PML is required for telomere stability in non-neoplastic human cells.

Telomeres interact with numerous proteins, including components of the shelterin complex, whose alteration, similarly to proliferation-induced telomere shortening, initiates cellular senescence. In tumors, telomere length is maintained by Telomerase activity or by the Alternative Lengthening of Telomeres mechanism, whose hallmark is the telomeric localization of the promyelocytic leukemia (PML) protein. Whether PML contributes to telomeres maintenance in normal cells is unknown. We show that in normal human fibroblasts the PML protein associates with few telomeres, preferentially when they are damaged. Proliferation-induced telomere attrition or their damage due to alteration of the shelterin complex enhances the telomeric localization of PML, which is increased in human T-lymphocytes derived from patients genetically deficient in telomerase. In normal fibroblasts, PML depletion induces telomere damage, nuclear and chromosomal abnormalities, and senescence. Expression of the leukemia protein PML/RARα in hematopoietic progenitors displaces PML from telomeres and induces telomere shortening in the bone marrow of pre-leukemic mice. Our work provides a novel view of the physiologic function of PML, which participates in telomeres surveillance in normal cells. Our data further imply that a diminished PML function may contribute to cell senescence, genomic instability, and tumorigenesis.

Negative pressure wound therapy with Bio-Dome dressing technology in the treatment of complex wounds: a case series.

The treatment of complex wounds is difficult and not always effective. Various treatment options are used with varying degrees of success. Negative pressure wound therapy (NPWT) is a cost-efficient and effective way to help treat these wounds. The use of a vacuum device applies the negative pressure to the site of the wound and promotes waste removal and increases circulation and tissue formation. While various NPWT systems are currently on the market, we utilised the ConvaTec Engenex® system with Bio-DomeTM technology; however, our case study is not intended to advocate the specific use of this system, but instead focuses on the use of NPWT as a viable option for wound healing. Each of the following case study patients presented with difficult-to-heal wounds that failed traditional therapeutic approaches. Through the use of NPWT, our patients saw major wound size reductions. Each patient exhibited at least a 94% reduction in wound area, wound volume or both.

Selective case study describing the use of Apligraf on necrobiosis lipoidica associated with diabetes.

Necrobiosis lipoidica is a rare skin disease characterised by large, well-demarcated, symmetrical plaques with overlying telangiectasias and atrophic, fibrotic features. The disease is associated with diabetes mellitus (1 in 300 cases), but can also be linked to other diseases such as rheumatoid arthritis. Women are three times more likely to develop necrobiosis lipoidica compared to men. Ulcerations are the most serious type of complications in necrobiosis lipoidica, and they occur most frequently on the legs of patients. However, the aetiology of necrobiosis lipoidica still remains unclear. Although many studies have been conducted in order to determine necrobiosis lipoidica's pathophysiology, a clear and definite path to disease has not been recorded. In this case study, a patient with necrobiosis lipoidica that had been refractory to conventional therapy received treatment with Apligraf® bioengineered wound dressings. Apligraf was shown to be effective in managing the patient's multiple hard-to-heal wounds. It was more successful than previous therapies in achieving granulation tissue formation and wound volume reduction, in addition to being a more rapid form of treatment.

Photoactivation of pa-GFP in 3D: optical tools for spatial confinement.

Photoactivatable fluorescent proteins represent an innovative tool for the direct observation of time dependent macromolecular events in living systems. The possibility of switching on a selected and confined subset of the expressed target proteins allows to follow biological processes reaching high signal to noise ratios. In particular, use of non-linear interactions to bring the molecules in the activated fluorescent form make it possible to extend the advantages of photoactivation to events that requires 3D spatial localization. In this work, we show the possibility to realize confined activated volumes in living cells, by employing photoactivatable green fluorescent protein (paGFP) in two-photon microscopy. The analysis of the kinetics of two-photon paGFP activation in dependence of the wavelength, the laser intensity and the exposure time is provided. This study allowed to assess the optimal conditions to induce photoactivation in living samples and to track the behaviour of tagged histone H2B during cellular division. Furthermore we investigate paGFP photoactivation under evanescent wave illumination. Total internal reflection set-up has been used to selectively activate subresolved distribution of proteins localized in the basal membrane surroundings. These two photoactivation methods provide a suitable tool for many biological applications, combining subresolved surface and in-depth three-dimensionally confined investigations.

