Nucleus-associated actin in Amoeba proteus

The presence, spatial distribution and forms of intranuclear and nucleus-associated cytoplasmic actin were studied in Amoeba proteus with immunocytochemical approaches. Labeling with different anti-actin antibodies and staining with TRITC-phalloidin and fluorescent deoxyribonuclease I were used. We showed that actin is abundant within the nucleus as well as in the cytoplasm of A. proteus cells. According to DNase I experiments, the predominant form of intranuclear actin is G-actin which is associated with chromatin strands. Besides, unpolymerized actin was shown to participate in organization of a prominent actin layer adjacent to the outer surface of nuclear envelope. No significant amount of F-actin was found in the nucleus. At the same time, the amoeba nucleus is enclosed in a basket-like structure formed by circumnuclear actin filaments and bundles connected with global cytoplasmic actin cytoskeleton. A supposed architectural function of actin filaments was studied by treatment with actin-depolymerizing agent latrunculin A. It disassembled the circumnuclear actin system, but did not affect the intranuclear chromatin structure. The results obtained for amoeba cells support the modern concept that actin is involved in fundamental nuclear processes that have evolved in the cells of multicellular organisms.

Molecular Pathways in Invasive Bladder Cancer: New Insights Into Mechanisms, Progression, and Target Identification

Papillary and invasive cancers of the urinary bladder appear to evolve and progress through distinct molecular pathways. Invasion in bladder cancer forebodes a graver prognosis, and these tumors are generally characterized by alterations in the p53 and retinoblastoma (RB) pathways that normally regulate the cell cycle by interacting with the Ras–mitogen activated protein kinase signal transduction pathway. Tumor angiogenesis further contributes to the neoplastic growth by providing a constant supply of oxygen and nutrients. Distinct epigenetic and genetic events characterize the interplay between the molecules involved in these pathways, thus affording their use as indicators of prognosis. Efforts are now underway to construct molecular panels comprising multiple markers that can serve as more robust predictors of outcome. While clinical trials for targeted chemotherapy for bladder cancer have commenced, novel genetic and pharmacologic agents that can target pathway-specific molecules are currently under development. The next generation of clinical management for urothelial carcinoma will witness the use of multimarker panels for prognostic prediction and combination therapy directed at novel molecular targets for treatment.

Modulation of α7-integrin-mediated adhesion and expression by platelet-derived growth factor in vascular smooth muscle cells

We showed previously that the expression of α7-integrin in aortic vascular smooth muscle cells (VSMC) is enhanced in a rat model of atherosclerosis. In the present study, we investigated the effects of platelet-derived growth factor (PDGF) on α7-integrin expression and VSMC adhesion and migration. Expression of the α7-integrin gene was determined by real-time RT-PCR, whereas protein levels were determined by fluorescence-activated cell sorting analysis. PDGF increased α7cell surface protein expression (12 and 24 h: 3.3 ± 0.8- and 3.6 ± 0.4-fold, P < 0.05 vs. control) and mRNA levels (24 h: 3.1-fold, P < 0.05 vs. control) in a time-dependent manner. Actinomycin D and cycloheximide attenuated PDGF-induced increases in α7-integrin, indicating the involvement of de novo mRNA and protein synthesis. Treatment with the MAPK inhibitors PD-98059, SP-600125, and SB-203580 attenuated PDGF-induced increases in mRNA. In contrast, PD-98059 and SP-600125, but not SB-203580, attenuated PDGF-induced increases in cell surface protein levels. PDGF-treated VSMC adhered to laminin more efficiently (42 ± 6% increase, P < 0.01), and this increase was partially inhibited by anti-α7-integrin function-blocking antibody. However, PDGF did not alter migration on laminin, and there was no effect of the anti-α7-integrin function-blocking antibody on basal or PDGF-stimulated migration. Immunofluorescence imaging revealed an increase in α7-integrin distribution along the stress fibers. Together, these observations indicate that PDGF enhances α7-integrin expression in VSMC and promotes α7-integrin-mediated adhesion to laminin.

