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Contact Inhibition (contact + inhibition)
Selected AbstractsImpaired intercellular adhesion and immature adherens junctions in merlin-deficient human primary schwannoma cellsGLIA, Issue 5 2008C. Flaiz Abstract Schwannomas that occur spontaneously or in patients with neurofibromatosis Type 2, lack both alleles for the tumor suppressor and plasma membrane-cytoskeleton linker merlin. We have shown that human primary schwannoma cells display activation of the RhoGTPases Rac1 and Cdc42 which results in highly dynamic and ongoing protrusive activity like ruffling. Ruffling is an initial and temporally limited step in the formation of intercellular contacts like adherens junctions that are based on the cadherin-catenin system. We tested if there is a connection between Rac1-induced ongoing ruffling and the maintenance, stabilization and functionality of adherens junctions and if this is of relevance in human, merlin-deficient schwannoma cells. We show intense ongoing ruffling is not limited to membranes of single human primary schwannoma cells, but occurs also in membranes of contacting cells, even when confluent. Live cell imaging shows that newly formed contacts are released after a short time, suggesting disturbed formation or stabilization of adherens junctions. Morphology, high phospho-tyrosine levels and cortactin staining indicate that adherens junctions are immature in human primary schwannoma cells, whereas they display characteristics of mature adherens junctions in human primary Schwann cells. When merlin is reintroduced, human primary schwannoma cells show only initial ruffling in contacting cells and adherens junctions appear more mature. We therefore propose that ongoing Rac-induced ruffling causes immature adherens junctions and leads to impaired, nonfunctional intercellular adhesion in aggregation assays in merlin-deficient schwannoma cells that could be an explanation for increased proliferation rates due to loss of contact inhibition or tumor development in general. © 2008 Wiley-Liss, Inc. [source] Antibacterial activity of dental composites containing zinc oxide nanoparticles,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010Berdan Aydin Sevinç Abstract The resin-based dental composites commonly used in restorations result in more plaque accumulation than other materials. Bacterial biofilm growth contributes to secondary caries and failure of resin-based dental composites. Methods to inhibit biofilm growth on dental composites have been sought for several decades. It is demonstrated here that zinc oxide nanoparticles (ZnO-NPs) blended at 10% (w/w) fraction into dental composites display antimicrobial activity and reduce growth of bacterial biofilms by roughly 80% for a single-species model dental biofilm. Antibacterial effectiveness of ZnO-NPs was assessed against Streptococcus sobrinus ATCC 27352 grown both planktonically and as biofilms on composites. Direct contact inhibition was observed by scanning electron microscopy and confocal laser scanning microscopy while biofilm formation was quantified by viable counts. An 80% reduction in bacterial counts was observed with 10% ZnO-NP-containing composites compared with their unmodified counterpart, indicating a statistically significant suppression of biofilm growth. Although, 20% of the bacterial population survived and could form a biofilm layer again, 10% ZnO-NP-containing composites maintained at least some inhibitory activity even after the third generation of biofilm growth. Microscopy demonstrated continuous biofilm formation for unmodified composites after 1-day growth, but only sparsely distributed biofilms formed on 10% ZnO-NP-containing composites. The minimum inhibitory concentration of ZnO-NPs suspended in S. sobrinus planktonic culture was 50 ,g mL,1. ZnO-NP-containing composites (10%) qualitatively showed less biofilm after 1-day-anaerobic growth of a three-species initial colonizer biofilm after being compared with unmodified composites, but did not significantly reduce growth after 3 days. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010. [source] Cell transformation induced by hepatitis C virus NS3 serine proteaseJOURNAL OF VIRAL HEPATITIS, Issue 2 2001R. Zemel Persistent infection with hepatitis C virus (HCV) may lead to hepatocellular carcinoma (HCC). It has been suggested that HCV-encoded proteins are directly involved in the tumorigenic process. The HCV nonstructural protein NS3 has been identified as a virus-encoded serine protease. To study whether HCV NS3 has oncogenic activity, nontumorigenic rat fibroblast (RF) cells were stably transfected with an expression vector containing cDNA for the NS3 serine protease (nucleotides 3356,4080). The NS3 serine protease activity was determined in the transfected cells. The transfected cells grew rapidly and proliferated serum independently, lost contact inhibition, grew anchorage independently in soft agar and induced significant tumour formation in nude mice. Cells transfected with an expression vector containing a mutated NS3 serine protease (serine 139 to alanine at the catalytic site) showed no transforming abilities; their growth was dependent on serum and they did not grow anchorage independently in soft agar. Moreover, cells transfected with the NS3 serine protease and treated with the chymotrypsin inhibitors TPCK and PMSF (a serine protease inhibitor) lost their transforming feature. These results suggest that the NS3 serine