates with increased expression of the hypoxia-inducible REDD1 gene. Disruption of REDD1 abrogates the hypoxia-induced inhibition of mTOR, and REDD1 overexpression is sufficient to down-regulate S6K phosphorylation in a TSC1/TSC2-dependent manner. Inhibition of mTOR function by hypoxia is likely to be important for tumor suppression as TSC2-deficient cells maintain abnormally high levels of cell proliferation under hypoxia.     

候选肿瘤抑制因子——HINT1的研究与进展

越来越多的研究结果显示,HIT家族的一员--HINT1是一个新近发现的肿瘤抑制因子.但它抑制肿瘤发生的机制尚未明确.已涉及的研究包括HINT1通过抑制T细胞/β-catenin介导的转录调控影响Wnt通路;调节多种分子从而介入对细胞周期、凋亡及DNA损伤后修复的调控.而对肿瘤细胞系和样本中Hint1启动子区甲基化的研究也受到越来越多的关注.本文就目前对H1NT1的研究进展及潜在的临床意义作一综述.

Abstract：

There are accumulating evidences that histidine traid (HIT) nucleotide-binding protein 1 ( HINT1 ) , a member of the HIT protein super-family, is a novel tumor suppressor. However,the underlying mechanism of its tumor suppressing activity is still unknown. It has been found that HINT1regulates various proteins and thus is involved in Wnt pathway, cell cycle, apoptosis and DNA damage repair regulation. The studies on the promoter CpG island methylation of Hint 1 in tumor cell lines and tumor samples have received more and more attentions. In this article, we will review the current research advances of HINT1 and the potental clinical significance in future.     

hScrib: a potential novel tumor suppressor

Establishment and maintenance of epithelial cell polarity rely on finely tuned protein networks comprising cell surface molecules, cytoplasmic adaptors, and enzymes connected to the actin cytoskeleton. Oncogenes and tumor suppressors promote cell proliferation and resistance to apoptosis and, in many cases, alter some of these molecular scaffolds, and profoundly affect the epithelial cytoarchitecture. Reciprocally, loss of central actors of epithelial polarity unleashes normally repressed signaling pathways and perturb the shape and functions of epithelial tissues. Among the newcomers impacting on epithelial integrity, Scribble is a scaffold protein of a remarkable importance that furthermore displays a tumor suppressing activity in Drosophila melanogaster. Together with Discs Large (Dlg) and Lethal Giant Larvae (Lgl), two known tumor suppressors, Scribble acts on the correct positioning of epithelial junctions required to organize functional epithelial sheets. Scribble, Dlg and Lgl proteins are well conserved during evolution at the molecular and subcellular level implying their potential role in cell polarity and tumorigenesis in humans. Recent findings on hScrib, the human orthologue of Scribble, are discussed here.     

Potential role for inhibition of protein phosphatase 2A tumor suppressor in salivary gland malignancies

The aetiology and pathogenesis of salivary gland malignancies remain unknown. To reveal novel molecular factors behind the development of salivary gland cancer, we performed gene expression analyses from Smgb‐Tag mouse salivary gland samples. The overall purpose was to apply these results for clinical use to find new approaches for both possible therapeutic targets and more accurate diagnostic tools. Smgb‐Tag mouse strain, in which salivary neoplasms arise through a dysplastic phase in submandibular glands, was investigated using genome‐wide microarray expression analysis, ingenuity pathway analysis, RT‐PCR, and immunohistochemistry. Thirty‐eight human salivary gland adenoid cystic carcinoma samples were investigated using immunohistochemistry for validation purposes. Our genome‐wide study showed that Ppp2r1b, a PP2A subunit encoding tumor suppressor gene, is underexpressed in submandibular gland tumors of Smgb‐Tag mice. mTOR signaling pathway was significantly enriched and mTOR linked PP2A subunit gene B55 gamma was significantly underexpressed in the analyses. Furthermore, parallel immunohistochemical analysis of three PP2A inhibitors demonstrated that two PP2A inhibitors, CIP2A and SET, are highly expressed in both dysplastic and adenocarcinomatous tumors of the Smgb‐Tag mice. In addition, all 38 investigated human salivary adenoid cystic carcinoma samples stained positively for CIP2A and most for SET. Finally, p‐S6 staining showed activation of mTOR pathway in human adenoid cystic carcinoma samples. Our results suggest that PP2A inhibition either via PP2A subunit underexpression or PP2A inhibitor overexpression play an important role in the formation of salivary gland malignancy, potentially due to mTOR signaling activation. © 2015 Wiley Periodicals, Inc.     

ASPP2 is a haploinsufficient tumor suppressor that cooperates with p53 to suppress tumor growth

ASPP2 stimulates the apoptotic function of the p53 family in vivo. We show here that ASPP2-/- pups died before weaning. This postnatal lethality was significantly enhanced in p53+/- background and both deletions are synthetic lethal. ASPP2+/- mice developed spontaneous tumors. The tumor onset was accelerated by gamma-irradiation or in p53+/- background. Tumors derived from ASPP2+/- mice retained wild-type ASPP2 allele even though some of them lost p53. These provide the first genetic evidence that ASPP2 is a haploinsufficient tumor suppressor that shares overlapping function(s) with p53 in mouse development and tumor suppression.     

