MyoScreen, a High-Throughput Phenotypic Screening Platform Enabling Muscle Drug Discovery.

Despite the need for more effective drug treatments to address muscle atrophy and disease, physiologically accurate in vitro screening models and higher information content preclinical assays that aid in the discovery and development of novel therapies are lacking. To this end, MyoScreen was developed: a robust and versatile high-throughput high-content screening (HT/HCS) platform that integrates a physiologically and pharmacologically relevant micropatterned human primary skeletal muscle model with a panel of pertinent phenotypic and functional assays. MyoScreen myotubes form aligned, striated myofibers, and they show nerve-independent accumulation of acetylcholine receptors (AChRs), excitation-contraction coupling (ECC) properties characteristic of adult skeletal muscle and contraction in response to chemical stimulation. Reproducibility and sensitivity of the fully automated MyoScreen platform are highlighted in assays that quantitatively measure myogenesis, hypertrophy and atrophy, AChR clusterization, and intracellular calcium release dynamics, as well as integrating contractility data. A primary screen of 2560 compounds to identify stimulators of myofiber regeneration and repair, followed by further biological characterization of two hits, validates MyoScreen for the discovery and testing of novel therapeutics. MyoScreen is an improvement of current in vitro muscle models, enabling a more predictive screening strategy for preclinical selection of the most efficacious new chemical entities earlier in the discovery pipeline process.

Fully Automated One-Step Production of Functional 3D Tumor Spheroids for High-Content Screening.

Adoption of spheroids within high-content screening (HCS) has lagged behind high-throughput screening (HTS) due to issues with running complex assays on large three-dimensional (3D) structures.To enable multiplexed imaging and analysis of spheroids, different cancer cell lines were grown in 3D on micropatterned 96-well plates with automated production of nine uniform spheroids per well. Spheroids achieve diameters of up to 600 µm, and reproducibility was experimentally validated (interwell and interplate CV(diameter) <5%). Biphoton imaging confirmed that micropatterned spheroids exhibit characteristic cell heterogeneity with distinct microregions. Furthermore, central necrosis appears at a consistent spheroid size, suggesting standardized growth.Using three reference compounds (fluorouracil, irinotecan, and staurosporine), we validated HT-29 micropatterned spheroids on an HCS platform, benchmarking against hanging-drop spheroids. Spheroid formation and imaging in a single plate accelerate assay workflow, and fixed positioning prevents structures from overlapping or sticking to the well wall, augmenting image processing reliability. Furthermore, multiple spheroids per well increase the statistical confidence sufficiently to discriminate compound mechanisms of action and generate EC50 values for endpoints of cell death, architectural change, and size within a single-pass read. Higher quality data and a more efficient HCS work chain should encourage integration of micropatterned spheroid models within fundamental research and drug discovery applications.

Functional consequences of the over-expression of TRPC6 channels in HEK cells: impact on the homeostasis of zinc.

The canonical transient receptor potential 6 (TRPC6) protein is a non-selective cation channel able to transport essential trace elements like iron (Fe) and zinc (Zn) through the plasma membrane. Its over-expression in HEK-293 cells causes an intracellular accumulation of Zn, indicating that it could be involved in Zn transport. This finding prompted us to better understand the role played by TRPC6 in Zn homeostasis. Experiments done using the fluorescent probe FluoZin-3 showed that HEK cells possess an intracellular pool of mobilisable Zn present in compartments sensitive to the vesicular proton pump inhibitor Baf-A, which affects endo/lysosomes. TRPC6 over-expression facilitates the basal uptake of Zn and enhances the size of the pool of Zn sensitive to Baf-A. Quantitative RT-PCR experiments showed that TRPC6 over-expression does not affect the mRNA expression of Zn transporters (ZnT-1, ZnT-5, ZnT-6, ZnT-7, ZnT-9, Zip1, Zip6, Zip7, and Zip14); however it up-regulates the mRNA expression of metallothionein-I and -II. This alters the Zn buffering capacities of the cells as illustrated by the experiments done using the Zn ionophore Na pyrithione. In addition, HEK cells over-expressing TRPC6 grow slower than their parental HEK cells. This feature can be mimicked by growing HEK cells in a culture medium supplemented with 5 µM of Zn acetate. Finally, a proteomic analysis revealed that TRPC6 up-regulates the expression of the actin-associated proteins ezrin and cofilin-1, and changes the organisation of the actin cytoskeleton without changing the cellular actin content. Altogether, these data indicate that TRPC6 is participating in the transport of Zn and influences the Zn storage and buffering capacities of the cells.

A novel organelle map framework for high-content cell morphology analysis in high throughput.