protease of HCV is involved in cell transformation and that the ability to transform requires an active enzyme. [source] Protein phosphatase 1, activity prevents oncogenic transformationMOLECULAR CARCINOGENESIS, Issue 9 2006Cathy W.Y. Liu Abstract Cyclin-dependent kinase 2 (Cdk2) phosphorylates Thr320 of protein phosphatase 1, (PP1,) in late G1, thereby inhibiting its activity. Phosphorylation-resistant PP1,T320A, acting as a constitutively active (CA) mutant, causes a late G1 arrest by preventing the phosphorylation and inactivation of the retinoblastoma protein (pRb). Both PP1,-mediated G1 arrest and PP1, phosphorylation in late G1 require the presence of pRb, indicating that PP1, is a crucial regulator of the pRb pathway, which is almost invariably mutated in human cancer. These findings prompted us to investigate whether PP1, interferes with oncogenic transformation. The ability of NIH 3T3 cells to form foci after transformation with ras/cyclin D1 was significantly inhibited by co-transfection with PP1,T320A, but not PP1,. Likewise, cells expressing PP1,T320A or PP1,T320A fused to green fluorescent protein (GFP) were unable to form colonies in soft agar, regardless of whether PP1, constructs were co-transfected with ras/cyclin D1 or transfected into stably transformed cells. Overexpressed wild-type (Wt) PP1, and GFP-PP1, were phosphorylated in Thr320, most likely explaining its lack of effect. Expression of GFP-PP1,T320A was associated with caspase-cleaved pRb in Western blots (WB) and morphological signs of cell death. These findings demonstrate that PP1, activity can override oncogenic signaling by causing cell-cycle arrest and/or apoptosis rather than restoring contact inhibition or anchorage dependence. © 2006 Wiley-Liss, Inc. [source] Cryopreservation and in Vitro Expansion of Chondroprogenitor Cells Isolated from the Superficial Zone of Articular CartilageBIOTECHNOLOGY PROGRESS, Issue 1 2005Juan M. Melero Martin Understanding the proliferation mechanisms of chondroprogenitor cells and their influence on cell differentiation is crucial in order to develop large-scale expansion processes for tissue engineering applications. Proliferation control mechanisms were mainly attributed to substrate limitation and cell-cell contact inhibition. The limiting substrates were found to be components of the FCS, with an optimal proliferation rate achieved in the presence of 40% FCS. In addition, the medium supply rate was found to be essential in reducing substrate limitation. In terms of FCS, 10 ,L FCS cm,2 h,1 was the threshold feed rate required to prevent substrate limitation. Above this rate, maximum cell densities of 5.3 × 105 cells/cm2 were achieved, representing a 53-fold expansion. To reduce the need for high supply rates, the effect of specific growth factors was also investigated. Cell densities of 3.3 × 105 cells/cm2 were achieved in batch cultures using 40% FCS and 1 ng/mL TGF-,1. Chondroprogenitor cells were expanded in this medium up to three passages without compromising their ability to differentiate and produce cartilage-like matrix in pellet cultures. In addition to substrate limitation, cell-cell contact, even at very sparse subconfluent densities, appeared capable of exerting some degree of growth inhibition. The cells exhibited deceleratory growth kinetics, characterized by a decrease of specific growth rates over time. [source] Recent Insights into PDGF-Induced GliomagenesisBRAIN PATHOLOGY, Issue 3 2010Filippo Calzolari Abstract Gliomas are aggressive and almost incurable glial brain tumors which frequently display abnormal platelet-derived growth factor (PDGF) signaling. Evidence gained from studies on several in vivo animal models has firmly established a causal connection between aberrant PDGF signaling and the formation of some gliomas. However, only recently has significant knowledge been gained regarding crucial issues such as the glioma cell of origin and the relationship between the transforming stimulus and the cellular characteristics of the resulting tumor. Based on recent evidence, we propose that PDGF can bias cell-fate decisions, driving the acquisition of cell type-specific features by the progeny of multipotent neural progenitors, thus determining the shape and direction of the transformation path. Furthermore, recent data about the cellular mechanisms of PDGF-driven glioma progression and maintenance indicate that PDGF may be required, unexpectedly, to override cell contact inhibition and promote glioma cell infiltration rather than to stimulate cell proliferation. [source] Effect of transfection with a gene coding for the fibronectin FNIII/10 fragment upon contact inhibition of C3H10T1/2 fibroblastsCELL PROLIFERATION, Issue 3 2006J. Mi, oszewska To verify this concept, the C3H10T1/2 fibroblasts were stably transfected with the gene coding for the fibronectin fragment III/10 (FNIII/10). This resulted in differences in gene's expression between original C3H10T1/2 cells and their FNIII/10 transfectants. No significant differences in growth properties were observed in the original or in the transfected cells. C3H10T1/2 cells and their transfectants, when co-cultured, displayed more cells at confluence than the cells cultured alone. Moreover, co-cultured C3H10T1/2 cells and their transfectants showed elevated levels of phospho-ERK1/2 compared to homogenous cultures. Results obtained indicate that cellular homogeneity is responsible for density-dependent growth inhibition. [source] | |||||||||||||