Growth arrest by the LKB1 tumor suppressor: induction of p21(WAF1/CIP1)

Germline mutations of the LKB1 tumor suppressor gene lead to Peutz-Jeghers syndrome (PJS), with a predisposition to cancer. LKB1 encodes for a nuclear and cytoplasmic serine/threonine kinase, which is inactivated by mutations observed in PJS patients. Restoring LKB1 activity into cancer cell lines defective for its expression results in a G(1) cell cycle arrest. Here we have investigated molecular mechanisms leading to this arrest. Reintroduced active LKB1 was cytoplasmic and nuclear, whereas most kinase-defective PJS mutants of LKB1 localized predominantly to the nucleus. Moreover, when LKB1 was forced to remain cytoplasmic through disruption of the nuclear localization signal, it retained full growth suppression activity in a kinase-dependent manner. LKB1-mediated G(1) arrest was found to be bypassed by co-expression of the G(1) cyclins cyclin D1 and cyclin E. In addition, the protein levels of the CDK inhibitor p21(WAF1/CIP1) and p21 promoter activity were specifically upregulated in LKB1-transfected cells. Both the growth arrest and the induction of the p21 promoter were found to be p53-dependent. These results suggest that growth suppression by LKB1 is mediated through signaling of cytoplasmic LKB1 to induce p21 through a p53-dependent mechanism.     

Growth inhibition of MCF-7 tumor cell line by phenylacetate linked to functionalized dextran

We investigated the antiproliferative effect of phenylacetate covalently linked to dextran derivatives (DMCBPA conjugates) on human breast cancer MCF-7 cells. We show that free sodium phenylacetate (NaPA) inhibits the cell growth (IC50 = 14 mM), while an important inhibitory effect is observed for DMCBPA conjugates. The IC50 dose of these conjugates is as low as 1.0 mg/ml, corresponding to 1.3 mM of phenylacetate. The precursors, dextran substituted with methylcarboxylate and benzylamide groups, did not affect the growth of MCF-7 tumor cells. We have observed that MCF-7 cell growth inhibition depends on amount of phenylacetate linked to the conjugate. The data indicated that an optimum antiproliferative effect is more significant when the amount of phenylacetate groups present on the dextran backbone is high. Analysis of doubling time by growth kinetics study shows that conjugates have more time-sustained effect than free NaPA. It is noteworthy that the inhibitory effect is observed at non-toxic concentration. Theses conjugates could be considered as acceptable derivatives to prevent tumor progression.     

Evaluation of ETF1/eRF1, mapping to 5q31, as a candidate myeloid tumor suppressor gene

Interstitial deletion of the long arm of chromosome 5 is a recurrent abnormality, mainly associated with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), and it has been proposed therefore that the deleted region may contain a myeloid tumor suppressor gene. We have recently mapped a human translation termination factor gene, ETF1, to band 5q31 at D5S500, and thus to the smallest commonly deleted segment. We have evaluated ETF1 as a candidate myeloid tumor suppressor gene by analysis of the human acute myeloid leukemia cell line HL60, and of patients suffering from malignant myeloid diseases with cytogenetically-defined abnormalities of chromosome 5. Fluorescence in situ hybridization analysis revealed hemizygous loss of the ETF1 locus in HL60 cells and in four of five leukemic samples, but no inactivating mutations were identified by sequencing of the remaining ETF1 allele.     

Growth inhibition of MCF-7 tumor cell line by phenylacetate linked to functionalized dextran

We investigated the antiproliferative effect of phenylacetate covalently linked to dextran derivatives (DMCBPA conjugates) on human breast cancer MCF-7 cells. We show that free sodium phenylacetate (NaPA) inhibits the cell growth (IC₅₀ = 14 mM), while an important inhibitory effect is observed for DMCBPA conjugates. The IC₅₀ dose of these conjugates is as low as 1.0 mg/ml, corresponding to 1.3 mM of phenylacetate. The precursors, dextran substituted with methylcarboxylate and benzylamide groups, did not affect the growth of MCF-7 tumor cells. We have observed that MCF-7 cell growth inhibition depends on amount of phenylacetate linked to the conjugate. The data indicated that an optimum antiproliferative effect is more significant when the amount of phenylacetate groups present on the dextran backbone is high. Analysis of doubling time by growth kinetics study shows that conjugates have more time-sustained effect than free NaPA. It is noteworthy that the inhibitory effect is observed at non-toxic concentration. Theses conjugates could be considered as acceptable derivatives to prevent tumor progression.     

Localization of the candidate tumor suppressor geneING1 to human chromosome 13q34

A novel gene ING1 was recently cloned and defined as a candidate tumor suppressor gene. Reduced expression and rearrangements of ING1 are found in several tumor cell lines, ING1 overexpression is associated with cell growth arrest and ING1 suppression promotes neoplastic transformation (1). Using radiation hybrid mapping technique ING1 was assigned to subtelomeric region of the long arm of human chromosome 13 (13q34) which is known to be frequently rearranged in squamous carcinomas of head and neck.     