A screening procedure was developed that takes advantage of the cellular normalization by micropatterning and a novel quantitative organelle mapping approach that allows unbiased and automated cell morphology comparison using black-box statistical testing. Micropatterns of extracellular matrix proteins force cells to adopt a reproducible shape and distribution of intracellular compartments avoiding strong cell-to-cell variation that is a major limitation of classical culture conditions. To detect changes in cell morphology induced by compound treatment, fluorescently labeled intracellular structures from several tens of micropatterned cells were transformed into probabilistic density maps. Then, the similarity or difference between two given density maps was quantified using statistical testing that evaluates differences directly from the data without additional analysis or any subjective decision. The versatility of this organelle mapping approach for different magnifications and its performance for different cell shapes has been assessed. Density-based analysis detected changes in cell morphology due to compound treatment in a small-scale proof-of-principle screen demonstrating its compatibility with high-throughput screening. This novel tool for high-content and high-throughput cellular phenotyping can potentially be used for a wide range of applications from drug screening to careful characterization of cellular processes.

Perispeckles are major assembly sites for the exon junction core complex.

The exon junction complex (EJC) is loaded onto mRNAs as a consequence of splicing and regulates multiple posttranscriptional events. MLN51, Magoh, Y14, and eIF4A3 form a highly stable EJC core, but where this tetrameric complex is assembled in the cell remains unclear. Here we show that EJC factors are enriched in domains that we term perispeckles and are visible as doughnuts around nuclear speckles. Fluorescence resonance energy transfer analyses and EJC assembly mutants show that perispeckles do not store free subunits, but instead are enriched for assembled cores. At the ultrastructural level, perispeckles are distinct from interchromatin granule clusters that may function as storage sites for splicing factors and intermingle with perichromatin fibrils, where nascent RNAs and active RNA Pol II are present. These results support a model in which perispeckles are major assembly sites for the tetrameric EJC core. This subnuclear territory thus represents an intermediate region important for mRNA maturation, between transcription sites and splicing factor reservoirs and assembly sites.

Improved visualization and quantitative analysis of drug effects using micropatterned cells.

To date, most HCA (High Content Analysis) studies are carried out with adherent cell lines grown on a homogenous substrate in tissue-culture treated micro-plates. Under these conditions, cells spread and divide in all directions resulting in an inherent variability in cell shape, morphology and behavior. The high cell-to-cell variance of the overall population impedes the success of HCA, especially for drug development. The ability of micropatterns to normalize the shape and internal polarity of every individual cell provides a tremendous opportunity for solving this critical bottleneck (1-2). To facilitate access and use of the micropatterning technology, CYTOO has developed a range of ready to use micropatterns, available in coverslip and microwell formats. In this video article, we provide detailed protocols of all the procedures from cell seeding on CYTOOchip micropatterns, drug treatment, fixation and staining to automated acquisition, automated image processing and final data analysis. With this example, we illustrate how micropatterns can facilitate cell-based assays. Alterations of the cell cytoskeleton are difficult to quantify in cells cultured on homogenous substrates, but culturing cells on micropatterns results in a reproducible organization of the actin meshwork due to systematic positioning of the cell adhesion contacts in every cell. Such normalization of the intracellular architecture allows quantification of even small effects on the actin cytoskeleton as demonstrated in these set of protocols using blebbistatin, an inhibitor of the actin-myosin interaction.

Kinase requirements in human cells: I. Comparing kinase requirements across various cell types.

shRNA loss-of-function screens were used to identify kinases that were rate-limiting for promoting cell proliferation and survival. Here, we study the differences in kinase requirements among various human cells, including freshly prepared primary cells, isogenic cells, immortalized cells, and cancer cell lines. Closely related patterns of kinase requirements among the various cell types were observed in three cases: (i) in repeat experiments using the same cells, (ii) with multiple populations of freshly prepared primary epithelial cells isolated from the same tissue source, and (iii) between nearly isogenic cells that differ from each other by the expression of a single gene. Other commonly used cancer cell lines were distinct from one another, even when they were isolated from similar tumor types. Even primary cells of different lineages isolated from the same tissue source showed many differences. The differences in kinase requirements among cell lines observed in this study suggest that the control of proliferation and survival may be significantly different between cell lines and that simple comparisons from any one cell to another may be misleading. Although the regulation of cell proliferation and survival are heavily studied areas, we did not see a bias in these screens toward the identification of previously known and well studied kinases, suggesting that our knowledge of molecular events in these areas is still meager.

The exon-junction-complex-component metastatic lymph node 51 functions in stress-granule assembly.