Spatial control of pa-GFP photoactivation in living cells.

Photoactivatable green fluorescent protein (paGFP) exhibits peculiar photo-physical properties making it an invaluable tool for protein/cell tracking in living cells/organisms. paGFP is normally excited in the violet range (405 nm), with an emission peak centred at 520 nm. Absorption cross-section at 488 nm is low in the not-activated form. However, when irradiated with high-energy fluxes at 405 nm, the protein shows a dramatic change in its absorption spectra becoming efficiently excitable at 488 nm. Confocal microscopes allow to control activation in the focal plane. Unfortunately, irradiation extends to the entire illumination volume, making impracticable to limit the process in the 3D (three-dimensional) space. In order to confine the process, we used two advanced intrinsically 3D confined optical methods, namely: total internal reflection fluorescence (TIRF) and two-photon excitation fluorescence (2PE) microscopy. TIRF allows for spatially selected excitation of fluorescent molecules within a thin region at interfaces, i.e. cellular membranes. Optimization of the TIRF optical set-up allowed us to demonstrate photoactivation of paGFP fused to different membrane localizing proteins. Exploitation of the penetration depth showed that activation is efficiently 3D confined even if limited at the interface. 2PE microscopy overcomes both the extended excitation volume of the confocal case and the TIRF constraint of operating at interfaces, providing optical confinement at any focal plane in the specimen within subfemtoliter volumes. The presented results emphasize how photoactivation by non-linear excitation can provide a tool to increase contrast in widefield and confocal cellular imaging.

Mad2 binding to Mad1 and Cdc20, rather than oligomerization, is required for the spindle checkpoint.

Mad2 is a key component of the spindle checkpoint, a device that controls the fidelity of chromosome segregation in mitosis. The ability of Mad2 to form oligomers in vitro has been correlated with its ability to block the cell cycle upon injection into Xenopus embryos. Here we show that Mad2 forms incompatible complexes with Mad1 and Cdc20, neither of which requires Mad2 oligomerization. A monomeric point mutant of Mad2 can sustain a cell cycle arrest of comparable strength to that of the wild-type protein. We show that the interaction of Mad2 with Mad1 is crucial for the localization of Mad2 to kinetochores, where Mad2 interacts with Cdc20. We propose a model that features the kinetochore as a 'folding factory' for the formation of a Mad2-Cdc20 complex endowed with inhibitory activity on the anaphase promoting complex.

A repertoire library that allows the selection of synthetic SH2s with altered binding specificities.

Tyrosine phosphorylation is one of the major mechanisms involved in the intracellular propagation of external signals. Strategies aimed at interfering with this process might allow the control of several cellular phenotypes. SH2 domains mediate protein-protein interactions by recognizing phosphotyrosine (pY) residues in the context of specific phosphopeptides. We created an SH2-scaffolded repertoire library by randomly mutagenizing five critical amino acid positions in the specificity-determining region of the PLCgamma C-terminal SH2 domain. Synthetic SH2 domains were selected from the library using biotinylated phosphopeptides derived from a natural PLCgamma-SH2 ligand as well as unrelated SH2 ligands. The isolated SH2s displayed high binding affinity constants for the selecting peptides and were capable of interacting with the corresponding proteins.

Cell cycle effects of gemcitabine.

