Taxol, vincristine or nocodazole induces lethality in G1-checkpoint-defective human astrocytoma U373MG cells by triggering hyperploid progression.
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In this report, we describe a novel lytic mechanism exploited by antimicrotubule drugs (AMDs) such as Taxol which are frequently used to treat multiple human cancers including breast and ovarian cancers. In cells lacking the G1-arresting capacity due to the defect in retinoblastoma or p53 gene function, AMDs trigger hyperploid progression and death. The hyperploid progression occurs via continued cell-cycle progression without cell division. Blocking hyperploid progression through hydroxyurea or ectopically expressed p27(Kip1), a G1-specific Cdk inhibitor, abrogates AMD cytotoxicity. Thus, AMDs induce lethality in G1-checkpoint-defective cells by triggering hyperploid progression. The phenomenon is reminiscent of that observed previously with bub-1 yeast mutant. The potential significance of this finding lies in that hyperploid progression-mediated death may be exploited to develop a therapy with tumor-specificity at the genetic level. As a large fraction of human cancers are mutated in p53 gene, it may have a wide therapeutic applicability. (+info)
A correlative study of gliomas using in vivo bromodeoxyuridine labeling index and computer-aided malignancy grading.
(26/1796)
An in vivo bromodeoxyuridine (BrdU) labeling index (LI) was estimated in 43 cases of astrocytic tumors and mixed gliomas by one hour intra-operative intravenous infusion at a dose of 200 mg/m2 and correlated with (a) histological grading using a computer aided malignancy classifier TESTAST-268; and (b) histological typing using WHO classification. The lowest BrdU LI was seen in pilocytic and gemistocytic astrocytomas followed by astrocytomas, anaplastic astrocytomas and glioblastoma multiforme in that order. Mixed oligoastrocytomas followed the pattern of their astrocytic counterparts. Tumors of similar histological type showed different BrdU LI values especially amongst astrocytomas and glioblastomas. A statistically significant difference in the BrdU LI was also noted between the higher TESTAST grades of astrocytomas (T III and IV) versus the lower TESTAST grades (T II). Unlike earlier reports in literature, in the present study the category of BrdU LI of <1 contained no case of anaplastic astrocytoma or glioblastoma multiforme (TESTAST grades III and IV). Likewise, the category of BrdU LI >5 contained only anaplastic astrocytoma and glioblastoma multiforme (TESTAST grades III and IV). Maximum spread of cases was seen in the BrdU LI category of 1-5, not only in terms of histological types but also TESTAST grades. Thus there appeared to be a positive trend of increasing BrdU LI values both with histological types and increasing TESTAST grades. Further, an interesting observation was that by using a combination of TESTAST grades and BrdU LI, the histologically homogenous glioblastoma group could be further subdivided into 4 categories which showed a trend towards prognostic correlation. Thus, this study though preliminary with number of cases being small in some groups, highlights the possible usefulness of combined histological typing, TESTAST grading and in vivo BrdU LI for prognostication of gliomas especially glioblastoma multiforme. (+info)
Human cytomegalovirus infection decreases expression of thrombospondin-1 independent of the tumor suppressor protein p53.
(27/1796)
Thrombospondin-1 (TSP-1) is a potent inhibitor of angiogenesis. It has been shown that promoter sequences of the TSP-1 gene can be transactivated by the wild-type tumor suppressor protein p53. As human cytomegalovirus (HCMV) infection inactivates wild-type p53 of various cell types, we investigated whether HCMV infection is associated with reduced TSP-1 production. We found, in conjunction with accumulated p53, that TSP-1 mRNA and protein expression was significantly reduced in HCMV-infected cultured human fibroblasts. To determine whether the observed TSP-1 suppression depends on p53 inactivation, the p53-defective astrocytoma cell line U373MG was infected with HCMV. In these cells TSP-1 expression was also significantly reduced by HCMV infection whereas expression of the p53 mutant variant remained unaltered. In both cell lines the decreased expression of TSP-1 mRNA occurred early after infection (4 hours), indicating that HCMV inhibits TSP-1 transcription during the immediate-early phase of infection before HCMV DNA replication. Inhibition of HCMV DNA synthesis by ganciclovir did not influence TSP-1 reduction whereas the antisense oligonucleotide ISIS 2922, complementary to HCMV immediate-early mRNA, completely prevented the HCMV-mediated TSP-1 suppression. These findings strongly suggest a novel role for HCMV in the modulation of angiogenesis due to p53-independent down-regulation of TSP-1 expression. (+info)
Characterization of Mayven, a novel actin-binding protein predominantly expressed in brain.
(28/1796)
The cytoskeleton plays an important role in neuronal morphogenesis. We have identified and characterized a novel actin-binding protein, termed Mayven, predominantly expressed in brain. Mayven contains a BTB (broad complex, tramtrack, bric-a-brac)/POZ (poxvirus, zinc finger) domain-like structure in the predicted N terminus and "kelch repeats" in the predicted C-terminal domain. Mayven shares 63% identity (77% similarity) with the Drosophila ring canal ("kelch") protein. Somatic cell-hybrid analysis indicated that the human Mayven gene is located on chromosome 4q21.2, whereas the murine homolog gene is located on chromosome 8. The BTB/POZ domain of Mayven can self-dimerize in vitro, which might be important for its interaction with other BTB/POZ-containing proteins. Confocal microscopic studies of endogenous Mayven protein revealed a highly dynamic localization pattern of the protein. In U373-MG astrocytoma/glioblastoma cells, Mayven colocalized with actin filaments in stress fibers and in patchy cortical actin-rich regions of the cell margins. In primary rat hippocampal neurons, Mayven is highly expressed in the cell body and in neurite processes. Binding assays and far Western blotting analysis demonstrated association of Mayven with actin. This association is mediated through the "kelch repeats" within the C terminus of Mayven. Depolarization of primary hippocampal neurons with KCl enhanced the association of Mayven with actin. This increased association resulted in dynamic changes in Mayven distribution from uniform to punctate localization along neuronal processes. These results suggest that Mayven functions as an actin-binding protein that may be translocated along axonal processes and might be involved in the dynamic organization of the actin cytoskeleton in brain cells. (+info)
Failure of cerebellar patients to time finger opening precisely causes ball high-low inaccuracy in overarm throws.