Characterization ofAmoeba proteus myosin VI immunoanalog

Amoeba proteus, the highly motile free-living unicellular organism, has been widely used as a model to study cell motility. However, molecular mechanisms underlying its unique locomotion and intracellular actin-based-only trafficking remain poorly understood. A search for myosin motors responsible for vesicular transport in these giant cells resulted in detection of 130-kDa protein interacting with several polyclonal antibodies against different tail regions of human and chicken myosin VI. This protein was binding to actin in the ATP-dependent manner, and immunoprecipitated with anti-myosin VI antibodies. In order to characterize its possible functions in vivo, its cellular distribution and colocalization with actin filaments and dynamin II during migration and pinocytosis were examined. In migrating amoebae, myosin VI immunoanalog localized to vesicular structures, particularly within the perinuclear and sub-plasma membrane areas, and colocalized with dynamin II immunoanalog and actin filaments. The colocalization was even more evident in pinocytotic cells as proteins concentrated within pinocytotic pseudopodia. Moreover, dynamin II and myosin VI immunoanalogs cosedimented with actin filaments, and were found on the same isolated vesicles. Blocking endogenous myosin VI immunoanalog with anti-myosin VI antibodies inhibited the rate of pseudopodia protrusion (about 19% decrease) and uroidal retraction (about 28% decrease) but did not affect cell morphology and the manner of cell migration. Treatment with anti-human dynamin II antibodies led to changes in directionality of amebae migration and affected the rate of only uroidal translocation (about 30% inhibition). These results indicate that myosin VI immunoanalog is expressed in protist Amoeba proteus and may be involved in vesicle translocation and cell locomotion.

A capillary electrophoretic method for monitoring the presence of α-tubulin in nuclear preparations

A sensitive capillary electrophoretic method was developed to detect the presence of alpha-tubulin, a microtubular cytoskeletal component, in isolated nuclear preparations. These preparations are treated with anti-alpha-tubulin primary mouse antibodies and then stained with a fluorescently labeled anti-mouse IgG antibody. The stained preparation is then analyzed by capillary electrophoresis with laser-induced fluorescence detection, a technique that allows for sensitive detection of fluorescently labeled species. Using this method, it is feasible to count individual subcellular aggregates containing alpha-tubulin (SATs), estimate the number of alpha-tubulin molecules per SAT, determine the cumulative intensity of all SATs as an estimate of the relative level of alpha-tubulin in a preparation, and obtain their apparent electrophoretic mobility distribution. The method was validated by comparing SATs from untreated cells with those from colchicine-treated cells. Since colchicine is a microtubule-disrupting agent, treatment reduced the number of SATs per cell as well as the cumulative intensity of all SATs in a preparation. In contrast, the apparent electrophoretic mobility distribution was not influenced by colchicine treatment, suggesting that this parameter is not strongly dependent on the alpha-tubulin content. Given the zeptomolar sensitivity of laser-induced fluorescence detection and the widespread availability of antibodies, the approach used here represents an improvement in the detection of cytoskeletal impurities in subcellular fractions.

Capillary Electrophoretic Separation of Nuclei Released from Single Cells

We report here the first capillary electrophoresis analysis of intact nuclei released on-column from single cells. Expression of the nuclear-targeted protein nuDsRed2 and the plasma membrane-bound farnesylated enhanced green fluorescent protein in cultured human DeltaH2-1 cells allowed fluorescent monitoring of the fate of these subcellular compartments upon injection of a single cell into the separation capillary. On-column treatment with digitonin allowed for the separation of the plasma membrane from the nucleus as indicated by their selective laser-induced fluorescence detection in two separate spectral regions. The data suggest that less than 0.1% of the plasma membrane remains bound to individually detected nuclei. In digitonin-treated cells, the electropherograms consisted of a prominent fluorescent peak attributed to nuDsRed2 localized to the nucleus and a collection of weakly fluorescent events (barely distinguishable from scattering) that seem to indicate additional localization of this protein to other subcellular regions. Taken together, this report points to the feasibility of studying intact organelles released from a single mammalian cell by capillary electrophoresis, which is a prerequisite to understanding the relevance of subcellular heterogeneity in biological systems.