Programmed cell death 2 functions as a tumor suppressor in osteosarcoma

Objectives: To investigate the role of programmed cell death 2 (PDCD2) in osteosarcoma (OS), along with correlations between PDCD2 and CD4⁺/CD8⁺. Methods: Sprague-Dawley (SD) rats were randomly assigned to control group and OS group. The OS group rats were subjected to induce models of OS by transplantation with UMR106 cells. Peripheral blood was collected to test the percentages of the CD4⁺ and CD8⁺ cell subsets using flow cytometry (FCM). Western blotting was performed to determine the PDCD2 protein level. The correlations between PDCD2 and CD4⁺/CD8⁺ were analyzed by Pearson correlation coefficient. Besides, specific small interfering RNAs (siRNA) against PDCD2 and nonspecific (NS)-siRNA were transfected into UMR106 cells. Cell viability and invasive ability were determined after transfection. Results: CD4⁺ cells percentages were significantly decreased in the OS group, while CD8⁺ cells were significantly increased (P < 0.05). The PDCD2 protein levels were markedly lower than that in the control group (P < 0.05). Additionally, PDCD2 was positively correlated with CD4⁺ (R² = 0.66, P < 0.05), but was negatively correlated with CD8⁺ (R² = -0.94, P < 0.05). Moreover, the cell viability and invasion ability were significantly higher than that in the control group and the NS siRNA group after transfection with PDCD2 siRNA (P < 0.05). Conclusion: These results suggest that PDCD2 is involved in the pathogenesis of OS, and PDCD2 may play an important role in tumor suppression. These mechanisms might be related to immune response induced by CD4⁺ and CD8⁺ T cells.     

Anticancer activity of the PR domain of tumor suppressor RIZ1

Human tumor suppressor gene RIZ encodes two protein products, tumor suppressor RIZ1 and proto-oncoprotein RIZ2, which regulate cellular functions in a Yin-Yang fashion. The only structural difference between them is that RIZ2 lacks the N-terminal PR domain. In this study, we showed that RIZ1 mRNA expression level was elevated in stage IV of eight different types of cancer (stage III for prostate cancer), indicating that RIZ1 might play an important role in tumor metastasis, and the PR domain alone possessed anticancer activity.     

Dppa2 and Dppa4 are closely linked SAP motif genes restricted to pluripotent cells and the germ line

Despite the enormous medical potential of ESCs, the molecular mechanisms conferring the ability to differentiate into all cell types of the embryo remain elusive. We used an in silico approach to identify genes expressed exclusively in mouse preimplantation embryos and pluripotent cell lines. Two of these genes were developmental pluripotency-associated gene 2 (Dppa2) and Dppa4, which we show are closely linked genes encoding putative nuclear SAP domain proteins expressed in human and mouse pluripotent stem cells and germ cell tumor-derived embryonal carcinoma cells. In the mouse, these genes are transcribed in germinal vesicle-stage oocytes and throughout the cleavage stages of embryogenesis. They then become restricted to the pluripotent inner cell mass of blastocysts and are subsequently downregulated. After gastrulation, Dppa2 and Dppa4 are expressed only in the developing germ line, showing that these genes mark cells of the pluripotent cycle. In the germ line, both genes are downregulated as the germ cells commit to the oogenic pathway or soon after commitment to the spermatogenic pathway. We have observed similar germ line expression profiles for other pluripotent markers, and these results are consistent with the hypothesis that pluripotent markers must be downregulated during fetal germ line development, a process that may be required to facilitate appropriate germ line differentiation. The study of expression and function of pluripotent markers such as Dppa2 and Dppa4 is likely to unveil new aspects of the regulation of pluripotency and germ line development in mammals.     

Molecular alterations of h-warts/LATS1 tumor suppressor in human soft tissue sarcoma

h-warts/LATS1 is a human homolog of the Drosophila warts tumor suppressor gene, which functions as a component of the mitotic apparatus. LATS1-deficient (Lats1(-/-)) mice have been reported to develop ovarian stromal tumors and soft tissue sarcomas. We investigated the status of the h-warts/LATS1 in 50 human soft tissue sarcomas to address its potential function as a tumor suppressor in human sarcoma development. In our RT-PCR assay, 7 (14%) (3 of 4 myxoid liposarcomas, 3 of 7 leiomyosarcomas, 1 of 9 malignant fibrous histiocytomas) of 50 sarcomas examined had no or a reduced expression of the h-warts/LATS1, indicating down-regulated gene expression. We further analyzed alterations of the h-warts/LATS1 in these seven sarcomas. Using microsatellite markers for chromosome 6q23-25.1, to which the h-warts/LATS1 is localized, an allelic loss of this locus was detected in one leiomyosarcoma, in which a missense point mutation of the h-warts/LATS1 was detected by PCR single-strand conformation polymorphism. Clusters of CpG dinucleotides in a 5' putative promoter region were hypermethylated in the other six sarcomas. Our data suggest that the molecular alterations of the h-warts/LATS1 could be of pathologic importance in human sarcomagenesis.