Gemcitabine (2',2'-difluoro-2'-deoxycytidine, or dFdC) is a promising anticancer agent with demonstrated clinical activity in solid tumours currently undergoing clinical trials. Despite extensive studies on the biochemical mechanism of action, cell cycle perturbations induced by dFdC have not yet been thoroughly investigated, apart from the expected inhibition of DNA synthesis. The aim of our study was to clarify whether cell population kinetics is a vital factor in the cytotoxicity of dFdC in single or repeated treatments and in the dFdC-cisplatin combination. Ovarian cancer cells growing in vitro were treated with dFdC for 1 hr in a range of concentrations from 10 nM to 10 microM. Cell kinetics was investigated by DNA-bromodeoxyuridine flow cytometry, using different experimental protocols to measure either the time course of DNA-synthesis inhibition or the fate of cells in G(1), S or G(2)M at the time of dFdC treatment or 24 hr later. A modified sulforhodamine B test was used to assess the growth inhibition caused by dFdC given alone or with cisplatin. Although dFdC promptly inhibited DNA synthesis, cytotoxicity on proliferating cells was not specific for cells initially in the S phase. DNA synthesis was restored after a G(1) block of variable, dose-dependent length, but recycling cells were intercepted at the subsequent checkpoints, resulting in delays in the G(2)M and G(1) phases. The activity of repeated treatment with dFdC + dFdC or dFdC + cisplatin was highly dependent on the interval length between them. These results suggest that the kinetics of cell recycling from a first dFdC treatment strongly affects the outcome of a second treatment with either dFdC itself or cisplatin.

Effects of the acute myeloid leukemia--associated fusion proteins on nuclear architecture.

Acute myeloid leukemias (AMLs) are consistently associated with chromosomal rearrangements that result in the generation of chimeric genes and fusion proteins. One of the two affected genes is frequently a transcription factor Involved in the regulation of hematopoletic differentiation. Recent findings suggest a common leukemogenic mechanism for the fused transcription factor: abnormal recruitment of histone deacetylase (HDAC)-containing complexes to its target promoters. Inhibition of HDAC enzymatic activity reverts the leukemic phenotype in vitro and therefore represents a plausible strategy for antileukemic therapy. In this review, we first briefly describe the molecular structure and mechanisms of the most frequent AML associated fusion proteins (RAR, MLL, and CBF fusions) and then summarize available knowledge about their effects on the nuclear architecture. We propose that alteration of nuclear compartmentalization might represent an additional common mechanism of leukemogenesis.

Dose estimate of exposure to radioisotopes in molecular and cellular biology.

A method for prospectively evaluating the annual equivalent doses and effective dose to biomedical researchers working with unsealed radioisotopes, and their classification, is presented here. Simplified formulae relate occupational data to a reasonable overestimate of the annual effective dose, and the equivalent doses to the hands and to the skin. The procedure, up to the classification of personnel and laboratories, can be made fully automatic, using a common spreadsheet on a personal computer. The method is based on occupational data, accounting for the amounts of each radioisotope used by a researcher, the time of exposure and the overall amounts employed in the laboratories where experiments are performed. The former data serve to forecast a contribution to the dose arising from a researcher's own work, the latter to a forecast of an 'environmental' contribution deriving simply from the presence in a laboratory where other people are working with radioisotopes. The estimates of the doses due to one's own radioisotope handling and to 'environment' were corrected for accidental exposure, considered as a linear function of the manipulated activity or of the time spent in the laboratories respectively, and summed up to give the effective dose. The effective dose associated with some common experiments in molecular and cellular biology is pre-evaluated by this method.

Mode of action of thiocoraline, a natural marine compound with anti-tumour activity.

Thiocoraline, a new anticancer agent derived from the marine actinomycete Micromonospora marina, was found to induce profound perturbations of the cell cycle. On both LoVo and SW620 human colon cancer cell lines, thiocoraline caused an arrest in G1 phase of the cell cycle and a decrease in the rate of S phase progression towards G2/M phases, as assessed by using bromodeoxyuridine/DNA biparametric flow cytometric analysis. Thiocoraline does not inhibit DNA-topoisomerase II enzymes in vitro, nor does it induce DNA breakage in cells exposed to effective drug concentrations. The cell cycle effects observed after exposure to thiocoraline appear related to the inhibition of DNA replication. By using a primer extension assay it was found that thiocoraline inhibited DNA elongation by DNA polymerase alpha at concentrations that inhibited cell cycle progression and clonogenicity. These studies indicate that the new anticancer drug thiocoraline probably acts by inhibiting DNA polymerase alpha activity.

Cell cycle perturbations and apoptosis induced by isohomohalichondrin B (IHB), a natural marine compound.