(29/1796)
We investigated the idea that the cerebellum is required for precise timing of fast skilled arm movements by studying one situation where timing precision is required, namely finger opening in overarm throwing. Specifically, we tested the hypothesis that in overarm throws made by cerebellar patients, ball high-low inaccuracy is due to disordered timing of finger opening. Six cerebellar patients and six matched control subjects were instructed to throw tennis balls at three different speeds from a seated position while angular positions in three dimensions of five arm segments were recorded at 1,000 Hz with the search-coil technique. Cerebellar patients threw more slowly than controls, were markedly less accurate, had more variable hand trajectories, and showed increased variability in the timing, amplitude, and velocity of finger opening. Ball high-low inaccuracy was not related to variability in the height or direction of the hand trajectory or to variability in finger amplitude or velocity. Instead, the cause was variable timing of finger opening and thereby ball release occurring on a flattened arc hand trajectory. The ranges of finger opening times and ball release times (timing windows) for 95% of the throws were on average four to five times longer for cerebellar patients; e.g., across subjects mean ball release timing windows for throws made under the medium-speed instruction were 11 ms for controls and 55 ms for cerebellar patients. This increased timing variability could not be explained by disorder in control of force at the fingers. Because finger opening in throwing is likely controlled by a central command, the results implicate the cerebellum in timing the central command that initiates finger opening in this fast skilled multijoint arm movement. (+info)
The cytosolic tail of class I MHC heavy chain is required for its dislocation by the human cytomegalovirus US2 and US11 gene products.
(30/1796)
The US2 and US11 glycoproteins of human cytomegalovirus facilitate destruction of MHC class I heavy chains by proteasomal proteolysis through acceleration of endoplasmic reticulum-to-cytosol dislocation. Modification of the class I heavy chain was used to probe the structural requirements for this sequence of reactions. The cytosolic domain of the class I heavy chain is required for dislocation to the cytosol and for its subsequent destruction. However, interactions between US2 or US11 and the heavy chain are maintained in the absence of the class I cytosolic domain, as shown by chemical crosslinking in vivo and coprecipitation when translated in vitro. Thus, substrate recognition and accelerated destruction of the heavy chain, as facilitated by US2 or US11, are separable events. (+info)
Astrocytoma infiltrating lymphocytes include major T cell clonal expansions confined to the CD8 subset.
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Anaplastic astrocytoma and glioblastoma are frequent and malignant brain tumors that are infiltrated by T lymphocytes. Whether these cells result from non-specific inflammation following blood-brain barrier disruption or an antigen-driven specific immune response is unknown. In this study, an in-depth characterization of TCR diversity in tumor and blood RNA biopsies was performed in a series of 16 patients with malignant astrocytoma. Whilst there was no obvious restriction of the AV and BV gene segment usage, complementarity-determining region 3 size analysis and sequencing of amplified TCR transcripts revealed multiple T cell oligoclonal expansions in all astrocytomas analyzed. Unique T cell clones were present in different adjacent areas of a given tumor, but never detected in the blood. Quantification of the number of TCR clonal transcripts per microg of tumor RNA indicated that certain T cell clonal expansions may represent at least 300 cells/10(6) tumor cells. Furthermore, we demonstrated that the in vivo expanded clones were almost exclusively confined to the CD8(+) subset. Overall, these data suggest that spontaneous antigen-driven immune responses may be elicited against human astrocytoma despite the immunosuppressive microenvironment generated by the brain and the tumor itself. However, the ultimate failure of the immune system to control tumor growth could be the consequence of a deficient CD4 T(h) component of the response. This observation could have important consequences for the development of immunotherapies for astrocytoma patients. (+info)
Molecular genetic aspects of oligodendrogliomas including analysis by comparative genomic hybridization.
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Oligodendroglial neoplasms are a subgroup of gliomas with distinctive morphological characteristics. In the present study we have evaluated a series of these tumors to define their molecular profiles and to determine whether there is a relationship between molecular genetic parameters and histological pattern in this tumor type. Loss of heterozygosity (LOH) for 1p and 19q was seen in 17/23 (74%) well-differentiated oligodendrogliomas, in 18/23 (83%) anaplastic oligodendrogliomas, and in 3/8 (38%) oligoastrocytomas grades II and III. LOH for 17p and/or mutations of the TP53 gene occurred in 14 of these 55 tumors. Only one of the 14 cases with 17p LOH/TP53 gene mutation also had LOH for 1p and 19q, and significant astrocytic elements were seen histologically in the majority of these 14 tumors. LOH for 9p and/or deletion of the CDKN2A gene occurred in 15 of these 55 tumors, and 11 of these cases were among the 24 (42%) anaplastic oligodendrogliomas. Comparative genomic hybridization (CGH) identified the majority of cases with 1p and 19q loss and, in addition, showed frequent loss of chromosomes 4, 14, 15, and 18. These findings demonstrate that oligodendroglial neoplasms usually have loss of 1p and 19q whereas astrocytomas of the progressive type frequently contain mutations of the TP53 gene, and that 9p loss and CDKN2A deletions are associated with progression from well-differentiated to anaplastic oligodendrogliomas. (+info)