Metastatic lymph node 51 [MLN51 (also known as CASC3)] is a component of the exon junction complex (EJC), which is assembled on spliced mRNAs and plays important roles in post-splicing events. The four proteins of the EJC core, MLN51, MAGOH, Y14 and EIF4AIII shuttle between the cytoplasm and the nucleus. However, unlike the last three, MLN51 is mainly detected in the cytoplasm, suggesting that it plays an additional function in this compartment. In the present study, we show that MLN51 is recruited into cytoplasmic aggregates known as stress granules (SGs) together with the SG-resident proteins, fragile X mental retardation protein (FMRP), poly(A) binding protein (PABP) and poly(A)(+) RNA. MLN51 specifically associates with SGs via its C-terminal region, which is dispensable for its incorporation in the EJC. MLN51 does not promote SG formation but its silencing, or the overexpression of a mutant lacking its C-terminal region, alters SG assembly. Finally, in human breast carcinomas, MLN51 is sometimes present in cytoplasmic foci also positive for FMRP and PABP, suggesting that SGs formation occurs in malignant tumours.

Association of the breast cancer protein MLN51 with the exon junction complex via its speckle localizer and RNA binding module.

MLN51 is a nucleocytoplasmic shuttling protein that is overexpressed in breast cancer. The function of MLN51 in mammals remains elusive. Its fly homolog, named barentsz, as well as the proteins mago nashi and tsunagi have been shown to be required for proper oskar mRNA localization to the posterior pole of the oocyte. Magoh and Y14, the human homologs of mago nashi and tsunagi, are core components of the exon junction complex (EJC). The EJC is assembled on spliced mRNAs and plays important roles in post-splicing events including mRNA export, nonsense-mediated mRNA decay, and translation. In the present study, we show that human MLN51 is an RNA-binding protein present in ribonucleo-protein complexes. By co-immunoprecipitation assays, endogenous MLN51 protein is found to be associated with EJC components, including Magoh, Y14, and NFX1/TAP, and subcellular localization studies indicate that MLN51 transiently co-localizes with Magoh in nuclear speckles. Moreover, we demonstrate that MLN51 specifically associates with spliced mRNAs in co-precipitation experiments, both in the nucleus and in the cytoplasm, at the position where the EJC is deposited. Most interesting, we have identified a region within MLN51 sufficient to bind RNA, to interact with Magoh and spliced mRNA, and to address the protein to nuclear speckles. This conserved region of MLN51 was therefore named SELOR for speckle localizer and RNA binding module. Altogether our data demonstrate that MLN51 associates with EJC in the nucleus and remains stably associated with mRNA in the cytoplasm, suggesting that its overexpression might alter mRNA metabolism in cancer.

Metastatic lymph node 64 (MLN64), a gene overexpressed in breast cancers, is regulated by Sp/KLF transcription factors.

MLN64, is invariably coamplified and coexpressed with erbB-2 in breast cancers. The human MLN64 and ERBB2 genes are positioned at less than 50 kb from each other, on chromosome 17q12. To understand the molecular basis of MLN64 overexpression in cancer, the genomic region containing the MLN64 and ERBB2 genes was isolated and mapped. The two genes, DARPP32 and Telethonin, flanking MLN64 respectively on its centromeric and telomeric sides, although coamplified, are not overexpressed in breast cancer cells, indicating that gene amplification is not sufficient to allow overexpression. The MLN64 minimal promoter was isolated and found to be a housekeeping gene promoter containing four potential Sp1 binding elements. Using Sp1-deficient Drosophila SL2 cells, MLN64 promoter activity was induced in a dose-dependent manner by exogenous Sp1 addition. Furthermore, mutation of each individual Sp1 element resulted in a significant decrease in reporter gene activity, indicating that all the Sp1 binding elements are functional and act together to promote gene expression. Since the ERBB2 promoter is also positively regulated by Sp1, this study indicates that MLN64 and ERBB2 genes share common transcriptional controls together with a physical link on chromosome 17q. We speculate that, in addition to the oncogenic potential of erbB-2 overexpression, the unbalanced action of MLN64 contributes to the poor clinical outcome of breast tumors bearing this amplified region.

Metastatic Lymph Node 51, a novel nucleo-cytoplasmic protein overexpressed in breast cancer.

Metastatic Lymph Node 51 (MLN51) cDNA was isolated by differential screening of a human breast cancer metastasis cDNA library. MLN51 cDNA encodes a novel human protein of 703 residues that shares no significant homology to any known protein. However MLN51 is well conserved between vertebrate and invertebrate species suggesting an important biological function. The amino terminal half of the protein contains a coiled-coil domain and two potential nuclear localization signals (NLS). The carboxy terminal half contains one SH2 and four SH3 binding motifs. The coiled-coil domain promotes MLN51 oligomerization in transfected cells. When transiently expressed, the MLN51 protein is mainly found in the cytoplasm with a weak nuclear staining. However, deletion of the carboxy terminal half of the protein allows the targeting of the protein to the nucleus, demonstrating that the NLSs are functional. MLN51 is ubiquitously expressed in normal tissues. Human breast carcinomas show MLN51 overexpression in malignant epithelial cells. The uncommon association of protein-protein interaction domains often found either in nuclear or in cytoplasmic signaling proteins raises a possible nucleo-cytoplasmic function for MLN51.