Isohomohalichondrin B (IHB), a novel marine compound with anti-tumoral activity, extracted from the Lissodendorix sponge, inhibits GTP binding to tubulin, preventing microtubule assembly. Cell cycle perturbations and apoptosis induced by IHB were investigated on selected human cancer cell lines by using flow cytometric and biochemical techniques. Monoparameter flow cytometric analysis showed that 1 h IHB exposure caused a delayed progression through S-phase, a dramatic block in G2M phase of the cell cycle and the appearance of tetraploid cell population in LoVo, LoVo/DX, MOLT-4 and K562 cells. At 24 h after IHB exposure, the majority of cells blocked in G2M were in prophase as assessed by morphological analysis and by the fact that they expressed high levels of cyclin A/cdc2 and cyclin B1/cdc2. At 48 h, all cells were tetraploid as assessed by biparameter cyclin A/DNA and cyclin B1/DNA content analysis. Apoptotic death was detected in both leukaemic MOLT-4 and K562 cells, which express wild-type and mutated p53 respectively, when the cells were blocked in mitotic prophase. In conclusion, IHB is a novel potent anti-tumour drug that causes delayed S-phase progression, mitotic block, tetraploidy and apoptosis in cancer cell lines.

Characterization of cyclin B1 expression in human cancer cell lines by a new three-parameter BrdUrd/cyclin B1/DNA analysis.

Flow cytometric cyclin expression/DNA content analysis, now commonly used, provides useful information on the mechanisms regulating cell cycle progression. However, this biparametric analysis does not make a clear-cut distinction between G1 and S-early or between S-late and G2M phase cells. This paper proposes a new three-parameter flow cytometric method with which to determine cyclin B1 levels in single cells in different cell cycle phases by coupling bromodeoxyuridine (BrdUrd) immunodetection and DNA content. DNA denaturation by HCl did not alter the level of cyclin B1. Differences in cyclin B1 expression were observed in seven human cancer cell lines of different origin. The percentage of cyclin B1-positive cells and the cyclin B1 content per cell indicated different patterns. In some cases cyclin B1 accumulation preceded the G2M checkpoint, at which its content usually started to rise. Using available easily reproducible techniques, this flow cytometric approach gives details of intracellular variability in cyclin expression.

Redundant functions of B-Myb and c-Myb in differentiating myeloid cells.

We show in this report that the human myeloid leukemia cell line GFD8 is a useful model to compare the biological function of the structurally related c-Myb and B-Myb proto-oncogenes and to investigate the c-myb domains required for this function. GFD8 cells are dependent for growth on granulocyte-macrophage colony-stimulating factor and differentiate in response to phorbol myristate acetate (PMA). We have stably transfected this cell line with constructs constitutively expressing c-Myb or B-Myb. Deregulated expression of both c-Myb and B-Myb inhibited the differentiation observed in response to PMA and, in particular, the induction of the CD11b and CD11c antigens on the cell surface, and the induction of adherence. Furthermore, c-Myb and B-Myb enhanced expression of CD13 upon PMA treatment. Although deregulated Myb expression did not alter the growth factor dependence of the cells, it led to an increase in G2 relative to G1 arrest in cells induced to differentiate in response to PMA, whereas control vector-transfected cells were blocked mostly in G1. This decrease in G1 block took place despite normal induction of the cyclin-dependent kinase inhibitor protein p21 (CIP1/WAF1). Thus, GFD8 cells stably expressing the human B-Myb protein behaved in a manner indistinguishable from those stably expressing C-Myb for both differentiation and cell cycle parameters. In agreement with these findings and differently from most previous reports, transactivation assays show that B-myb can indeed act as a strong activator of transcription. Finally, we demonstrated that although the DNA-binding domain of c-myb is required for both the differentiation block and the shift in cell cycle after PMA treatment, phosphorylation by casein kinase II and mitogen-activated protein kinase at positions 11 and 12 or 532 of c-myb, respectively, are not. We conclude that c-Myb and B-Myb may activate a common cellular program in the GFD8 cell line involved in both differentiation and cell cycle control.